View source for Aeroplankton

{{Short description|Tiny lifeforms floating and drifting in the air, carried by the wind}}
{{use British English|date=August 2021}}
{{Use dmy dates|date=August 2021}}
[[File:Ocean mist and spray 2.jpg|thumb|upright=1.35 |right| [[Sea spray]] containing [[marine microorganisms]] can be swept high into the atmosphere and may travel the globe before falling back to earth.]]
{{plankton sidebar|habitat}}

'''Aeroplankton''' (or '''aerial plankton''') are tiny lifeforms that float and drift in the air, carried by [[wind]]. Most of the living things that make up aeroplankton are very small to [[Microscope|microscopic]] in size, and many can be difficult to identify because of their tiny size. Scientists collect them for study in traps and sweep nets from [[aircraft]], kites or balloons.<ref>A. C. Hardy and P. S. Milne (1938) Studies in the Distribution of Insects by Aerial Currents. Journal of Animal Ecology, 7(2):199-229</ref> The study of the dispersion of these particles is called [[aerobiology]].

Aeroplankton is made up mostly of [[microorganism]]s, including [[virus]]es, about 1,000 different species of [[bacteria]], around 40,000 varieties of [[Fungus|fungi]], and hundreds of species of [[protist]]s, [[algae]], [[moss]]es, and [[Marchantiophyta|liverworts]] that live some part of their life cycle as aeroplankton, often as [[spore]]s, [[pollen]], and wind-scattered [[seed]]s. Additionally, microorganisms are swept into the air from terrestrial [[dust storm]]s, and an even larger amount of airborne marine microorganisms are propelled high into the atmosphere in [[sea spray]]. Aeroplankton deposits hundreds of millions of airborne viruses and tens of millions of bacteria every day on every square meter around the planet.

Small, drifting aeroplankton are found everywhere in the atmosphere, reaching concentration up to 10<sup>6</sup> microbial cells per cubic metre. Processes such as [[aerosolisation|aerosolization]] and wind transport determine how the microorganisms are distributed in the atmosphere. Air mass circulation globally disperses vast numbers of the floating aerial organisms, which travel across and between continents, creating [[Biogeography|biogeographic patterns]] by surviving and settling in remote environments. As well as the colonization of pristine environments, the globetrotting behaviour of these organisms has human health consequences. Airborne microorganisms are also involved in [[cloud formation]] and [[precipitation]], and play important roles in the formation of the [[phyllosphere]], a vast terrestrial habitat involved in [[nutrient cycling]].

==Overview==
[[File:Samplers of airborne microorganisms 2.png|thumb|right|upright=1.2| {{center|'''Sampling airborne microorganisms'''}}Left: [[Bioaerosol#Impingers|Impinger sampling]] of bioaerosols<br />Right: Six-stage Andersen [[cascade impactor]]]]

The atmosphere is the least understood biome on Earth despite its critical role as a microbial transport medium.<ref name=Archer2019 /> Recent studies have shown microorganisms are ubiquitous in the atmosphere and reach concentration up to 10<sup>6</sup> microbial cells per cubic metre ({{convert|1,000,000|/m3|/cuft|disp=out|abbr=on}}){{hsp}}<ref name=Zhen2017>{{cite journal |doi=10.1016/j.scitotenv.2017.05.049 |title=Meteorological factors had more impact on airborne bacterial communities than air pollutants |year=2017 |last1=Zhen |first1=Quan |last2=Deng |first2=Ye |last3=Wang |first3=Yaqing |last4=Wang |first4=Xiaoke |last5=Zhang |first5=Hongxing |last6=Sun |first6=Xu |last7=Ouyang |first7=Zhiyun |journal=Science of the Total Environment |volume=601-602 |pages=703–712 |pmid=28577405 |bibcode=2017ScTEn.601..703Z |s2cid=4576024}}</ref> and that they might be metabolically active.<ref name="Šantl-Temkiv2018">{{cite journal |doi=10.1093/femsec/fiy031 |title=Aeolian dispersal of bacteria in southwest Greenland: Their sources, abundance, diversity and physiological states |year=2018 |last1=Šantl-Temkiv |first1=Tina |last2=Gosewinkel |first2=Ulrich |last3=Starnawski |first3=Piotr |last4=Lever |first4=Mark |last5=Finster |first5=Kai |journal=FEMS Microbiology Ecology |volume=94 |issue=4 |pmid=29481623 |doi-access=free |hdl=20.500.11850/266148 |hdl-access=free}}</ref><ref>{{cite journal |doi=10.3389/fmicb.2016.00772 |doi-access=free |title=Molecular Evidence for Metabolically Active Bacteria in the Atmosphere |year=2016 |last1=Klein |first1=Ann M. |last2=Bohannan |first2=Brendan J. M. |last3=Jaffe |first3=Daniel A. |last4=Levin |first4=David A. |last5=Green |first5=Jessica L. |journal=Frontiers in Microbiology |volume=7 |page=772 |pmid=27252689 |pmc=4878314}}</ref> Different processes, such as [[aerosolisation]], might be important in selecting which microorganisms exist in the atmosphere.<ref name="Tignat-Perrier2019" /> Another process, microbial transport in the atmosphere, is critical for understanding the role microorganisms play in meteorology, atmospheric chemistry and public health.<ref name="Tignat-Perrier2019" />

Changes in species geographic distributions can have strong ecological and socioeconomic consequences.<ref>{{cite journal |doi=10.1126/science.aai9214 |title=Biodiversity redistribution under climate change: Impacts on ecosystems and human well-being |year=2017 |last1=Pecl |first1=Gretta T. |last2=Araújo |first2=Miguel B. |last3=Bell |first3=Johann D. |last4=Blanchard |first4=Julia |last5=Bonebrake |first5=Timothy C. |last6=Chen |first6=I-Ching |last7=Clark |first7=Timothy D. |last8=Colwell |first8=Robert K. |last9=Danielsen |first9=Finn|last10 = Evengård|first10 = Birgitta |last11=Falconi |first11=Lorena |last12=Ferrier |first12=Simon |last13=Frusher |first13=Stewart |last14=Garcia |first14=Raquel A. |last15=Griffis |first15=Roger B. |last16=Hobday |first16=Alistair J. |last17=Janion-Scheepers |first17=Charlene |last18=Jarzyna |first18=Marta A. |last19=Jennings |first19=Sarah|last20 = Lenoir|first20 = Jonathan |last21=Linnetved |first21=Hlif I. |last22=Martin |first22=Victoria Y. |last23=McCormack |first23=Phillipa C. |last24=McDonald |first24=Jan |last25=Mitchell |first25=Nicola J. |last26=Mustonen |first26=Tero |last27=Pandolfi |first27=John M. |last28=Pettorelli |first28=Nathalie |last29=Popova |first29=Ekaterina|last30 = Robinson|first30 = Sharon A. |journal=Science |volume=355 |issue=6332 |pmid=28360268 |hdl=10019.1/120851 |s2cid=206653576 |url=http://ecite.utas.edu.au/115569 |display-authors=1 |hdl-access=free}}</ref> In the case of microorganisms, air mass circulation disperses vast amounts of individuals and interconnects remote environments. Airborne microorganisms can travel between continents,<ref name=Creamean2013>{{cite journal |doi=10.1126/science.1227279 |title=Dust and Biological Aerosols from the Sahara and Asia Influence Precipitation in the Western U.S. |year=2013 |last1=Creamean |first1=J. M. |last2=Suski |first2=K. J. |last3=Rosenfeld |first3=D. |last4=Cazorla |first4=A. |last5=Demott |first5=P. J. |last6=Sullivan |first6=R. C. |last7=White |first7=A. B. |last8=Ralph |first8=F. M. |last9=Minnis |first9=P.|last10 = Comstock|first10 = J. M. |last11=Tomlinson |first11=J. M. |last12=Prather |first12=K. A. |journal=Science |volume=339 |issue=6127 |pages=1572–1578 |pmid=23449996 |bibcode=2013Sci...339.1572C |s2cid=2276891}}</ref> survive and settle on remote environments,<ref name="Hervàs2009">{{cite journal |doi=10.1111/j.1462-2920.2009.01926.x |title=Viability and potential for immigration of airborne bacteria from Africa that reach high mountain lakes in Europe |year=2009 |last1=Hervàs |first1=Anna |last2=Camarero |first2=Lluís |last3=Reche |first3=Isabel |last4=Casamayor |first4=Emilio O. |journal=Environmental Microbiology |volume=11 |issue=6 |pages=1612–1623 |pmid=19453609|bibcode=2009EnvMi..11.1612H }}</ref> which creates [[Biogeography|biogeographic patterns]].<ref name="Continental-scale distributions of"/> The circulation of atmospheric microorganisms results in global health concerns and ecological processes such as widespread dispersal of both pathogens{{hsp}}<ref name="Aerial Dispersal of Pathogens on th">{{cite journal |doi=10.1126/science.1072678 |title=Aerial Dispersal of Pathogens on the Global and Continental Scales and Its Impact on Plant Disease |year=2002 |last1=Brown |first1=James K. M. |last2=Hovmøller |first2=Mogens S. |journal=Science |volume=297 |issue=5581 |pages=537–541 |pmid=12142520 |bibcode=2002Sci...297..537B |s2cid=4207803}}</ref> and antibiotic resistances,<ref>{{cite journal |doi=10.1021/acs.est.5b06348 |title=Effect of Dust Storms on the Atmospheric Microbiome in the Eastern Mediterranean |year=2016 |last1=Mazar |first1=Yinon |last2=Cytryn |first2=Eddie |last3=Erel |first3=Yigal |last4=Rudich |first4=Yinon |journal=Environmental Science & Technology |volume=50 |issue=8 |pages=4194–4202 |pmid=27001166 |bibcode=2016EnST...50.4194M}}</ref> cloud formation and precipitation,<ref name=Creamean2013 /> and colonization of pristine environments.<ref name="Hervàs2009" /> Airborne microorganisms also play a role in the formation of the [[phyllosphere]], which is one of the vastest habitats on the Earth's surface{{hsp}}<ref>{{cite journal |doi=10.1007/s12229-015-9151-9 |title=The Ecology and Natural History of Foliar Bacteria with a Focus on Tropical Forests and Agroecosystems |year=2015 |last1=Griffin |first1=Eric A. |last2=Carson |first2=Walter P. |journal=The Botanical Review |volume=81 |issue=2 |pages=105–149 |bibcode=2015BotRv..81..105G |s2cid=14608948}}</ref> involved in [[nutrient cycling]].<ref>{{cite journal |doi=10.1111/1365-2745.13288 |title=Partitioning between atmospheric deposition and canopy microbial nitrification into throughfall nitrate fluxes in a Mediterranean forest |year=2020 |last1=Guerrieri |first1=Rossella |last2=Lecha |first2=Lucas |last3=Mattana |first3=Stefania |last4=Cáliz |first4=Joan |last5=Casamayor |first5=Emilio O. |last6=Barceló |first6=Anna |last7=Michalski |first7=Greg |last8=Peñuelas |first8=Josep |last9=Avila |first9=Anna |last10=Mencuccini |first10=Maurizio |journal=Journal of Ecology |volume=108 |issue=2 |pages=626–640 |s2cid=203880534 |doi-access=free |bibcode=2020JEcol.108..626G |hdl=11585/790081 |hdl-access=free}}</ref><ref>{{cite journal |doi=10.1016/j.atmosres.2016.07.018 |title=Bioaerosols in the Earth system: Climate, health, and ecosystem interactions |year=2016 |last1=Fröhlich-Nowoisky |first1=Janine |last2=Kampf |first2=Christopher J. |last3=Weber |first3=Bettina |last4=Huffman |first4=J. Alex |last5=Pöhlker |first5=Christopher |last6=Andreae |first6=Meinrat O. |last7=Lang-Yona |first7=Naama |last8=Burrows |first8=Susannah M. |last9=Gunthe |first9=Sachin S.|last10 = Elbert|first10 = Wolfgang |last11=Su |first11=Hang |last12=Hoor |first12=Peter |last13=Thines |first13=Eckhard |last14=Hoffmann |first14=Thorsten |last15=Després |first15=Viviane R. |last16=Pöschl |first16=Ulrich |journal=Atmospheric Research |volume=182 |pages=346–376 |bibcode=2016AtmRe.182..346F |doi-access=free}}</ref><ref name= Ontiveros2021 />

The field of bioaerosol research studies the taxonomy and community composition of airborne microbial organisms, also referred to as the air microbiome. A recent series of technological and analytical advancements include high-volumetric air samplers, an ultra-low biomass processing pipeline, low-input DNA sequencing libraries, as well as high-throughput sequencing technologies. Applied in unison, these methods have enabled comprehensive and meaningful characterization of the airborne microbial organismal dynamics found in the near-surface atmosphere.<ref name="Microbial communities in the tropic">{{cite journal |doi=10.1073/pnas.1908493116 |title=Microbial communities in the tropical air ecosystem follow a precise diel cycle |year=2019 |last1=Gusareva |first1=Elena S. |last2=Acerbi |first2=Enzo |last3=Lau |first3=Kenny J. X. |last4=Luhung |first4=Irvan |last5=Premkrishnan |first5=Balakrishnan N. V. |last6=Kolundžija |first6=Sandra |last7=Purbojati |first7=Rikky W. |last8=Wong |first8=Anthony |last9=Houghton |first9=James N. I.|last10 = Miller|first10 = Dana |last11=Gaultier |first11=Nicolas E. |last12=Heinle |first12=Cassie E. |last13=Clare |first13=Megan E. |last14=Vettath |first14=Vineeth Kodengil |last15=Kee |first15=Carmon |last16=Lim |first16=Serene B. Y. |last17=Chénard |first17=Caroline |last18=Phung |first18=Wen Jia |last19=Kushwaha |first19=Kavita K.|last20 = Nee|first20 = Ang Poh |last21=Putra |first21=Alexander |last22=Panicker |first22=Deepa |last23=Yanqing |first23=Koh |last24=Hwee |first24=Yap Zhei |last25=Lohar |first25=Sachin R. |last26=Kuwata |first26=Mikinori |last27=Kim |first27=Hie Lim |last28=Yang |first28=Liang |last29=Uchida |first29=Akira|last30 = Drautz-Moses|first30 = Daniela I. |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=46 |pages=23299–23308 |pmid=31659049 |pmc=6859341 |bibcode=2019PNAS..11623299G |display-authors=1 |doi-access=free}}</ref> Airborne microbial organisms also impact agricultural productivity, as bacterial and fungal species distributed by air movement act as plant blights.<ref>{{cite journal |doi=10.1139/b95-128 |title=Classification of airborne plant pathogens based on sporulation and infection characteristics |year=1995 |last1=Sache |first1=Ivan |last2=Vallavieille-Pope |first2=Claude de |journal=Canadian Journal of Botany |volume=73 |issue=8 |pages=1186–1195|bibcode=1995CaJB...73.1186S }}</ref> Furthermore, atmospheric processes, such as cloud condensation and ice nucleation events were shown to depend on airborne microbial particles.<ref>{{cite journal |doi=10.1126/sciadv.1501630 |title=Ice-nucleating bacteria control the order and dynamics of interfacial water |year=2016 |last1=Pandey |first1=Ravindra |last2=Usui |first2=Kota |last3=Livingstone |first3=Ruth A. |last4=Fischer |first4=Sean A. |last5=Pfaendtner |first5=Jim |last6=Backus |first6=Ellen H. G. |last7=Nagata |first7=Yuki |last8=Fröhlich-Nowoisky |first8=Janine |last9=Schmüser |first9=Lars|last10 = Mauri|first10 = Sergio |last11=Scheel |first11=Jan F. |last12=Knopf |first12=Daniel A. |last13=Pöschl |first13=Ulrich |last14=Bonn |first14=Mischa |last15=Weidner |first15=Tobias |journal=Science Advances |volume=2 |issue=4 |pages=e1501630 |pmid=27152346 |pmc=4846457 |bibcode=2016SciA....2E1630P}}</ref> Therefore, understanding the dynamics of microbial organisms in air is crucial for insights into the atmosphere as an ecosystem, but also will inform on human wellbeing and respiratory health.<ref>{{cite journal |doi=10.1038/s41598-020-78604-8 |title=Taxonomic composition and seasonal dynamics of the air microbiome in West Siberia |year=2020 |last1=Gusareva |first1=Elena S. |last2=Gaultier |first2=Nicolas P. E. |last3=Premkrishnan |first3=Balakrishnan N. V. |last4=Kee |first4=Carmon |last5=Lim |first5=Serene Boon Yuean |last6=Heinle |first6=Cassie E. |last7=Purbojati |first7=Rikky W. |last8=Nee |first8=Ang Poh |last9=Lohar |first9=Sachin R.|last10 = Yanqing|first10 = Koh |last11=Kharkov |first11=Vladimir N. |last12=Drautz-Moses |first12=Daniela I. |last13=Stepanov |first13=Vadim A. |last14=Schuster |first14=Stephan C. |journal=Scientific Reports |volume=10 |issue=1 |page=21515 |pmid=33299064 |pmc=7726148 |bibcode=2020NatSR..1021515G |s2cid=228089556}} [[File:CC-BY icon.svg|50px]] Modified text from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

In recent years, next generation [[DNA sequencing|DNA sequencing technologies]], such as [[metabarcoding]] as well as coordinated [[metagenomics]] and [[metatranscriptomics]] studies, have been providing new insights into [[Microbial ecology|microbial ecosystem functioning]], and the relationships that microorganisms maintain with their environment. There have been studies in soils,<ref>{{cite journal |doi=10.1038/ismej.2011.95 |title=Active and total microbial communities in forest soil are largely different and highly stratified during decomposition |year=2012 |last1=Baldrian |first1=Petr |last2=Kolařík |first2=Miroslav |last3=Štursová |first3=Martina |last4=Kopecký |first4=Jan |last5=Valášková |first5=Vendula |last6=Větrovský |first6=Tomáš |last7=Žifčáková |first7=Lucia |last8=Šnajdr |first8=Jaroslav |last9=Rídl |first9=Jakub|last10 = Vlček|first10 = Čestmír |last11=Voříšková |first11=Jana |journal=The ISME Journal |volume=6 |issue=2 |pages=248–258 |pmid=21776033 |pmc=3260513|bibcode=2012ISMEJ...6..248B }}</ref> the ocean,<ref>{{cite journal |doi=10.1038/ismej.2010.141 |title=Quantitative analysis of a deeply sequenced marine microbial metatranscriptome |year=2011 |last1=Gifford |first1=Scott M. |last2=Sharma |first2=Shalabh |last3=Rinta-Kanto |first3=Johanna M. |last4=Moran |first4=Mary Ann |journal=The ISME Journal |volume=5 |issue=3 |pages=461–472 |pmid=20844569 |pmc=3105723|bibcode=2011ISMEJ...5..461G }}</ref><ref>{{cite journal |doi=10.1371/journal.pone.0003042 |title=Detection of Large Numbers of Novel Sequences in the Metatranscriptomes of Complex Marine Microbial Communities |year=2008 |last1=Gilbert |first1=Jack A. |last2=Field |first2=Dawn |last3=Huang |first3=Ying |last4=Edwards |first4=Rob |last5=Li |first5=Weizhong |last6=Gilna |first6=Paul |last7=Joint |first7=Ian |journal=PLOS ONE |volume=3 |issue=8 |pages=e3042 |pmid=18725995 |pmc=2518522 |bibcode=2008PLoSO...3.3042G |doi-access=free}}</ref> the human gut,<ref>{{cite journal |last1=Franzosa |first1=E. A. |last2=Morgan |first2=X. C. |last3=Segata |first3=N. |last4=Waldron |first4=L. |last5=Reyes |first5=J. |last6=Earl |first6=A. M. |last7=Giannoukos |first7=G. |last8=Boylan |first8=M. R. |last9=Ciulla |first9=D. |last10=Gevers |first10=D. |last11=Izard |first11=J. |last12=Garrett |first12=W. S. |author-link12=Wendy Garrett |last13=Chan |first13=A. T. |last14=Huttenhower |first14=C. |year=2014 |title=Relating the metatranscriptome and metagenome of the human gut |journal=Proceedings of the National Academy of Sciences |volume=111 |issue=22 |pages=E2329–E2338 |bibcode=2014PNAS..111E2329F |doi=10.1073/pnas.1319284111 |pmc=4050606 |pmid=24843156 |doi-access=free}}</ref> and elsewhere.<ref>{{cite journal |doi=10.1186/2049-2618-2-17 |title=The Amazon continuum dataset: Quantitative metagenomic and metatranscriptomic inventories of the Amazon River plume, June 2010 |year=2014 |last1=Satinsky |first1=Brandon M. |last2=Zielinski |first2=Brian L. |last3=Doherty |first3=Mary |last4=Smith |first4=Christa B. |last5=Sharma |first5=Shalabh |last6=Paul |first6=John H. |last7=Crump |first7=Byron C. |last8=Moran |first8=Mary |journal=Microbiome |volume=2 |page=17 |pmid=24883185 |pmc=4039049 |doi-access=free}}</ref><ref>{{cite journal |doi=10.1038/ismej.2014.245 |title=Comparative metagenomic and metatranscriptomic analyses of microbial communities in acid mine drainage |year=2015 |last1=Chen |first1=Lin-Xing |last2=Hu |first2=Min |last3=Huang |first3=Li-nan |last4=Hua |first4=Zheng-Shuang |last5=Kuang |first5=Jia-Liang |last6=Li |first6=Sheng-jin |last7=Shu |first7=Wen-Sheng |journal=The ISME Journal |volume=9 |issue=7 |pages=1579–1592 |pmid=25535937 |pmc=4478699|bibcode=2015ISMEJ...9.1579C }}</ref><ref name=Amato2019 /><ref>See also: [[Pollen DNA barcoding]]</ref>

