View source for Ozone

{{Short description|Triatomic oxygen molecule}}
{{Other uses}}
{{Redirect|Oxygen 3|the Jean-Michel Jarre album|Oxygène 3}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 451527415
| Name = Ozone 
| ImageFile = Ozone-1,3-dipole.svg
| ImageClass = skin-invert-image
| ImageFile_Ref = {{chemboximage|correct|??}}
| ImageName = Structural formula of ozone with partial charges shown
| ImageFile1 = Ozone-resonance-Lewis-2D.svg
| ImageClass1 = skin-invert-image
| ImageName1 = Resonance structures of ozone with lone pairs indicated
| ImageFileR2 = Ozone-CRC-MW-3D-vdW.png
| ImageClassR2 = bg-transparent
| ImageFileR2_Ref = {{Chemboximage|correct|??}}
| ImageNameR2 = Spacefill model of ozone
| ImageFileL2 = Ozone-CRC-MW-3D-balls.png
| ImageClassL2 = bg-transparent
| ImageFileL2_Ref = {{chemboximage|correct|??}}
| ImageNameL2 = Ball and stick model of ozone
| IUPACName = Ozone
| OtherNames = 2λ<sup>4</sup>-trioxidiene; ''catena''-trioxygen
| SystematicName = Trioxygen
| Section1 = {{Chembox Identifiers
| IUPHAR_ligand = 6297
| CASNo = 10028-15-6
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 24823
| ChemSpiderID = 23208
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| UNII = 66H7ZZK23N
| UNII_Ref = {{fdacite|correct|FDA}}
| EINECS = 233–069–2
| MeSHName = Ozone
| RTECS = RS8225000
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 25812
| Gmelin = 1101
| SMILES = [O-][O+]=O
| StdInChI = 1S/O3/c1-3-2
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| InChI = 1/O3/c1-3-2
| StdInChIKey = CBENFWSGALASAD-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| InChIKey = CBENFWSGALASAD-UHFFFAOYAY
}}
| Section2 = {{Chembox Properties
| Solvent = other solvents
| O=3
| Appearance = Colourless to pale blue gas<ref name=PGCH/>
| Odour = Pungent, metallic, dry<ref name=PGCH/>
| Density = 2.144 g/L (at 0&nbsp;°C)
| Solubility = 1.05 g L<sup>−1</sup> (at 0&nbsp;°C)
| SolubleOther = Very soluble in [[carbon tetrachloride|CCl<sub>4</sub>]], [[sulphuric acid]]
| MeltingPtK = 81
| BoilingPtK = 161
| RefractIndex = 1.2226 (liquid), 1.00052 (gas, STP, 546 nm—note high dispersion)<ref>{{cite journal |last1=Cuthbertson |first1=Clive |last2=Cuthbertson |first2=Maude |date=1914 |title=On the Refraction and Dispersion of the Halogens, Halogen Acids, Ozone, Steam Oxides of Nitrogen, and Ammonia |url=https://archive.org/stream/philtrans08506476/08506476#page/n17/mode/1up |journal=[[Philosophical Transactions of the Royal Society A]] |volume=213 |issue=497–508 |pages=1–26 |bibcode=1914RSPTA.213....1C |doi=10.1098/rsta.1914.0001 |access-date=4 February 2016 |doi-access=free}}</ref>
| VaporPressure = 55.7 atm<ref>Gas Encyclopedia; [https://encyclopedia.airliquide.com/ozone Ozone]</ref> ({{convert|−12.15|C|F K|disp=or}}){{efn|This vapor pressure is for the [[critical temperature]], which is below [[room temperature]].}}
| MagSus = +6.7·10<sup>−6</sup> cm<sup>3</sup>/mol
| ConjugateAcid = [[Protonated ozone]]
}}
| Section3 = {{Chembox Structure
| SpaceGroup = C<sub>2v</sub>
| Coordination = Digonal
| MolShape = Dihedral
| OrbitalHybridisation = ''sp''<sup>2</sup> for O1
| Dipole = 0.53 D
}}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = 142.67 kJ mol<sup>−1</sup>
| Entropy = 238.92 J K<sup>−1</sup> mol<sup>−1</sup>
}}
| Section5 = {{Chembox Hazards
| GHSPictograms = {{GHS exploding bomb}}{{GHS flame over circle}}{{GHS gas cylinder}}{{GHS corrosion}}{{GHS skull and crossbones}}{{GHS exclamation mark}}{{GHS health hazard}}{{GHS environment}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|270|314|330|335|341|361|370|410}}
| PPhrases = {{P-phrases|203|220|244|260|264+265|270|271|273|280|284|301+330+331|302+361+354|304+340|305+351+338|308+316|362+364|370+376|391|403+233|405}}
| NFPA-H = 4
| NFPA-F = 0
| NFPA-R = 4
| NFPA-S = Ox
| IDLH = 5 ppm<ref name="PGCH">{{PGCH|0476}}</ref>
| REL = C 0.1 ppm (0.2 mg/m<sup>3</sup>)<ref name=PGCH/>
| PEL = TWA 0.1 ppm (0.2 mg/m<sup>3</sup>)<ref name=PGCH/>
| LCLo = 12.6 ppm (mouse, 3 hr)<br />50 ppm (human, 30 min)<br />36 ppm (rabbit, 3 hr)<br />21 ppm (mouse, 3 hr)<br />21.8 ppm (rat, 3 hr)<br />24.8 ppm (guinea pig, 3 hr)<br />4.8 ppm (rat, 4 hr)<ref>{{IDLH|10028156|Ozone}}</ref>
}}
| Section6 = 
| Section8 = {{Chembox Related
| OtherCompounds = [[Sulphur dioxide]]<br />[[Trisulphur]]<br />[[Disulphur monoxide]]<br />[[Cyclic ozone]]
}}
}}

'''Ozone''' ({{IPAc-en|ˈ|oʊ|z|oʊ|n|audio=en-us-ozone.ogg}}), also called '''trioxygen''', is an [[Inorganic compound|inorganic]] [[molecule]] with the [[chemical formula]] '''{{chem|O|3|}}'''. It is a pale-blue gas with a distinctively [[pungency|pungent]] odour. It is an [[allotrope]] of [[oxygen]] that is much less stable than the [[diatomic]] allotrope {{chem|O|2}}, breaking down in the lower atmosphere to {{chem|O|2}} ([[dioxygen]]). Ozone is formed from dioxygen by the action of [[ultraviolet]] (UV) light and electrical discharges within the [[Earth's atmosphere]]. It is present in very low concentrations throughout the atmosphere, with its highest concentration high in the [[ozone layer]] of the [[stratosphere]], which absorbs most of the [[Sun]]'s [[Ultraviolet|ultraviolet (UV)]] radiation.

Ozone's odour is reminiscent of [[chlorine]], and detectable by many people at concentrations of as little as {{val|0.1|ul=ppm}} in air. Ozone's O<sub>3</sub> [[chemical structure|structure]] was determined in 1865. The molecule was later proven to have a bent structure and to be weakly [[diamagnetism|diamagnetic]]. At [[standard temperature and pressure]], ozone is a pale blue gas that condenses at [[cryogenic fuel|cryogenic]] temperatures to a dark blue [[liquid]] and finally a violet-black [[solid]]. Ozone's instability with regard to more common dioxygen is such that both concentrated gas and liquid ozone may decompose explosively at elevated temperatures, physical shock, or fast warming to the boiling point.<ref name="streng">{{cite journal |last=Streng |first=A. G. |year=1961 |title=Tables of Ozone Properties |journal=[[Journal of Chemical & Engineering Data]] |volume=6 |issue=3 |pages=431–436 |doi=10.1021/je00103a031}}</ref><ref>{{cite journal |last1=Batakliev |first1=Todor |last2=Georgiev |first2=Vladimir |last3=Anachkov |first3=Metody |last4=Rakovsky |first4=Slavcho |last5=Zaikov |first5=Gennadi E. |title=Ozone decomposition |date=June 2014 |journal=Interdisciplinary Toxicology |volume=7 |issue=2 |pages=47–59 |issn=1337-6853 |pmid=26109880 |doi=10.2478/intox-2014-0008 |pmc=4427716}}</ref> It is therefore used commercially only in low concentrations.

Ozone is a powerful [[oxidising agent]] (far more so than dioxygen) and has many industrial and consumer applications related to oxidation. This same high oxidising potential, however, causes ozone to damage mucous and respiratory tissues in animals, and also tissues in plants, above concentrations of about {{val|0.1|u=ppm}}. While this makes ozone a potent respiratory hazard and pollutant near [[ground-level ozone|ground level]], a higher concentration in the ozone layer (from two to eight ppm) is beneficial, preventing damaging UV light from reaching the Earth's surface.

{{TOC limit|3}}

==Nomenclature==
The [[trivial name]] ''ozone'' is the most commonly used and [[preferred IUPAC name]]. The systematic names ''2λ<sup>4</sup>-trioxidiene''{{dubious|date=February 2019}} and ''catena-trioxygen'', valid [[IUPAC]] names, are constructed according to the [[chemical nomenclature#Substitutive nomenclature|substitutive]] and [[chemical nomenclature#Additive nomenclature|additive nomenclatures]], respectively. The name ''ozone'' derives from ''ozon'' (ὄζον), the [[Greek language|Greek]] neuter present participle of ''ozein'' (ὄζειν) "to smell",<ref>{{cite web |title=ozone (n.) |publisher=Merriam-Webster |website=Online Etymological Dictionary |url=https://www.etymonline.com/search?q=ozone%20,%20https://www.merriam-webster.com/dictionary/ozone |access-date=24 May 2023}}</ref> referring to ozone's distinctive smell.

