Peroxyacetyl nitrate: Difference between revisions
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}} | }}'''Peroxyacetyl nitrate''' is a [[Peroxyacyl nitrates|peroxyacyl nitrate]].<ref name=":0">{{Cite journal |last=E V |first=Fischer |date=March 14, 2014 |title=Atmospheric Peroxyacetyl Nitrate (PAN): a global budget and source attribution |url=https://acp.copernicus.org/articles/14/2679/2014/ |journal=National Library of Medicine |via=NCBI Literature Resources}}</ref> It is a secondary [[pollutant]] present in [[photochemical smog]] and PAN concentrations can be sensitive to precursor emissions.<ref name=":2">{{Cite journal |last=Shogrin |first=Madison J. |date=February 27, 2024 |title=Changes to Peroxyacyl Nitrates (PANs) Over Megacities in Response to COVID-19 Tropospheric NO2 Reductions Observed by the Cross-Track Infrared Sounder (CrIS) |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023GL104854 |journal=AGU publications |via=Wiley & Sons}}</ref><ref name=":0" /> It is thermally unstable and decomposes into peroxyethanoyl radicals and [[nitrogen dioxide]] gas. It is a [[Tears|lachrymatory]] substance, meaning that it irritates the lungs and eyes.<ref name=":1">{{Cite journal |last=Vyskocil |first=Adolf |date=April 17, 1998 |title=Peroxyacetyl nitrate: review of toxicity |url=https://pubmed.ncbi.nlm.nih.gov/9617633/ |journal=Sage Journal |via=National Library of Medicine}}</ref> | ||
Peroxyacetyl nitrate, or PAN, is an oxidant that is more stable than [[ozone]].<ref name=":0" /> Hence, it is more capable of long-range transport than ozone.<ref name=":0" /> It serves as a carrier for [[Nitrogen oxide|oxides of nitrogen]] (NOx) into rural regions and causes ozone formation in the global [[troposphere]].<ref name=":0" /> | |||
== Atmospheric chemistry == | |||
PAN is produced in the atmosphere via photochemical oxidation of [[hydrocarbon]]s (e.g. [[Alkenes]], [[Aromatic compound|Aromatics]], and [[isoprene]]s).<ref name=":3">{{Cite journal |last=Xueqi |first=Qiao |date=June 1, 2023 |title=Strong relations of peroxyacetyl nitrate (PAN) formation to alkene and nitrous acid during various episodes |url=https://www.sciencedirect.com/science/article/pii/S0269749123004670 |journal=Science Direct |via=Elsevier B.V., its licensors, and contributors}}</ref><ref name=":1" /> Carbonyls (oxidized VOCs) create acyl radicals which then become [[peroxyacetic acid]] (PA) radicals.<ref name=":3" /> [[Acetaldehyde]] is the dominant carbonyl species to produce PA radicals followed by [[Methylglyoxal]], combined they can account for up to 80% of PA radical formation.<ref name=":0" /><ref name=":3" /> The PA radicals can reversibly react with [[nitrogen dioxide]] (NO2) to form PAN.<ref name=":0" /> Night-time reaction of [[acetaldehyde]] with [[nitrogen trioxide]] is another possible source.<ref name=":3" /> Since there are no direct PAN emissions, it is a secondary pollutant.<ref name=":0" /> Next to [[ozone]] and [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>), it is an important component of [[Smog|photochemical smog]].<ref name=":0" /> | |||
<chem>CH3C(O)OO + NO2 + M <=> PAN + M | |||
</chem><ref name=":0" /> | |||
<chem>R2: CH3CHO + OH ->[O2] CH3C(O)OO + H2O</chem> | |||
<chem> | |||
R3: CH3COCHO + hv ->[O2] CH3C(O)OO + HCO</chem> | |||
Other [[peroxyacyl nitrates]] in the atmosphere are peroxypropionyl nitrate (PPN), peroxybutyryl nitrate (PBN), and peroxybenzoyl nitrate (PBzN). Chlorinated forms have also been observed.<ref name=":0" /> PAN is the most important peroxyacyl nitrate. PAN and its homologues reach about 5 to 20 percent of the concentration of ozone in urban areas.<ref name=":0" /> At lower temperatures, these peroxy-nitrates are stable and can be transported over long distances,<ref name=":0" /> providing nitrogen oxides to otherwise unpolluted areas. At higher temperatures, they decompose into NO<sub>2</sub> and the peroxyacyl radical.<ref name=":0" /> | |||