In the atmosphere, though, microbial gene expression and metabolic functioning remain largely unexplored, in part due to low biomass and sampling difficulties.<ref name=Amato2019 /> So far, metagenomics has confirmed high fungal, bacterial, and viral biodiversity,<ref>{{cite journal |doi=10.1007/s00248-014-0517-z |title=Metagenomic Analysis of the Airborne Environment in Urban Spaces |year=2015 |last1=Be |first1=Nicholas A. |last2=Thissen |first2=James B. |last3=Fofanov |first3=Viacheslav Y. |last4=Allen |first4=Jonathan E. |last5=Rojas |first5=Mark |last6=Golovko |first6=George |last7=Fofanov |first7=Yuriy |last8=Koshinsky |first8=Heather |last9=Jaing |first9=Crystal J. |journal=Microbial Ecology |volume=69 |issue=2 |pages=346–355 |pmid=25351142 |pmc=4312561|bibcode=2015MicEc..69..346B }}</ref><ref>{{cite journal |doi=10.1128/JVI.00293-12 |title=Metagenomic Characterization of Airborne Viral DNA Diversity in the Near-Surface Atmosphere |year=2012 |last1=Whon |first1=T. W. |last2=Kim |first2=M.-S. |last3=Roh |first3=S. W. |last4=Shin |first4=N.-R. |last5=Lee |first5=H.-W. |last6=Bae |first6=J.-W. |journal=Journal of Virology |volume=86 |issue=15 |pages=8221–8231 |pmid=22623790 |pmc=3421691}}</ref><ref>{{cite journal |doi=10.1371/journal.pone.0081862 |title=A Metagenomic Framework for the Study of Airborne Microbial Communities |year=2013 |last1=Yooseph |first1=Shibu |last2=Andrews-Pfannkoch |first2=Cynthia |last3=Tenney |first3=Aaron |last4=McQuaid |first4=Jeff |last5=Williamson |first5=Shannon |last6=Thiagarajan |first6=Mathangi |last7=Brami |first7=Daniel |last8=Zeigler-Allen |first8=Lisa |last9=Hoffman |first9=Jeff|last10 = Goll|first10 = Johannes B. |last11=Fadrosh |first11=Douglas |last12=Glass |first12=John |last13=Adams |first13=Mark D. |last14=Friedman |first14=Robert |last15=Venter |first15=J. Craig |journal=PLOS ONE |volume=8 |issue=12 |pages=e81862 |pmid=24349140 |pmc=3859506 |bibcode=2013PLoSO...881862Y |doi-access=free}}</ref><ref>{{cite journal |doi=10.1016/j.scitotenv.2016.12.081 |title=Investigation of diverse bacteria in cloud water at Mt. Tai, China |year=2017 |last1=Xu |first1=Caihong |last2=Wei |first2=Min |last3=Chen |first3=Jianmin |last4=Sui |first4=Xiao |last5=Zhu |first5=Chao |last6=Li |first6=Jiarong |last7=Zheng |first7=Lulu |last8=Sui |first8=Guodong |last9=Li |first9=Weijun|last10 = Wang|first10 = Wenxing |last11=Zhang |first11=Qingzhu |last12=Mellouki |first12=Abdelwahid |journal=Science of the Total Environment |volume=580 |pages=258–265 |pmid=28011017 |bibcode=2017ScTEn.580..258X |s2cid=27205968 |url=https://hal.archives-ouvertes.fr/hal-01740453/file/Xu_Science_of_the_Total_Environment_2017.pdf}}</ref> and targeted [[genomics]] and [[transcriptomics]] towards [[ribosomal gene]]s has supported earlier findings about the maintenance of metabolic activity in aerosols{{hsp}}<ref>{{cite journal |doi=10.3389/fmicb.2016.00772 |title=Molecular Evidence for Metabolically Active Bacteria in the Atmosphere |year=2016 |last1=Klein |first1=Ann M. |last2=Bohannan |first2=Brendan J. M. |last3=Jaffe |first3=Daniel A. |last4=Levin |first4=David A. |last5=Green |first5=Jessica L. |journal=Frontiers in Microbiology |volume=7 |page=772 |pmid=27252689 |pmc=4878314 |doi-access=free}}</ref><ref>{{cite journal |doi=10.5194/bg-12-6337-2015 |title=Characterization of active and total fungal communities in the atmosphere over the Amazon rainforest |year=2015 |last1=Womack |first1=A. M. |last2=Artaxo |first2=P. E. |last3=Ishida |first3=F. Y. |last4=Mueller |first4=R. C. |last5=Saleska |first5=S. R. |last6=Wiedemann |first6=K. T. |last7=Bohannan |first7=B. J. M. |last8=Green |first8=J. L. |journal=Biogeosciences |volume=12 |issue=21 |pages=6337–6349 |bibcode=2015BGeo...12.6337W |doi-access=free}}</ref> and in clouds.<ref name=Amato2017 /> In atmospheric chambers airborne bacteria have been consistently demonstrated to react to the presence of a carbon substrate by regulating [[ribosomal gene]] expressions.<ref>{{cite journal |doi=10.1021/ez500245y |title=Substrate-Dependent rRNA Production in an Airborne Bacterium |year=2014 |last1=Krumins |first1=Valdis |last2=Mainelis |first2=Gediminas |last3=Kerkhof |first3=Lee J. |last4=Fennell |first4=Donna E. |journal=Environmental Science & Technology Letters |volume=1 |issue=9 |pages=376–381|bibcode=2014EnSTL...1..376K }}</ref><ref name=Amato2019 />
{{clear}}

==Types==

===Pollen grains===
{{see also|Palynology}}
Effective pollen dispersal is vital for maintenance of genetic diversity and fundamental for connectivity between spatially separated populations.<ref>{{cite journal |doi=10.1111/j.1365-294X.2007.03448.x |title=Long distance pollen-mediated gene flow at a landscape level: The weed beet as a case study |year=2007 |last1=Fénart |first1=Stéphane |last2=Austerlitz |first2=Frédéric |last3=Cuguen |first3=Joël |last4=Arnaud |first4=Jean-François |journal=Molecular Ecology |volume=16 |issue=18 |pages=3801–3813 |pmid=17850547 |bibcode=2007MolEc..16.3801F |s2cid=6382777}}</ref> An efficient transfer of the pollen guarantees successful reproduction in flowering plants. No matter how pollen is dispersed, the male-female recognition is possible by mutual contact of stigma and pollen surfaces. [[Cytochemistry|Cytochemical reactions]] are responsible for pollen binding to a specific [[Stigma (botany)|stigma]].<ref>{{cite journal |doi=10.1105/tpc.015800 |title=Pollen and Stigma Structure and Function: The Role of Diversity in Pollination |year=2004 |last1=Edlund |first1=A. F. |last2=Swanson |first2=R. |last3=Preuss |first3=D. |journal=The Plant Cell Online |volume=16 |issue=Suppl |pages=S84–S97 |pmid=15075396 |pmc=2643401|bibcode=2004PlanC..16S..84E }}</ref><ref name=Denisow2015 />

Allergic diseases are considered to be one of the most important contemporary public health problems affecting up to 15–35% of humans worldwide.<ref name=WAO2011>{{Cite book |url=https://books.google.com/books?id=BwZKMwEACAAJ&q=%22WAO+white+book+on+allergy%22 |title=World Allergy Organization (WAO) White Book on Allergy |year=2011 |isbn=9780615461823}}</ref> There is a body of evidence suggesting that allergic reactions induced by pollen are on the increase, particularly in highly industrial countries.<ref name=WAO2011 /><ref name="Allergenic Pollen"/><ref name=Denisow2015 />

[[File:Misc pollen colorized.jpg|thumb|upright=1.5|left| Colourised [[scanning electron microscope|SEM]] image of [[pollen grain]]s from common plants]]

[[File:Pollen grains observed in aeroplankton of South Europe.png|thumb|upright=1.2|right| {{center|Pollen grains observed in aeroplankton of South Europe<ref name=Denisow2015>Denisow, B. and Weryszko-Chmielewska, E. (2015) "Pollen grains as airborne allergenic particles". ''Acta Agrobotanica'', '''68'''(4). {{doi|10.5586/aa.2015.045}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>}}]]

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===Fungal spores===
[[File:Drawings of fungal spores found in air.tif|thumb|upright=1.2|right|{{center|'''Drawings of fungal spores found in air'''<br /> Some cause asthma, such as ''[[Alternaria alternata]]''. A drawing of a very small "dust" seed from the flower ''[[Orchis maculata]]'' is provided for comparison.<ref name=Pringle2013>Pringle, A. (2013) "Asthma and the diversity of fungal spores in air". ''PLoS Pathogens'', '''9'''(6): e1003371. {{doi|10.1371/journal.ppat.1003371|doi-access=free}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref><ref>Figure adapted from: Ingold CT (1971) ''Fungal spores: their liberation and dispersal'', Oxford: Clarendon Press.</ref>}}{{space|4}}<small>A = [[ascospore]], B = [[basidiospore]], M = [[mitospore]]</small>]]

[[Fungi]], a major element of atmospheric [[bioaerosol]]s, are capable of existing and surviving in the air for extended periods of time.<ref>{{Cite book |url=https://books.google.com/books?id=cdcNYXGKPJIC&q=Dowd%2C+S.+C.%2C+Maier%2C+R.+M.+%281999%29+Aeromicrobiology+%22Environmental+microbiology%22&pg=PP1 |title=Environmental Microbiology |isbn=9780080919409 |last1=Pepper |first1=Ian L. |last2=Gerba |first2=Charles P. |last3=Gentry |first3=Terry J. |last4=Maier |first4=Raina M. |date=13 October 2011 |publisher=Academic Press}}</ref> Both the spores and the mycelium may be dangerous for people suffering from allergies, causing various health issues including asthma.<ref>{{cite journal |doi=10.1159/000066780 |title=Immunobiology of Fungal Allergens |year=2002 |last1=Kurup |first1=Viswanath P. |last2=Shen |first2=Horng-Der |last3=Vijay |first3=Hari |journal=International Archives of Allergy and Immunology |volume=129 |issue=3 |pages=181–188 |pmid=12444314 |s2cid=6588557}}</ref><ref name=Asan2004>{{cite journal |doi=10.1177/1420326X04033843 |title=Airborne Fungi and Actinomycetes Concentrations in the Air of Eskisehir City (Turkey) |year=2004 |last1=Asan |first1=Ahmet |last2=Ilhan |first2=Semra |last3=Sen |first3=Burhan |last4=Erkara |first4=Ismuhan Potoglu |last5=Filik |first5=Cansu |last6=Cabuk |first6=Ahmet |last7=Demirel |first7=Rasime |last8=Ture |first8=Mevlut |last9=Okten |first9=Suzan Sarica|last10 = Tokur|first10 = Suleyman |journal=Indoor and Built Environment |volume=13 |pages=63–74 |s2cid=84241303}}</ref> Apart from their negative impact on human health, atmospheric fungi may be dangerous for plants as sources of infection.<ref name=Pusz2013>{{cite journal |doi=10.1007/s11629-013-2704-7 |title=Airborne fungal spores of subalpine zone of the Karkonosze and Izerskie Mountains (Poland) |year=2013 |last1=Pusz |first1=Wojciech |last2=Kita |first2=Włodzimierz |last3=Dancewicz |first3=Andrzej |last4=Weber |first4=Ryszard |journal=Journal of Mountain Science |volume=10 |issue=6 |pages=940–952 |bibcode=2013JMouS..10..940P |s2cid=129157372}}</ref><ref name="Jędryczka2014">{{cite journal |last=Jędryczka |first=Małgorzata |title=Aeromycology: studies of fungi in aeroplankton |journal=Folia Biologica et Oecologica |date=25 November 2014 |volume=10 |pages=18–26 |doi=10.2478/fobio-2014-0013 |hdl=11089/9908 |s2cid=37133585 |issn=1730-2366 |url=http://hdl.handle.net/11089/9908 |language=pl |access-date=5 August 2021 |hdl-access=free}}</ref> Moreover, fungal organisms may be capable of creating additional toxins that are harmful to humans and animals, such as [[endotoxin]]s or [[mycotoxin]]s.<ref>{{cite journal |doi=10.1007/s10453-012-9276-9 |title=Size distribution of viable, cultivable, airborne microbes and their relationship to particulate matter concentrations and meteorological conditions in a Mediterranean site |year=2013 |last1=Raisi |first1=Louisa |last2=Aleksandropoulou |first2=Victoria |last3=Lazaridis |first3=Mihalis |last4=Katsivela |first4=Eleftheria |journal=Aerobiologia |volume=29 |issue=2 |pages=233–248 |bibcode=2013Aerob..29..233R |s2cid=84305807}}</ref><ref name=Pusz2021>{{cite journal |doi=10.1007/s10661-021-09090-2 |title=Airborne fungi in Longyearbyen area (Svalbard, Norway) — case study |year=2021 |last1=Pusz |first1=Wojciech |last2=Urbaniak |first2=Jacek |journal=Environmental Monitoring and Assessment |volume=193 |issue=5 |page=290 |pmid=33890180 |pmc=8062393|bibcode=2021EMnAs.193..290P }} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

Considering this aspect, aeromycological research is considered capable of predicting future symptoms of plant diseases in both crops and wild plants.<ref name=Pusz2013 /><ref name="Jędryczka2014" /> Fungi capable of travelling extensive distances with wind despite natural barriers, such as tall mountains, may be particularly relevant to understanding the role of fungi in plant disease.<ref>{{cite book |doi=10.1007/1-4020-5497-1_8 |chapter=Epidemiology of Puccinia Triticina in Gangetic Plain and planned containment of crop losses |title=Wheat Production in Stressed Environments |series=Developments in Plant Breeding |year=2007 |last1=Nagarajan |first1=S. |last2=Saharan |first2=M. S. |volume=12 |pages=71–76 |isbn=978-1-4020-5496-9}}</ref><ref>{{cite journal |doi=10.1016/j.cropro.2011.04.015 |title=First documentation on status of barley diseases from the high altitude cold arid Trans-Himalayan Ladakh region of India |year=2011 |last1=Vaish |first1=S.S. |last2=Bilal Ahmed |first2=Sheikh |last3=Prakash |first3=K. |journal=Crop Protection |volume=30 |issue=9 |pages=1129–1137|bibcode=2011CrPro..30.1129V }}</ref><ref name=Pusz2013 /><ref name=Pusz2017>{{cite journal |doi=10.1007/s10661-017-6243-5 |title=Analysis of selected fungi variation and its dependence on season and mountain range in southern Poland—key factors in drawing up trial guidelines for aeromycological monitoring |year=2017 |last1=Pusz |first1=Wojciech |last2=Weber |first2=Ryszard |last3=Dancewicz |first3=Andrzej |last4=Kita |first4=Włodzimierz |journal=Environmental Monitoring and Assessment |volume=189 |issue=10 |page=526 |pmid=28952055 |s2cid=29293277 |pmc=5614908|bibcode=2017EMnAs.189..526P }}</ref> Notably, the presence of numerous fungal organisms pathogenic to plants has been determined in mountainous regions.<ref name=Pusz2021 />

A wealth of correlative evidence suggests [[asthma]] is associated with [[fungi]] and triggered by elevated numbers of [[fungal spore]]s in the environment.<ref>Denning, D.W., O'driscoll, B.R., Hogaboam, C.M., Bowyer, P. and Niven, R.M. (2006) "The link between fungi and severe asthma: a summary of the evidence". ''European Respiratory Journal'', '''27'''(3): 615–626. {{doi|10.1183/09031936.06.00074705}}.</ref> Intriguing are reports of [[thunderstorm asthma]]. In a now classic study from the United Kingdom, an outbreak of acute asthma was linked to increases in ''[[Didymella exitialis]]'' ascospores and ''[[Sporobolomyces]]'' basidiospores associated with a severe weather event.<ref>Packe, G.E. and Ayres, J. (1985) "Asthma outbreak during a thunderstorm". ''The Lancet'', '''326'''(8448): 199–204. {{doi|10.1016/S0140-6736(85)91510-7}}.</ref> Thunderstorms are associated with spore plumes: when spore concentrations increase dramatically over a short period of time, for example from 20,000 spores/m<sup>3</sup> to over 170,000 spores/m<sup>3</sup> in 2 hours.<ref>Burch, M. and Levetin, E., 2002. Effects of meteorological conditions on spore plumes. International journal of biometeorology, 46(3), pp.107–117. {{doi|10.1007/s00484-002-0127-1}}.</ref> However, other sources consider pollen or pollution as causes of thunderstorm asthma.<ref>Bernstein, J.A., Alexis, N., Barnes, C., Bernstein, I.L., Nel, A., Peden, D., Diaz-Sanchez, D., Tarlo, S.M. and Williams, P.B., 2004. Health effects of air pollution. Journal of allergy and clinical immunology, 114(5), pp.1116-1123. {{doi|10.1016/j.jaci.2004.08.030}}.</ref> Transoceanic and transcontinental dust events move large numbers of spores across vast distances and have the potential to impact public health,<ref>Kellogg CA, Griffin DW (2006) "Aerobiology and the global transport of desert dust". ''Trends Ecol Evol'', '''21''': 638–644. {{doi|10.1016/j.tree.2006.07.004}}.</ref> and similar correlative evidence links dust blown off the Sahara with pediatric emergency room admissions on the island of Trinidad.<ref>Gyan, K., Henry, W., Lacaille, S., Laloo, A., Lamsee-Ebanks, C., McKay, S., Antoine, R.M. and Monteil, M.A. (2005) "African dust clouds are associated with increased paediatric asthma accident and emergency admissions on the Caribbean island of Trinidad". ''International Journal of Biometeorology'', '''49'''(6): 371–376. {{doi|10.1007/s00484-005-0257-3}}.</ref><ref name=Pringle2013 />

===Pteridophyte spores===

[[File:Pteridophyta spores in the air of Lublin.png|thumb|upright=1.2|right|{{center|[[Pteridophyta]] spores, including fern spores, in the air of Lublin}}]]

[[File:Pteridophyte lifecycle.jpg|thumb|160px|left| {{center|Pteridophyte life cycle}}]]

[[Pteridophyte]]s are [[vascular plant]]s that disperse [[spore]]s, such as fern spores. Pteridophyte spores are similar to pollen grains and fungal spores, and are also components of aeroplankton.<ref>{{cite journal |doi=10.2307/3454401 |jstor=3454401 |title=Outdoor Allergens |year=2000 |last1=Burge |first1=Harriet A. |last2=Rogers |first2=Christine A. |journal=Environmental Health Perspectives |volume=108 |issue=Suppl 4 |pages=653–659 |pmid=10931783 |pmc=1637672 |s2cid=16407560 |url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:4569473}}</ref><ref>Weryszko-Chmielewska, E. (2007). "Zakres badań i znaczenie aerobiologii". ''Aerobiologia''. Lublin: Wydawnictwo Akademii Rolniczej, pages 6-10 (in Polish).</ref> Fungal spores usually rank first among bioaerosol constituents due to their count numbers which can reach to between {{convert|1,000 and 10,000|/m3|/cuft}}, while pollen grains and fern spores can each reach to between {{convert|10 and 100|/m3|/cuft}}.<ref name="Allergenic Pollen">{{cite book |doi=10.1007/978-94-007-4881-1_1 |chapter=Introduction |title=Allergenic Pollen |year=2013 |last1=Cecchi |first1=Lorenzo |pages=1–7 |isbn=978-94-007-4880-4}}</ref><ref name="Després2012" />

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===Arthropods===
[[File:Spider ballooning structures.png|thumb|upright=1.2|right| Spider ballooning structures. Black, thick points represent the spider's body. Black lines represent ballooning threads.<ref>Cho, M., Neubauer, P., Fahrenson, C. and Rechenberg, I. (2018) "An observational study of ballooning in large spiders: Nanoscale multifibers enable large spiders' soaring flight". ''PLoS biology'', '''16'''(6): e2004405. {{doi|10.1371/journal.pbio.2004405.g007|doi-access=free}}. [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

Many small animals, mainly [[arthropod]]s (such as [[insect]]s and [[spider]]s), are also carried upwards into the atmosphere by air currents and may be found floating several thousand feet up. [[Aphid]]s, for example, are frequently found at high altitudes.

[[Ballooning (spider)|Ballooning]], sometimes called kiting, is a process by which [[spider]]s, and some other small [[invertebrate]]s, move through the air by releasing one or more [[Gossamer (spider silk)|gossamer threads]] to catch the wind, causing them to become airborne at the mercy of [[air current]]s.<ref>{{cite book |last1=Heinrichs |first1=Ann |title=Spiders |page=21 |date=2004 |publisher=Compass Point Books |isbn=9780756505905 |oclc=54027960 |url-access=registration |url=https://archive.org/details/spiders0000hein}}</ref><ref name=instar>{{cite journal |last=Valerio |first=C.E. |year=1977 |title=Population structure in the spider ''Achaearranea Tepidariorum'' (Aranae, Theridiidae) |journal=Journal of Arachnology |volume=3 |issue=3 |pages=185–190 |jstor=3704941}}</ref> A spider (usually limited to individuals of a small species), or spiderling after hatching,<ref>{{cite thesis |last1=Bond |first1=Jason Edward |title=Systematics and Evolution of the Californian Trapdoor Spider Genus Aptostichus Simon (Araneae: Mygalomorphae: Euctenizidae) |date=22 September 1999 |hdl=10919/29114 |citeseerx=10.1.1.691.8754}}</ref> will climb as high as it can, stand on raised legs with its abdomen pointed upwards ("tiptoeing"),<ref name=lab>{{cite journal |last=Weyman |first=G.S. |year=1995 |title=Laboratory studies of the factors stimulating ballooning behavior by Linyphiid spiders (Araneae, Linyphiidae) |journal=Journal of Arachnology |volume=23 |issue=2 |pages=75–84 |jstor=3705494}}</ref> and then release several silk threads from its [[Spinneret (spider)|spinnerets]] into the air. These automatically form a triangular shaped parachute<ref name=anchor>{{cite journal |last=Schneider |first=J.M. |author2=Roos, J. |author3=Lubin, Y. |author4=Henschel, J.R. |date=October 2001 |title=Dispersal of ''Stegodyphus Dumicola'' (Araneae, Eresidae): They do balloon after all! |journal=Journal of Arachnology |volume=29 |issue=1 |pages=114–116 |doi=10.1636/0161-8202(2001)029[0114:DOSDAE]2.0.CO;2 |s2cid=4707752 |url=https://www.biodiversitylibrary.org/part/226550}}</ref> which carries the spider away on updrafts of winds where even the slightest of breezes will disperse the arachnid.<ref name=lab/><ref name=anchor/> The flexibility of their silk draglines can aid the aerodynamics of their flight, causing the spiders to drift an unpredictable and sometimes long distance.<ref>{{cite web |title=Leap forward for 'flying' spiders |url=http://news.bbc.co.uk/2/hi/science/nature/5174012.stm |work=BBC News |access-date=23 July 2014 |date=12 July 2006}}</ref> Even atmospheric samples collected from balloons at {{cvt|5|km}} altitude and ships mid-ocean have reported spider landings. Mortality is high.<ref>{{cite journal |last1=Morley |first1=Erica L. |last2=Robert |first2=Daniel |title=Electric Fields Elicit Ballooning in Spiders |journal=Current Biology |date=July 2018 |volume=28 |issue=14 |pages=2324–2330.e2 |doi=10.1016/j.cub.2018.05.057 |pmid=29983315 |pmc=6065530|bibcode=2018CBio...28E2324M }}</ref>

Enough lift for ballooning may occur, even in windless conditions, if an [[static electric field|electrostatic charge gradient]] is present in the atmosphere.<ref>{{cite arXiv |last=Gorham |first=Peter |title=Ballooning spiders: The case for electrostatic flight |date=Sep 2013 |eprint=1309.4731 |class=physics.bio-ph}}</ref>

===Nematodes===
[[File:DIstribution modes and possible geographic ranges of nematodes.webp|thumb|upright=1.2|right|{{center|Distribution modes and possible geographic ranges of nematodes{{hsp}}<ref>{{cite journal |doi=10.1007/s10750-020-04373-0 |title=The ability to get everywhere: Dispersal modes of free-living, aquatic nematodes |year=2020 |last1=Ptatscheck |first1=Christoph |last2=Traunspurger |first2=Walter |journal=Hydrobiologia |volume=847 |issue=17 |pages=3519–3547 |s2cid=221110776 |doi-access=free|bibcode=2020HyBio.847.3519P }} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>}}]]

[[Nematode]]s (roundworms), the most common animal taxon, are also found among aeroplankton.<ref name=Nkem2006 /><ref name=Maguire1963 /><ref name=Vanschoenwinkel2007 /> Nematodes are an essential [[Trophic level|trophic link]] between [[unicellular organism]]s like bacteria, and larger organisms such as [[tardigrade]]s, [[copepod]]s, [[flatworm]]s, and [[fish]]es.<ref name=Ptatscheck2018 /> For nematodes, [[anhydrobiosis]] is a widespread strategy allowing them to survive unfavorable conditions for months and even years.<ref>Hendriksen, N. B. (1982) "Anhydrobiosis in nematodes: studies on Plectus sp." In: ''New trends in soil biology'' (Eds: Lebrun, P. André, H. M., De Medts, A., Grégoire-Wibo, C. Wauthy, G.) pages 387–394, Louvain-la-Neurve, Belgium.</ref><ref>Watanabe, M. (2006). "Anhydrobiosis in invertebrates". ''Applied Entomology and Zoology'', '''41'''(1): 15–31. {{doi|10.1303/aez.2006.15}}.</ref> Accordingly, nematodes can be readily dispersed by wind. However, as reported by Vanschoenwinkel et al.,<ref name=Vanschoenwinkel2007 /> nematodes account for only about one per cent of wind-drifted animals. Among the habitats colonized by nematodes are those that are strongly exposed to wind erosion as e.g., the shorelines of permanent waters, soils, mosses, dead wood, and tree bark.<ref>Andrássy, I. (2009) "Free-living nematodes of Hungary III (''Nematoda errantia'')". ''Pedozoologica Hungarica'' No. 5. Hungarian Natural History Museum and Systematic Zoology, Research Group of the Hungarian Academy of Sciences.</ref><ref name=Ptatscheck2018 /> In addition, within a few days of forming temporary waters such as [[phytotelmata]] were shown to be colonized by numerous nematode species.<ref name=Ptatscheck2014 /><ref>{{cite journal |doi=10.1163/15685411-00002913 |title=Nematode colonisation of artificial water-filled tree holes |year=2015 |last1=Ptatscheck |first1=Christoph |last2=Dümmer |first2=Birgit |last3=Traunspurger |first3=Walter |journal=Nematology |volume=17 |issue=8 |pages=911–921}}</ref><ref name=Ptatscheck2018 />