In appropriate contexts, ozone can be viewed as [[trioxidane]] with two hydrogen atoms removed, and as such, ''trioxidanylidene'' may be used as a systematic name, according to substitutive nomenclature. By default, these names pay no regard to the radicality of the ozone molecule. In an even more specific context, this can also name the non-radical singlet ground state, whereas the diradical state is named ''trioxidanediyl''.

''Trioxidanediyl'' (or ''ozonide'') is used, non-systematically, to refer to the substituent group (-OOO-). Care should be taken to avoid confusing the name of the group for the context-specific name for the ozone given above.

==History==
[[File:Schönbein.jpg|upright|thumb|[[Christian Friedrich Schönbein]] (18 October 1799 – 29 August 1868)]]
[[File:Smyths revised ozonometer, 1865. (9660571191).jpg|thumb|A prototype ozonometer built by John Smyth in 1865]]
In 1785, Dutch chemist [[Martinus van Marum]] was conducting experiments involving electrical sparking above water when he noticed an unusual smell, which he attributed to the electrical reactions, failing to realize that he had in fact produced ozone.<ref name="colostate"/><ref>{{cite web |title=electrochemical reaction {{!}} Definition, Process, Types, Examples, & Facts {{!}} Britannica |language=en |website=britannica.com |url=https://www.britannica.com/science/electrochemical-reaction |access-date=2022-09-24}}</ref>

A half century later, [[Christian Friedrich Schönbein]] noticed the same pungent odour and recognized it as the smell often following a bolt of [[lightning]]. In 1839, he succeeded in isolating the gaseous chemical and named it "ozone", from the Greek word ''{{lang|el|ozein}}'' ({{lang|el|ὄζειν}}) meaning "to smell".<ref name="ozo">{{cite journal |last=Rubin |first=Mordecai B. |year=2001 |title=The History of Ozone: The Schönbein Period, 1839–1868 |journal=[[Bull. Hist. Chem.]] |volume=26 |issue=1 |pages=40–56 |doi=10.70359/bhc2001v026p040 |url=https://acshist.scs.illinois.edu/bulletin_open_access/v26-1/v26-1%20p40-56.pdf |access-date=2025-01-29 |url-status=live |archive-url=https://web.archive.org/web/20080411012834/http://www.scs.uiuc.edu/~mainzv/HIST/awards/OPA%20Papers/2001-Rubin.pdf |archive-date=2008-04-11}}</ref><ref>{{cite web |title=Scientists born on October 18th |website=Today in Science History |url=https://www.todayinsci.com/10/10_18.htm#Schonbein}}</ref>
For this reason, Schönbein is generally credited with the discovery of ozone.<ref name="Distillations">{{cite journal |last1=Jacewicz |first1=Natalie |title=A Killer of a Cure |journal=Distillations |date=2017 |volume=3 |issue=1 |pages=34–37 |url=https://www.sciencehistory.org/distillations/magazine/a-killer-of-a-cure |access-date=April 13, 2018}}</ref><ref name="Le Prestre">{{cite book |editor1-last=Le Prestre |editor1-first=Philippe G. |title=Protecting the ozone layer: lessons, models, and prospects; [product of the Tenth Anniversary Colloquium of the Montreal Protocol, held on September 13, 1997; part of a series of events held in Montreal to mark the 10th anniversary of the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer, September 16, 1987] |date=1998 |publisher=Kluwer |location=Boston |isbn=978-0-7923-8245-4 |page=2 |url=https://books.google.com/books?id=zuesUPcIOq8C&pg=PA2}}</ref><ref name="Letter">{{cite journal |last1=Schönbein |first1=Christian Friedrich |title=Research on the nature of the odour in certain chemical reactions |journal=Letter to the Académie des Sciences in Paris |date=1840}}</ref><ref name="colostate">{{cite web |title=Precursor Era Contributors to Meteorology |work=colostate.edu |last1=Toth |first1=Gary |last2=Hillger |first2=Don |url=https://rammb.cira.colostate.edu/dev/hillger/precursor.htm#schonbein}}</ref> He also noted the similarity of ozone smell to the smell of phosphorus, and in 1844 proved that the product of reaction of [[white phosphorus]] with air is identical.<ref name="ozo"/> A subsequent effort to call ozone "electrified oxygen" he ridiculed by proposing to call the ozone from white phosphorus "phosphorized oxygen".<ref name="ozo"/> The [[chemical formula]] for ozone, O<sub>3</sub>, was not determined until 1865 by [[Jacques-Louis Soret]]<ref>{{cite journal
|title=Recherches sur la densité de l'ozone
|author=Jacques-Louis Soret
|journal=[[Comptes rendus de l'Académie des sciences]]
|volume=61
|page=941
|year=1865
|url=http://gallica.bnf.fr/ark:/12148/bpt6k3018b/f941.table}}
</ref> and confirmed by Schönbein in 1867.<ref name="ozo"/><ref>{{cite web |title=Ozone FAQ |publisher=Global Change Master Directory |url=http://gcmd.gsfc.nasa.gov/Resources/FAQs/ozone.html |access-date=2006-05-10 |archive-url=https://web.archive.org/web/20060601061532/http://gcmd.gsfc.nasa.gov/Resources/FAQs/ozone.html |archive-date=2006-06-01}}</ref>

For much of the second half of the 19th century and well into the 20th, ozone was considered a healthy component of the environment by naturalists and health-seekers. [[Beaumont, California]], had as its official slogan "Beaumont: Zone of Ozone", as evidenced on postcards and Chamber of Commerce letterhead.<ref>Redlands Chamber of Commerce Collection, City Archives, A.K. Smiley Public Library, Redlands, CA</ref> Naturalists working outdoors often considered the higher elevations beneficial because of their ozone content which was readily monitored.<ref>{{cite journal |title=Ozone. |journal=Hall's Journal of Health |date=March 1879 |volume=26 |issue=3 |page=772 |pmid=36488870|pmc=9211524 }}</ref> "There is quite a different atmosphere [at higher elevation] with enough ozone to sustain the necessary energy [to work]", wrote naturalist [[Henry Henshaw]], working in Hawaii.<ref>Henry Henshaw to William Brewster, July 2, 1902, Harvard Museum of Comparative Zoology Archives.</ref> Seaside air was considered to be healthy because of its believed ozone content. The smell giving rise to this belief is in fact that of [[halogenation|halogenated]] seaweed metabolites<ref name="ashfield">{{cite news |title=The science behind that fresh seaside smell |work=The Telegraph |last=O'Connell |first=Sanjida |date=18 August 2009 |url=https://www.telegraph.co.uk/news/science/6044238/The-science-behind-that-fresh-seaside-smell.html |url-access=subscription |url-status=live |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/news/science/6044238/The-science-behind-that-fresh-seaside-smell.html |archive-date=2022-01-12}}{{cbignore}}</ref> and [[dimethyl sulphide]].<ref>{{cite web |title=Secrets of 'bracing' sea air bottled by scientists |date=2 February 2007 |website=telegraph.co.uk |url=https://www.telegraph.co.uk/news/uknews/1541342/Secrets-of-bracing-sea-air-bottled-by-scientists.html |access-date=2022-05-13}}</ref>

Much of ozone's appeal seems to have resulted from its "fresh" smell, which evoked associations with purifying properties. Scientists noted its harmful effects. In 1873 [[James Dewar]] and [[John Gray McKendrick]] documented that frogs grew sluggish, birds gasped for breath, and rabbits' blood showed decreased levels of oxygen after exposure to "ozonized air", which "exercised a destructive action".<ref name="Anstie">{{cite journal |last1=Anstie |first1=Francis |title=Clinic of the Month: Dr. McKendrick on Ozone |journal=The Practitioner: A Journal of Therapeutics and Public Health |date=1874 |volume=12 |issue=January–June |page=123 |url=https://books.google.com/books?id=CrsvAQAAMAAJ&pg=PA123}}</ref><ref name="Distillations"/> Schönbein himself reported that chest pains, irritation of the [[mucous membranes]], and difficulty breathing occurred as a result of inhaling ozone, and small mammals died.<ref name="Rubin">{{cite journal |last1=Rubin |first1=Mordecai B. |title=The History of Ozone: The Schönbein Period, 1839–1868 |journal=Bulletin for the History of Chemistry |date=2001 |volume=26 |issue=1 |page=48 |doi=10.70359/bhc2001v026p040 |url=https://acshist.scs.illinois.edu/bulletin_open_access/v26-1/v26-1%20p40-56.pdf |access-date=13 April 2018}}</ref> In 1911, [[Leonard Hill (physiologist)|Leonard Hill]] and [[Martin Flack]] stated in the ''[[Proceedings of the Royal Society]] B'' that ozone's healthful effects "have, by mere iteration, become part and parcel of common belief; and yet exact physiological evidence in favour of its good effects has been hitherto almost entirely wanting ... The only thoroughly well-ascertained knowledge concerning the physiological effect of ozone, so far attained, is that it causes irritation and œdema of the lungs, and death if inhaled in relatively strong concentration for any time."<ref name="Distillations"/><ref name="Hill">{{cite journal |last1=Hill |first1=L. |last2=Flack |first2=M. |title=The Physiological Influence of Ozone |journal=Proceedings of the Royal Society B: Biological Sciences |date=28 December 1911 |volume=84 |issue=573 |pages=404–415 |bibcode=1911RSPSB..84..404H |doi=10.1098/rspb.1911.0086 |doi-access=free}}</ref>