The decay of PAN in the atmosphere is mainly thermal. Thus, the long-range transport occurs through cold regions of the atmosphere, whereas the decomposition takes place at warmer levels. PAN can also be | The decay of PAN in the atmosphere is mainly thermal.<ref name=":0" /> Thus, the long-range transport occurs through cold regions of the atmosphere, whereas the decomposition takes place at warmer levels.<ref name=":0" /> PAN can also be photolyzed by UV radiation.<ref name=":0" /> It is a reservoir gas that serves both as a source and a sink of RO<sub>x</sub>- and NO<sub>x</sub> radicals.<ref name=":0" /> Nitrogen oxides from PAN decomposition enhance ozone production in the lower [[troposphere]].<ref name=":0" /> | ||
The natural concentration of PAN in the atmosphere is below 0.1 | The natural concentration of PAN in the atmosphere is below 0.1 μg/m<sup>3</sup>.<ref name=":0" /> Measurements in German cities showed values up to 25 μg/m<sup>3</sup>.<ref name=":0" /> Peak values above 200 μg/m<sup>3</sup> have been measured in [[Los Angeles]] in the second half of the 20th century (1 ppb of PAN corresponds to 4.37 μg/m<sup>3</sup>).<ref name=":0" /> Due to the complexity of the measurement setup, only sporadic measurements are available.<ref name=":2" /><ref name=":4">{{Cite journal |last=Vivienne H. |first=Payne |date=June 10, 2022 |title=Satellite measurements of peroxyacetyl nitrate from the Cross-Track Infrared Sounder: comparison with ATom aircraft measurements |url=https://amt.copernicus.org/articles/15/3497/2022/ |journal=European Geosciences Union |via=Creative Commons Attribution}}</ref> The satellite based Cross-Track Infrared sounder (CrIS) instrument is able to provide mid-tropospheric PAN measurements on a global scale.<ref name=":4" /><ref name=":2" /> | ||
PAN is a [[greenhouse gas]]. | PAN is a [[greenhouse gas]]. | ||
== Sensitivity == | |||
PAN has a sensitivity to precursor emissions, mainly from VOCs and NOx.<ref name=":0" /><ref name=":2" /><ref name=":3" /> PANs sensitivity towards VOCs is greater than that of NOx.<ref name=":3" /> VOC reductions have more of an effect on PA radicals than on NOx.<ref name=":3" /> Notably, global emissions of precursor during Covid-19 demonstrated that PAN concentrations do not always decrease with a decrease in NOx concentrations.<ref name=":2" /><ref name=":5">{{Cite journal |last=Yulu |first=Qiu |date=September 16, 2020 |title=Markedly Enhanced Levels of Peroxyacetyl Nitrate (PAN) During COVID‐19 in Beijing |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL089623 |journal=AGU Publications |via=Wiley & Sons}}</ref> Similarly, PAN responds non-linearly to precursor changes.<ref name=":0" /><ref name=":2" /> Alkenes and oxidized VOCs strongly influence the formation of PA radicals.<ref name=":3" /> Meteorological effects also influence the availability of these radicals and hence PAN formation.<ref name=":5" /> | |||
== Synthesis == | == Synthesis == | ||
PAN can be produced in a lipophilic solvent from [[peroxyacetic acid]].<ref | PAN can be produced in a lipophilic solvent from [[peroxyacetic acid]].<ref>{{Cite journal |last=Gaffney |first=J.S. |last2=Fajer |first2=R. |last3=Senum |first3=G.I. |date=January 1984 |title=An improved procedure for high purity gaseous peroxyacyl nitrate production: Use of heavy lipid solvents |url=https://linkinghub.elsevier.com/retrieve/pii/0004698184902452 |journal=Atmospheric Environment (1967) |language=en |volume=18 |issue=1 |pages=215–218 |doi=10.1016/0004-6981(84)90245-2|url-access=subscription }}</ref><ref name=":6" /> For the synthesis, concentrated sulfuric acid is added to degassed ''n''-[[tridecane]] and peroxyacetic acid in an ice bath. Next, concentrated nitric acid is added.<ref name=":6">{{Cite journal |last=Talukdar |first=Ranajit K. |last2=Burkholder |first2=James B. |last3=Schmoltner |first3=Anne‐Marie |last4=Roberts |first4=James M. |last5=Wilson |first5=Robert R. |last6=Ravishankara |first6=A. R. |date=1995-07-20 |title=Investigation of the loss processes for peroxyacetyl nitrate in the atmosphere: UV photolysis and reaction with OH |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/95JD00545 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=100 |issue=D7 |pages=14163–14173 |doi=10.1029/95JD00545 |issn=0148-0227|url-access=subscription }}</ref><ref name=":7" /> | ||