===Unicellular microorganisms===
A stream of [[unicellular]] airborne microorganisms circles the planet above weather systems but below commercial air lanes.<ref>[https://www.smithsonianmag.com/science-nature/living-bacteria-are-riding-earths-air-currents-180957734/ Living Bacteria Are Riding Earth's Air Currents] ''Smithsonian Magazine'', 11 January 2016.</ref> Some microorganisms are swept up from terrestrial dust storms, but most originate from [[marine microorganisms]] in [[sea spray]]. In 2018, scientists reported that hundreds of millions of viruses and tens of millions of bacteria are deposited daily on every square meter around the planet.<ref>{{cite news |last=Robbins |first=Jim |title=Trillions Upon Trillions of Viruses Fall From the Sky Each Day |url=https://www.nytimes.com/2018/04/13/science/virosphere-evolution.html |date=13 April 2018 |work=[[The New York Times]] |access-date=14 April 2018}}</ref><ref name="ISME-2018">{{cite journal |last1=Reche |first1=Isabel |last2=D'Orta |first2=Gaetano |last3=Mladenov |first3=Natalie |last4=Winget |first4=Danielle M |last5=Suttle |first5=Curtis A |title=Deposition rates of viruses and bacteria above the atmospheric boundary layer |journal=ISME Journal |volume=12 |issue=4 |pages=1154–1162 |date=29 January 2018 |doi=10.1038/s41396-017-0042-4 |pmid=29379178 |pmc=5864199|bibcode=2018ISMEJ..12.1154R }}</ref>

The presence of airborne [[cyanobacteria]] and [[microalgae]] as well as their negative impacts on human health have been documented by many researchers worldwide. However, studies on cyanobacteria and microalgae are few compared with those on other [[bacteria]] and [[virus]]es. Research is especially lacking on the presence and taxonomic composition of cyanobacteria and microalgae near economically important water bodies with much tourism.<ref name="Wiśniewska2020">{{cite journal |doi=10.1371/journal.pone.0238808 |title=The first characterization of airborne cyanobacteria and microalgae in the Adriatic Sea region |year=2020 |last1=Wiśniewska |first1=Kinga A. |last2=Śliwińska-Wilczewska |first2=Sylwia |last3=Lewandowska |first3=Anita U. |journal=PLOS ONE |volume=15 |issue=9 |pages=e0238808 |pmid=32913356 |pmc=7482968 |bibcode=2020PLoSO..1538808W |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> Research on airborne algae is especially important in tourist areas near water-bodies. Sunbathers are exposed to particularly high quantities of harmful cyanobacteria and microalgae. Additionally, harmful microalgae and cyanobacteria [[harmful algal blooms|blooms]] tend to occur in both marine and freshwater reservoirs during summer.<ref name="Approaches to monitoring, control a">{{cite journal |doi=10.1016/j.ocecoaman.2009.04.006 |title=Approaches to monitoring, control and management of harmful algal blooms (HABs) |year=2009 |last1=Anderson |first1=Donald M. |journal=Ocean & Coastal Management |volume=52 |issue=7 |pages=342–347 |pmid=20161650 |pmc=2818325 |bibcode=2009OCM....52..342A}}</ref><ref>{{cite journal |doi=10.3390/toxins7041048 |doi-access=free |title=Cyanobacteria and Algae Blooms: Review of Health and Environmental Data from the Harmful Algal Bloom-Related Illness Surveillance System (HABISS) 2007–2011 |year=2015 |last1=Backer |first1=Lorraine |last2=Manassaram-Baptiste |first2=Deana |last3=Leprell |first3=Rebecca |last4=Bolton |first4=Birgit |journal=Toxins |volume=7 |issue=4 |pages=1048–1064 |pmid=25826054 |pmc=4417954}}</ref><ref>{{cite journal |doi=10.1038/s41579-018-0040-1 |title=Cyanobacterial blooms |year=2018 |last1=Huisman |first1=Jef |last2=Codd |first2=Geoffrey A. |last3=Paerl |first3=Hans W. |last4=Ibelings |first4=Bas W. |last5=Verspagen |first5=Jolanda M. H. |last6=Visser |first6=Petra M. |journal=Nature Reviews Microbiology |volume=16 |issue=8 |pages=471–483 |pmid=29946124 |s2cid=49427202}}</ref><ref>{{cite journal |doi=10.3390/toxins10020076 |doi-access=free |title=Mitigating Toxic Planktonic Cyanobacterial Blooms in Aquatic Ecosystems Facing Increasing Anthropogenic and Climatic Pressures |year=2018 |last1=Paerl |first1=Hans |journal=Toxins |volume=10 |issue=2 |page=76 |pmid=29419777 |pmc=5848177}}</ref> Previous work has shown that the Mediterranean Sea is dominated by the [[picocyanobacteria]] ''[[Synechococcus]]'' sp. and ''[[Synechocystis]]'' sp., which are responsible for the production of a group of [[hepatotoxin]]s known as [[microcystin]]s.<ref>{{cite journal |doi=10.1016/j.hal.2011.12.005 |title=Microcystin producing cyanobacterial communities in Amvrakikos Gulf (Mediterranean Sea, NW Greece) and toxin accumulation in mussels (Mytilus galloprovincialis) |year=2012 |last1=Vareli |first1=Katerina |last2=Zarali |first2=Ekaterini |last3=Zacharioudakis |first3=Georgios S.A. |last4=Vagenas |first4=Georgios |last5=Varelis |first5=Vasileios |last6=Pilidis |first6=George |last7=Briasoulis |first7=Evangelos |last8=Sainis |first8=Ioannis |journal=Harmful Algae |volume=15 |pages=109–118|bibcode=2012HAlga..15..109V }}</ref> Because most tourism occurs in summer, many tourists are exposed to the most extreme negative impacts of airborne microalgae.<ref name="Wiśniewska2020" />

[[File:Comparison of aeolian and surface-water prokaryote communities 2.jpg|thumb|upright=2|{{center|Comparison of windborne and surface-water [[prokaryote]]<br />(bacteria plus [[archaea]]) communities over the [[Red Sea]], showing<br />their relative abundance during two years of [[DNA sequencing]].<ref name=Aalismail2020>{{cite journal |last1=Aalismail |first1=Nojood A. |last2=Díaz-Rúa |first2=Rubén |last3=Ngugi |first3=David K. |last4=Cusack |first4=Michael |last5=Duarte |first5=Carlos M. |title=Aeolian Prokaryotic Communities of the Global Dust Belt Over the Red Sea |journal=Frontiers in Microbiology |publisher=Frontiers Media SA |volume=11 |date=12 November 2020 |page=538476 |issn=1664-302X |doi=10.3389/fmicb.2020.538476 |pmid=33262740 |pmc=7688470 |doi-access=free}}</ref>}}]]

Airborne bacteria are emitted by most Earth surfaces (plants, oceans, land, and urban areas) to the atmosphere via a variety of mechanical processes such as [[eolian dust|aeolian]] [[soil erosion]], [[sea spray]] production, or mechanical disturbances including anthropogenic activities.<ref name="Bioaerosol generation by raindrops">{{cite journal |doi=10.1038/ncomms14668 |title=Bioaerosol generation by raindrops on soil |year=2017 |last1=Joung |first1=Young Soo |last2=Ge |first2=Zhifei |last3=Buie |first3=Cullen R. |journal=Nature Communications |volume=8 |page=14668 |pmid=28267145 |pmc=5344306 |bibcode=2017NatCo...814668J}}</ref><ref name=Michaud2018 /> Due to their relatively small size (the median [[aerodynamic diameter]] of bacteria-containing particles is around 2–4 μm),<ref name="Després2012" /> these can then be transported upward by turbulent fluxes{{hsp}}<ref name="Measurements and modeling of surfac">{{cite journal |doi=10.5194/acp-17-14919-2017 |title=Measurements and modeling of surface–atmosphere exchange of microorganisms in Mediterranean grassland |year=2017 |last1=Carotenuto |first1=Federico |last2=Georgiadis |first2=Teodoro |last3=Gioli |first3=Beniamino |last4=Leyronas |first4=Christel |last5=Morris |first5=Cindy E. |last6=Nardino |first6=Marianna |last7=Wohlfahrt |first7=Georg |last8=Miglietta |first8=Franco |journal=Atmospheric Chemistry and Physics |volume=17 |issue=24 |pages=14919–14936 |bibcode=2017ACP....1714919C |doi-access=free}}</ref> and carried by wind to long distances. As a consequence, bacteria are present in the air up to at least the lower [[stratosphere]].<ref>{{cite journal |doi=10.1111/j.1574-6968.2003.tb11513.x |title=Microorganisms cultured from stratospheric air samples obtained at 41 km |year=2003 |last1=Wainwright |first1=M. |last2=Wickramasinghe |first2=N.C |last3=Narlikar |first3=J.V |last4=Rajaratnam |first4=P. |journal=FEMS Microbiology Letters |volume=218 |issue=1 |pages=161–165 |pmid=12583913 |doi-access=free}}</ref><ref name="Microbiome of the upper troposphere"/><ref name="Airborne Bacteria in Earth's Lower">{{cite journal |doi=10.3389/fmicb.2018.01752 |doi-access=free |title=Airborne Bacteria in Earth's Lower Stratosphere Resemble Taxa Detected in the Troposphere: Results from a New NASA Aircraft Bioaerosol Collector (ABC) |year=2018 |last1=Smith |first1=David J. |last2=Ravichandar |first2=Jayamary Divya |last3=Jain |first3=Sunit |last4=Griffin |first4=Dale W. |last5=Yu |first5=Hongbin |last6=Tan |first6=Qian |last7=Thissen |first7=James |last8=Lusby |first8=Terry |last9=Nicoll |first9=Patrick|last10 = Shedler|first10 = Sarah |last11=Martinez |first11=Paul |last12=Osorio |first12=Alejandro |last13=Lechniak |first13=Jason |last14=Choi |first14=Samuel |last15=Sabino |first15=Kayleen |last16=Iverson |first16=Kathryn |last17=Chan |first17=Luisa |last18=Jaing |first18=Crystal |last19=McGrath |first19=John |journal=Frontiers in Microbiology |volume=9 |page=1752 |pmid=30154759 |pmc=6102410|bibcode=2018FrMic...901752S }}</ref> Given that the atmosphere is a large conveyor belt that moves air over thousands of kilometers, microorganisms are disseminated globally.<ref>{{cite journal |doi=10.1007/s00248-012-0088-9 |title=Free Tropospheric Transport of Microorganisms from Asia to North America |year=2012 |last1=Smith |first1=David J. |last2=Jaffe |first2=Daniel A. |last3=Birmele |first3=Michele N. |last4=Griffin |first4=Dale W. |last5=Schuerger |first5=Andrew C. |last6=Hee |first6=Jonathan |last7=Roberts |first7=Michael S. |journal=Microbial Ecology |volume=64 |issue=4 |pages=973–985 |pmid=22760734 |bibcode=2012MicEc..64..973S |s2cid=17601337}}</ref><ref name="Intercontinental Dispersal of Bacte">{{cite journal |doi=10.1128/AEM.03029-12 |title=Intercontinental Dispersal of Bacteria and Archaea by Transpacific Winds |year=2013 |last1=Smith |first1=David J. |last2=Timonen |first2=Hilkka J. |last3=Jaffe |first3=Daniel A. |last4=Griffin |first4=Dale W. |last5=Birmele |first5=Michele N. |last6=Perry |first6=Kevin D. |last7=Ward |first7=Peter D. |last8=Roberts |first8=Michael S. |journal=Applied and Environmental Microbiology |volume=79 |issue=4 |pages=1134–1139 |pmid=23220959 |pmc=3568602 |bibcode=2013ApEnM..79.1134S}}</ref><ref name=Griffin2017 /> Airborne transport of microbes is therefore likely pervasive at the global scale, yet there have been only a limited number of studies that have looked at the spatial distribution of microbes across different geographical regions.<ref name="Continental-scale distributions of">{{cite journal |doi=10.1073/pnas.1420815112 |title=Continental-scale distributions of dust-associated bacteria and fungi |year=2015 |last1=Barberán |first1=Albert |last2=Ladau |first2=Joshua |last3=Leff |first3=Jonathan W. |last4=Pollard |first4=Katherine S. |last5=Menninger |first5=Holly L. |last6=Dunn |first6=Robert R. |last7=Fierer |first7=Noah |journal=Proceedings of the National Academy of Sciences |volume=112 |issue=18 |pages=5756–5761 |pmid=25902536 |pmc=4426398 |bibcode=2015PNAS..112.5756B |doi-access=free}}</ref><ref name=Griffin2017 /> One of the main difficulties is linked with the low microbial biomass associated with a high diversity existing in the atmosphere outdoor (~10<sup>2</sup>–10<sup>5</sup> cells/m<sup>3</sup>)<ref name=Burrows2009b>{{cite journal |doi=10.5194/acp-9-9263-2009 |title=Bacteria in the global atmosphere – Part 1: Review and synthesis of literature data for different ecosystems |year=2009 |last1=Burrows |first1=S. M. |last2=Elbert |first2=W. |author3-link=Mark G. Lawrence |last3=Lawrence |first3=M. G. |last4=Pöschl |first4=U. |journal=Atmospheric Chemistry and Physics |volume=9 |issue=23 |pages=9263–9280 |bibcode=2009ACP.....9.9263B |doi-access=free}}</ref><ref name=Bowers2013 /><ref name="Amato2017"/> thus requiring reliable sampling procedures and controls. Furthermore, the site location and its environmental specificities have to be accounted for to some extent by considering chemical and meteorological variables.<ref>{{cite journal |doi=10.5194/acp-14-1485-2014 |title=Classification of clouds sampled at the puy de Dôme (France) based on 10 yr of monitoring of their physicochemical properties |year=2014 |last1=Deguillaume |first1=L. |last2=Charbouillot |first2=T. |last3=Joly |first3=M. |last4=Vaïtilingom |first4=M. |last5=Parazols |first5=M. |last6=Marinoni |first6=A. |last7=Amato |first7=P. |last8=Delort |first8=A.-M. |last9=Vinatier |first9=V.|last10 = Flossmann|first10 = A. |last11=Chaumerliac |first11=N. |last12=Pichon |first12=J. 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The environmental role of airborne cyanobacteria and microalgae is only partly understood. While present in the air, cyanobacteria and microalgae can contribute to [[ice nucleation]] and [[cloud droplet formation]]. Cyanobacteria and microalgae can also impact human health.<ref name="Després2012" /><ref name="Wiśniewska2019" /><ref name=Genitsaris2011 /><ref>{{cite journal |doi=10.1016/0021-8707(66)90039-6 |title=Sensitivity of skin and bronchial mucosa to green algae |year=1966 |last1=Bernstein |first1=I.Leonard |last2=Safferman |first2=Robert S. |journal=Journal of Allergy |volume=38 |issue=3 |pages=166–173 |pmid=5223702}}</ref><ref>{{cite journal |doi=10.5194/acp-12-9817-2012 |title=Heterogeneous ice nucleation on atmospheric aerosols: A review of results from laboratory experiments |year=2012 |last1=Hoose |first1=C. |last2=Möhler |first2=O. |journal=Atmospheric Chemistry and Physics |volume=12 |issue=20 |pages=9817–9854 |bibcode=2012ACP....12.9817H |doi-access=free}}</ref><ref>{{cite journal |doi=10.3389/fmicb.2018.02681 |doi-access=free |title=Ice Nucleation Activity and Aeolian Dispersal Success in Airborne and Aquatic Microalgae |year=2018 |last1=Tesson |first1=Sylvie V. M. |last2=Šantl-Temkiv |first2=Tina |journal=Frontiers in Microbiology |volume=9 |page=2681 |pmid=30483227 |pmc=6240693}}</ref> Depending on their size, airborne cyanobacteria and microalgae can be inhaled by humans and settle in different parts of the respiratory system, leading to the formation or intensification of numerous diseases and ailments, e.g., allergies, dermatitis, and rhinitis.<ref name=Genitsaris2011 /><ref>{{cite journal |doi=10.1016/j.ecoenv.2006.08.006 |title=Allergenicity of airborne cyanobacteria Phormidium fragile and Nostoc muscorum |year=2008 |last1=Sharma |first1=Naveen Kumar |last2=Rai |first2=Ashwani K. |journal=Ecotoxicology and Environmental Safety |volume=69 |issue=1 |pages=158–162 |pmid=17011621|bibcode=2008EcoES..69..158S }}</ref><ref>{{cite journal |doi=10.1016/j.marpolbul.2017.07.064 |title=Identification of cyanobacteria and microalgae in aerosols of various sizes in the air over the Southern Baltic Sea |year=2017 |last1=Lewandowska |first1=Anita Urszula |last2=Śliwińska-Wilczewska |first2=Sylwia |last3=Woźniczka |first3=Dominika |journal=Marine Pollution Bulletin |volume=125 |issue=1–2 |pages=30–38 |pmid=28823424 |bibcode=2017MarPB.125...30L}}</ref> According to Wiśniewska et al.,<ref name="Wiśniewska2019" /> these harmful microorganisms can constitute between 13% and 71% of sampled taxa.<ref name="Wiśniewska2020" /> However, the interplay between microbes and atmospheric physical and chemical conditions is an open field of research that can only be fully addressed using multidisciplinary approaches.<ref name=Dommergue2019>{{cite journal |doi=10.3389/fmicb.2019.00243 |title=Methods to Investigate the Global Atmospheric Microbiome |year=2019 |last1=Dommergue |first1=Aurelien |last2=Amato |first2=Pierre |last3=Tignat-Perrier |first3=Romie |last4=Magand |first4=Olivier |last5=Thollot |first5=Alban |last6=Joly |first6=Muriel |last7=Bouvier |first7=Laetitia |last8=Sellegri |first8=Karine |last9=Vogel |first9=Timothy|last10 = Sonke|first10 = Jeroen E. |last11=Jaffrezo |first11=Jean-Luc |last12=Andrade |first12=Marcos |last13=Moreno |first13=Isabel |last14=Labuschagne |first14=Casper |last15=Martin |first15=Lynwill |last16=Zhang |first16=Qianggong |last17=Larose |first17=Catherine |journal=Frontiers in Microbiology |volume=10 |page=243 |pmid=30967843 |pmc=6394204 |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

Airborne microalgae and cyanobacteria are the most poorly studied organisms in [[aerobiology]] and [[phycology]].<ref name=Sahu2015 /><ref>{{cite journal |doi=10.1111/j.1529-8817.2007.00373.x |title=Airborne Algae: Their Present Status and Relevance1 |year=2007 |last1=Sharma |first1=Naveen Kumar |last2=Rai |first2=Ashwani Kumar |last3=Singh |first3=Surendra |last4=Brown |first4=Richard Malcolm |journal=Journal of Phycology |volume=43 |issue=4 |pages=615–627 |bibcode=2007JPcgy..43..615S |s2cid=85314169}}</ref><ref name="Wiśniewska2020" /> This lack of knowledge may result from the lack of standard methods for both sampling and further analysis, especially quantitative analytical methods.<ref name="Wiśniewska2019" /> Few studies have been performed to determine the number of cyanobacteria and microalgae in the atmosphere <ref>Schlichting HE Jr. (1964) "Meteorological conditions affecting the dispersal of airborne algae and Protozoa". ''Lloydia'', '''27''': 64–78.</ref><ref>{{cite journal |doi=10.1080/09670260110001735538 |title=A quantitative investigation of airborne algae and lichen soredia obtained from pollen traps in south-west Spain |year=2001 |last1=Tormo |first1=R. |last2=Recio |first2=D. |last3=Silva |first3=I. |last4=Muñoz |first4=A.F. |journal=European Journal of Phycology |volume=36 |issue=4 |pages=385–390 |s2cid=85653057 |doi-access=|bibcode=2001EJPhy..36..385T }}</ref> However, it was shown in 2012 that the average quantity of atmospheric algae is between 100 and 1000 cells per cubic meter of air.<ref name="Després2012" /> As of 2019, about 350 taxa of cyanobacteria and microalgae have been documented in the atmosphere worldwide.<ref name="Wiśniewska2019" /><ref name=Genitsaris2011>{{cite journal |doi=10.2741/e285 |title=Airborne Algae and Cyanobacteria Occurrence and Related Health Effects |year=2011 |last1=Moustaka-Gouni |first1=Maria |last2=Kormas |first2=K. A. |last3=Moustaka-Gouni |first3=M. |journal=Frontiers in Bioscience |volume=3 |issue=2 |pages=772–787 |pmid=21196350 |doi-access=free}}</ref> Cyanobacteria and microalgae end up in the air as a consequence of their emission from soil, buildings, trees, and roofs.<ref name="Wiśniewska2019" /><ref>{{cite journal |doi=10.1007/BF01084602 |title=Meteorological effects on variation of airborne algae in Mexico |year=1989 |last1=Rosas |first1=Irma |last2=Roy-Ocotla |first2=Guadalupe |last3=Mosiño |first3=Pedro |journal=International Journal of Biometeorology |volume=33 |issue=3 |pages=173–179 |bibcode=1989IJBm...33..173R |s2cid=84781386}}</ref><ref>{{cite journal |doi=10.1016/j.envres.2006.04.003 |title=Diversity and seasonal variation of viable algal particles in the atmosphere of a subtropical city in India |year=2006 |last1=Sharma |first1=Naveen Kumar |last2=Singh |first2=Surendra |last3=Rai |first3=Ashwani K. |journal=Environmental Research |volume=102 |issue=3 |pages=252–259 |pmid=16780831 |bibcode=2006ER....102..252S}}</ref><ref name="Wiśniewska2020" />