During [[World War I]], ozone was tested at [[Queen Alexandra Military Hospital]] in London as a possible [[disinfectant]] for wounds. The gas was applied directly to wounds for as long as 15 minutes. This resulted in damage to both bacterial cells and human tissue. Other sanitizing techniques, such as irrigation with [[antiseptics]], were found preferable.<ref name="Distillations"/><ref name="Stoker">{{cite journal |last=Stoker |first=George |title=The Surgical Uses of Ozone |journal=Lancet |volume=188 |issue=4860 |year=1916 |page=712 |doi=10.1016/S0140-6736(01)31717-8}}</ref>

Until the 1920s, it was not certain whether small amounts of [[tetraoxygen|oxozone]], {{Chem|O|4}}, were also present in ozone samples due to the difficulty of applying analytical chemistry techniques to the explosive concentrated chemical.<ref name="ozo2">{{cite journal |last=Rubin |first=Mordecai B. |year=2004 |title=The History of Ozone. IV. The Isolation of Pure Ozone and Determination of its Physical Properties (1) |journal=[[Bull. Hist. Chem.]] |volume=29 |issue=2 |pages=99–106 |doi=10.70359/bhc2004v029p099 |url=https://acshist.scs.illinois.edu/bulletin_open_access/v26-1/v26-1%20p40-56.pdf |access-date=2021-04-12}}</ref><ref name="Block-1986">{{citation |last=Block |first=J. H. |title=Georg-Maria Schwab: Early Endeavours in the Science of Catalysis |date=1986 |work=Chemistry and Physics of Solid Surfaces VI |pages=1–8 |editor-last=Vanselow |editor-first=R. |series=Springer Series in Surface Sciences |volume=5 |place=Berlin, Heidelberg |publisher=Springer |language=en |isbn=978-3-642-82727-3 |editor2-last=Howe |editor2-first=R. |doi=10.1007/978-3-642-82727-3_1}}</ref> In 1923, [[Georg-Maria Schwab]] (working for his doctoral thesis under [[Ernst Hermann Riesenfeld]]) was the first to successfully solidify ozone and perform accurate analysis which conclusively refuted the oxozone hypothesis.<ref name="ozo2"/><ref name="Block-1986"/> Further hitherto unmeasured physical properties of pure concentrated ozone were determined by the Riesenfeld group in the 1920s.<ref name="ozo2"/>

==Physical properties==
[[File:Liquid ozone.png|thumb|Liquid ozone]]
Ozone is a colourless or pale blue gas, slightly soluble in water, and much more soluble in inert [[non-polar]] solvents such as [[carbon tetrachloride]] or fluorocarbons, in which it forms a blue solution. At {{convert|161|K}}, it condenses to form a dark blue [[liquid]]. It is dangerous to allow this liquid to warm to its boiling point, because both concentrated gaseous ozone and liquid ozone can detonate. At temperatures below {{convert|80|K}}, it forms a violet-black [[solid]].<ref>{{cite web
|title=Oxygen
|work=WebElements
|url=http://www.webelements.com/oxygen/
|access-date=2006-09-23
}}</ref>

Ozone has a very specific sharp odour somewhat resembling [[chlorine bleach]]. Most people can detect it at the 0.01&nbsp;μmol/mol level in air. Exposure of 0.1 to 1&nbsp;μmol/mol produces headaches and burning eyes and irritates the respiratory passages.<ref name=brown>{{cite book
|last1=Brown |first1=Theodore L.
|last2=LeMay |first2=H. Eugene Jr.
|last3=Bursten |first3=Bruce E.
|last4=Burdge |first4=Julia R.
|editor=Nicole Folchetti
|title=Chemistry: The Central Science
|edition=9th
|year=2003
|publisher=Pearson Education
|isbn=978-0-13-066997-1
|pages=882–883
|chapter=22
|orig-date=1977}}</ref>
Even low concentrations of ozone in air are very destructive to organic materials such as latex, plastics, and animal lung tissue.

The ozone molecule is weakly [[diamagnetism|diamagnetic]].<ref>{{cite book |last1=Cotton |first1=F. Albert |last2=Wilkinson |first2=Geoffrey |title=Advanced Inorganic Chemistry |date=1988 |publisher=John Wiley & Sons |isbn=0-471-84997-9 |page=452 |edition=5th |quote=Ozone. The diamagnetic triatomic molecule ...}}</ref>

==Structure==
According to experimental evidence from [[microwave spectroscopy]], ozone is a bent molecule, with C<sub>2v</sub> [[molecular symmetry|symmetry]] (similar to the [[water]] molecule).<ref>{{cite web |title=Microwave Rotational Spectroscopy |date=2013-10-02 |language=en |website=Chemistry LibreTexts |url=https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Rotational_Spectroscopy/Microwave_Rotational_Spectroscopy |access-date=2022-07-13}}</ref> The O–O distances are {{convert|127.2|pm|Å|abbr=on|lk=on}}. The O–O–O angle is 116.78°.<ref>{{cite journal |last1=Tanaka |first1=Takehiko |last2=Morino |first2=Yonezo |year=1970 |title=Coriolis interaction and anharmonic potential function of ozone from the microwave spectra in the excited vibrational states |journal=Journal of Molecular Spectroscopy |volume=33 |issue=3 |pages=538–551 |bibcode=1970JMoSp..33..538T |doi=10.1016/0022-2852(70)90148-7}}</ref> The central atom is ''sp''² hybridized with one lone pair. Ozone is a polar molecule with a [[molecular dipole moment|dipole moment]] of 0.53&nbsp;[[Debye|D]].<ref>{{cite journal |last1=Mack |first1=Kenneth M. |last2=Muenter |first2=J. S. |year=1977 |title=Stark and Zeeman properties of ozone from molecular beam spectroscopy |journal=Journal of Chemical Physics |volume=66 |issue=12 |pages=5278–5283 |bibcode=1977JChPh..66.5278M |doi=10.1063/1.433909}}</ref> The molecule can be represented as a [[resonance (chemistry)|resonance]] hybrid with two contributing structures, each with a [[single bond]] on one side and [[double bond]] on the other. The arrangement possesses an overall [[bond order]] of 1.5 for both sides. It is [[isoelectronicity|isoelectronic]] with [[nitrite|the nitrite anion]]. Naturally occurring ozone can be composed of substituted isotopes (<sup>16</sup>O, <sup>17</sup>O, <sup>18</sup>O). A [[cyclic ozone|cyclic form]] has been predicted but not observed.

[[File:Ozone-resonance-Lewis-2D.svg|class=skin-invert-image|thumb|upright=2|center|Resonance Lewis structures of the ozone molecule]]

==Reactions==
{{More citations needed section|date=March 2022}}
Ozone is among the most powerful [[oxidising agent]]s known, far stronger than {{chem2|O2}}. It is also unstable at high concentrations, decaying into ordinary diatomic oxygen. Its [[half-life]] varies with atmospheric conditions such as temperature, humidity, and air movement. Under laboratory conditions, the half-life will average ~1500 minutes (25 hours) in still air at room temperature (24&nbsp;°C), zero humidity with zero air changes per hour.<ref>{{cite journal | last1 = McClurkin | first1 = J. D. | last2 = Maier | first2 = D. E. | title = Half-life time of ozone as a function of air conditions and movement | journal = Julius-Kühn-Archiv; 425 | date = 2010 | pages = 381–385 | doi = 10.5073/jka.2010.425.167.326 }}</ref>
:<chem>2 O3 -> 3 O2</chem>

This reaction proceeds more rapidly with increasing temperature. [[Deflagration]] of ozone can be triggered by a spark and can occur in ozone concentrations of 10 [[wt%]] or higher.<ref>{{cite journal |title=Explosion properties of highly concentrated ozone gas |year=2005 |last1=Koike |first1=K |last2=Nifuku |first2=M |last3=Izumi |first3=K |last4=Nakamura |first4=S |last5=Fujiwara |first5=S |last6=Horiguchi |first6=S |journal=Journal of Loss Prevention in the Process Industries |volume=18 |page=465 |issue=4–6 |bibcode=2005JLPPI..18..465K |doi=10.1016/j.jlp.2005.07.020 |url=http://www.iitk.ac.in/che/jpg/papersb/full%20papers/K-106.pdf |archive-url=https://web.archive.org/web/20090327085613/http://www.iitk.ac.in/che/jpg/papersb/full%20papers/K-106.pdf |archive-date=2009-03-27}}</ref>

Ozone can also be produced from oxygen at the anode of an electrochemical cell. This reaction can create smaller quantities of ozone for research purposes.<ref>{{cite web |title=Electrochemical Production of High-Concentration Ozone-Water Using Freestanding Perforated Diamond Electrodes |url=https://www.researchgate.net/publication/244688668}}</ref>
:<math chem>\ce{O3_{(g)}{} + 2H+{} + 2e- <=> O2_{(g)}{} + H2O} \quad (E^\circ = \text{2.075 V})</math><ref>{{cite book |title= Quantitative Chemical Analysis |last=Harris |first=Daniel C. |publisher=W. H. Freeman |year=2007 |isbn=978-0-7167-7694-9 |pages=[https://archive.org/details/quantitativechem00harr_464/page/n297 279] |url=https://archive.org/details/quantitativechem00harr_464 |url-access=limited}}</ref>

This can be observed as an unwanted reaction in a [[Hoffman apparatus]] during the [[electrolysis of water]] when the voltage is set above the necessary voltage.