As an alternative, PAN can also be synthesized in the gas phase via photolysis of [[acetone]] and NO<sub>2</sub> with a [[mercury lamp]]. [[Methyl nitrate]] (CH<sub>3</sub>ONO<sub>2</sub>) is created as a by-product.<ref name=":7">{{Cite journal |last=Nielsen |first=Torben |last2=Hansen |first2=Anne Maria |last3=Thomsen |first3=Erling Lund |date=January 1982 |title=A convenient method for preparation of pure standards of peroxyacetyl nitrate for atmospheric analyses |url=https://linkinghub.elsevier.com/retrieve/pii/0004698182901342 |journal=Atmospheric Environment (1967) |language=en |volume=16 |issue=10 |pages=2447–2450 |doi=10.1016/0004-6981(82)90134-2|url-access=subscription }}</ref> | |||
== Atmospheric effects == | |||
Seasonal cycles of PAN have been observed.<ref name=":0" /> Meteorological effects such as temperatures, wind patterns, and the availability of radicals influence PANs stability as well as transportation in the atmosphere.<ref name=":0" /><ref name=":5" /> During the springtime in the northern hemisphere, high concentrations are attributed to an increase in photochemical activity.<ref name=":5" /> In addition, concentrations of PAN increase due to it having a relatively large lifetime against thermal decomposition.<ref name=":0" /> Transportation of PAN can also occur by wildfire smoke moving it into an otherwise unpolluted region.<ref name=":2" /> In the northern hemisphere winter however, PAN levels become limited when there is reduced hydrocarbons, NO2, and low solar radiation.<ref name=":0" /> | |||
== Toxicity == | == Toxicity == | ||
The toxicity of PAN is higher than | The toxicity of PAN is similar to that of NO2 but higher than [[sulfur dioxide]] (SO2).<ref name=":1" /> Populations with [[pulmonary disease]] tend to be more sensitive to the toxic effects of PAN.<ref name=":1" /> Eye irritation from photochemical smog can be caused by an increase in PAN levels.<ref name=":1" /> Concentrations at or above 0.64 mg/m<sup>3</sup> increase the likelihood of eye irritation.<ref name=":1" /> PAN is a very weak [[mutagen]].<ref name=":1" /> | ||
==References== | ==References== | ||
Latest revision as of 15:12, 8 December 2025
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| Abbreviations | PAN |
| ChEBI | Template:Unbulleted list |
| ChemSpider | Template:Unbulleted list |
| DrugBank | Template:Unbulleted list |
| EC Number | Template:Unbulleted list |
| KEGG | Template:Unbulleted list |
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| Script error: No such module "collapsible list". | |
| Script error: No such module "collapsible list". | |
| Template:Longitem | C2H3NO5 |
| Molar mass | 121.05 g mol−1 |
| log P | −0.19 |
| Vapor pressure | 29.2 mmHg at 298 K |
| Template:Longitem | 0.000278 m3 atm mol−1 at 298 K |
| Template:Longitem | 10−13 cm3 molecule−1 s−1 at 298 K |
Template:Chembox Footer/tracking container onlyScript error: No such module "TemplatePar".Template:Short descriptionPeroxyacetyl nitrate is a peroxyacyl nitrate.[1] It is a secondary pollutant present in photochemical smog and PAN concentrations can be sensitive to precursor emissions.[2][1] It is thermally unstable and decomposes into peroxyethanoyl radicals and nitrogen dioxide gas. It is a lachrymatory substance, meaning that it irritates the lungs and eyes.[3]
Peroxyacetyl nitrate, or PAN, is an oxidant that is more stable than ozone.[1] Hence, it is more capable of long-range transport than ozone.[1] It serves as a carrier for oxides of nitrogen (NOx) into rural regions and causes ozone formation in the global troposphere.[1]
Atmospheric chemistry
PAN is produced in the atmosphere via photochemical oxidation of hydrocarbons (e.g. Alkenes, Aromatics, and isoprenes).[4][3] Carbonyls (oxidized VOCs) create acyl radicals which then become peroxyacetic acid (PA) radicals.[4] Acetaldehyde is the dominant carbonyl species to produce PA radicals followed by Methylglyoxal, combined they can account for up to 80% of PA radical formation.[1][4] The PA radicals can reversibly react with nitrogen dioxide (NO2) to form PAN.[1] Night-time reaction of acetaldehyde with nitrogen trioxide is another possible source.[4] Since there are no direct PAN emissions, it is a secondary pollutant.[1] Next to ozone and hydrogen peroxide (H2O2), it is an important component of photochemical smog.[1]