Biological particles are known to represent a significant fraction (~20–70%) of the total number of [[aerosol]]s > 0.2 μm, with large spatial and temporal variations.<ref>{{cite journal |doi=10.1016/0169-8095(95)00017-8 |title=The size distribution of primary biological aerosol particles with radii > 0.2 μm in an urban/Rural influenced region |year=1995 |last1=Matthias-Maser |first1=S. |last2=Jaenicke |first2=R. |journal=Atmospheric Research |volume=39 |issue=4 |pages=279–286 |bibcode=1995AtmRe..39..279M}}</ref><ref name="Composition and diurnal variability">{{cite journal |doi=10.1029/2003JD004049 |title=Composition and diurnal variability of the natural Amazonian aerosol |year=2003 |last1=Graham |first1=Bim |last2=Guyon |first2=Pascal |last3=Maenhaut |first3=Willy |last4=Taylor |first4=Philip E. |last5=Ebert |first5=Martin |last6=Matthias-Maser |first6=Sabine |last7=Mayol-Bracero |first7=Olga L. |last8=Godoi |first8=Ricardo H. 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T. |last8=Andreae |first8=M. O. |last9=Pöschl |first9=U. |journal=Atmospheric Chemistry and Physics |volume=12 |issue=24 |pages=11997–12019 |bibcode=2012ACP....1211997H |doi-access=free}}</ref> Among these, microorganisms are of particular interest in fields as diverse as epidemiology, including [[phytopathology]],<ref>{{cite journal |doi=10.1016/j.meegid.2006.05.002 |title=Surprising niche for the plant pathogen ''Pseudomonas syringae'' |year=2007 |last1=Morris |first1=Cindy E. |last2=Kinkel |first2=Linda L. |last3=Xiao |first3=Kun |last4=Prior |first4=Philippe |last5=Sands |first5=David C. |journal=Infection, Genetics and Evolution |volume=7 |issue=1 |pages=84–92 |pmid=16807133|bibcode=2007InfGE...7...84M }}</ref> bioterrorism, forensic science, and public health,<ref>Galán Soldevilla C., Cariñanos González P., Alcázar Teno P., Domínguez Vilches E. (2007). "Management and Quality Manual". ''Spanish Aerobiology Network'' (REA), Cordoba: Servicio de Publicaciones.</ref> and environmental sciences, like [[microbial ecology]],<ref>{{cite journal |doi=10.1038/ismej.2014.55 |title=Features of air masses associated with the deposition of ''Pseudomonas syringae'' and ''Botrytis cinerea'' by rain and snowfall |year=2014 |last1=Monteil |first1=Caroline L. |last2=Bardin |first2=Marc |last3=Morris |first3=Cindy E. |journal=The ISME Journal |volume=8 |issue=11 |pages=2290–2304 |pmid=24722630 |pmc=4992071|bibcode=2014ISMEJ...8.2290M }}</ref><ref name="Long-range transport of airborne mi">{{cite journal |doi=10.1038/s41467-017-00110-9 |title=Long-range transport of airborne microbes over the global tropical and subtropical ocean |year=2017 |last1=Mayol |first1=Eva |last2=Arrieta |first2=Jesús M. |last3=Jiménez |first3=Maria A. |last4=Martínez-Asensio |first4=Adrián |last5=Garcias-Bonet |first5=Neus |last6=Dachs |first6=Jordi |last7=González-Gaya |first7=Belén |last8=Royer |first8=Sarah-J. |last9=Benítez-Barrios |first9=Verónica M.|last10 = Fraile-Nuez|first10 = Eugenio |last11=Duarte |first11=Carlos M. |journal=Nature Communications |volume=8 |issue=1 |page=201 |pmid=28779070 |pmc=5544686 |bibcode=2017NatCo...8..201M}}</ref><ref name=Michaud2018>{{cite journal |doi=10.1038/s41467-018-04409-z |title=Taxon-specific aerosolization of bacteria and viruses in an experimental ocean-atmosphere mesocosm |year=2018 |last1=Michaud |first1=Jennifer M. |last2=Thompson |first2=Luke R. |last3=Kaul |first3=Drishti |last4=Espinoza |first4=Josh L. |last5=Richter |first5=R. Alexander |last6=Xu |first6=Zhenjiang Zech |last7=Lee |first7=Christopher |last8=Pham |first8=Kevin M. |last9=Beall |first9=Charlotte M.|last10 = Malfatti|first10 = Francesca |last11=Azam |first11=Farooq |last12=Knight |first12=Rob |last13=Burkart |first13=Michael D. |last14=Dupont |first14=Christopher L. |last15=Prather |first15=Kimberly A. |journal=Nature Communications |volume=9 |issue=1 |page=2017 |pmid=29789621 |pmc=5964107 |bibcode=2018NatCo...9.2017M |s2cid=43969729}}</ref> meteorology and climatology.<ref>{{cite journal |doi=10.5194/acp-12-8645-2012 |title=Bacteria in the ECHAM5-HAM global climate model |year=2012 |last1=Sesartic |first1=A. |last2=Lohmann |first2=U. |last3=Storelvmo |first3=T. |journal=Atmospheric Chemistry and Physics |volume=12 |issue=18 |pages=8645–8661 |bibcode=2012ACP....12.8645S |hdl=20.500.11850/44091 |hdl-access=free |doi-access=free}}</ref><ref>{{cite journal |doi=10.3390/atmos8110229 |doi-access=free |title=Atmospheric Processing and Variability of Biological Ice Nucleating Particles in Precipitation at Opme, France |year=2017 |last1=Pouzet |first1=Glwadys |last2=Peghaire |first2=Elodie |last3=Aguès |first3=Maxime |last4=Baray |first4=Jean-Luc |last5=Conen |first5=Franz |last6=Amato |first6=Pierre |journal=Atmosphere |volume=8 |issue=12 |page=229 |bibcode=2017Atmos...8..229P}}</ref> More precisely concerning the latter, airborne microorganisms contribute to the pool of particles nucleating the condensation and crystallization of water and they are thus potentially involved in cloud formation and in the triggering of precipitation.<ref>{{cite journal |doi=10.1111/gcb.12447 |title=Bioprecipitation: A feedback cycle linking Earth history, ecosystem dynamics and land use through biological ice nucleators in the atmosphere |year=2014 |last1=Morris |first1=Cindy E. |last2=Conen |first2=Franz |last3=Alex Huffman |first3=J. |last4=Phillips |first4=Vaughan |last5=Pöschl |first5=Ulrich |last6=Sands |first6=David C. |journal=Global Change Biology |volume=20 |issue=2 |pages=341–351 |pmid=24399753 |bibcode=2014GCBio..20..341M |s2cid=10572570 |url=https://hal.inrae.fr/hal-02637995/file/2014_Morris_Global%20Change%20Biology_postprint_1.pdf}}</ref><ref name="FröhlichNowoisky2016" /> Additionally, viable microbial cells act as chemical catalyzers interfering with atmospheric chemistry.<ref name="ReferenceA">{{cite journal |doi=10.1073/pnas.1205743110 |title=Potential impact of microbial activity on the oxidant capacity and organic carbon budget in clouds |year=2013 |last1=Vaitilingom |first1=M. |last2=Deguillaume |first2=L. |last3=Vinatier |first3=V. |last4=Sancelme |first4=M. |last5=Amato |first5=P. |last6=Chaumerliac |first6=N. |last7=Delort |first7=A.-M. |journal=Proceedings of the National Academy of Sciences |volume=110 |issue=2 |pages=559–564 |pmid=23263871 |pmc=3545818 |bibcode=2013PNAS..110..559V |doi-access=free}}</ref> The constant flux of bacteria from the atmosphere to the Earth's surface due to precipitation and dry deposition can also affect global biodiversity, but they are rarely taken into account when conducting ecological surveys.<ref name="ISME-2018" /><ref>{{cite journal |doi=10.1016/j.gloenvcha.2009.09.005 |title=The protection of Antarctic terrestrial ecosystems from inter- and intra-continental transfer of non-indigenous species by human activities: A review of current systems and practices |year=2010 |last1=Hughes |first1=Kevin A. |last2=Convey |first2=Pete |journal=Global Environmental Change |volume=20 |issue=1 |pages=96–112|bibcode=2010GEC....20...96H }}</ref><ref>{{cite journal |doi=10.1073/pnas.1711842115 |title=The biomass distribution on Earth |year=2018 |last1=Bar-On |first1=Yinon M. |last2=Phillips |first2=Rob |last3=Milo |first3=Ron |journal=Proceedings of the National Academy of Sciences |volume=115 |issue=25 |pages=6506–6511 |pmid=29784790 |pmc=6016768 |bibcode=2018PNAS..115.6506B |doi-access=free}}</ref><ref>{{cite journal |doi=10.3389/fmicb.2018.02257 |doi-access=free |title=Assessing the Aerial Interconnectivity of Distant Reservoirs of Sclerotinia sclerotiorum |year=2018 |last1=Leyronas |first1=Christel |last2=Morris |first2=Cindy E. |last3=Choufany |first3=Maria |last4=Soubeyrand |first4=Samuel |journal=Frontiers in Microbiology |volume=9 |page=2257 |pmid=30337908 |pmc=6178138}}</ref> As stressed by these studies attempting to decipher and understand the spread of microbes over the planet,<ref name="Burrows2009a">{{cite journal |doi=10.5194/acp-9-9281-2009 |title=Bacteria in the global atmosphere – Part 2: Modeling of emissions and transport between different ecosystems |year=2009 |last1=Burrows |first1=S. M. |last2=Butler |first2=T. |last3=Jöckel |first3=P. |last4=Tost |first4=H. |last5=Kerkweg |first5=A. |last6=Pöschl |first6=U. |last7=Lawrence |first7=M. G. |journal=Atmospheric Chemistry and Physics |volume=9 |issue=23 |pages=9281–9297 |bibcode=2009ACP.....9.9281B |doi-access=free}}</ref><ref name= Bowers2013>{{cite journal |doi=10.1021/es402970s |title=Seasonal Variability in Bacterial and Fungal Diversity of the Near-Surface Atmosphere |year=2013 |last1=Bowers |first1=Robert M. |last2=Clements |first2=Nicholas |last3=Emerson |first3=Joanne B. |last4=Wiedinmyer |first4=Christine |last5=Hannigan |first5=Michael P. |last6=Fierer |first6=Noah |journal=Environmental Science & Technology |volume=47 |issue=21 |pages=12097–12106 |pmid=24083487 |bibcode=2013EnST...4712097B}}</ref><ref name="Šantl-Temkiv2018"/> concerted data are needed for documenting the abundance and distribution of airborne microorganisms, including at remote and altitudes sites.<ref name=Dommergue2019 />

==Bioaerosols==
[[Bioaerosol]]s, known also as primary biological [[aerosol]]s, are the subset of [[Particulates|atmospheric particles]] that are directly released from the [[biosphere]] into the atmosphere. They include living and dead organisms (e.g., [[algae]], [[archaea]], [[bacteria]]{{hsp}}<ref>{{cite journal |doi=10.1126/science.143.3606.583 |title=Airborne Algae: Their Abundance and Heterogeneity |year=1964 |last1=Brown |first1=R. M. |last2=Larson |first2=D. A. |last3=Bold |first3=H. C. |journal=Science |volume=143 |issue=3606 |pages=583–585 |pmid=17815653 |bibcode=1964Sci...143..583B |s2cid=44328547}}</ref><ref>{{cite journal |doi=10.1128/AEM.03333-15 |title=Airborne Microalgae: Insights, Opportunities, and Challenges |year=2016 |last1=Tesson |first1=Sylvie V. M. |last2=Skjøth |first2=Carsten Ambelas |last3=Šantl-Temkiv |first3=Tina |last4=Löndahl |first4=Jakob |journal=Applied and Environmental Microbiology |volume=82 |issue=7 |pages=1978–1991 |pmid=26801574 |pmc=4807511 |bibcode=2016ApEnM..82.1978T |s2cid=4790872}}</ref><ref>{{cite journal |doi=10.1016/S0169-8095(98)00109-4 |title=Abundance of airborne heterotrophic protists in ground level air of South Dakota |year=1999 |last1=Rogerson |first1=Andrew |last2=Detwiler |first2=Andrew |journal=Atmospheric Research |volume=51 |issue=1 |pages=35–44 |bibcode=1999AtmRe..51...35R}}</ref>), dispersal units (e.g., [[fungal spore]]s and plant [[pollen]]{{hsp}}<ref>{{cite journal |doi=10.1016/0021-8502(94)90216-X |title=Fungal aerosols: A review |year=1994 |last1=Madelin |first1=T.M. |journal=Journal of Aerosol Science |volume=25 |issue=8 |pages=1405–1412 |bibcode=1994JAerS..25.1405M}}</ref>), and various fragments or excretions (e.g., plant debris and [[brochosome]]s).<ref>{{cite journal |doi=10.1016/j.atmosenv.2003.12.006 |title=New Directions: The role of bioaerosols in atmospheric chemistry and physics |year=2004 |last1=Ariya |first1=Parisa A. |last2=Amyot |first2=Marc |journal=Atmospheric Environment |volume=38 |issue=8 |pages=1231–1232 |bibcode=2004AtmEn..38.1231A}}</ref><ref>{{Cite book |url=https://books.google.com/books?id=7zkLEAAAQBAJ&q=%22Bioaerosols+Handbook%22 |title=Bioaerosols Handbook |isbn=9781000115048 |last1=Cox |first1=Christopher S. |last2=Wathes |first2=Christopher M. |date=25 November 2020 |publisher=CRC Press}}</ref><ref name="Després2012" /><ref name="Composition and diurnal variability"/><ref>{{cite journal |doi=10.1016/0021-8502(95)97180-M |title=Seasonal variation of primary biological aerosol particles |year=1995 |last1=Matthias-Maser |first1=Sabine |last2=Peters |first2=Kristina |last3=Jaenicke |first3=Ruprecht |journal=Journal of Aerosol Science |volume=26 |pages=S545–S546 |bibcode=1995JAerS..26S.545M}}</ref><ref name=Womack2010>{{cite journal |doi=10.1098/rstb.2010.0283 |title=Biodiversity and biogeography of the atmosphere |year=2010 |last1=Womack |first1=Ann M. |last2=Bohannan |first2=Brendan J. M. |last3=Green |first3=Jessica L. |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=365 |issue=1558 |pages=3645–3653 |pmid=20980313 |pmc=2982008}}</ref> Bioaerosol particle diameters range from [[nanometer]]s up to about a tenth of a millimeter. The upper limit of the aerosol particle size range is determined by rapid sedimentation, i.e., larger particles are too heavy to remain airborne for extended periods of time.<ref name=Hinds1999>{{Cite book |url=https://books.google.com/books?id=qIkyjPXfWK4C&q=%22Aerosol+Technology%22 |title=Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles |isbn=9781118591970 |last1=Hinds |first1=William C. |date=6 December 2012 |publisher=John Wiley & Sons}}</ref><ref name="Atmospheric Aerosols: Composition">{{cite journal |doi=10.1002/anie.200501122 |title=Atmospheric Aerosols: Composition, Transformation, Climate and Health Effects |year=2005 |last1=Pöschl |first1=Ulrich |journal=Angewandte Chemie International Edition |volume=44 |issue=46 |pages=7520–7540 |pmid=16302183}}</ref><ref name="FröhlichNowoisky2016">{{cite journal |doi=10.1016/j.atmosres.2016.07.018 |title=Bioaerosols in the Earth system: Climate, health, and ecosystem interactions |year=2016 |last1=Fröhlich-Nowoisky |first1=Janine |last2=Kampf |first2=Christopher J. |last3=Weber |first3=Bettina |last4=Huffman |first4=J. Alex |last5=Pöhlker |first5=Christopher |last6=Andreae |first6=Meinrat O. |last7=Lang-Yona |first7=Naama |last8=Burrows |first8=Susannah M. |last9=Gunthe |first9=Sachin S.|last10 = Elbert|first10 = Wolfgang |last11=Su |first11=Hang |last12=Hoor |first12=Peter |last13=Thines |first13=Eckhard |last14=Hoffmann |first14=Thorsten |last15=Després |first15=Viviane R. |last16=Pöschl |first16=Ulrich |journal=Atmospheric Research |volume=182 |pages=346–376 |bibcode=2016AtmRe.182..346F |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> Bioaerosols include living and dead organisms as well as their fragments and excrements emitted from the biosphere into the atmosphere.<ref name=Urbano2011>{{cite journal |doi=10.5194/bg-8-301-2011 |title=Detection and phylogenetic analysis of coastal bioaerosols using culture dependent and independent techniques |year=2011 |last1=Urbano |first1=R. |last2=Palenik |first2=B. |last3=Gaston |first3=C. J. |last4=Prather |first4=K. A. |journal=Biogeosciences |volume=8 |issue=2 |pages=301–309 |bibcode=2011BGeo....8..301U |doi-access=free}}</ref>
<ref name= "Després2012" /><ref name="FröhlichNowoisky2016"/> Included are archaea, fungi, microalgae, cyanobacteria, bacteria, viruses, plant cell debris, and pollen.<ref name="Urbano2011"/><ref name="Després2012">{{cite journal |doi=10.3402/tellusb.v64i0.15598 |title=Primary biological aerosol particles in the atmosphere: A review |year=2012 |last1=Després |first1=Vivianer. |last2=Huffman |first2=J.Alex |last3=Burrows |first3=Susannah M. |last4=Hoose |first4=Corinna |last5=Safatov |first5=Aleksandrs. |last6=Buryak |first6=Galina |last7=Fröhlich-Nowoisky |first7=Janine |last8=Elbert |first8=Wolfgang |last9=Andreae |first9=Meinrato.|last10 = Pöschl|first10 = Ulrich |last11=Jaenicke |first11=Ruprecht |journal=Tellus B: Chemical and Physical Meteorology |volume=64 |page=15598 |bibcode=2012TellB..6415598D |s2cid=98741728 |doi-access=free}}</ref><ref name="FröhlichNowoisky2016" /><ref name=Sahu2015>{{cite journal |doi=10.1007/s10453-014-9349-z |title=Airborne algae: Overview of the current status and its implications on the environment |year=2015 |last1=Sahu |first1=Nivedita |last2=Tangutur |first2=Anjana Devi |journal=Aerobiologia |volume=31 |issue=1 |pages=89–97 |bibcode=2015Aerob..31...89S |s2cid=83855537}}</ref><ref name="Wiśniewska2019">{{cite journal |doi=10.1016/j.envint.2019.104964 |title=The importance of cyanobacteria and microalgae present in aerosols to human health and the environment – Review study |year=2019 |last1=Wiśniewska |first1=K. |last2=Lewandowska |first2=A.U. |last3=Śliwińska-Wilczewska |first3=S. |journal=Environment International |volume=131 |page=104964 |pmid=31351382 |doi-access=free|bibcode=2019EnInt.13104964W }}</ref>

Historically, the first investigations of the occurrence and dispersion of microorganisms and spores in the air can be traced back to the early 19th century.<ref>Ehrenberg C.G. (1830) "Neue Beobachtungen über blutartige Erscheinungen in Aegypten, Arabien und Sibirien, nebst einer Übersicht und Kritik der früher bekannten". ''Ann. Phys. Chem.'', '''94''': 477–514.</ref><ref>Pasteur L. (1860) "Expériences relatives aux generations dites spontanées". ''C. R. Hebd. Seances Acad. Sci.'', '''50''': 303–307</ref><ref>Pasteur L. (1860) "Suite à une précédente communication relative aux generations dites spontanées". ''C. R. Hebd. Seances Acad. Sci.'', '''51''': 675–678.</ref> Since then, the study of bioaerosols has come a long way, and air samples collected with aircraft, balloons, and rockets have shown that bioaerosols released from land and ocean surfaces can be transported over long distances and up to very high altitudes, i.e., between continents and beyond the [[troposphere]].<ref name=Brown2002>{{cite journal |doi=10.1126/science.1072678 |title=Aerial Dispersal of Pathogens on the Global and Continental Scales and Its Impact on Plant Disease |year=2002 |last1=Brown |first1=J. K. M. |last2=Hovmøller |first2=M. S. |journal=Science |volume=297 |issue=5581 |pages=537–541 |pmid=12142520 |bibcode=2002Sci...297..537B |s2cid=4207803}}</ref><ref name="Microbiome of the upper troposphere"/><ref>{{cite journal |doi=10.5194/acp-7-4569-2007 |title=Contribution of fungi to primary biogenic aerosols in the atmosphere: Wet and dry discharged spores, carbohydrates, and inorganic ions |year=2007 |last1=Elbert |first1=W. |last2=Taylor |first2=P. E. |last3=Andreae |first3=M. O. |last4=Pöschl |first4=U. |journal=Atmospheric Chemistry and Physics |volume=7 |issue=17 |pages=4569–4588 |bibcode=2007ACP.....7.4569E |s2cid=17512396 |doi-access=free}}</ref><ref>{{cite journal |doi=10.1016/S0007-1536(45)80041-4 |title=The dispersion of air-borne spores |year=1945 |last1=Gregory |first1=P.H. |journal=Transactions of the British Mycological Society |volume=28 |issue=1–2 |pages=26–72}}</ref><ref>{{cite journal |doi=10.1023/A:1011868218901 |title=African desert dust in the Caribbean atmosphere: Microbiology and public health |year=2001 |last1=Griffin |first1=Dale W. |last2=Garrison |first2=Virginia H. |last3=Herman |first3=Jay R. |last4=Shinn |first4=Eugene A. |journal=Aerobiologia |volume=17 |issue=3 |pages=203–213 |bibcode=2001Aerob..17..203G |s2cid=82040406 |hdl=11603/28524 |hdl-access=free}}</ref><ref>{{cite journal |doi=10.1029/2011GL048166 |title=Atmospheric bioaerosols transported via dust storms in the western United States |year=2011 |last1=Hallar |first1=A. Gannet |last2=Chirokova |first2=Galina |last3=McCubbin |first3=Ian |last4=Painter |first4=Thomas H. |last5=Wiedinmyer |first5=Christine |last6=Dodson |first6=Craig |journal=Geophysical Research Letters |volume=38 |issue=17 |pages=n/a |bibcode=2011GeoRL..3817801H |s2cid=54218062}}</ref><ref>{{cite journal |doi=10.1099/00221287-48-3-357 |title=Long-distance Spore Transport: Vertical Sections of Spore Clouds over the Sea |year=1967 |last1=Hirst |first1=J. M. |last2=Stedman |first2=O. J. |last3=Hurst |first3=G. W. |journal=Journal of General Microbiology |volume=48 |issue=3 |pages=357–377 |pmid=6052629 |doi-access=free}}</ref><ref name="auto">{{cite journal |doi=10.1016/j.atmosenv.2013.03.029 |title=Assessment of composition and origin of airborne bacteria in the free troposphere over Japan |year=2013 |last1=Maki |first1=Teruya |last2=Kakikawa |first2=Makiko |last3=Kobayashi |first3=Fumihisa |last4=Yamada |first4=Maromu |last5=Matsuki |first5=Atsushi |last6=Hasegawa |first6=Hiroshi |last7=Iwasaka |first7=Yasunobu |journal=Atmospheric Environment |volume=74 |pages=73–82 |bibcode=2013AtmEn..74...73M |hdl=2297/34677 |url=https://kanazawa-u.repo.nii.ac.jp/?action=repository_action_common_download&item_id=8829&item_no=1&attribute_id=26&file_no=1 |hdl-access=free}}</ref><ref>{{cite journal |doi=10.1289/ehp.10684 |title=Particle Size Distribution of Airborne Microorganisms and Pathogens during an Intense African Dust Event in the Eastern Mediterranean |year=2008 |last1=Polymenakou |first1=Paraskevi N. |last2=Mandalakis |first2=Manolis |last3=Stephanou |first3=Euripides G. |last4=Tselepides |first4=Anastasios |journal=Environmental Health Perspectives |volume=116 |issue=3 |pages=292–296 |pmid=18335093 |pmc=2265054|bibcode=2008EnvHP.116..292P }}</ref><ref>{{cite journal |doi=10.1099/ijs.0.64029-0 |title=''Bacillus aerius'' sp. nov., ''Bacillus aerophilus'' sp. nov., ''Bacillus stratosphericus'' sp. nov. And ''Bacillus altitudinis'' sp. nov., isolated from cryogenic tubes used for collecting air samples from high altitudes |year=2006 |last1=Shivaji |first1=S. |last2=Chaturvedi |first2=P. |last3=Suresh |first3=K. |last4=Reddy |first4=G. S. N. |last5=Dutt |first5=C. B. S. |last6=Wainwright |first6=M. |last7=Narlikar |first7=J. V. |last8=Bhargava |first8=P. M. |journal=International Journal of Systematic and Evolutionary Microbiology |volume=56 |issue=7 |pages=1465–1473 |pmid=16825614 |doi-access=free}}</ref><ref name="Intercontinental Dispersal of Bacte"/><ref name="FröhlichNowoisky2016" />

<gallery style="float:left" mode="packed" heights="360px">
File:Bioaerosol cycling in the Earth system.jpg| {{center|'''Global bioaerosol cycling'''}} After emission from the biosphere, bioaerosol particles interact with other aerosol particles and trace gases in the atmosphere and can be involved in the formation of clouds and precipitation. After dry or wet deposition to the Earth's surface, viable bioparticles can contribute to biological reproduction and further emission. This feedback can be particularly efficient when coupled to the water cycle (bioprecipitation).<ref>{{cite journal |doi=10.1021/cr500487s |title=Multiphase Chemistry at the Atmosphere–Biosphere Interface Influencing Climate and Public Health in the Anthropocene |year=2015 |last1=Pöschl |first1=Ulrich |last2=Shiraiwa |first2=Manabu |journal=Chemical Reviews |volume=115 |issue=10 |pages=4440–4475 |pmid=25856774 |s2cid=206901179}}</ref><ref name="Atmospheric Aerosols: Composition"/><ref name="FröhlichNowoisky2016" />
</gallery>