===With metals===
Ozone oxidises most [[metal]]s (except [[gold]], [[platinum]], and [[iridium]]) into [[oxide]]s of the metals in their highest [[oxidation state]]. For example:
:<math chem>\begin{align}
& \ce{Cu + O3 -> CuO + O2} \\
& \ce{2 Ag + O3 -> Ag2O + O2}
\end{align}</math>

===With nitrogen and carbon compounds===
Ozone oxidises [[nitric oxide]] to [[nitrogen dioxide]]:
: <chem>NO + O3 -> NO2 + O2</chem>
This reaction is accompanied by [[chemiluminescence]].

The {{chem2|NO2}} can be further oxidised to [[nitrate radical]]:
: <chem>NO2 + O3 -> NO3 + O2</chem>
The {{chem2|NO3}} formed can react with {{chem2|NO2}} to form [[dinitrogen pentoxide]] ({{chem2|N2O5}}).

Solid [[nitronium perchlorate]] can be made from {{chem2|NO2, ClO2}}, and {{chem2|O3}} gases:
: <chem>NO2 + ClO2 + 2 O3 -> NO2ClO4 + 2 O2</chem>

Ozone does not react with ammonium [[salt (chemistry)|salts]], but it oxidises [[ammonia]] to [[ammonium nitrate]]:
: <chem>2 NH3 + 4 O3 -> NH4NO3 + 4 O2 + H2O</chem>

Ozone reacts with [[carbon]]<!--graphite?--> to form [[carbon dioxide]], even at room temperature:
: <chem>C + 2 O3 -> CO2 + 2 O2</chem>

===With sulphur compounds===
Ozone oxidizes [[sulphide]]s to [[sulphate]]s. For example, [[lead(II) sulfide|lead(II) sulphide]] is oxidized to [[lead(II) sulphate]]:
: <chem>PbS + 4 O3 -> PbSO4 + 4 O2</chem>

[[Sulphuric acid]] can be produced from ozone, water and either elemental [[sulphur]] or [[sulphur dioxide]]:
:<math chem>\begin{align}
& \ce{S + H2O + O3 -> H2SO4} \\
& \ce{3 SO2 + 3 H2O + O3 -> 3 H2SO4}
\end{align}</math>

In the [[gas phase]], ozone reacts with [[hydrogen sulphide]] to form sulphur dioxide:
: <chem>H2S + O3 -> SO2 + H2O</chem>

In an [[aqueous]] solution, however, two competing simultaneous reactions occur, one to produce elemental sulphur, and one to produce sulphuric acid:
:<math chem>\begin{align}
& \ce{H2S + O3 -> S + O2 + H2O} \\
& \ce{3 H2S + 4 O3 -> 3 H2SO4}
\end{align}</math>

===With alkenes and alkynes===
{{Main|Ozonolysis}}
Alkenes can be oxidatively cleaved by ozone, in a process called [[ozonolysis]], giving [[Alcohol (chemistry)|alcohols]], [[Aldehyde|aldehydes]], [[Ketone|ketones]], and [[Carboxylic acid|carboxylic acids]], depending on the second step of the workup.

[[File:General reaction equation of ozonolysis.svg|class=skin-invert-image|frameless|upright=2.2|center|General reaction equation of ozonolysis]]

Ozone can also cleave alkynes to form an [[acid anhydride]] or [[diketone]] product.<ref>{{cite book |last=Bailey |first=P. S. |chapter=Chapter 2 |title=Ozonation in Organic Chemistry |volume=2 |publisher=Academic Press |location=New York, NY |year=1982 |isbn=978-0-12-073102-2}}</ref> If the reaction is performed in the presence of water, the anhydride hydrolyzes to give two [[carboxylic acid]]s.

:[[File:Ozonolysis-alkyne.svg|class=skin-invert-image|none|450px]]

Usually ozonolysis is carried out in a solution of [[dichloromethane]], at a temperature of −78&nbsp;°C. After a sequence of cleavage and rearrangement, an organic ozonide is formed. With reductive workup (e.g. [[zinc]] in [[acetic acid]] or [[dimethyl sulphide]]), ketones and aldehydes will be formed, with oxidative workup (e.g. aqueous or alcoholic [[hydrogen peroxide]]), carboxylic acids will be formed.<ref name="OrgChem">{{cite book
|title=Organic Chemistry, 9th Edition
|chapter=Chapter 8 Alkenes and Alkynes – Part II: Addition Reactions and Synthesis
|author1=Solomons, T.W. Graham |author2=Fryhle, Craig B.
|name-list-style=amp |publisher=Wiley
|year=2008
|isbn=978-0-470-16982-7
|page=344
}}</ref>

===Other substrates===
All three [[atom]]s of ozone may also react, as in the reaction of [[tin(II) chloride]] with [[hydrochloric acid]] and ozone:
: <chem>3 SnCl2 + 6 HCl + O3 -> 3 SnCl4 + 3 H2O</chem>
Iodine perchlorate can be made by treating [[iodine]] dissolved in cold [[anhydrous]] [[perchloric acid]] with ozone:
: <chem>I2 + 6 HClO4 + O3 -> 2 I(ClO4)3 + 3 H2O</chem>
Ozone can also react with [[potassium iodide]] to give oxygen and iodine gas that can be [[Titration|titrated]] for quantitative determination:<ref>{{cite journal |last1=Al-Baarri |first1=A. N. |last2=Legowo |first2=A. M. |last3=Abduh |first3=S. B. M. |last4=Mawarid |first4=A. A. |last5=Farizha |first5=K. M. |last6=Silvia |first6=M. |title=Production of Ozone and the Simple Detection using Potassium Iodide Titration Method |date=June 2019 |journal=IOP Conference Series: Earth and Environmental Science |language=en |volume=292 |issue=1 |article-number=012062 |bibcode=2019E&ES..292a2062A |issn=1755-1315 |doi=10.1088/1755-1315/292/1/012062 |doi-access=free |s2cid=198344024}}</ref>
: <chem>2KI + O3 + H2O -> 2KOH + O2 + I2</chem>

===Combustion===
Ozone can be used for [[combustion]] reactions and combustible gases; ozone provides higher temperatures than burning in [[dioxygen]] ({{chem2|O2}}). The following is a reaction for the combustion of [[carbon subnitride]] which can also cause higher temperatures:
: <chem>3 C4N2 + 4 O3 -> 12 CO + 3 N2</chem>

Ozone can react at cryogenic temperatures. At {{convert|77|K}}, atomic [[hydrogen]] reacts with liquid ozone to form a hydrogen [[superoxide]] [[radical (chemistry)|radical]], which [[dimerizes]]:<ref name="Horvath M. 1985. pg 44">{{cite book |year=1985 |title=Ozone |pages=44–49 |author1=Horvath M. |author2=Bilitzky L. |author3=Huttner J. |isbn=978-0-444-99625-1 |publisher=Elsevier}}</ref>
:<math chem>\begin{align}
& \ce{H + O3 -> HO2 + O} \\
& \ce{2 HO2 -> H2O4}
\end{align}</math>

===Ozone decomposition===

====Types of ozone decomposition====
Ozone is a toxic substance,<ref>{{cite journal |last=Menzel |first=D. B. |title=Ozone: an overview of its toxicity in man and animals |date=1984 |journal=Journal of Toxicology and Environmental Health |volume=13 |issue=2–3 |pages=183–204 |issn=0098-4108 |bibcode=1984JTEH...13..181M |pmid=6376815 |doi=10.1080/15287398409530493}}</ref><ref name="EPA-2022">{{cite web |publisher=United States Environmental Protection Agency |title=Ozone Generators that are Sold as Air Cleaners |date=28 February 2022 |website=EPA |url=https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners#info-sources |access-date=28 February 2022 |url-status=live |archive-url=https://web.archive.org/web/20220209015459/https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners |archive-date=9 February 2022}}</ref> commonly found or generated in human environments (aircraft cabins, offices with photocopiers, laser printers, sterilisers, ...).

The [[catalysis|catalytic]] decomposition of ozone is very important to reduce pollution. This type of decomposition is the most widely used, especially with solid catalysts, and it has many advantages such as a higher conversion with a lower temperature. Furthermore, the product and the catalyst can be instantaneously separated, and this way the catalyst can be easily recovered without using any separation operation. The most-used materials in the catalytic decomposition of ozone in the gas phase are [[manganese dioxide]], transition metals such as Mn, Co, Cu, Fe, Ni, or Ag, and noble metals such as Pt, Rh, or Pd.