Other peroxyacyl nitrates in the atmosphere are peroxypropionyl nitrate (PPN), peroxybutyryl nitrate (PBN), and peroxybenzoyl nitrate (PBzN). Chlorinated forms have also been observed.[1] PAN is the most important peroxyacyl nitrate. PAN and its homologues reach about 5 to 20 percent of the concentration of ozone in urban areas.[1] At lower temperatures, these peroxy-nitrates are stable and can be transported over long distances,[1] providing nitrogen oxides to otherwise unpolluted areas. At higher temperatures, they decompose into NO2 and the peroxyacyl radical.[1]
The decay of PAN in the atmosphere is mainly thermal.[1] Thus, the long-range transport occurs through cold regions of the atmosphere, whereas the decomposition takes place at warmer levels.[1] PAN can also be photolyzed by UV radiation.[1] It is a reservoir gas that serves both as a source and a sink of ROx- and NOx radicals.[1] Nitrogen oxides from PAN decomposition enhance ozone production in the lower troposphere.[1]
The natural concentration of PAN in the atmosphere is below 0.1 μg/m3.[1] Measurements in German cities showed values up to 25 μg/m3.[1] Peak values above 200 μg/m3 have been measured in Los Angeles in the second half of the 20th century (1 ppb of PAN corresponds to 4.37 μg/m3).[1] Due to the complexity of the measurement setup, only sporadic measurements are available.[2][5] The satellite based Cross-Track Infrared sounder (CrIS) instrument is able to provide mid-tropospheric PAN measurements on a global scale.[5][2]
PAN is a greenhouse gas.
Sensitivity
PAN has a sensitivity to precursor emissions, mainly from VOCs and NOx.[1][2][4] PANs sensitivity towards VOCs is greater than that of NOx.[4] VOC reductions have more of an effect on PA radicals than on NOx.[4] Notably, global emissions of precursor during Covid-19 demonstrated that PAN concentrations do not always decrease with a decrease in NOx concentrations.[2][6] Similarly, PAN responds non-linearly to precursor changes.[1][2] Alkenes and oxidized VOCs strongly influence the formation of PA radicals.[4] Meteorological effects also influence the availability of these radicals and hence PAN formation.[6]
Synthesis
PAN can be produced in a lipophilic solvent from peroxyacetic acid.[7][8] For the synthesis, concentrated sulfuric acid is added to degassed n-tridecane and peroxyacetic acid in an ice bath. Next, concentrated nitric acid is added.[8][9]
As an alternative, PAN can also be synthesized in the gas phase via photolysis of acetone and NO2 with a mercury lamp. Methyl nitrate (CH3ONO2) is created as a by-product.[9]
Atmospheric effects
Seasonal cycles of PAN have been observed.[1] Meteorological effects such as temperatures, wind patterns, and the availability of radicals influence PANs stability as well as transportation in the atmosphere.[1][6] During the springtime in the northern hemisphere, high concentrations are attributed to an increase in photochemical activity.[6] In addition, concentrations of PAN increase due to it having a relatively large lifetime against thermal decomposition.[1] Transportation of PAN can also occur by wildfire smoke moving it into an otherwise unpolluted region.[2] In the northern hemisphere winter however, PAN levels become limited when there is reduced hydrocarbons, NO2, and low solar radiation.[1]
Toxicity
The toxicity of PAN is similar to that of NO2 but higher than sulfur dioxide (SO2).[3] Populations with pulmonary disease tend to be more sensitive to the toxic effects of PAN.[3] Eye irritation from photochemical smog can be caused by an increase in PAN levels.[3] Concentrations at or above 0.64 mg/m3 increase the likelihood of eye irritation.[3] PAN is a very weak mutagen.[3]
References
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