<gallery style="float:right" mode="packed" heights="360px">
File:Ecosystem interactions of biogenic aerosol particles in the Earth system.jpg| {{center|'''Global ecosystem interactions of bioaerosol particles'''}} Key aspects and areas of research required to determine and quantify the interactions and effects of biogenic aerosol particles in the Earth system, including primary biological aerosols directly emitted to the atmosphere and secondary organic aerosols formed upon oxidation and gas-to-particle conversion of volatile organic compounds.<ref name="FröhlichNowoisky2016" />
</gallery>

{{clear}}

Bioaerosols play a key role in the dispersal of reproductive units from plants and microbes (pollen, spores, etc.), for which the atmosphere enables transport over geographic barriers and long distances.<ref name=Brown2002 /><ref name=Burrows2009a /><ref name=Burrows2009b /><ref name="Després2012" /><ref name=Womack2010 /> Bioaerosols are thus highly relevant for the spread of organisms, allowing genetic exchange between habitats and geographic shifts of biomes. They are central elements in the development, evolution, and dynamics of ecosystems.<ref name="FröhlichNowoisky2016" />

==Dispersal==
[[Biological dispersal|Dispersal]] is a vital component of an organism's life-history,<ref>{{cite journal |doi=10.1111/oik.03801 |title=Dispersal: A central and independent trait in life history |year=2017 |last1=Bonte |first1=Dries |last2=Dahirel |first2=Maxime |journal=Oikos |volume=126 |issue=4 |pages=472–479 |doi-access=free|bibcode=2017Oikos.126..472B }}</ref> and the potential for dispersal determines the distribution, abundance, and thus, the community dynamics of species at different sites.<ref name=Rundle2002>{{Cite book |url=https://books.google.com/books?id=BZ3wAAAAMAAJ&q=%22Freshwater+meiofauna:+Biology+and+ecology%22 |title=Freshwater Meiofauna: Biology and Ecology |isbn=9789057821097 |last1=Rundle |first1=Simon D. |last2=Robertson |first2=Anne L. |last3=Schmid-Araya |first3=Jenny M. |year=2002 |publisher=Backhuys}}</ref><ref>{{cite journal |doi=10.1086/376585 |title=Dispersal Rates Affect Species Composition in Metacommunities of Sarracenia purpurea Inquilines |year=2003 |last1=Kneitel |first1=Jamie M. |last2=Miller |first2=Thomas E. |journal=The American Naturalist |volume=162 |issue=2 |pages=165–171 |pmid=12858261 |bibcode=2003ANat..162..165K |s2cid=17576931}}</ref><ref>{{cite journal |doi=10.1111/j.1461-0248.2005.00820.x |title=Integrating environmental and spatial processes in ecological community dynamics |year=2005 |last1=Cottenie |first1=Karl |journal=Ecology Letters |volume=8 |issue=11 |pages=1175–1182 |pmid=21352441|bibcode=2005EcolL...8.1175C }}</ref> A new habitat must first be reached before filters such as organismal abilities and adaptations, the quality of a habitat, and the established biological community determine the [[Colonisation (biology)|colonization]] efficiency of a species.<ref name=Incagnone2015>{{cite journal |doi=10.1007/s10750-014-2110-3 |title=How do freshwater organisms cross the "dry ocean"? A review on passive dispersal and colonization processes with a special focus on temporary ponds |year=2015 |last1=Incagnone |first1=Giulia |last2=Marrone |first2=Federico |last3=Barone |first3=Rossella |last4=Robba |first4=Lavinia |last5=Naselli-Flores |first5=Luigi |journal=Hydrobiologia |volume=750 |issue=1 |pages=103–123 |bibcode=2015HyBio.750..103I |hdl=10447/101976 |s2cid=13892871 |hdl-access=free}}</ref> While larger animals can cover distances on their own and actively seek suitable habitats, small (<2 mm) organisms are often passively dispersed,<ref name=Incagnone2015 /> resulting in their more ubiquitous occurrence.<ref>{{cite journal |doi=10.1126/science.1070710 |title=Global Dispersal of Free-Living Microbial Eukaryote Species |year=2002 |last1=Finlay |first1=B. J. |journal=Science |volume=296 |issue=5570 |pages=1061–1063 |pmid=12004115 |bibcode=2002Sci...296.1061F |s2cid=19508548}}</ref> While active dispersal accounts for rather predictable distribution patterns, passive dispersal leads to a more randomized immigration of organisms.<ref name=Rundle2002 /> Mechanisms for passive dispersal are the transport on ([[epizoochory]]) or in ([[endozoochory]]) larger animals (e.g., flying insects, birds, or mammals) and the erosion by wind.<ref name=Incagnone2015 /><ref name=Ptatscheck2018>{{cite journal |doi=10.1038/s41598-018-24747-8 |title=The extent of wind-mediated dispersal of small metazoans, focusing nematodes |year=2018 |last1=Ptatscheck |first1=Christoph |last2=Gansfort |first2=Birgit |last3=Traunspurger |first3=Walter |journal=Scientific Reports |volume=8 |issue=1 |page=6814 |pmid=29717144 |pmc=5931521 |bibcode=2018NatSR...8.6814P}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

A [[propagule]] is any material that functions in propagating an organism to the next stage in its life cycle, such as by [[Biological dispersal|dispersal]]. The propagule is usually distinct in form from the parent organism. Propagules are produced by [[plants]] (in the form of [[seeds]] or [[spores]]), [[fungi]] (in the form of [[spores]]), and [[bacteria]] (for example [[endospore]]s or [[microbial cyst]]s).<ref name="Chuang">T.Y. Chuang and W.H. Ko. 1981. Propagule size: Its relation to population density of microorganisms in soil. Soil Biology and Biochemistry. 13(3).</ref> Often cited as an important requirement for effective wind dispersal is the presence of propagules (e.g., resting eggs, cysts, [[ephippia]], juvenile and adult resting stages),<ref name=Incagnone2015 /><ref>{{cite journal |doi=10.4081/jlimnol.2004.s1.56 |title=Role of diapause in dispersal and invasion success by aquatic invertebrates |year=2004 |last1=Panov |first1=Vadim E. |last2=Krylov |first2=Piotr I. |last3=Riccardi |first3=Nicoletta |journal=Journal of Limnology |volume=63 |page=56 |doi-access=free}}</ref><ref name=Nkem2006>{{cite journal |doi=10.1007/s00300-005-0061-x |title=Wind dispersal of soil invertebrates in the Mc ''Murdo'' Dry Valleys, Antarctica |year=2006 |last1=Nkem |first1=Johnson N. |last2=Wall |first2=Diana H. |last3=Virginia |first3=Ross A. |last4=Barrett |first4=John E. |last5=Broos |first5=Emma J. |last6=Porazinska |first6=Dorota L. |last7=Adams |first7=Byron J. |journal=Polar Biology |volume=29 |issue=4 |pages=346–352 |bibcode=2006PoBio..29..346N |s2cid=32516212}}</ref> which also enables organisms to survive unfavorable environmental conditions until they enter a suitable habitat. These dispersal units can be blown from surfaces such as soil, moss, and the desiccated sediments of temporary or intermittent waters. The passively dispersed organisms are typically pioneer colonizers.<ref name=Maguire1963>{{cite journal |doi=10.2307/1948560 |jstor=1948560 |title=The Passive Dispersal of Small Aquatic Organisms and Their Colonization of Isolated Bodies of Water |last1=Maguire |first1=Bassett |journal=Ecological Monographs |year=1963 |volume=33 |issue=2 |pages=161–185|bibcode=1963EcoM...33..161M }}</ref><ref>{{cite journal |doi=10.1007/s10452-014-9483-2 |title=The meiofauna of artificial water-filled tree holes: Colonization and bottom-up effects |year=2014 |last1=Ptatscheck |first1=Chistoph |last2=Traunspurger |first2=Walter |journal=Aquatic Ecology |volume=48 |issue=3 |pages=285–295 |bibcode=2014AqEco..48..285P |s2cid=15256569}}</ref><ref name=Ptatscheck2014>{{cite journal |doi=10.1007/s00442-002-0897-5 |title=Blowing in the wind: A field test of overland dispersal and colonization by aquatic invertebrates |year=2002 |last1=Cáceres |first1=Carla E. |last2=Soluk |first2=Daniel A. |journal=Oecologia |volume=131 |issue=3 |pages=402–408 |pmid=28547712 |bibcode=2002Oecol.131..402C |s2cid=9941895}}</ref><ref name=Ptatscheck2018 />

However, wind-drifted species vary in their [[vagility]] (probability to be transported with the wind),<ref>{{cite journal |doi=10.1007/BF00025926 |title=Dispersal-limited zooplankton distribution and community composition in new ponds |year=1995 |last1=Jenkins |first1=David G. |journal=Hydrobiologia |volume=313-314 |issue=1 |pages=15–20 |bibcode=1995HyBio.313...15J |s2cid=45667054}}</ref> with the weight and form of the propagules, and therefore, the wind speed required for their transport,<ref>{{cite journal |doi=10.1007/s10750-014-1936-z |title=Historical frequency of wind dispersal events and role of topography in the dispersal of anostracan cysts in a semi-arid environment |year=2014 |last1=Parekh |first1=Priya A. |last2=Paetkau |first2=Mark J. |last3=Gosselin |first3=Louis A. |journal=Hydrobiologia |volume=740 |issue=1 |pages=51–59 |bibcode=2014HyBio.740...51P |s2cid=18458173}}</ref> determining the dispersal distance. For example, in nematodes, resting eggs are less effectively transported by wind than other life stages,<ref name=Carroll1981>Carroll, J.J. and Viglierchio, D.R. (1981). "On the transport of nematodes by the wind". ''Journal of Nematology'', '''13'''(4): 476.</ref> while organisms in [[anhydrobiosis]] are lighter and thus more readily transported than [[Hydrated|hydrated forms]].<ref>{{cite journal |doi=10.1146/annurev.py.03.090165.000355 |title=Factors in Survival of Nematodes |year=1965 |last1=Van Gundy |first1=Seymour D. |journal=Annual Review of Phytopathology |volume=3 |issue=1 |pages=43–68|bibcode=1965AnRvP...3...43V }}</ref><ref>{{cite journal |doi=10.1093/icb/45.5.759 |title=Anhydrobiosis in Bdelloid Species, Populations and Individuals |year=2005 |last1=Ricci |first1=C. |last2=Caprioli |first2=M. |journal=Integrative and Comparative Biology |volume=45 |issue=5 |pages=759–763 |pmid=21676827 |s2cid=42270008 |doi-access=free}}</ref> Because different organisms are, for the most part, not dispersed over the same distances, source habitats are also important, with the number of organisms contained in air declining with increasing distance from the source system.<ref name=Maguire1963 /><ref name=Vanschoenwinkel2007>{{cite journal |doi=10.1111/j.2007.0030-1299.16349.x |title=Any way the wind blows - frequent wind dispersal drives species sorting in ephemeral aquatic communities |year=2008 |last1=Vanschoenwinkel |first1=Bram |last2=Gielen |first2=Saïdja |last3=Seaman |first3=Maitland |last4=Brendonck |first4=Luc |journal=Oikos |volume=117 |issue=1 |pages=125–134|bibcode=2008Oikos.117..125V }}</ref> The distances covered by small animals range from a few meters,<ref name=Vanschoenwinkel2007 /> to hundreds,<ref name=Maguire1963 /> to thousands of meters.<ref name=Carroll1981 /> While the wind dispersal of aquatic organisms is possible even during the wet phase of a transiently aquatic habitat,<ref name=Incagnone2015 /> during the dry stages a larger number of dormant propagules are exposed to wind and thus dispersed.<ref name=Nkem2006 /><ref name=Vanschoenwinkel2007 /><ref name=Vanschoenwinkel2008>{{cite journal |doi=10.1111/j.0906-7590.2008.05442.x |title=Relative importance of different dispersal vectors for small aquatic invertebrates in a rock pool metacommunity |year=2008 |last1=Vanschoenwinkel |first1=Bram |last2=Gielen |first2=Saïdja |last3=Vandewaerde |first3=Hanne |last4=Seaman |first4=Maitland |last5=Brendonck |first5=Luc |journal=Ecography |volume=31 |issue=5 |pages=567–577 |bibcode=2008Ecogr..31..567V |url=https://lirias.kuleuven.be/handle/123456789/184854}}</ref> Freshwater organisms that must "cross the dry ocean"{{hsp}}<ref name=Incagnone2015 /> to enter new aquatic island systems will be passively dispersed more successfully than terrestrial taxa.<ref name=Incagnone2015 /> Numerous taxa from both soil and freshwater systems have been captured from the air (e.g., bacteria, several [[algae]], [[ciliate]]s, [[flagellate]]s, [[rotifer]]s, [[crustacean]]s, [[mite]]s, and [[tardigrade]]s).<ref name=Maguire1963 /><ref name=Vanschoenwinkel2007 /><ref name=Vanschoenwinkel2008 /><ref>{{cite journal |doi=10.1098/rspl.1886.0077 |title=X. The distribution of micro-organisms in air |journal=Proceedings of the Royal Society of London |year=1886 |volume=40 |issue=242–245 |pages=509–526 |s2cid=129825037 |doi-access=}}</ref> While these have been qualitatively well studied, accurate estimates of their dispersal rates are lacking.<ref name=Ptatscheck2018 />

==Transport and distribution==
<gallery mode="packed" style="float:right" heights="300px">
File:Factors controlling microbial communities of the planetary boundary layer.webp | {{center|Factors controlling microbial communities<br />of the [[planetary boundary layer]]{{hsp}}<ref name=TignatPerrier2020 />}}|alt=Factors controlling microbial communitiesof the planetary boundary layer
</gallery>

Once aerosolized, microbial cells enter the [[planetary boundary layer]], defined as the air layer near the ground directly influenced by the planetary surface. The concentration and taxonomic diversity of airborne microbial communities in the planetary boundary layer has been recently described,<ref>{{cite journal |doi=10.1007/s10453-019-09606-x |title=Microbial composition in seasonal time series of free tropospheric air and precipitation reveals community separation |year=2019 |last1=Els |first1=Nora |last2=Larose |first2=Catherine |last3=Baumann-Stanzer |first3=Kathrin |last4=Tignat-Perrier |first4=Romie |last5=Keuschnig |first5=Christoph |last6=Vogel |first6=Timothy M. |last7=Sattler |first7=Birgit |journal=Aerobiologia |volume=35 |issue=4 |pages=671–701 |s2cid=201834075 |doi-access=free|bibcode=2019Aerob..35..671E }}</ref><ref name="Innocente2017"/><ref name="Tignat-Perrier2019" /> though the functional potential of airborne microbial communities remains unknown.<ref name="Tignat-Perrier2020" />

From the planetary boundary layer, the microbial community might eventually be transported upwards by air currents into the free [[troposphere]] (air layer above the planetary boundary layer) or even higher into the [[stratosphere]].<ref name=Griffin2017>{{cite book |doi=10.1002/9781119132318.ch2c |chapter=Global-Scale Atmospheric Dispersion of Microorganisms |title=Microbiology of Aerosols |year=2017 |last1=Griffin |first1=D.W. |last2=Gonzalez-Martin |first2=C. |last3=Hoose |first3=C. |last4=Smith |first4=D.J. |pages=155–194 |isbn=9781119132318}}</ref><ref name=David2011>{{cite journal |doi=10.1029/2011EO300001 |title=The high life: Transport of microbes in the atmosphere |year=2011 |last1=Smith |first1=David J. |last2=Griffin |first2=Dale W. |last3=Jaffe |first3=Daniel A. |journal=Eos, Transactions American Geophysical Union |volume=92 |issue=30 |pages=249–250 |bibcode=2011EOSTr..92..249S |doi-access=free}}</ref><ref name="Airborne Bacteria in Earth's Lower"/><ref name="auto"/> Microorganisms might undergo a selection process during their way up into the troposphere and the stratosphere.<ref>{{cite journal |doi=10.1002/geo2.69 |title=Beyond the planetary boundary layer: Bacterial and fungal vertical biogeography at Mount Sonnblick, Austria |year=2019 |last1=Els |first1=Nora |last2=Baumann-Stanzer |first2=Kathrin |last3=Larose |first3=Catherine |last4=Vogel |first4=Timothy M. |last5=Sattler |first5=Birgit |journal=Geo: Geography and Environment |volume=6 |issue=1 |s2cid=134665478 |doi-access=free|bibcode=2019GeoGE...6E..69E }}</ref><ref name="Tignat-Perrier2019" />

Subject to gravity, [[aerosol]]s (or [[particulate matter]]) as well as [[bioaerosol]]s become concentrated in the lower part of the [[troposphere]] that is called the [[planetary boundary layer]]. Microbial concentrations thus usually show a vertical stratification from the bottom to the top of the troposphere with average estimated bacterial concentrations of 900 to 2 × 10<sup>7</sup> cells per cubic metre in the planetary boundary layer{{hsp}}<ref name="Zhen2017"/><ref>{{cite journal |doi=10.1016/j.atmosenv.2017.03.018 |title=Variability of airborne bacteria in an urban Mediterranean area (Thessaloniki, Greece) |year=2017 |last1=Genitsaris |first1=Savvas |last2=Stefanidou |first2=Natassa |last3=Katsiapi |first3=Matina |last4=Kormas |first4=Konstantinos A. |last5=Sommer |first5=Ulrich |last6=Moustaka-Gouni |first6=Maria |journal=Atmospheric Environment |volume=157 |pages=101–110 |bibcode=2017AtmEn.157..101G}}</ref><ref name="Spatio-temporal variability of airb">{{cite journal |doi=10.1007/s00253-014-6348-5 |title=Spatio-temporal variability of airborne bacterial communities and their correlation with particulate matter chemical composition across two urban areas |year=2015 |last1=Gandolfi |first1=I. |last2=Bertolini |first2=V. |last3=Bestetti |first3=G. |last4=Ambrosini |first4=R. |last5=Innocente |first5=E. |last6=Rampazzo |first6=G. |last7=Papacchini |first7=M. |last8=Franzetti |first8=A. |journal=Applied Microbiology and Biotechnology |volume=99 |issue=11 |pages=4867–4877 |pmid=25592734 |hdl=10281/90570 |s2cid=16731037 |hdl-access=free}}</ref><ref>{{cite journal |doi=10.1111/j.1574-6941.2011.01053.x |title=Prokaryotic abundance and 16S rRNA gene sequences detected in marine aerosols on the East Sea (Korea) |year=2011 |last1=Cho |first1=Byung Cheol |last2=Hwang |first2=Chung Yeon |journal=FEMS Microbiology Ecology |volume=76 |issue=2 |pages=327–341 |pmid=21255051 |doi-access=free|bibcode=2011FEMME..76..327C }}</ref><ref>{{cite journal |doi=10.1016/j.jes.2017.12.019 |title=Effects of Asian dust events on atmospheric bacterial communities at different distances downwind of the source region |year=2018 |last1=Park |first1=Jonguk |last2=Li |first2=Pin-Fang |last3=Ichijo |first3=Tomoaki |last4=Nasu |first4=Masao |last5=Yamaguchi |first5=Nobuyasu |journal=Journal of Environmental Sciences |volume=72 |pages=133–139 |pmid=30244740 |bibcode=2018JEnvS..72..133P |s2cid=52334609}}</ref> and 40 to 8 × 10<sup>4</sup> cells per cubic metre in the highest part of the troposphere called the free troposphere.<ref>{{cite journal |doi=10.3389/fbioe.2019.00012 |doi-access=free |title=Airborne Microbial Communities at High-Altitude and Suburban Sites in Toyama, Japan Suggest a New Perspective for Bioprospecting |year=2019 |last1=Tanaka |first1=Daisuke |last2=Sato |first2=Kei |last3=Goto |first3=Motoshi |last4=Fujiyoshi |first4=So |last5=Maruyama |first5=Fumito |last6=Takato |first6=Shunsuke |last7=Shimada |first7=Takamune |last8=Sakatoku |first8=Akihiro |last9=Aoki |first9=Kazuma|last10 = Nakamura|first10 = Shogo |journal=Frontiers in Bioengineering and Biotechnology |volume=7 |page=12 |pmid=30805335 |pmc=6370616}}</ref><ref>{{cite journal |doi=10.1007/s10453-012-9250-6 |title=High bacterial 16S rRNA gene diversity above the atmospheric boundary layer |year=2012 |last1=Zweifel |first1=Ulla Li |last2=Hagström |first2=Åke |last3=Holmfeldt |first3=Karin |last4=Thyrhaug |first4=Runar |last5=Geels |first5=Camilla |last6=Frohn |first6=Lise Marie |last7=Skjøth |first7=Carsten A. |last8=Karlson |first8=Ulrich Gosewinkel |journal=Aerobiologia |volume=28 |issue=4 |pages=481–498 |bibcode=2012Aerob..28..481Z |s2cid=84270694}}</ref><ref name="Microbiome of the upper troposphere">{{cite journal |doi=10.1073/pnas.1212089110 |title=Microbiome of the upper troposphere: Species composition and prevalence, effects of tropical storms, and atmospheric implications |year=2013 |last1=Deleon-Rodriguez |first1=N. |last2=Lathem |first2=T. L. |last3=Rodriguez-r |first3=L. M. |last4=Barazesh |first4=J. M. |last5=Anderson |first5=B. E. |last6=Beyersdorf |first6=A. J. |last7=Ziemba |first7=L. D. |last8=Bergin |first8=M. |last9=Nenes |first9=A.|last10 = Konstantinidis|first10 = K. T. |journal=Proceedings of the National Academy of Sciences |volume=110 |issue=7 |pages=2575–2580 |pmid=23359712 |pmc=3574924 |bibcode=2013PNAS..110.2575D |doi-access=free}}</ref> The troposphere is the most dynamic layer in terms of chemistry and physics of aerosols and harbors complex chemical reactions and meteorological phenomena that lead to the coexistence of a gas phase, liquid phases (i.e., cloud, rain, and fog water) and solid phases (i.e., microscopic particulate matter, sand dust). The various atmospheric phases represent multiple biological niches.<ref name=TignatPerrier2020 />