[[Radical (chemistry)|Free radicals]] of [[chlorine]] (Cl{{sup|'''·'''}}), formed by the action of ultraviolet radiation on [[Chlorofluorocarbon|chlorofluorocarbons]] (CFCs) and sea salt, are known to catalyse the breakdown of ozone in the atmosphere.

There are two other possibilities for decomposing ozone in the gas phase:
* [[Thermal decomposition]], in which the ozone is decomposed using only the action of heat. The problem is that this type of decomposition is very slow with temperatures below 250&nbsp;°C. However, the decomposition rate can be increased working with higher temperatures but this would involve a high energy cost.
* [[Photodissociation|Photochemical decomposition]], which consists of radiating ozone with ultraviolet radiation (UV) and it gives rise to oxygen and radical peroxide.<ref>{{cite thesis |last=Roca Sánchez |first=Anna |title=Estudio cinético de la descomposición catalítica de ozono |date=2015-09-01 |url=https://riunet.upv.es/handle/10251/54140}}</ref>

====Kinetics of ozone decomposition into molecular oxygen====
The uncatalysed process of ozone decomposition in the gas phase is a complex reaction involving two [[Elementary reaction|elementary reactions]] that finally lead to molecular oxygen,<ref>{{Cite web |last1=Flowers |first1=Paul |last2=Theopold |first2=Klaus |last3=Langley |first3=Richard |last4=William R. Robinson |first4=PhD |date=2019-02-14 |title=12.6 Reaction Mechanisms - Chemistry 2e {{!}} OpenStax |url=https://openstax.org/books/chemistry-2e/pages/12-6-reaction-mechanisms |access-date=2025-05-02 |website=openstax.org |language=English}}</ref> and this means that the reaction order and the [[rate equation|rate law]] cannot be determined by the stoichiometry of the overall reaction.

Overall reaction: <chem>2 O3 -> 3 O2</chem>

Rate law (observed): <math chem>V = \frac{K_{obs} \cdot [\ce{O3}]^2}{[\ce{O2}]}</math>

where <math> K_{obs} </math> is the observed [[Reaction rate constant|rate constant]] and <math> V </math> is the reaction rate. From the rate law above it can be determined that the partial order respect to molecular oxygen is −1 and respect to ozone is 2; therefore, the global reaction order is 1.

The first step is a unimolecular reaction wherein one molecule of ozone decomposes into two products (molecular oxygen and oxygen). The oxygen atom from the first step is a [[reactive intermediate]] because it participates as a reactant in the second step, which is a bimolecular reaction because there are two different reactants (ozone and oxygen) that give rise to molecular oxygen.

Step 1: Unimolecular reaction &nbsp; &nbsp;<chem>O3 -> O2 + O</chem>

Step 2: Bimolecular reaction &nbsp; &nbsp; <chem>O3 + O -> 2 O2</chem>

These two steps have different reaction rates and rate constants. The reaction rate laws for each of these steps are shown below:
:<math chem>V_1 = K_1 \cdot [\ce{O3}] \qquad V_2 = K_2 \cdot [\ce{O}] \cdot [\ce{O3}]</math>

The following mechanism allows to explain the rate law of the ozone decomposition observed experimentally, and also it allows to determine the reaction orders with respect to ozone and oxygen, with which the overall reaction order will be determined. 

The first step is assumed reversible and faster than the second reaction, which means that the slower [[Rate-determining step|rate determining step]] is the second reaction. This step determines the rate of product formation, and so <math> V=V_2 </math>. However, this equation depends on the concentration of oxygen (intermediate), which does not appear in the observed rate law. Since the first step is a rapid equilibrium, the concentration of the intermediate can be determined as follows:
:<math chem>K_{eq} = \frac{K_1}{K_{-1}} = \frac{[\ce{O2}] \cdot [\ce{O}]}{[\ce{O3}]}</math>
:<math chem>[\ce{O}] = \frac{K_1 \cdot [\ce{O3}]}{K_{-1} \cdot [\ce{O2}]}</math>

Then using these equations, the formation rate of molecular oxygen is as shown below:
:<math chem>V={K_2 \cdot K_1 \cdot [\ce{O_3}]^2 \over K_{-1} \cdot [\ce{O_2}]}</math>

The mechanism is consistent with the rate law observed experimentally if the rate constant ({{math|''K''<sub>obs</sub>}}) is given in terms of the individual mechanistic steps' rate constants as follows:<ref>{{cite journal |last1=Batakliev |first1=Todor |last2=Georgiev |first2=Vladimir |last3=Anachkov |first3=Metody |last4=Rakovsky |first4=Slavcho |last5=Zaikov |first5=Gennadi E. |title=Ozone decomposition |date=June 2014 |journal=Interdisciplinary Toxicology |volume=7 |issue=2 |pages=47–59 |issn=1337-6853 |pmid=26109880 |doi=10.2478/intox-2014-0008 |pmc=4427716}}</ref>
:<math chem>V={K_\text{obs} \cdot [\ce{O_3}]^2 \over [\ce{O_2}]} </math>

where <math> K_\text{obs}={K_{2} \cdot K_{1} \over K_{-1}}</math>

===Reduction to ozonides===
Reduction of ozone gives the [[ozonide]] anion, {{chem2|O3-}}. Derivatives of this anion are explosive and must be stored at cryogenic temperatures. Ozonides for all the [[alkali metal]]s are known. {{chem2|KO3, RbO3}}, and {{chem2|CsO3}} can be prepared from their respective superoxides:
: <chem>KO2 + O3 -> KO3 + O2</chem>
Although {{chem2|KO3}} can be formed as above, it can also be formed from [[potassium hydroxide]] and ozone:<ref>{{Housecroft2nd|page=439}}</ref>
: <chem>2 KOH + 5 O3 -> 2 KO3 + 5 O2 + H2O</chem>
{{chem2|NaO3}} and {{chem2|LiO3}} must be prepared by action of {{chem2|CsO3}} in liquid {{chem2|NH3}} on an [[ion-exchange resin]] containing {{chem2|Na+}} or {{chem2|Li+}} ions:<ref>{{Housecroft2nd|page=265}}</ref>
: <chem>CsO3 + Na+ -> Cs+ + NaO3</chem>
A solution of [[calcium]] in ammonia reacts with ozone to give [[ammonium ozonide]] and not calcium ozonide:<ref name="Horvath M. 1985. pg 44"/>
: <math chem>\begin{align}
\ce{3 Ca + 10 NH3 + 6 O3 ->\ } & \ce{Ca*6NH3 + Ca(OH)2 + Ca(NO3)2} \\
& + \ce{2 NH4O3 + 2 O2 + H2}
\end{align}</math>

===Applications===
Ozone can be used to remove [[iron]] and [[manganese]] from [[water]], forming a [[precipitate]] which can be filtered:
:<math chem>\begin{align}
& \ce{2 Fe^2+{} + O3 + 5 H2O -> 2 Fe(OH)_3{(s)}{} + O2{} + 4 H+} \\
& \ce{2 Mn^2+{} + 2 O3 + 4 H2O -> 2 MnO(OH)_2{(s)}{} + 2 O2{} + 4 H+}
\end{align}</math>
Ozone oxidizes dissolved hydrogen sulphide in water to [[sulphurous acid]]:
: <chem>3 O3 + H2S -> H2SO3 + 3 O2</chem>

These three reactions are central in the use of ozone-based well-water treatment.

Ozone detoxifies [[cyanide]]s by converting them to [[cyanate]]s.
: <chem>CN- + O3 -> CNO- + O2</chem>

Ozone completely decomposes [[urea]]:<ref>{{cite book |year=1985 |title=Ozone |pages=259, 269–270 |author1=Horvath M. |author2=Bilitzky L. |author3=Huttner J. |isbn=978-0-444-99625-1 |publisher=Elsevier}}</ref>
:<chem>(NH2)2CO + O3 -> N2 + CO2 + 2 H2O</chem>

==Spectroscopic properties==

Ozone is a bent [[triatomic molecule]] with three vibrational modes: the symmetric stretch (1103.157&nbsp;cm<sup>−1</sup>), bend (701.42&nbsp;cm<sup>−1</sup>) and antisymmetric stretch (1042.096&nbsp;cm<sup>−1</sup>).<ref>{{cite journal |title=Ozone |volume=6 |issue=3 |pages=993–1102 |publisher=U.S. Department of Commerce |year=1972 |last1=Shimanouchi |first1=T. |website=NIST: National Institute of Standards and Technology |url=https://webbook.nist.gov/cgi/cbook.cgi?ID=B4000064&Units=SI&Mask=800#ref-1}}</ref> The symmetric stretch and bend are weak absorbers, but the antisymmetric stretch is strong and responsible for ozone being an important minor [[greenhouse gas]]. This [[Infrared|IR]] band is also used to detect ambient and atmospheric ozone although UV-based measurements are more common.<ref>{{cite book |chapter-url=https://www.wmo.int/pages/prog/www/IMOP/publications/CIMO-Guide/Ed2008Up2010/Part-I/WMO8_Ed2008_PartI_Ch16_Up2010_en.pdf |chapter=Chapter 16: Measurement of Ozone |title=Part I: Measurement of Meteorological Variables |last=World Meteorological Organization |archive-url=https://web.archive.org/web/20160331164807/https://www.wmo.int/pages/prog/www/IMOP/publications/CIMO-Guide/Ed2008Up2010/Part-I/WMO8_Ed2008_PartI_Ch16_Up2010_en.pdf |archive-date=31 March 2016}}</ref>

The electromagnetic spectrum of ozone is quite complex. An overview can be seen at the MPI Mainz UV/VIS Spectral Atlas of Gaseous Molecules of Atmospheric Interest.<ref>{{cite web |title=The MPI-Mainz UV/VIS Spectral Atlas of Gaseous Molecules of Atmospheric Interest |last=Max Planck Institute – Mainz |url=https://uv-vis-spectral-atlas-mainz.org/uvvis_data/cross_sections_plots/Ozone/O3_overview_log.jpg}}</ref>

All of the bands are dissociative, meaning that the molecule falls apart to {{nowrap|O + O<sub>2</sub>}} after absorbing a photon. The most important absorption is the Hartley band, extending from slightly above 300&nbsp;nm down to slightly above 200&nbsp;nm. It is this band that is responsible for absorbing UV&nbsp;C in the stratosphere.

On the high wavelength side, the Hartley band transitions to the so-called Huggins band, which falls off rapidly until disappearing by ~360&nbsp;nm. Above 400&nbsp;nm, extending well out into the NIR, are the Chappius and Wulf bands. There, unstructured absorption bands are useful for detecting high ambient concentrations of ozone, but are so weak that they do not have much practical effect.

There are additional absorption bands in the far UV, which increase slowly from 200&nbsp;nm down to reaching a maximum at ~120&nbsp;nm.

==Ozone in Earth's atmosphere==
[[File:Atmospheric ozone.svg|thumb|upright=1.25|The distribution of atmospheric ozone in partial pressure as a function of altitude]]
[[File:Nimbus ozone Brewer-Dobson circulation.jpg|thumb|upright=1.25|Concentration of ozone as measured by the [[Nimbus program|Nimbus-7]] satellite]]
[[File:IM ozavg ept 200006.png|thumb|Total ozone concentration in June 2000 as measured by the NASA EP-TOMS satellite instrument]]
The standard way to express total ozone levels (the amount of ozone in a given vertical column) in the atmosphere is by using [[Dobson unit]]s. Point measurements are reported as [[mole fraction]]s in nmol/mol (parts per billion, ppb) or as [[concentration]]s in μg/m<sup>3</sup>. The study of ozone concentration in the atmosphere started in the 1920s.<ref>{{cite web |title=Measured Ozone Depletion |work=Ozone-Information.com |url=http://www.albany.edu/faculty/rgk/atm101/ozmeas.htm |access-date=2014-01-22 |archive-url=https://web.archive.org/web/20130914112129/http://www.albany.edu/faculty/rgk/atm101/ozmeas.htm |archive-date=2013-09-14}}</ref>

===Ozone layer===
{{Main|Ozone layer}}

====Location and production====
{{See also|Ozone–oxygen cycle|Ozone depletion}}

The highest levels of ozone in the atmosphere are in the [[stratosphere]], in a region also known as the [[ozone layer]] between about 10 and 50&nbsp;km above the surface (or between about 6 and 31 miles). However, even in this "layer", the ozone concentrations are only two to eight parts per million, so most of the oxygen there is dioxygen, O<sub>2</sub>, at about 210,000 parts per million by volume.<ref name="Hultman">{{cite book |last=Hultman |first=G. Eric |title=The Ozone Survival Manual |date=1980-01-01 |publisher=McGraw-Hill |isbn=978-0-915498-73-4}}</ref>

Ozone in the stratosphere is mostly produced from short-wave ultraviolet rays between 240 and 160&nbsp;nm. Oxygen starts to absorb weakly at 240&nbsp;nm in the Herzberg bands, but most of the oxygen is dissociated by absorption in the strong [[Schumann–Runge bands]] between 200 and 160&nbsp;nm where ozone does not absorb. While shorter wavelength light, extending to even the X-Ray limit, is energetic enough to dissociate molecular oxygen, there is relatively little of it, and, the strong solar emission at Lyman-alpha, 121&nbsp;nm, falls at a point where molecular oxygen absorption is a minimum.<ref>{{cite web |title=The MPI-Mainz UV/VIS Spectral Atlas of Gaseous Molecules of Atmospheric Interest: O2, Lyman-alpha |last=Keller-Rudek |first=Hannelore |url=http://joseba.mpch-mainz.mpg.de/spectral_atlas_data/cross_sections_plots/Oxygen/O2_Lyman%20alpha%20line_lin.jpg |archive-url=https://web.archive.org/web/20151117015120/http://joseba.mpch-mainz.mpg.de/spectral_atlas_data/cross_sections_plots/Oxygen/O2_Lyman%20alpha%20line_lin.jpg |archive-date=2015-11-17}}</ref>

The process of ozone creation and destruction is called the [[Chapman cycle]] and starts with the photolysis of molecular oxygen
: <chem>O2 -> [\ce{photon}] [(\ce{radiation}\ \lambda\ <\ 240\ \ce{nm})] 2O</chem>

followed by reaction of the oxygen atom with another molecule of oxygen to form ozone.
:<chem>O + O2 + M -> O3 + M</chem>

where "M" denotes the third body that carries off the excess energy of the reaction. The ozone molecule can then absorb a UV-C photon and dissociate
:<math chem>\ce{O3 -> O + O2} + \text{kinetic energy}</math>

The excess kinetic energy heats the stratosphere when the O atoms and the molecular oxygen fly apart and collide with other molecules. This conversion of UV light into kinetic energy warms the stratosphere. The oxygen atoms produced in the photolysis of ozone then react back with other oxygen molecule as in the previous step to form more ozone. In the clear atmosphere, with only nitrogen and oxygen, ozone can react with the atomic oxygen to form two molecules of {{chem2|O2}}:
:<chem>O3 + O -> 2 O2</chem>

An estimate of the rate of this termination step to the cycling of atomic oxygen back to ozone can be found simply by taking the ratios of the concentration of O<sub>2</sub> to O<sub>3</sub>. The termination reaction is [[catalysis|catalysed]] by the presence of certain free radicals, of which the most important are hydroxyl (OH), nitric oxide (NO) and atomic chlorine (Cl) and bromine (Br). In the second half of the 20th century, the amount of ozone in the stratosphere was [[ozone depletion|discovered to be declining]], mostly because of increasing concentrations of [[chlorofluorocarbon]]s (CFC) and similar [[haloalkane|chlorinated and brominated organic molecules]]. The concern over the health effects of the decline led to the 1987 [[Montreal Protocol]], the ban on the production of many [[ozone depletion|ozone-depleting]] chemicals and in the first and second decade of the 21st century the beginning of the recovery of stratospheric ozone concentrations.

====Importance to surface-dwelling life on Earth====
[[File:Ozone altitude UV graph.svg|thumb|upright=1.25|Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UVC (100–280&nbsp;nm) is blocked by dioxygen (at 100–200&nbsp;nm) or by ozone (at 200–280&nbsp;nm) in the atmosphere. The shorter portion of this band and even more energetic UV causes the formation of the ozone layer, when single oxygen atoms produced by UV [[photolysis]] of dioxygen (below 240&nbsp;nm) react with more dioxygen. The ozone layer itself then blocks most, but not quite all, sunburn-producing UVB (280–315&nbsp;nm). The band of UV closest to visible light, UVA (315–400&nbsp;nm), is hardly affected by ozone, and most of it reaches the ground.]]

Ozone in the ozone layer filters out sunlight wavelengths from about 200&nbsp;nm UV rays to 315&nbsp;nm, with ozone peak absorption at about 250&nbsp;nm.<ref>{{cite journal |title=Photolysis of Atmospheric Ozone in the Ultraviolet Region |year=2003 |last1=Matsumi |first1=Yutaka |last2=Kawasaki |first2=Masahiro |journal=Chemical Reviews |volume=103 |issue=12 |pages=4767–82 |pmid=14664632 |doi=10.1021/cr0205255 |bibcode=2003ChRv..103.4767M }} See the graphical absorption of ozone in two of its absorption bands, as a function of wavelength.</ref> This ozone UV absorption is important to life, since it extends the absorption of UV by ordinary oxygen and nitrogen in air (which absorb all wavelengths < 200&nbsp;nm) through the lower UV-C (200–280&nbsp;nm) and the entire UV-B band (280–315&nbsp;nm). The small unabsorbed part that remains of UV-B after passage through ozone causes sunburn in humans, and direct DNA damage in living tissues in both plants and animals. Ozone's effect on mid-range UV-B rays is illustrated by its effect on UV-B at 290&nbsp;nm, which has a radiation intensity 350 million times as powerful at the top of the atmosphere as at the surface. Nevertheless, enough of UV-B radiation at similar frequency reaches the ground to cause some sunburn, and these same wavelengths are also among those responsible for the production of [[vitamin D]] in humans.