Possible processes in the way atmospheric [[microbial communities]] can distribute themselves have recently been investigated in meteorology,<ref name=Zhen2017 /><ref name="Šantl-Temkiv2018" /><ref name="Continental-scale distributions of"/><ref name=Innocente2017>{{cite journal |doi=10.1016/j.scitotenv.2017.03.199 |title=Influence of seasonality, air mass origin and particulate matter chemical composition on airborne bacterial community structure in the Po Valley, Italy |year=2017 |last1=Innocente |first1=Elena |last2=Squizzato |first2=Stefania |last3=Visin |first3=Flavia |last4=Facca |first4=Chiara |last5=Rampazzo |first5=Giancarlo |last6=Bertolini |first6=Valentina |last7=Gandolfi |first7=Isabella |last8=Franzetti |first8=Andrea |last9=Ambrosini |first9=Roberto|last10 = Bestetti|first10 = Giuseppina |journal=Science of the Total Environment |volume=593-594 |pages=677–687 |pmid=28363180 |bibcode=2017ScTEn.593..677I |hdl=10278/3691685 |hdl-access=free}}</ref><ref name=Uetake2019>{{cite journal |doi=10.3389/fmicb.2019.01572 |biorxiv=10.1101/542001 |title=Seasonal changes of airborne bacterial communities over Tokyo and influence of local meteorology |year=2019 |last1=Uetake |first1=Jun |last2=Tobo |first2=Yutaka |last3=Uji |first3=Yasushi |last4=Hill |first4=Thomas C. J. |last5=Demott |first5=Paul J. |last6=Kreidenweis |first6=Sonia M. |last7=Misumi |first7=Ryohei |journal=Frontiers in Microbiology |volume=10 |page=1572 |pmid=31379765 |pmc=6646838 |s2cid=92236469 |doi-access=free}}</ref> seasons,<ref name=Innocente2017 /><ref name=Bowers2011>{{cite journal |doi=10.1038/ismej.2010.167 |title=Spatial variability in airborne bacterial communities across land-use types and their relationship to the bacterial communities of potential source environments |year=2011 |last1=Bowers |first1=Robert M. |last2=McLetchie |first2=Shawna |last3=Knight |first3=Rob |last4=Fierer |first4=Noah |journal=The ISME Journal |volume=5 |issue=4 |pages=601–612 |pmid=21048802 |pmc=3105744|bibcode=2011ISMEJ...5..601B }}</ref><ref name=Bowers2012>{{cite journal |doi=10.1016/j.atmosenv.2012.01.005 |title=Seasonal variability in airborne bacterial communities at a high-elevation site |year=2012 |last1=Bowers |first1=Robert M. |last2=McCubbin |first2=Ian B. |last3=Hallar |first3=Anna G. |last4=Fierer |first4=Noah |journal=Atmospheric Environment |volume=50 |pages=41–49 |bibcode=2012AtmEn..50...41B}}</ref><ref name="Bowers2013"/><ref name=Mhuireach2019>{{cite journal |doi=10.3389/fevo.2019.00043 |doi-access=free |title=Spatiotemporal Controls on the Urban Aerobiome |year=2019 |last1=Mhuireach |first1=Gwynne Á. |last2=Betancourt-Román |first2=Clarisse M. |last3=Green |first3=Jessica L. |last4=Johnson |first4=Bart R. |journal=Frontiers in Ecology and Evolution |volume=7}}</ref> surface conditions{{hsp}}<ref name=Uetake2019 /><ref name=Bowers2011 /><ref name=Bowers2012 /><ref name=Mhuireach2019 /> and global air circulation.<ref name=Innocente2017 /><ref name="Cáliz2018">{{cite journal |doi=10.1073/pnas.1812826115 |title=A long-term survey unveils strong seasonal patterns in the airborne microbiome coupled to general and regional atmospheric circulations |year=2018 |last1=Cáliz |first1=Joan |last2=Triadó-Margarit |first2=Xavier |last3=Camarero |first3=Lluís |last4=Casamayor |first4=Emilio O. |journal=Proceedings of the National Academy of Sciences |volume=115 |issue=48 |pages=12229–12234 |pmid=30420511 |pmc=6275539 |bibcode=2018PNAS..11512229C |doi-access=free}}</ref><ref name="Spatio-temporal variability of airb"/><ref name="Fröhlich-Nowoisky2012">{{cite journal |doi=10.5194/bg-9-1125-2012 |title=Biogeography in the air: Fungal diversity over land and oceans |year=2012 |last1=Fröhlich-Nowoisky |first1=J. |last2=Burrows |first2=S. M. |last3=Xie |first3=Z. |last4=Engling |first4=G. |last5=Solomon |first5=P. A. |last6=Fraser |first6=M. P. |last7=Mayol-Bracero |first7=O. L. |last8=Artaxo |first8=P. |last9=Begerow |first9=D.|last10 = Conrad|first10 = R. |last11=Andreae |first11=M. O. |last12=Després |first12=V. R. |last13=Pöschl |first13=U. |journal=Biogeosciences |volume=9 |issue=3 |pages=1125–1136 |bibcode=2012BGeo....9.1125F |doi-access=free}}</ref><ref name="Long-range transport of airborne mi"/><ref name="Tignat-Perrier2019">{{cite journal |doi=10.1038/s41598-019-51073-4 |title=Global airborne microbial communities controlled by surrounding landscapes and wind conditions |year=2019 |last1=Tignat-Perrier |first1=Romie |last2=Dommergue |first2=Aurélien |last3=Thollot |first3=Alban |last4=Keuschnig |first4=Christoph |last5=Magand |first5=Olivier |last6=Vogel |first6=Timothy M. |last7=Larose |first7=Catherine |journal=Scientific Reports |volume=9 |issue=1 |page=14441 |pmid=31595018 |pmc=6783533 |bibcode=2019NatSR...914441T}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

===Over space and time===
Microorganisms attached to aerosols can travel intercontinental distances, survive, and further colonize remote environments. Airborne microbes are influenced by environmental and climatic patterns that are predicted to change in the near future, with unknown consequences.<ref name= Ontiveros2021>{{cite journal |last1=Ontiveros |first1=Vicente J. |last2=Cáliz |first2=Joan |last3=Triadó-Margarit |first3=Xavier |last4=Alonso |first4=David |last5=Casamayor |first5=Emilio O. |title=General decline in the diversity of the airborne microbiota under future climatic scenarios |journal=Scientific Reports |publisher=Springer Science and Business Media LLC |volume=11 |issue=1 |date=12 October 2021 |page=20223 |issn=2045-2322 |doi=10.1038/s41598-021-99223-x |pmid=34642388 |pmc=8511268 |bibcode=2021NatSR..1120223O}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> Airborne microbial communities play significant roles in public health and meteorological processes,<ref>{{cite journal |doi=10.1080/01442350802597438 |title=Physical and chemical characterization of bioaerosols – Implications for nucleation processes |year=2009 |last1=Ariya |first1=P. A. |last2=Sun |first2=J. |last3=Eltouny |first3=N. A. |last4=Hudson |first4=E. D. |last5=Hayes |first5=C. T. |last6=Kos |first6=G. |journal=International Reviews in Physical Chemistry |volume=28 |issue=1 |pages=1–32 |bibcode=2009IRPC...28....1A |s2cid=95932745 |url=https://escholarship.mcgill.ca/concern/articles/2z10ww34s}}</ref><ref>{{cite journal |doi=10.1890/01-0619 |title=Spread of Plant Disease on a Continental Scale: Role of Aerial Dispersal of Pathogens |year=2003 |last1=Aylor |first1=Donald E. |journal=Ecology |volume=84 |issue=8 |pages=1989–1997|bibcode=2003Ecol...84.1989A }}</ref><ref name="Aerial Dispersal of Pathogens on th"/><ref>{{cite journal |doi=10.1016/j.atmosres.2010.07.004 |title=A short overview of the microbial population in clouds: Potential roles in atmospheric chemistry and nucleation processes |year=2010 |last1=Delort |first1=Anne-Marie |last2=Vaïtilingom |first2=Mickael |last3=Amato |first3=Pierre |last4=Sancelme |first4=Martine |last5=Parazols |first5=Marius |last6=Mailhot |first6=Gilles |last7=Laj |first7=Paolo |last8=Deguillaume |first8=Laurent |journal=Atmospheric Research |volume=98 |issue=2–4 |pages=249–260 |bibcode=2010AtmRe..98..249D}}</ref><ref>{{cite journal |doi=10.1128/CMR.00039-06 |title=Atmospheric Movement of Microorganisms in Clouds of Desert Dust and Implications for Human Health |year=2007 |last1=Griffin |first1=Dale W. |journal=Clinical Microbiology Reviews |volume=20 |issue=3 |pages=459–477 |pmid=17630335 |pmc=1932751|bibcode=2007CMbRv..20..459G }}</ref> so it is important to understand how these communities are distributed over time and space.<ref name="Tignat-Perrier2020" />

<gallery mode="packed" style="float:right" heights="400px">
File:Atmosphere layers, temperature and airborne emission sources.png| {{center|Atmosphere layers, temperature and airborne emission sources}}
</gallery>

Most studies have focused on [[Microbiological culture|laboratory cultivation]] to identify possible metabolic functions of microbial strains of atmospheric origin, mainly from cloud water.<ref name=Amato2007 /><ref>{{cite journal |doi=10.1029/2002GL015637 |title=Microbiological degradation of atmospheric organic compounds |year=2002 |last1=Ariya |first1=Parisa A. |last2=Nepotchatykh |first2=Oleg |last3=Ignatova |first3=Olga |last4=Amyot |first4=Marc |journal=Geophysical Research Letters |volume=29 |issue=22 |page=2077 |bibcode=2002GeoRL..29.2077A |s2cid=129578943 |url=https://escholarship.mcgill.ca/concern/articles/pk02cf737 |doi-access=free}}</ref><ref>{{cite journal |doi=10.1029/2006JD008002 |title=Processing of atmospheric nitrogen by clouds above a forest environment |year=2007 |last1=Hill |first1=Kimberly A. |last2=Shepson |first2=Paul B. |last3=Galbavy |first3=Edward S. |last4=Anastasio |first4=Cort |last5=Kourtev |first5=Peter S. |last6=Konopka |first6=Allan |last7=Stirm |first7=Brian H. |journal=Journal of Geophysical Research |volume=112 |issue=D11 |bibcode=2007JGRD..11211301H}}</ref><ref>{{cite journal |doi=10.1128/AEM.01127-09 |title=Contribution of Microbial Activity to Carbon Chemistry in Clouds |year=2010 |last1=VaïTilingom |first1=Mickaël |last2=Amato |first2=Pierre |last3=Sancelme |first3=Martine |last4=Laj |first4=Paolo |last5=Leriche |first5=Maud |last6=Delort |first6=Anne-Marie |journal=Applied and Environmental Microbiology |volume=76 |issue=1 |pages=23–29 |pmid=19854931 |pmc=2798665 |bibcode=2010ApEnM..76...23V}}</ref><ref name="ReferenceA"/> Given that cultivable organisms represent about 1% of the entire microbial community,<ref>{{cite journal |doi=10.1111/j.1574-6968.2010.02000.x |title=Strategies for culture of 'unculturable' bacteria |year=2010 |last1=Vartoukian |first1=Sonia R. |last2=Palmer |first2=Richard M. |last3=Wade |first3=William G. |journal=FEMS Microbiology Letters |volume=309 |issue=1 |pages=1–7 |pmid=20487025 |doi-access=free}}</ref> culture-independent techniques and especially [[metagenomic|metagenomic studies]] applied to atmospheric microbiology have the potential to provide additional information on the selection and genetic adaptation of airborne microorganisms.<ref name="Tignat-Perrier2020" />

There are some metagenomic studies on airborne microbial communities over specific sites.<ref>{{cite journal |doi=10.1038/s41598-019-50194-0 |title=Functional metagenomic analysis of dust-associated microbiomes above the Red Sea |year=2019 |last1=Aalismail |first1=Nojood A. |last2=Ngugi |first2=David K. |last3=Díaz-Rúa |first3=Rubén |last4=Alam |first4=Intikhab |last5=Cusack |first5=Michael |last6=Duarte |first6=Carlos M. |journal=Scientific Reports |volume=9 |issue=1 |page=13741 |pmid=31551441 |pmc=6760216 |bibcode=2019NatSR...913741A}}</ref><ref>{{cite journal |doi=10.1038/s41598-019-41032-4 |title=Metatranscriptomic exploration of microbial functioning in clouds |year=2019 |last1=Amato |first1=Pierre |last2=Besaury |first2=Ludovic |last3=Joly |first3=Muriel |last4=Penaud |first4=Benjamin |last5=Deguillaume |first5=Laurent |last6=Delort |first6=Anne-Marie |journal=Scientific Reports |volume=9 |issue=1 |page=4383 |pmid=30867542 |pmc=6416334 |bibcode=2019NatSR...9.4383A}}</ref><ref>{{cite journal |doi=10.1021/es4048472 |title=Inhalable Microorganisms in Beijing's PM2.5 and PM10 Pollutants during a Severe Smog Event |year=2014 |last1=Cao |first1=Chen |last2=Jiang |first2=Wenjun |last3=Wang |first3=Buying |last4=Fang |first4=Jianhuo |last5=Lang |first5=Jidong |last6=Tian |first6=Geng |last7=Jiang |first7=Jingkun |last8=Zhu |first8=Ting F. |journal=Environmental Science & Technology |volume=48 |issue=3 |pages=1499–1507 |pmid=24456276 |pmc=3963435 |bibcode=2014EnST...48.1499C}}</ref><ref name="Microbial communities in the tropic"/><ref name="A Metagenomic Framework for the Stu">{{cite journal |doi=10.1371/journal.pone.0081862 |doi-access=free |title=A Metagenomic Framework for the Study of Airborne Microbial Communities |year=2013 |last1=Yooseph |first1=Shibu |last2=Andrews-Pfannkoch |first2=Cynthia |last3=Tenney |first3=Aaron |last4=McQuaid |first4=Jeff |last5=Williamson |first5=Shannon |last6=Thiagarajan |first6=Mathangi |last7=Brami |first7=Daniel |last8=Zeigler-Allen |first8=Lisa |last9=Hoffman |first9=Jeff|last10 = Goll|first10 = Johannes B. |last11=Fadrosh |first11=Douglas |last12=Glass |first12=John |last13=Adams |first13=Mark D. |last14=Friedman |first14=Robert |last15=Venter |first15=J. Craig |journal=PLOS ONE |volume=8 |issue=12 |pages=e81862 |pmid=24349140 |pmc=3859506 |bibcode=2013PLoSO...881862Y}}</ref> Metagenomic investigations of complex microbial communities in many ecosystems (for example, soil, seawater, lakes, feces and sludge) have provided evidence that microorganism functional signatures reflect the abiotic conditions of their environment, with different relative abundances of specific microbial functional classes.<ref>{{cite journal |doi=10.1038/ismej.2011.61 |title=Metagenomic mining for microbiologists |year=2011 |last1=Delmont |first1=Tom O. |last2=Malandain |first2=Cedric |last3=Prestat |first3=Emmanuel |last4=Larose |first4=Catherine |last5=Monier |first5=Jean-Michel |last6=Simonet |first6=Pascal |last7=Vogel |first7=Timothy M. |journal=The ISME Journal |volume=5 |issue=12 |pages=1837–1843 |pmid=21593798 |pmc=3223302|bibcode=2011ISMEJ...5.1837D }}</ref><ref>{{cite journal |doi=10.1038/s41598-019-42260-4 |title=Comparative metagenomics study reveals pollution induced changes of microbial genes in mangrove sediments |year=2019 |last1=Li |first1=Yingdong |last2=Zheng |first2=Liping |last3=Zhang |first3=Yue |last4=Liu |first4=Hongbin |last5=Jing |first5=Hongmei |journal=Scientific Reports |volume=9 |issue=1 |page=5739 |pmid=30952929 |pmc=6450915 |bibcode=2019NatSR...9.5739L}}</ref><ref>{{cite journal |doi=10.1126/science.1107851 |title=Comparative Metagenomics of Microbial Communities |year=2005 |last1=Tringe |first1=Susannah Green |last2=von Mering |first2=Christian |last3=Kobayashi |first3=Arthur |last4=Salamov |first4=Asaf A. |last5=Chen |first5=Kevin |last6=Chang |first6=Hwai W. |last7=Podar |first7=Mircea |last8=Short |first8=Jay M. |last9=Mathur |first9=Eric J.|last10 = Detter|first10 = John C. |last11=Bork |first11=Peer |last12=Hugenholtz |first12=Philip |last13=Rubin |first13=Edward M. |journal=Science |volume=308 |issue=5721 |pages=554–557 |pmid=15845853 |bibcode=2005Sci...308..554T |s2cid=161283 |url=https://digital.library.unt.edu/ark:/67531/metadc1407164/}}</ref><ref>{{cite journal |doi=10.1038/ismej.2010.144 |title=Comparative metagenomics of microbial communities inhabiting deep-sea hydrothermal vent chimneys with contrasting chemistries |year=2011 |last1=Xie |first1=Wei |last2=Wang |first2=Fengping |last3=Guo |first3=Lei |last4=Chen |first4=Zeling |last5=Sievert |first5=Stefan M. |last6=Meng |first6=Jun |last7=Huang |first7=Guangrui |last8=Li |first8=Yuxin |last9=Yan |first9=Qingyu|last10 = Wu|first10 = Shan |last11=Wang |first11=Xin |last12=Chen |first12=Shangwu |last13=He |first13=Guangyuan |last14=Xiao |first14=Xiang |last15=Xu |first15=Anlong |journal=The ISME Journal |volume=5 |issue=3 |pages=414–426 |pmid=20927138 |pmc=3105715|bibcode=2011ISMEJ...5..414X }}</ref> This observed correlation of microbial-community functional potential and the physical and chemical characteristics of their environments could have resulted from genetic modifications (microbial adaptation{{hsp}}<ref>{{cite journal |doi=10.1111/j.1574-6976.2000.tb00567.x |title=Life at the oxic–anoxic interface: Microbial activities and adaptations |year=2000 |last1=Brune |first1=Andreas |last2=Frenzel |first2=Peter |last3=Cypionka |first3=Heribert |journal=FEMS Microbiology Reviews |volume=24 |issue=5 |pages=691–710 |pmid=11077159 |s2cid=8638694 |doi-access=}}</ref><ref>{{cite journal |doi=10.1038/nrmicro2750 |title=New insights into bacterial adaptation through in vivo and in silico experimental evolution |year=2012 |last1=Hindré |first1=Thomas |last2=Knibbe |first2=Carole |last3=Beslon |first3=Guillaume |last4=Schneider |first4=Dominique |journal=Nature Reviews Microbiology |volume=10 |issue=5 |pages=352–365 |pmid=22450379 |s2cid=22286095}}</ref><ref>{{cite journal |doi=10.1016/j.tree.2016.03.013 |title=Adaptation to Global Change: A Transposable Element–Epigenetics Perspective |year=2016 |last1=Rey |first1=Olivier |last2=Danchin |first2=Etienne |last3=Mirouze |first3=Marie |last4=Loot |first4=Céline |last5=Blanchet |first5=Simon |journal=Trends in Ecology & Evolution |volume=31 |issue=7 |pages=514–526 |pmid=27080578|bibcode=2016TEcoE..31..514R }}</ref><ref name="A Metagenomic Framework for the Stu"/>) and/or physical selection. The latter refers to the death of sensitive cells and the survival of resistant or previously adapted cells. This physical selection can occur when microorganisms are exposed to physiologically adverse conditions.<ref name="Tignat-Perrier2020">{{cite journal |doi=10.5194/bg-17-6081-2020 |title=Microbial functional signature in the atmospheric boundary layer |year=2020 |last1=Tignat-Perrier |first1=Romie |last2=Dommergue |first2=Aurélien |last3=Thollot |first3=Alban |last4=Magand |first4=Olivier |last5=Vogel |first5=Timothy M. |last6=Larose |first6=Catherine |journal=Biogeosciences |volume=17 |issue=23 |pages=6081–6095 |bibcode=2020BGeo...17.6081T |s2cid=234687848 |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

The presence of a specific microbial functional signature in the atmosphere has not been investigated yet.<ref name="Tignat-Perrier2020" /> Microbial strains of airborne origin have been shown to survive and develop under conditions typically found in cloud water (i.e., high concentrations of H<sub>2</sub>O<sub>2</sub>, typical cloud carbonaceous sources, ultraviolet – UV – radiation etc.<ref name=Amato2007 /><ref>{{cite journal |doi=10.1016/j.atmosenv.2015.07.009 |title=Survival of microbial isolates from clouds toward simulated atmospheric stress factors |year=2015 |last1=Joly |first1=Muriel |last2=Amato |first2=Pierre |last3=Sancelme |first3=Martine |last4=Vinatier |first4=Virginie |last5=Abrantes |first5=Magali |last6=Deguillaume |first6=Laurent |last7=Delort |first7=Anne-Marie |journal=Atmospheric Environment |volume=117 |pages=92–98 |bibcode=2015AtmEn.117...92J}}</ref><ref name="ReferenceA"/> While atmospheric chemicals might lead to some microbial adaptation, physical and unfavorable conditions of the atmosphere such as UV radiation, low water content and cold temperatures might select which microorganisms can survive in the atmosphere. From the pool of microbial cells being aerosolized from Earth's surfaces, these adverse conditions might act as a filter in selecting cells already resistant to unfavorable physical conditions. Fungal cells and especially fungal spores might be particularly adapted to survive in the atmosphere due to their innate resistance{{hsp}}<ref>{{cite journal |doi=10.1007/s00294-017-0694-7 |title=Sporulation: How to survive on planet Earth (And beyond) |year=2017 |last1=Huang |first1=Mingwei |last2=Hull |first2=Christina M. |journal=Current Genetics |volume=63 |issue=5 |pages=831–838 |pmid=28421279 |pmc=5647196}}</ref> and might behave differently than bacterial cells. Still, the proportion and nature (i.e., fungi versus bacteria) of microbial cells that are resistant to the harsh atmospheric conditions within airborne microbial communities are unknown.<ref name="Tignat-Perrier2020" />

Airborne microbial transport is central to dispersal outcomes{{hsp}}<ref>{{cite journal |doi=10.1038/nrmicro2795 |title=Beyond biogeographic patterns: Processes shaping the microbial landscape |year=2012 |last1=Hanson |first1=China A. |last2=Fuhrman |first2=Jed A. |last3=Horner-Devine |first3=M. Claire |last4=Martiny |first4=Jennifer B. H. |journal=Nature Reviews Microbiology |volume=10 |issue=7 |pages=497–506 |pmid=22580365 |s2cid=19575573}}</ref> and several studies have demonstrated diverse microbial biosignatures are recoverable from the atmosphere. Microbial transport has been shown to occur across inter-continental distances above terrestrial habitats.<ref>{{cite journal |doi=10.1016/j.scitotenv.2014.04.030 |title=Structure, inter-annual recurrence, and global-scale connectivity of airborne microbial communities |year=2014 |last1=Barberán |first1=Albert |last2=Henley |first2=Jessica |last3=Fierer |first3=Noah |last4=Casamayor |first4=Emilio O. |journal=Science of the Total Environment |volume=487 |pages=187–195 |pmid=24784743 |bibcode=2014ScTEn.487..187B}}</ref><ref>{{cite journal |doi=10.5194/acp-14-9051-2014 |title=The contribution of fungal spores and bacteria to regional and global aerosol number and ice nucleation immersion freezing rates |year=2014 |last1=Spracklen |first1=D. V. |last2=Heald |first2=C. L. |journal=Atmospheric Chemistry and Physics |volume=14 |issue=17 |pages=9051–9059 |bibcode=2014ACP....14.9051S |s2cid=3290942 |doi-access=free}}</ref><ref name="Cáliz2018"/> Variation has been recorded seasonally, with underlying land use,<ref name="Bowers2011"/> and due to stochastic weather events such as dust storms.<ref>{{cite journal |doi=10.1038/ismej.2012.152 |title=Microbial hitchhikers on intercontinental dust: Catching a lift in Chad |year=2013 |last1=Favet |first1=Jocelyne |last2=Lapanje |first2=Ales |last3=Giongo |first3=Adriana |last4=Kennedy |first4=Suzanne |last5=Aung |first5=Yin-Yin |last6=Cattaneo |first6=Arlette |last7=Davis-Richardson |first7=Austin G. |last8=Brown |first8=Christopher T. |last9=Kort |first9=Renate|last10 = Brumsack|first10 = Hans-Jürgen |last11=Schnetger |first11=Bernhard |last12=Chappell |first12=Adrian |last13=Kroijenga |first13=Jaap |last14=Beck |first14=Andreas |last15=Schwibbert |first15=Karin |last16=Mohamed |first16=Ahmed H. |last17=Kirchner |first17=Timothy |last18=De Quadros |first18=Patricia Dorr |last19=Triplett |first19=Eric W.|last20 = Broughton|first20 = William J. |last21=Gorbushina |first21=Anna A. |journal=The ISME Journal |volume=7 |issue=4 |pages=850–867 |pmid=23254516 |pmc=3603401|bibcode=2013ISMEJ...7..850F }}</ref><ref name=Archer2019 /> There is evidence specific bacterial taxa (e.g., [[Actinomycetota]] and some [[Gammaproteobacteria]]) are preferentially aerosolized from oceans.<ref>{{cite journal |doi=10.1038/s41467-018-04409-z |title=Taxon-specific aerosolization of bacteria and viruses in an experimental ocean-atmosphere mesocosm |year=2018 |last1=Michaud |first1=Jennifer M. |last2=Thompson |first2=Luke R. |last3=Kaul |first3=Drishti |last4=Espinoza |first4=Josh L. |last5=Richter |first5=R. Alexander |last6=Xu |first6=Zhenjiang Zech |last7=Lee |first7=Christopher |last8=Pham |first8=Kevin M. |last9=Beall |first9=Charlotte M.|last10 = Malfatti|first10 = Francesca |last11=Azam |first11=Farooq |last12=Knight |first12=Rob |last13=Burkart |first13=Michael D. |last14=Dupont |first14=Christopher L. |last15=Prather |first15=Kimberly A. |journal=Nature Communications |volume=9 |issue=1 |page=2017 |pmid=29789621 |pmc=5964107 |bibcode=2018NatCo...9.2017M}}</ref><ref name="Tignat-Perrier2019" />