The ozone layer has little effect on the longer UV wavelengths called UV-A (315–400&nbsp;nm), but this radiation does not cause sunburn or direct DNA damage. While UV-A probably does cause long-term skin damage in certain humans, it is not as dangerous to plants and to the health of surface-dwelling organisms on Earth in general (see [[ultraviolet]] for more information on near ultraviolet).

===Ground-level ozone===
{{Main|Ground-level ozone|Photochemical smog}}
{{Pollution sidebar|Natural}}

Ground-level ozone (or tropospheric ozone) is an atmospheric pollutant.<ref name=who-Europe>[http://www.euro.who.int/__data/assets/pdf_file/0005/112199/E79097.pdf Health Aspects of Air Pollution with Particulate Matter, Ozone and Nitrogen Dioxide] {{Webarchive|url=https://web.archive.org/web/20120414204626/http://www.euro.who.int/__data/assets/pdf_file/0005/112199/E79097.pdf |date=2012-04-14}}. WHO-Europe report 13–15 January 2003 (PDF)</ref> It is not emitted directly by [[internal combustion engine|car engines]] or by industrial operations, but formed by the reaction of sunlight on air containing [[volatile organic compound|hydrocarbons]] and [[nitrogen oxide]]s that react to form ozone directly at the source of the pollution or many kilometres downwind.

Ozone reacts directly with some hydrocarbons such as [[aldehyde]]s and thus begins their removal from the air, but the products are themselves key components of [[photochemical smog|smog]]. Ozone [[photolysis]] by UV light leads to production of the [[hydroxyl radical]] HO• and this plays a part in the removal of hydrocarbons from the air, but is also the first step in the creation of components of smog such as [[peroxyacyl nitrates]], which can be powerful eye irritants. The atmospheric lifetime of tropospheric ozone is about 22 days; its main removal mechanisms are being deposited to the ground, the above-mentioned reaction giving HO•, and by reactions with OH and the peroxy radical HO<sub>2</sub>•.<ref>{{cite journal |author=Stevenson |year=2006 |title=Multimodel ensemble simulations of present-day and near-future tropospheric ozone |journal=Journal of Geophysical Research: Atmospheres |volume=111 |issue=D8 |publisher=[[American Geophysical Union]] |doi=10.1029/2005JD006338 |bibcode=2006JGRD..111.8301S |display-authors=etal |article-number=2005JD006338 |url=http://www.agu.org/pubs/crossref/2006/2005JD006338.shtml |access-date=2006-09-16 |archive-url=https://web.archive.org/web/20111104195423/http://www.agu.org/pubs/crossref/2006/2005JD006338.shtml |archive-date=2011-11-04}}</ref>

There is evidence of significant reduction in agricultural yields because of increased ground-level ozone and pollution which interferes with [[photosynthesis]] and stunts overall growth of some plant species.<ref>{{cite web |title=Rising Ozone Levels Pose Challenge to U.S. Soybean Production, Scientists Say |date=2003-07-31 |publisher=NASA Earth Observatory |url=http://earthobservatory.nasa.gov/Newsroom/view.php?id=23565 |access-date=2006-05-10 |archive-url=https://web.archive.org/web/20100316221804/http://earthobservatory.nasa.gov/Newsroom/view.php?id=23565 |archive-date=2010-03-16}}</ref><ref name="arb.ca.gov">{{cite web |last=Mutters |first=Randall |title=Statewide Potential Crop Yield Losses From Ozone Exposure |date=March 1999 |publisher=California Air Resources Board |url=http://www.arb.ca.gov/research/abstracts/94-345.htm |access-date=2006-05-10 |archive-url=https://web.archive.org/web/20040217151427/http://www.arb.ca.gov/research/abstracts/94-345.htm |archive-date=2004-02-17}}</ref> The [[United States Environmental Protection Agency]] (EPA) has proposed a secondary regulation to reduce crop damage, in addition to the primary regulation designed for the protection of human health.

====Ground-level ozone in urban areas====
Certain examples of cities with elevated ozone readings are [[Denver|Denver, Colorado]]; [[Houston, Texas]]; and [[Mexico City]], [[Mexico]]. Houston has a reading of around 41&nbsp;nmol/mol, while Mexico City is far more hazardous, with a reading of about 125&nbsp;nmol/mol.<ref name="arb.ca.gov"/>

Ground-level ozone, or tropospheric ozone, is the most concerning type of ozone pollution in urban areas and is increasing in general.<ref>{{cite book |title=Rethinking the Ozone Problem in Urban and Regional Air Pollution |date=1991-01-01 |isbn=978-0-309-04631-2 |doi=10.17226/1889 |url=https://archive.org/details/rethinkingozonep0000unse |url-access=registration}}</ref> Ozone pollution in urban areas affects denser populations, and is worsened by high populations of vehicles, which emit NO<sub>2</sub> and [[volatile organic compound]]s (VOCs), the main pollutants contributing to problematic ozone levels.<ref name="Sharma-2016">{{cite journal |last1=Sharma |first1=Sumit |last2=Sharma |first2=Prateek |last3=Khare |first3=Mukesh |last4=Kwatra |first4=Swati |title=Statistical behavior of ozone in urban environment |date=May 2016 |journal=Sustainable Environment Research |volume=26 |issue=3 |pages=142–148 |bibcode= 2016SusER..26..142S|doi=10.1016/j.serj.2016.04.006 |doi-access=free}}</ref> Ozone pollution in urban areas is especially concerning with increasing temperatures, raising heat-related mortality during [[heat wave]]s.<ref>{{cite journal |last1=Diem |first1=Jeremy E. |last2=Stauber |first2=Christine E. |last3=Rothenberg |first3=Richard |date=2017-05-16 |editor-last=Añel |editor-first=Juan A. |title=Heat in the southeastern United States: Characteristics, trends, and potential health impact |journal=PLOS ONE |volume=12 |issue=5 |article-number=e0177937 |issn=1932-6203 |bibcode=2017PLoSO..1277937D |pmid=28520817 |doi=10.1371/journal.pone.0177937 |doi-access=free |pmc=5433771}}</ref> During heat waves in urban areas, [[ground level ozone]] pollution can be 20% higher than usual.<ref>{{cite journal |last1=Hou |first1=Pei |last2=Wu |first2=Shiliang |title=Long-term Changes in Extreme Air Pollution Meteorology and the Implications for Air Quality |date=July 2016 |journal=Scientific Reports |volume=6 |issue=1 |article-number=23792 |issn=2045-2322 |bibcode=2016NatSR...623792H |pmid=27029386 |doi=10.1038/srep23792 |pmc=4815017}}</ref> Ozone pollution in urban areas reaches higher levels of exceedance in the summer and autumn, which may be explained by patterns of weather and traffic.<ref name="Sharma-2016"/> People experiencing poverty are more affected by pollution in general, even though these populations are less likely to be contributing to pollution levels.<ref>{{cite journal |last1=Tessum |first1=Christopher W. |last2=Apte |first2=Joshua S. |last3=Good kind |first3=Andrew L. |last4=Muller |first4=Nicholas Z. |last5=Mullins |first5=Kimberley A. |last6=Paolella |first6=David A. |last7=Polasky |first7=Stephen |last8=Springer |first8=Nathaniel P. |last9=Thakrar |first9=Sumil K. |title=Inequity in consumption of goods and services adds to racial–ethnic disparities in air pollution exposure |date=2019-03-11 |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=13 |pages=6001–6006 |bibcode=2019PNAS..116.6001T |issn=0027-8424 |pmid=30858319 |doi=10.1073/pnas.1818859116 |doi-access=free |pmc=6442600}}</ref>

As mentioned above, Denver, Colorado, is one of the many cities in the U.S. that have high amounts of ozone. According to the [[American Lung Association]], the [[Denver–Aurora combined statistical area|Denver–Aurora area]] is the 14th most ozone-polluted area in the U.S.<ref>American Lung Association. (n.d.). How healthy is the air you breathe? Retrieved March 20, 2019, from [https://www.lung.org/our-initiatives/healthy-air/sota/city-rankings/most-polluted-cities.html lung.org]</ref> The problem of high ozone levels is not new to this area. In 2004, the EPA allotted the [[Denver metropolitan area|Denver Metro]]/North Front Range{{efn|This includes Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson, and parts of Larimer and Weld counties.}} as [[non-attainment area]]s per 1997's 8-hour ozone standard,<ref>{{cite web |title=History of ozone in Colorado |website=Colorado Department of Public Health & Environment |url=https://cdphe.colorado.gov/ozone-and-your-health/history-of-ozone-in-colorado |access-date=2023-04-18}}</ref> but later deferred this status until 2007. The non-attainment standard indicates that an area does not meet the EPA's air quality standards. The Colorado Ozone Action Plan was created in response, and numerous changes were implemented from this plan. The first major change was that car emission testing was expanded across the state to more counties that did not previously mandate emissions testing, like areas of Larimer and Weld County. There have also been changes made to decrease emissions of nitrogen oxides (NOx) and VOCs, which should help lower ozone levels.