===Over urban areas===
[[File:Dust storms as a source of aerosolized bacteria.png|thumb|upright=1.7| {{center|Dust storms as a source of aerosolized bacteria}}]]

As a result of rapid industrialization and urbanization, global megacities have been impacted by extensive and intense [[particulate matter]] pollution events,<ref>{{cite journal |doi=10.1021/acs.chemrev.5b00067 |title=Formation of Urban Fine Particulate Matter |year=2015 |last1=Zhang |first1=Renyi |last2=Wang |first2=Gehui |last3=Guo |first3=Song |last4=Zamora |first4=Misti L. |last5=Ying |first5=Qi |last6=Lin |first6=Yun |last7=Wang |first7=Weigang |last8=Hu |first8=Min |last9=Wang |first9=Yuan |journal=Chemical Reviews |volume=115 |issue=10 |pages=3803–3855 |pmid=25942499}}</ref> which have potential human health consequences.<ref>{{cite journal |doi=10.1038/484161a |title=Cleaning China's air |year=2012 |last1=Zhang |first1=Qiang |last2=He |first2=Kebin |last3=Huo |first3=Hong |journal=Nature |volume=484 |issue=7393 |pages=161–162 |pmid=22498609 |s2cid=205071037}}</ref><ref>{{cite journal |doi=10.1038/s41598-017-05862-4 |title=Airborne Bacterial Communities in Three East Asian Cities of China, South Korea, and Japan |year=2017 |last1=Lee |first1=Jae Young |last2=Park |first2=Eun Ha |last3=Lee |first3=Sunghee |last4=Ko |first4=Gwangpyo |last5=Honda |first5=Yasushi |last6=Hashizume |first6=Masahiro |last7=Deng |first7=Furong |last8=Yi |first8=Seung-muk |last9=Kim |first9=Ho |journal=Scientific Reports |volume=7 |issue=1 |page=5545 |pmid=28717138 |pmc=5514139 |bibcode=2017NatSR...7.5545L}}</ref><ref>{{cite journal |doi=10.1038/ngeo2893 |title=Cleaner urban air tomorrow? |journal=Nature Geoscience |year=2017 |volume=10 |issue=2 |page=69 |bibcode=2017NatGe..10...69. |doi-access=free}}</ref> Severe particulate matter pollution is associated with [[chronic obstructive pulmonary disease]] and [[asthma]], as well as risks for early death.<ref>{{cite journal |doi=10.1016/j.envint.2014.10.005 |title=A review on the human health impact of airborne particulate matter |year=2015 |last1=Kim |first1=Ki-Hyun |last2=Kabir |first2=Ehsanul |last3=Kabir |first3=Shamin |journal=Environment International |volume=74 |pages=136–143 |pmid=25454230|bibcode=2015EnInt..74..136K }}</ref><ref>Walton, H., Dajnak, D., Beevers, S., Williams, M., Watkiss, P. and Hunt, A. (2015) "Understanding the health impacts of air pollution in London". King's College London, Transport for London and the Greater London Authority, '''1'''(1): 6–14.</ref><ref>{{cite journal |doi=10.5194/acp-15-5715-2015 |title=Long-term (2001–2012) concentrations of fine particulate matter (PM<sub>2.5</sub>) and the impact on human health in Beijing, China |year=2015 |last1=Zheng |first1=S. |last2=Pozzer |first2=A. |last3=Cao |first3=C. X. |last4=Lelieveld |first4=J. |journal=Atmospheric Chemistry and Physics |volume=15 |issue=10 |pages=5715–5725 |bibcode=2015ACP....15.5715Z |doi-access=free}}</ref><ref>{{cite journal |doi=10.1038/s41467-018-02986-7 |title=Residential energy use emissions dominate health impacts from exposure to ambient particulate matter in India |year=2018 |last1=Conibear |first1=Luke |last2=Butt |first2=Edward W. |last3=Knote |first3=Christoph |last4=Arnold |first4=Stephen R. |last5=Spracklen |first5=Dominick V. |journal=Nature Communications |volume=9 |issue=1 |page=617 |pmid=29434294 |pmc=5809377 |bibcode=2018NatCo...9..617C |s2cid=205559548}}</ref> While the chemical components of particulate matter pollution and their impacts on human health have been widely studied,<ref>{{cite journal |doi=10.1038/nature13774 |title=High secondary aerosol contribution to particulate pollution during haze events in China |year=2014 |last1=Huang |first1=Ru-Jin |last2=Zhang |first2=Yanlin |last3=Bozzetti |first3=Carlo |last4=Ho |first4=Kin-Fai |last5=Cao |first5=Jun-Ji |last6=Han |first6=Yongming |last7=Daellenbach |first7=Kaspar R. |last8=Slowik |first8=Jay G. |last9=Platt |first9=Stephen M.|last10 = Canonaco|first10 = Francesco |last11=Zotter |first11=Peter |last12=Wolf |first12=Robert |last13=Pieber |first13=Simone M. |last14=Bruns |first14=Emily A. |last15=Crippa |first15=Monica |last16=Ciarelli |first16=Giancarlo |last17=Piazzalunga |first17=Andrea |last18=Schwikowski |first18=Margit |last19=Abbaszade |first19=Gülcin|last20 = Schnelle-Kreis|first20 = Jürgen |last21=Zimmermann |first21=Ralf |last22=An |first22=Zhisheng |last23=Szidat |first23=Sönke |last24=Baltensperger |first24=Urs |last25=Haddad |first25=Imad El |last26=Prévôt |first26=André S. H. |journal=Nature |volume=514 |issue=7521 |pages=218–222 |pmid=25231863 |bibcode=2014Natur.514..218H |s2cid=205240719 |url=https://boris.unibe.ch/59537/7/Huang%20et%20al%202014_High%20secondary%20aerosol%20contribution%20to%20particulate%20pollution%20during%20haze%20events%20in%20China.pdf}}</ref> the potential impact of pollutant-associated microbes remains unclear. Airborne microbial exposure, including exposure to dust-associated organisms, has been established to both protect against and exacerbate certain diseases.<ref>{{cite journal |doi=10.1056/NEJMoa1508749 |title=Innate Immunity and Asthma Risk in Amish and Hutterite Farm Children |year=2016 |last1=Stein |first1=Michelle M. |last2=Hrusch |first2=Cara L. |last3=Gozdz |first3=Justyna |last4=Igartua |first4=Catherine |last5=Pivniouk |first5=Vadim |last6=Murray |first6=Sean E. |last7=Ledford |first7=Julie G. |last8=Marques Dos Santos |first8=Mauricius |last9=Anderson |first9=Rebecca L.|last10 = Metwali|first10 = Nervana |last11=Neilson |first11=Julia W. |last12=Maier |first12=Raina M. |last13=Gilbert |first13=Jack A. |last14=Holbreich |first14=Mark |last15=Thorne |first15=Peter S. |last16=Martinez |first16=Fernando D. |last17=von Mutius |first17=Erika |last18=Vercelli |first18=Donata |last19=Ober |first19=Carole|last20 = Sperling|first20 = Anne I. |journal=New England Journal of Medicine |volume=375 |issue=5 |pages=411–421 |pmid=27518660 |pmc=5137793}}</ref><ref>{{cite journal |doi=10.1111/ina.12427 |title=Microbial characteristics in homes of asthmatic and non-asthmatic adults in the ECRHS cohort |year=2018 |last1=Valkonen |first1=M. |last2=Täubel |first2=M. |last3=Pekkanen |first3=J. |last4=Tischer |first4=C. |last5=Rintala |first5=H. |last6=Zock |first6=J.-P. |last7=Casas |first7=L. |last8=Probst-Hensch |first8=N. |last9=Forsberg |first9=B.|last10 = Holm|first10 = M. |last11=Janson |first11=C. |last12=Pin |first12=I. |last13=Gislason |first13=T. |last14=Jarvis |first14=D. |last15=Heinrich |first15=J. |last16=Hyvärinen |first16=A. |journal=Indoor Air |volume=28 |issue=1 |pages=16–27 |pmid=28960492 |hdl=10138/238079 |s2cid=26769029 |doi-access=free|bibcode=2018InAir..28...16V }}</ref><ref>{{cite journal |doi=10.1164/rccm.201603-0451OC |title=Early-Life Exposure to the Great Smog of 1952 and the Development of Asthma |year=2016 |last1=Bharadwaj |first1=Prashant |last2=Zivin |first2=Joshua Graff |last3=Mullins |first3=Jamie T. |last4=Neidell |first4=Matthew |journal=American Journal of Respiratory and Critical Care Medicine |volume=194 |issue=12 |pages=1475–1482 |pmid=27392261 |pmc=5440984}}</ref> Understanding the temporal dynamics of the taxonomic and functional diversity of microorganisms in urban air, especially during smog events, will improve understanding of the potential microbe-associated health consequences.<ref>{{cite journal |doi=10.1021/es4048472 |title=Inhalable Microorganisms in Beijing's PM2.5 and PM10 Pollutants during a Severe Smog Event |year=2014 |last1=Cao |first1=Chen |last2=Jiang |first2=Wenjun |last3=Wang |first3=Buying |last4=Fang |first4=Jianhuo |last5=Lang |first5=Jidong |last6=Tian |first6=Geng |last7=Jiang |first7=Jingkun |last8=Zhu |first8=Ting F. |journal=Environmental Science & Technology |volume=48 |issue=3 |pages=1499–1507 |pmid=24456276 |pmc=3963435 |bibcode=2014EnST...48.1499C |s2cid=14761200}}</ref><ref name=Jiang12025>{{cite journal |doi=10.1038/nprot.2015.046 |title=Optimized DNA extraction and metagenomic sequencing of airborne microbial communities |year=2015 |last1=Jiang |first1=Wenjun |last2=Liang |first2=Peng |last3=Wang |first3=Buying |last4=Fang |first4=Jianhuo |last5=Lang |first5=Jidong |last6=Tian |first6=Geng |last7=Jiang |first7=Jingkun |last8=Zhu |first8=Ting F. |journal=Nature Protocols |volume=10 |issue=5 |pages=768–779 |pmid=25906115 |pmc=7086576}}</ref><ref name=Qin2020 />

Recent advances in airborne particle [[DNA extraction]] and [[metagenomic]] library preparation have enabled low biomass environments to be subject to [[shotgun sequencing]] analysis.<ref name=Jiang12025 /><ref name=Qin2020 /> In 2020, Qin ''et al.'' used shotgun sequencing analysis to reveal a great diversity of microbial species and [[antibiotic resistant]] genes in Beijing's particulate matter, largely consistent with a recent study.<ref>{{cite journal |doi=10.1186/s40168-016-0199-5 |title=The structure and diversity of human, animal and environmental resistomes |year=2016 |last1=Pal |first1=Chandan |last2=Bengtsson-Palme |first2=Johan |last3=Kristiansson |first3=Erik |last4=Larsson |first4=D. G. Joakim |journal=Microbiome |volume=4 |issue=1 |page=54 |pmid=27717408 |pmc=5055678 |doi-access=free}}</ref> The data suggest that potential pathogen and antibiotic resistance burden increases with increasing pollution levels and that severe smog events promote the exposure. In addition, the particulate matter also contained several bacteria that harbored antibiotic resistant genes flanked by mobile genetic elements, which could be associated with [[horizontal gene transfer]]. Many of these bacteria were typical or putative members of the [[human microbiome]].<ref name=Qin2020 />

{{clear}}

==Clouds==
[[File:Beautiful cloud.jpg|thumb|upright=1.7| Clouds can transport microorganisms and disperse them over long distances.<ref>{{cite journal |last=Amato |first=Pierre |title=Clouds Provide Atmospheric Oases for Microbes |journal=Microbe Magazine |publisher=American Society for Microbiology |volume=7 |issue=3 |date=1 January 2012 |issn=1558-7452 |doi=10.1128/microbe.7.119.1 |pages=119–123}}</ref>]]
[[File:Impacts of microbial activity on cloud processes.webp|thumb|upright=1.7| {{center|'''Impact of microbial activity on clouds'''{{hsp}}<ref name=Amato2019>{{cite journal |doi=10.1038/s41598-019-41032-4 |title=Metatranscriptomic exploration of microbial functioning in clouds |year=2019 |last1=Amato |first1=Pierre |last2=Besaury |first2=Ludovic |last3=Joly |first3=Muriel |last4=Penaud |first4=Benjamin |last5=Deguillaume |first5=Laurent |last6=Delort |first6=Anne-Marie |journal=Scientific Reports |volume=9 |issue=1 |page=4383 |pmid=30867542 |pmc=6416334 |bibcode=2019NatSR...9.4383A}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>}} Biological processes and their targets are indicated by green arrows, while red arrows indicate abiotic processes. {{center|<small>EPS: [[Exopolysaccharide]] {{space|12}} SOA: [[Secondary organic aerosol]]<br />Based on coordinated [[metagenomics]]/[[metatranscriptomics]]</small>}}]]

The outdoor atmosphere harbors diverse microbial assemblages composed of bacteria, fungi and viruses{{hsp}}<ref>{{cite book |doi=10.1002/9781119132318.ch1a |chapter=Main Biological Aerosols, Specificities, Abundance, and Diversity |title=Microbiology of Aerosols |year=2017 |last1=Amato |first1=P. |last2=Brisebois |first2=E. |last3=Draghi |first3=M. |last4=Duchaine |first4=C. |last5=Fröhlich-Nowoisky |first5=J. |last6=Huffman |first6=J.A. |last7=Mainelis |first7=G. |last8=Robine |first8=E. |last9=Thibaudon |first9=M. |pages=1–21 |isbn=9781119132318}}</ref> whose functioning remains largely unexplored.<ref name=Amato2019 /> While the occasional presence of human pathogens or opportunists can cause potential hazard,<ref name="Urban aerosols harbor diverse and d">{{cite journal |doi=10.1073/pnas.0608255104 |title=Urban aerosols harbor diverse and dynamic bacterial populations |year=2007 |last1=Brodie |first1=E. L. |last2=Desantis |first2=T. Z. |last3=Parker |first3=J. P. M. |last4=Zubietta |first4=I. X. |last5=Piceno |first5=Y. M. |last6=Andersen |first6=G. L. |journal=Proceedings of the National Academy of Sciences |volume=104 |issue=1 |pages=299–304 |pmid=17182744 |pmc=1713168 |bibcode=2007PNAS..104..299B |doi-access=free}}</ref><ref>{{cite journal |doi=10.1016/j.scitotenv.2017.03.105 |title=Assessment and risk modeling of airborne enteric viruses emitted from wastewater reused for irrigation |year=2017 |last1=Courault |first1=D. |last2=Albert |first2=I. |last3=Perelle |first3=S. |last4=Fraisse |first4=A. |last5=Renault |first5=P. |last6=Salemkour |first6=A. |last7=Amato |first7=P. |journal=Science of the Total Environment |volume=592 |pages=512–526 |pmid=28320526 |bibcode=2017ScTEn.592..512C}}</ref> in general the vast majority of airborne microbes originate from natural environments like soil or plants, with large spatial and temporal variations of [[Biomass (ecology)|biomass]] and [[biodiversity]].<ref name="Bowers2011"/><ref name=Amato2017>{{cite journal |doi=10.1371/journal.pone.0182869 |title=Active microorganisms thrive among extremely diverse communities in cloud water |year=2017 |last1=Amato |first1=Pierre |last2=Joly |first2=Muriel |last3=Besaury |first3=Ludovic |last4=Oudart |first4=Anne |last5=Taib |first5=Najwa |last6=Moné |first6=Anne I. |last7=Deguillaume |first7=Laurent |last8=Delort |first8=Anne-Marie |last9=Debroas |first9=Didier |journal=PLOS ONE |volume=12 |issue=8 |pages=e0182869 |pmid=28792539 |pmc=5549752 |bibcode=2017PLoSO..1282869A |doi-access=free}}</ref> Once ripped off and [[aerosolized]] from surfaces by mechanical disturbances such as those generated by wind, raindrop impacts or water bubbling,<ref>{{cite journal |doi=10.1016/j.jaerosci.2004.10.012 |title=The sea surface microlayer as a source of viral and bacterial enrichment in marine aerosols |year=2005 |last1=Aller |first1=Josephine Y. |last2=Kuznetsova |first2=Marina R. |last3=Jahns |first3=Christopher J. |last4=Kemp |first4=Paul F. |journal=Journal of Aerosol Science |volume=36 |issue=5–6 |pages=801–812 |bibcode=2005JAerS..36..801A}}</ref><ref name="Bioaerosol generation by raindrops"/> microbial cells are transported upward by [[Turbulent fluid|turbulent]] [[flux]]es.<ref name="Measurements and modeling of surfac"/> They remain aloft for an average of ~3 days,<ref name="Burrows2009a"/> a time long enough for being transported across oceans and continents{{hsp}}<ref name="Griffin2017"/><ref name="Šantl-Temkiv2018"/><ref name="Continental-scale distributions of"/> until being finally deposited, eventually helped by water condensation and precipitation processes; microbial aerosols themselves can contribute to form clouds and trigger precipitation by serving as [[cloud condensation nuclei]]{{hsp}}<ref>{{cite journal |doi=10.1029/2003JD003545 |title=Airborne bacteria as cloud condensation nuclei |year=2003 |last1=Bauer |first1=Heidi |last2=Giebl |first2=Heinrich |last3=Hitzenberger |first3=Regina |last4=Kasper-Giebl |first4=Anne |last5=Reischl |first5=Georg |last6=Zibuschka |first6=Franziska |last7=Puxbaum |first7=Hans |journal=Journal of Geophysical Research: Atmospheres |volume=108 |issue=D21 |page=4658 |bibcode=2003JGRD..108.4658B}}</ref> and [[ice nuclei]].<ref>{{cite journal |doi=10.1051/jp4:2004121004 |title=Ice nucleation active bacteria and their potential role in precipitation |year=2004 |last1=Morris |first1=C. E. |last2=Georgakopoulos |first2=D. G. |last3=Sands |first3=D. C. |journal=Journal de Physique IV (Proceedings) |volume=121 |pages=87–103}}</ref><ref name="Creamean2013"/><ref name=Amato2019 />

Living airborne microorganisms may end up concretizing aerial dispersion by [[Colonisation (biology)|colonizing]] their new habitat,<ref>{{cite book |doi=10.1002/9781119132318.ch4b |chapter=Impacts of Microbial Aerosols on Natural and Agro-ecosystems: Immigration, Invasions, and their Consequences |title=Microbiology of Aerosols |year=2017 |last1=Morris |first1=C.E. |last2=Sands |first2=D.C. |pages=269–279 |isbn=9781119132318}}</ref> provided that they survive their journey from emission to deposition. Bacterial survival is indeed naturally impaired during atmospheric transport,<ref>{{cite journal |doi=10.1007/s10453-011-9203-5 |title=Microbial survival in the stratosphere and implications for global dispersal |year=2011 |last1=Smith |first1=David J. |last2=Griffin |first2=Dale W. |last3=McPeters |first3=Richard D. |last4=Ward |first4=Peter D. |last5=Schuerger |first5=Andrew C. |journal=Aerobiologia |volume=27 |issue=4 |pages=319–332 |bibcode=2011Aerob..27..319S |s2cid=52107037}}</ref><ref>{{cite journal |doi=10.5194/acp-15-6455-2015 |title=Survival and ice nucleation activity of bacteria as aerosols in a cloud simulation chamber |year=2015 |last1=Amato |first1=P. |last2=Joly |first2=M. |last3=Schaupp |first3=C. |last4=Attard |first4=E. |last5=Möhler |first5=O. |last6=Morris |first6=C. E. |last7=Brunet |first7=Y. |last8=Delort |first8=A.-M. |journal=Atmospheric Chemistry and Physics |volume=15 |issue=11 |pages=6455–6465 |bibcode=2015ACP....15.6455A |doi-access=free}}</ref> but a fraction remains viable.<ref>{{cite journal |doi=10.1029/2006JD008002 |title=Processing of atmospheric nitrogen by clouds above a forest environment |year=2007 |last1=Hill |first1=Kimberly A. |last2=Shepson |first2=Paul B. |last3=Galbavy |first3=Edward S. |last4=Anastasio |first4=Cort |last5=Kourtev |first5=Peter S. |last6=Konopka |first6=Allan |last7=Stirm |first7=Brian H. |journal=Journal of Geophysical Research |volume=112 |issue=D11 |pages=D11301 |bibcode=2007JGRD..11211301H}}</ref><ref>{{cite journal |doi=10.1016/j.atmosenv.2011.11.050 |title=Bacterial abundance and viability in long-range transported dust |year=2012 |last1=Hara |first1=Kazutaka |last2=Zhang |first2=Daizhou |journal=Atmospheric Environment |volume=47 |pages=20–25 |bibcode=2012AtmEn..47...20H}}</ref> At high altitude, the peculiar environments offered by [[Cloud physics|cloud droplets]] are thus regarded in some aspects as temporary microbial habitats, providing water and nutrients to airborne living cells.<ref>{{cite journal |doi=10.1111/j.1574-6941.2012.01402.x |title=The microbial diversity of a storm cloud as assessed by hailstones |year=2012 |last1=Temkiv |first1=Tina Šantl |last2=Finster |first2=Kai |last3=Hansen |first3=Bjarne Munk |last4=Nielsen |first4=Niels Woetmann |last5=Karlson |first5=Ulrich Gosewinkel |journal=FEMS Microbiology Ecology |volume=81 |issue=3 |pages=684–695 |pmid=22537388 |doi-access=free|bibcode=2012FEMME..81..684T }}</ref><ref>{{cite journal |doi=10.1016/1352-2310(96)00160-4 |title=Fog droplets—an atmospheric source of secondary biological aerosol particles |year=1997 |last1=Fuzzi |first1=Sandro |last2=Mandrioli |first2=Paolo |last3=Perfetto |first3=Antonio |journal=Atmospheric Environment |volume=31 |issue=2 |pages=287–290 |bibcode=1997AtmEn..31..287F}}</ref><ref name=Amato2007>{{cite journal |doi=10.5194/acp-7-4159-2007 |title=A fate for organic acids, formaldehyde and methanol in cloud water: Their biotransformation by micro-organisms |year=2007 |last1=Amato |first1=P. |last2=Demeer |first2=F. |last3=Melaouhi |first3=A. |last4=Fontanella |first4=S. |last5=Martin-Biesse |first5=A.-S. |last6=Sancelme |first6=M. |last7=Laj |first7=P. |last8=Delort |first8=A.-M. |journal=Atmospheric Chemistry and Physics |volume=7 |issue=15 |pages=4159–4169 |bibcode=2007ACP.....7.4159A |doi-access=free}}</ref> In addition, the detection of low levels of [[heterotrophy]]{{hsp}}<ref>{{cite journal |doi=10.1029/2000GL011684 |title=Bacterial growth in supercooled cloud droplets |year=2001 |last1=Sattler |first1=Birgit |last2=Puxbaum |first2=Hans |last3=Psenner |first3=Roland |journal=Geophysical Research Letters |volume=28 |issue=2 |pages=239–242 |bibcode=2001GeoRL..28..239S |s2cid=129784139 |doi-access=free}}</ref> raises questions about microbial functioning in cloud water and its potential influence on the chemical reactivity of these complex and dynamic environments.<ref name=Amato2007 /><ref name="ReferenceA" /> The [[Metabolism|metabolic functioning]] of microbial cells in clouds is still albeit unknown, while fundamental for apprehending microbial life conditions during long distance aerial transport and their geochemical and ecological impacts.<ref name=Amato2019 />

Aerosols affect [[cloud formation]], thereby influencing sunlight [[irradiation]] and precipitation, but the extent to which and the manner in which they influence climate remains uncertain.<ref>{{cite journal |doi=10.1126/science.aav0566 |title=Aerosol-driven droplet concentrations dominate coverage and water of oceanic low-level clouds |year=2019 |last1=Rosenfeld |first1=Daniel |last2=Zhu |first2=Yannian |last3=Wang |first3=Minghuai |last4=Zheng |first4=Youtong |last5=Goren |first5=Tom |last6=Yu |first6=Shaocai |journal=Science |volume=363 |issue=6427 |pmid=30655446 |s2cid=58612273 |doi-access=free}}</ref> Marine aerosols consist of a complex mixture of sea salt, non-sea-salt sulfate and organic molecules and can function as [[Condensation nucleus|nuclei]] for [[cloud condensation]], influencing the [[radiation balance]] and, hence, climate.<ref name=Charlson1987>{{cite journal |doi=10.1038/326655a0 |title=Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate |year=1987 |last1=Charlson |first1=Robert J. |last2=Lovelock |first2=James E. |last3=Andreae |first3=Meinrat O. |last4=Warren |first4=Stephen G. |journal=Nature |volume=326 |issue=6114 |pages=655–661 |bibcode=1987Natur.326..655C |s2cid=4321239}}</ref><ref name=Gantt2013>{{cite journal |doi=10.5194/acp-13-3979-2013 |title=The physical and chemical characteristics of marine primary organic aerosol: A review |year=2013 |last1=Gantt |first1=B. |last2=Meskhidze |first2=N. |journal=Atmospheric Chemistry and Physics |volume=13 |issue=8 |pages=3979–3996 |bibcode=2013ACP....13.3979G |doi-access=free}}</ref> For example, biogenic aerosols in remote marine environments (for example, the Southern Ocean) can increase the number and size of cloud droplets, having similar effects on climate as aerosols in highly polluted regions.<ref name=Gantt2013 /><ref>{{cite journal |doi=10.1126/science.1131779 |title=Phytoplankton and Cloudiness in the Southern Ocean |year=2006 |last1=Meskhidze |first1=Nicholas |last2=Nenes |first2=Athanasios |journal=Science |volume=314 |issue=5804 |pages=1419–1423 |pmid=17082422 |bibcode=2006Sci...314.1419M |s2cid=36030601 |doi-access=free}}</ref><ref>{{cite journal |doi=10.1016/j.earscirev.2008.03.001 |title=Aerosol–cloud–precipitation interactions. Part 1. The nature and sources of cloud-active aerosols |year=2008 |last1=Andreae |first1=M.O. |last2=Rosenfeld |first2=D. |journal=Earth-Science Reviews |volume=89 |issue=1–2 |pages=13–41 |bibcode=2008ESRv...89...13A}}</ref><ref>{{cite journal |doi=10.5194/acp-13-4235-2013 |title=Droplet number uncertainties associated with CCN: An assessment using observations and a global model adjoint |year=2013 |last1=Moore |first1=R. H. |last2=Karydis |first2=V. A. |last3=Capps |first3=S. L. |last4=Lathem |first4=T. L. |last5=Nenes |first5=A. |journal=Atmospheric Chemistry and Physics |volume=13 |issue=8 |pages=4235–4251 |bibcode=2013ACP....13.4235M |doi-access=free}}</ref> Specifically, [[phytoplankton]] emit [[dimethylsulfide]], and its derivate [[sulfate]] promotes cloud condensation.<ref name=Charlson1987 /><ref name=Sanchez2018>{{cite journal |doi=10.1038/s41598-018-21590-9 |title=Substantial Seasonal Contribution of Observed Biogenic Sulfate Particles to Cloud Condensation Nuclei |year=2018 |last1=Sanchez |first1=Kevin J. |last2=Chen |first2=Chia-Li |last3=Russell |first3=Lynn M. |last4=Betha |first4=Raghu |last5=Liu |first5=Jun |last6=Price |first6=Derek J. |last7=Massoli |first7=Paola |last8=Ziemba |first8=Luke D. |last9=Crosbie |first9=Ewan C.|last10 = Moore|first10 = Richard H. |last11=Müller |first11=Markus |last12=Schiller |first12=Sven A. |last13=Wisthaler |first13=Armin |last14=Lee |first14=Alex K. Y. |last15=Quinn |first15=Patricia K. |last16=Bates |first16=Timothy S. |last17=Porter |first17=Jack |last18=Bell |first18=Thomas G. |last19=Saltzman |first19=Eric S.|last20 = Vaillancourt|first20 = Robert D. |last21=Behrenfeld |first21=Mike J. |journal=Scientific Reports |volume=8 |issue=1 |page=3235 |pmid=29459666 |pmc=5818515 |bibcode=2018NatSR...8.3235S}}</ref> Understanding the ways in which marine phytoplankton contribute to aerosols will allow better predictions of how changing ocean conditions will affect clouds and feed back on climate.<ref name=Sanchez2018 /> In addition, the atmosphere itself contains about 10<sup>22</sup> microbial cells, and determining the ability of atmospheric microorganisms to grow and form aggregates will be valuable for assessing their influence on climate.<ref>{{cite journal |doi=10.1038/s41579-019-0158-9 |title=Bacteria and archaea on Earth and their abundance in biofilms |year=2019 |last1=Flemming |first1=Hans-Curt |last2=Wuertz |first2=Stefan |journal=Nature Reviews Microbiology |volume=17 |issue=4 |pages=247–260 |pmid=30760902 |s2cid=61155774}}</ref><ref name=Cavicchioli2019>Cavicchioli, R., Ripple, W.J., Timmis, K.N., Azam, F., Bakken, L.R., Baylis, M., Behrenfeld, M.J., Boetius, A., Boyd, P.W., Classen, A.T. and Crowther, T.W. (2019) "Scientists' warning to humanity: microorganisms and climate change". ''Nature Reviews Microbiology'', '''17''': 569–586. {{doi|10.1038/s41579-019-0222-5}}</ref>

After the tantalizing detection of [[phosphine]] (PH<sub>3</sub>) in the atmosphere of the planet [[Venus (planet)|Venus]], and in the absence of a known and plausible chemical mechanism to explain the formation of this molecule, Greaves ''et al.'' speculated in 2020 that microorganisms might be present in suspension in the Venusian atmosphere.<ref name="Greaves_2020">{{cite journal |last1=Greaves |first1=Jane S. |last2=Richards |first2=Anita M. S. |last3=Bains |first3=William |last4=Rimmer |first4=Paul B. |last5=Sagawa |first5=Hideo |last6=Clements |first6=David L. |last7=Seager |first7=Sara |last8=Petkowski |first8=Janusz J. |last9=Sousa-Silva |first9=Clara|last10=Ranjan|first10=Sukrit |last11=Drabek-Maunder |first11=Emily |last12=Fraser |first12=Helen J. |last13=Cartwright |first13=Annabel |last14=Mueller-Wodarg |first14=Ingo |last15=Zhan |first15=Zhuchang |last16=Friberg |first16=Per |last17=Coulson |first17=Iain |last18=Lee |first18=E'lisa |last19=Hoge |first19=Jim |title=Phosphine gas in the cloud decks of Venus |journal=Nature Astronomy |year=2020 |volume=5 |issue=7 |pages=655–664 |issn=2397-3366 |doi=10.1038/s41550-020-1174-4 |arxiv=2009.06593 |s2cid=221655755 |url=http://oro.open.ac.uk/72838/1/2009.06593.pdf}}</ref> They have formulated the hypothesis of the microbial formation of phosphine, envisaging the possibility of a liveable window in the Venusian clouds at a certain altitude with an acceptable temperature range for microbial life.<ref name="Greaves_2020" /> However, in 2021 Hallsworth ''et al.'' examined the conditions required to support the life of [[extremophile]] microorganisms in the clouds at high altitude in the Venusian atmosphere where favorable temperature conditions might prevail.<ref name="Hallsworth_2021" /> Beside the presence of [[sulfuric acid]] in the clouds which already represent a major challenge for the survival of most of microorganisms, they came to the conclusion that the Venusian atmosphere is too dry to host microbial life. They determined a [[water activity]] ≤ 0.004, two orders of magnitude below the 0.585 limit for known extremophiles.<ref name="Hallsworth_2021">{{cite journal |last1=Hallsworth |first1=John E. |last2=Koop |first2=Thomas |last3=Dallas |first3=Tiffany D. |last4=Zorzano |first4=María-Paz |last5=Burkhardt |first5=Juergen |last6=Golyshina |first6=Olga V. |last7=Martín-Torres |first7=Javier |last8=Dymond |first8=Marcus K. |last9=Ball |first9=Philip|last10=McKay|first10=Christopher P. |title=Water activity in Venus's uninhabitable clouds and other planetary atmospheres |journal=Nature Astronomy |year=2021 |volume=5 |issue=7 |pages=665–675 |issn=2397-3366 |doi=10.1038/s41550-021-01391-3 |bibcode=2021NatAs...5..665H |hdl=10261/261774 |s2cid=237820246 |url=https://pureadmin.qub.ac.uk/ws/files/246962674/3997_3_merged_1619627059.pdf}}</ref>

==Airborne microbiomes==
{{see also|Microbiome}}
<gallery mode="packed" style="float:right" heights="300px">
File:Biological niches in aeromicrobiology.webp | {{center|Biological habitats ([[Ecological niche|niches]]) in aeromicrobiology{{hsp}}<ref name=TignatPerrier2020>{{cite journal |doi=10.3390/atmos11121296 |doi-access=free |title=Microbial Ecology of the Planetary Boundary Layer |year=2020 |last1=Tignat-Perrier |first1=Romie |last2=Dommergue |first2=Aurélien |last3=Vogel |first3=Timothy M. |last4=Larose |first4=Catherine |journal=Atmosphere |volume=11 |issue=12 |page=1296 |bibcode=2020Atmos..11.1296T}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>}}|alt=Biological habitats (niches) in aeromicrobiology
</gallery>

While the physical and chemical properties of airborne [[particulate matter]] have been extensively studied, their associated airborne [[microbiome]] remains largely unexplored.<ref name=Qin2020>{{cite journal |doi=10.1186/s13059-020-01964-x |title=Longitudinal survey of microbiome associated with particulate matter in a megacity |year=2020 |last1=Qin |first1=Nan |last2=Liang |first2=Peng |last3=Wu |first3=Chunyan |last4=Wang |first4=Guanqun |last5=Xu |first5=Qian |last6=Xiong |first6=Xiao |last7=Wang |first7=Tingting |last8=Zolfo |first8=Moreno |last9=Segata |first9=Nicola|last10 = Qin|first10 = Huanlong |last11=Knight |first11=Rob |last12=Gilbert |first12=Jack A. |last13=Zhu |first13=Ting F. |journal=Genome Biology |volume=21 |issue=1 |page=55 |pmid=32127018 |pmc=7055069 |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> Microbiomes are defined as characteristic [[microbial communities]], which include [[prokaryote]]s, [[fungi]], [[protozoa]], other micro-[[eukaryote]]s and [[virus]]es, that occupy [[habitat|well-defined habitats]].<ref name=Berg2020>{{cite journal |doi=10.1186/s40168-020-00875-0 |title=Microbiome definition re-visited: Old concepts and new challenges |year=2020 |last1=Berg |first1=Gabriele |authorlink1=Gabriele Berg |last2=Rybakova |first2=Daria |last3=Fischer |first3=Doreen |last4=Cernava |first4=Tomislav |last5=Vergès |first5=Marie-Christine Champomier |last6=Charles |first6=Trevor |last7=Chen |first7=Xiaoyulong |last8=Cocolin |first8=Luca |last9=Eversole |first9=Kellye|last10 = Corral|first10 = Gema Herrero |last11=Kazou |first11=Maria |last12=Kinkel |first12=Linda |last13=Lange |first13=Lene |last14=Lima |first14=Nelson |last15=Loy |first15=Alexander |last16=MacKlin |first16=James A. |last17=Maguin |first17=Emmanuelle |last18=Mauchline |first18=Tim |last19=McClure |first19=Ryan|last20 = Mitter|first20 = Birgit |last21=Ryan |first21=Matthew |last22=Sarand |first22=Inga |last23=Smidt |first23=Hauke |last24=Schelkle |first24=Bettina |last25=Roume |first25=Hugo |last26=Kiran |first26=G. Seghal |last27=Selvin |first27=Joseph |last28=Souza |first28=Rafael Soares Correa de |last29=Van Overbeek |first29=Leo|last30 = Singh|first30 = Brajesh K. |journal=Microbiome |volume=8 |issue=1 |page=103 |pmid=32605663 |pmc=7329523 |display-authors=4 |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> The term microbiome is broader than other terms, for example, microbial communities, microbial population, microbiota or microbial flora, as microbiome refers to both its composition (the microorganisms involved) and its functions (their members' activities and interactions with the host/environment), which contribute to ecosystem functions.<ref name=Berg2020 /><ref name=Meisner2021>{{cite journal |doi=10.1016/j.copbio.2021.08.003 |title=Calling for a systems approach in microbiome research and innovation |year=2022 |last1=Meisner |first1=Annelein |last2=Wepner |first2=Beatrix |last3=Kostic |first3=Tanja |last4=Van Overbeek |first4=Leo S. |last5=Bunthof |first5=Christine J. |last6=De Souza |first6=Rafael Soares Correa |last7=Olivares |first7=Marta |last8=Sanz |first8=Yolanda |last9=Lange |first9=Lene|last10 = Fischer|first10 = Doreen |last11=Sessitsch |first11=Angela |last12=Smidt |first12=Hauke |journal=Current Opinion in Biotechnology |volume=73 |pages=171–178 |pmid=34479027 |s2cid=237409945 |hdl=10261/251784 |hdl-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

Throughout Earth's history, microbial communities have changed the climate, and climate has shaped microbial communities.<ref>{{cite journal |doi=10.1038/s41579-019-0178-5 |title=Climate change microbiology — problems and perspectives |year=2019 |last1=Hutchins |first1=David A. |last2=Jansson |first2=Janet K. |last3=Remais |first3=Justin V. |last4=Rich |first4=Virginia I. |last5=Singh |first5=Brajesh K. |last6=Trivedi |first6=Pankaj |journal=Nature Reviews Microbiology |volume=17 |issue=6 |pages=391–396 |pmid=31092905 |s2cid=155102440}}</ref> Microorganisms can modify ecosystem processes or biogeochemistry on a global scale, and we start to uncover their role and potential involvement in changing the climate.<ref>{{cite journal |doi=10.1038/nrmicro2439 |title=Microorganisms and climate change: Terrestrial feedbacks and mitigation options |year=2010 |last1=Singh |first1=Brajesh K. |last2=Bardgett |first2=Richard D. |last3=Smith |first3=Pete |last4=Reay |first4=Dave S. |journal=Nature Reviews Microbiology |volume=8 |issue=11 |pages=779–790 |pmid=20948551 |s2cid=1522347}}</ref> However, the effects of climate change on microbial communities (i.e., diversity, dynamics, or distribution) are rarely addressed.<ref>{{cite journal |doi=10.1038/s41579-019-0222-5 |title=Scientists' warning to humanity: Microorganisms and climate change |year=2019 |last1=Cavicchioli |first1=Ricardo |last2=Ripple |first2=William J. |last3=Timmis |first3=Kenneth N. |last4=Azam |first4=Farooq |last5=Bakken |first5=Lars R. |last6=Baylis |first6=Matthew |last7=Behrenfeld |first7=Michael J. |last8=Boetius |first8=Antje |last9=Boyd |first9=Philip W.|last10 = Classen|first10 = Aimée T. |last11=Crowther |first11=Thomas W. |last12=Danovaro |first12=Roberto |last13=Foreman |first13=Christine M. |last14=Huisman |first14=Jef |last15=Hutchins |first15=David A. |last16=Jansson |first16=Janet K. |last17=Karl |first17=David M. |last18=Koskella |first18=Britt |last19=Mark Welch |first19=David B.|last20 = Martiny|first20 = Jennifer B. H. |last21=Moran |first21=Mary Ann |last22=Orphan |first22=Victoria J. |last23=Reay |first23=David S. |last24=Remais |first24=Justin V. |last25=Rich |first25=Virginia I. |last26=Singh |first26=Brajesh K. |last27=Stein |first27=Lisa Y. |last28=Stewart |first28=Frank J. |last29=Sullivan |first29=Matthew B.|last30 = Van Oppen|first30 = Madeleine J. H. |journal=Nature Reviews Microbiology |volume=17 |issue=9 |pages=569–586 |pmid=31213707 |pmc=7136171 |s2cid=190637591 |display-authors=1}}</ref> In the case of fungal aerobiota, its composition is likely influenced by dispersal ability, rather than season or climate.<ref>{{cite journal |doi=10.1073/pnas.1907414116 |title=Fungal aerobiota are not affected by time nor environment over a 13-y time series at the Mauna Loa Observatory |year=2019 |last1=Tipton |first1=Laura |last2=Zahn |first2=Geoffrey |last3=Datlof |first3=Erin |last4=Kivlin |first4=Stephanie N. |last5=Sheridan |first5=Patrick |last6=Amend |first6=Anthony S. |last7=Hynson |first7=Nicole A. |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=51 |pages=25728–25733 |pmid=31801876 |pmc=6926071 |bibcode=2019PNAS..11625728T |doi-access=free}}</ref> Indeed, the origin of air masses from marine, terrestrial, or anthropogenic-impacted environments, mainly shapes the atmospheric air microbiome.<ref name="Cáliz2018"/> However, recent studies have shown that meteorological factors and seasonality influence the composition of airborne bacterial communities.<ref name="Cáliz2018" /><ref>{{cite journal |doi=10.1007/s10453-018-9510-1 |title=Influence of meteorological factors on the level and characteristics of culturable bacteria in the air in Gliwice, Upper Silesia (Poland) |year=2018 |last1=Brągoszewska |first1=Ewa |last2=Pastuszka |first2=Józef S. |journal=Aerobiologia |volume=34 |issue=2 |pages=241–255 |pmid=29773927 |pmc=5945727 |bibcode=2018Aerob..34..241B |s2cid=21687542}}</ref><ref>{{cite journal |doi=10.1016/j.envint.2020.106156 |title=Airborne bacterial communities of outdoor environments and their associated influencing factors |year=2020 |last1=Ruiz-Gil |first1=Tay |last2=Acuña |first2=Jacquelinne J. |last3=Fujiyoshi |first3=So |last4=Tanaka |first4=Daisuke |last5=Noda |first5=Jun |last6=Maruyama |first6=Fumito |last7=Jorquera |first7=Milko A. |journal=Environment International |volume=145 |page=106156 |pmid=33039877 |s2cid=222301690 |doi-access=free|bibcode=2020EnInt.14506156R }}</ref> This evidence suggests that climatic conditions may act as an environmental filter for the aeroplankton, selecting a subset of species from the regional pool, and raises the question of the relative importance of the different factors affecting both bacterial and eukaryal aeroplankton.<ref name= Ontiveros2021 />

In 2020, Archer ''et al.'' reported evidence for a dynamic microbial presence at the ocean–atmosphere interface at the [[Great Barrier Reef]], and identified air mass trajectories over oceanic and continental surfaces associated with observed shifts in airborne bacterial and fungal diversity. Relative abundance of shared taxa between air and [[coral microbiome]]s varied between 2.2 and 8.8% and included those identified as part of the core coral microbiome.<ref name=Archer2019 /> Above marine systems, the abundance of microorganisms decreases exponentially with distance from land,<ref name="Long-range transport of airborne mi"/> but relatively little is known about potential patterns in biodiversity for airborne microorganisms above the oceans. Here we test the hypothesis that persistent microbial inputs to the ocean–atmosphere interface of the Great Barrier Reef ecosystem vary according to surface cover (i.e. land vs. ocean) during transit of the air-mass.
<ref name=Archer2019>{{cite journal |doi=10.1038/s41396-019-0555-0 |title=Air mass source determines airborne microbial diversity at the ocean–atmosphere interface of the Great Barrier Reef marine ecosystem |year=2020 |last1=Archer |first1=Stephen D. J. |last2=Lee |first2=Kevin C. |last3=Caruso |first3=Tancredi |last4=King-Miaow |first4=Katie |last5=Harvey |first5=Mike |last6=Huang |first6=Danwei |last7=Wainwright |first7=Benjamin J. |last8=Pointing |first8=Stephen B. |journal=The ISME Journal |volume=14 |issue=3 |pages=871–876 |pmid=31754205 |pmc=7031240|bibcode=2020ISMEJ..14..871A }} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

{{clear}}

==Airborne DNA==
In 2021, researchers demonstrated that [[environmental DNA]] (eDNA) can be collected from air and used to identify mammals.<ref>{{cite journal |last1=Lynggaard |first1=Christina |last2=Bertelsen |first2=Mads Frost |last3=Jensen |first3=Casper V. |last4=Johnson |first4=Matthew S. |last5=Frøslev |first5=Tobias Guldberg |last6=Olsen |first6=Morten Tange |last7=Bohmann |first7=Kristine |title=Airborne environmental DNA for terrestrial vertebrate community monitoring |journal=Current Biology |date=6 January 2022 |volume=32 |issue=3 |pages=701–707.e5 |doi=10.1016/j.cub.2021.12.014 |pmid=34995490 |pmc=8837273 |bibcode=2022CBio...32E.701L |s2cid=245772800}}</ref><ref>{{cite journal |last1=Clare |first1=Elizabeth L. |last2=Economou |first2=Chloe K. |last3=Bennett |first3=Frances J. |last4=Dyer |first4=Caitlin E. |last5=Adams |first5=Katherine |last6=McRobie |first6=Benjamin |last7=Drinkwater |first7=Rosie |last8=Littlefair |first8=Joanne E. |title=Measuring biodiversity from DNA in the air |journal=Current Biology |date=January 2022 |volume=32 |issue=3 |pages=693–700.e5 |doi=10.1016/j.cub.2021.11.064 |pmid=34995488 |s2cid=245772825 |doi-access=free|bibcode=2022CBio...32E.693C }}</ref><ref>{{cite journal |doi=10.7717/peerj.11030 |title=EDNAir: Proof of concept that animal DNA can be collected from air sampling |year=2021 |last1=Clare |first1=Elizabeth L. |last2=Economou |first2=Chloe K. |last3=Faulkes |first3=Chris G. |last4=Gilbert |first4=James D. |last5=Bennett |first5=Frances |last6=Drinkwater |first6=Rosie |last7=Littlefair |first7=Joanne E. |journal=PeerJ |volume=9 |pages=e11030 |pmid=33850648 |pmc=8019316 |doi-access=free}} [[File:CC-BY icon.svg|50px]] Modified text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref><ref>[https://www.livescience.com/dna-collected-air.html Researchers can now collect and sequence DNA from the air] ''Live Science '', 6 April 2021.</ref> In 2023, scientists developed a specialized sampling probe and aircraft surveys to assess biodiversity of multiple taxa, including mammals, using air eDNA.<ref name=":0">{{Cite journal |last1=Métris |first1=Kimberly L. |last2=Métris |first2=Jérémy |date=14 April 2023 |title=Aircraft surveys for air eDNA: probing biodiversity in the sky |journal=PeerJ |language=en |volume=11 |pages=e15171 |doi=10.7717/peerj.15171 |pmid=37077310 |pmc=10108859 |issn=2167-8359 |doi-access=free}}</ref>

==Gallery==
<gallery mode="packed" style="float:left;" heights="170px">
File:Some Airborne Fungal Spores.jpg|Airborne [[fungal spore]]s
</gallery>
{{clear}}

==See also==
{{div col|colwidth=30em}}
* [[Aeolian processes]]
* [[Aerobiology]]
* [[Airborne transmission]]
* [[Biological dispersal]]
** [[Dispersal vector]]
** [[Seed dispersal]]
* [[Organisms at high altitude]]
* [[Palynology]]
{{div col end}}

==References==
{{reflist}}

==General reference==
* {{Cite book |url=https://books.google.com/books?id=7zkLEAAAQBAJ&q=%22Bioaerosols+Handbook%22 |title=Bioaerosols Handbook |isbn=9781000115048 |last1=Cox |first1=Christopher S. |last2=Wathes |first2=Christopher M. |date=25 November 2020 |publisher=CRC Press}}

==External links==
{{commons}}
* [http://www.islandnet.com/~see/weather/almanac/arc_1998/98sep02.htm Living on the air]

{{plankton}}

[[Category:Ecology terminology]]
[[Category:Planktology]]