One large contributor to high ozone levels in the area is the oil and [[natural gas]] industry situated in the Denver-Julesburg Basin (DJB) which overlaps with a majority of Colorado's metropolitan areas. Ozone is produced naturally in the Earth's stratosphere, but is also produced in the troposphere from human efforts. Briefly mentioned above, NOx and VOCs react with sunlight to create ozone through a process called photochemistry. One hour elevated ozone events (<75&nbsp;ppb) "occur during June–August indicating that elevated ozone levels are driven by regional photochemistry".<ref name="Evans-2017">{{cite journal |last1=Evans |first1=Jason M. |last2=Helmig |first2=Detlev |title=Investigation of the influence of transport from oil and natural gas regions on elevated ozone levels in the northern Colorado front range |date=February 2017 |journal=Journal of the Air & Waste Management Association |volume=67 |issue=2 |pages=196–211 |bibcode=2017JAWMA..67..196E |issn=1096-2247 |pmid=27629587 |doi=10.1080/10962247.2016.1226989 |doi-access=free}}</ref> According to an article from the University of Colorado-Boulder, "Oil and natural gas VOC emission have a major role in ozone production and bear the potential to contribute to elevated O<sub>3</sub> levels in the Northern Colorado Front Range (NCFR)".<ref name="Evans-2017"/> Using complex analyses to research wind patterns and emissions from large oil and natural gas operations, the authors concluded that "elevated O<sub>3</sub> levels in the NCFR are predominantly correlated with air transport from N– ESE, which are the upwind sectors where the O&NG operations in the Wattenberg Field area of the DJB are located".<ref name="Evans-2017"/>

Contained in the Colorado Ozone Action Plan, created in 2008, plans exist to evaluate "emission controls for large industrial sources of NOx" and "statewide control requirements for new oil and gas condensate tanks and pneumatic valves".<ref>{{cite web |title=Colorado Ozone Action Plan |author=((Colorado Department of Public Health and Environment, Regional Air Quality Council, & North Front Range Metropolitan Planning Organization)) |url=https://massless.info/images/AP_PO_Denver-Ozone-Action-Plan-2008.pdf |access-date=2019-03-21}}</ref> In 2011, the Regional Haze Plan was released that included a more specific plan to help decrease NOx emissions. These efforts are increasingly difficult to implement and take many years to come to pass. Of course there are also other reasons that ozone levels remain high. These include: a growing population meaning more car emissions, and the mountains along the NCFR that can trap emissions. If interested, daily air quality readings can be found at the Colorado Department of Public Health and Environment's website.<ref>Colorado Department of Public Health and Environment. (n.d.). Colorado Air Quality. Retrieved March 20, 2019, from https://www.colorado.gov/airquality/air_quality.aspx</ref> As noted earlier, Denver continues to experience high levels of ozone to this day. It will take many years and a systems-thinking approach to combat this issue of high ozone levels in the Front Range of Colorado.

====Ozone cracking====
{{Main|Ozone cracking}}
[[File:Ozone cracks in tube1.jpg|thumb|Ozone cracking in [[natural rubber]] tubing]]
Ozone gas attacks any [[polymer]] possessing olefinic or [[double bond]]s within its chain structure, such as [[natural rubber]], [[nitrile rubber]], and [[styrene-butadiene]] rubber. Products made using these polymers are especially susceptible to attack, which causes cracks to grow longer and deeper with time, the rate of crack growth depending on the load carried by the rubber component and the concentration of ozone in the atmosphere. Such materials can be protected by adding [[antiozonant]]s, such as waxes, which bond to the surface to create a protective film or blend with the material and provide long term protection. [[Ozone cracking]] used to be a serious problem in car tyres,<ref>{{cite journal |last1=Layer |first1=Robert W. |last2=Lattimer |first2=Robert P. |title=Protection of Rubber against Ozone |journal=Rubber Chemistry and Technology |date=July 1990 |volume=63 |number=3 |pages=426–450 |doi=10.5254/1.3538264}}</ref> for example, but it is not an issue with modern tyres. On the other hand, many critical products, like [[gasket]]s and [[O-ring]]s, may be attacked by ozone produced within compressed-air systems. [[Fuel line]]s made of reinforced rubber are also susceptible to attack, especially within the engine compartment, where some ozone is produced by electrical components. Storing rubber products in close proximity to a [[Direct Current|DC]] [[electric motor]] can accelerate ozone cracking. The [[commutator (electric)|commutator]] of the motor generates sparks which in turn produce ozone.

===Ozone as a greenhouse gas===
[[File:1950- Ozone in upper and lower troposphere.svg|thumb|Ozone with an anthropogenic "fingerprint" contributes to global warming and climate change, especially when present in the upper troposphere.<ref>{{cite journal |last1=Yu |first1=Xinyuan |last2=Fiore |first2=Arlene M. |last3=Santer |first3=Benjamin D. |last4=Correa |first4=Gustavo P. |last5=Lamarque |first5=Jean-Francois |last6=Ziemke |first6=Jerald R. |last7=Eastham |first7=Sebastian d. |last8=Zhu |first8=Qindan |display-authors=4 |title=Anthropogenic Fingerprint Detectable in Upper Tropospheric Ozone Trends Retrieved from Satellite |journal=Environmental Science and Technology |date=2 August 2024 |volume=58 |issue=32 |pages=14306–14317 |doi=10.1021/acs.est.4c01289 |doi-access=free |pmid=39092829 |pmc=11325641|bibcode=2024EnST...5814306Y }} Further explained by {{cite web |last1=Chu |first1=Jennifer |title=Scientists find a human 'fingerprint' in the upper troposphere's increasing ozone |date=2 August 2024 |website=Phys.org |url=https://phys.org/news/2024-08-scientists-human-fingerprint-upper-troposphere.html|url-status=live |archive-url=https://web.archive.org/web/20240802154244/https://phys.org/news/2024-08-scientists-human-fingerprint-upper-troposphere.html |archive-date=2 August 2024}}</ref>]]
Although ozone was present at ground level before the [[Industrial Revolution]], peak concentrations are now far higher than the pre-industrial levels, and even background concentrations well away from sources of pollution are substantially higher.<ref>{{cite web |year=1998 |title=Tropospheric Ozone in EU – The consolidated report |publisher=European Environmental Agency |url=http://www.eea.europa.eu/publications/TOP08-98/page004.html |access-date=2006-05-10}}</ref><ref>{{cite web |title=Atmospheric Chemistry and Greenhouse Gases |publisher=Intergovernmental Panel on Climate Change |url=http://www.grida.no/climate/ipcc_tar/wg1/142.htm |access-date=2006-05-10 |archive-url=https://web.archive.org/web/20060710143636/http://www.grida.no/climate/ipcc_tar/wg1/142.htm |archive-date=2006-07-10}}</ref> Ozone acts as a [[greenhouse gas]], absorbing some of the [[infrared]] energy emitted by the earth. Quantifying the greenhouse gas potency of ozone is difficult because it is not present in uniform concentrations across the globe. However, the most widely accepted scientific assessments relating to [[climate change]] (e.g. the [[Intergovernmental Panel on Climate Change]] [[Third Assessment Report]])<ref>{{cite web |year=2001 |title=Climate Change 2001 |publisher=Intergovernmental Panel on Climate Change |url=http://www.grida.no/climate/ipcc_tar/ |access-date=2006-09-12 |archive-url=https://web.archive.org/web/20060913043522/http://www.grida.no/climate/ipcc_tar/ |archive-date=2006-09-13}}</ref> suggest that the [[radiative forcing]] of tropospheric ozone is about 25% that of [[carbon dioxide]].

The annual [[global warming potential]] of tropospheric ozone is between 918 and 1022 tons [[carbon dioxide equivalent]]/tons tropospheric ozone. This means on a per-molecule basis, ozone in the troposphere has a [[radiative forcing]] effect roughly 1,000 times as strong as [[carbon dioxide]]. However, tropospheric ozone is a short-lived greenhouse gas, which decays in the atmosphere much more quickly than [[carbon dioxide]]. This means that over a 20-year span, the global warming potential of tropospheric ozone is much less, roughly 62 to 69 tons [[carbon dioxide equivalent]] / ton tropospheric ozone.<ref>Life Cycle Assessment Methodology Sufficient to Support Public Declarations and Claims, Committee Draft Standard, Version 2.1. Scientific Certification Systems, February 2011. Annex B, Section 4.</ref>

Because of its short-lived nature, tropospheric ozone does not have strong global effects, but has very strong radiative forcing effects on regional scales. In fact, there are regions of the world where tropospheric ozone has a [[radiative forcing]] up to 150% of [[carbon dioxide]].<ref>[http://acdb-ext.gsfc.nasa.gov/Data_services/cloud_slice/ NASA GODDARD HOMEPAGE FOR TROPOSPHERIC OZONE NASA Goddard Space Flight Center Code 613.3, Chemistry and Dynamics Branch]. Acdb-ext.gsfc.nasa.gov (2006-09-20). Retrieved on 2012-02-01.</ref> For example, ozone increase in the [[troposphere]] is shown to be responsible for ~30% of upper [[Southern Ocean]] [[ocean heat content|interior warming]] between 1955 and 2000.<ref>{{cite journal |last1=Liu |first1=Wei |last2=Hegglin |first2=Michaela I. |last3=Checa-Garcia |first3=Ramiro |last4=Li |first4=Shouwei |last5=Gillett |first5=Nathan P. |last6=Lyu |first6=Kewei |last7=Zhang |first7=Xuebin |last8=Swart |first8=Neil C. |title=Stratospheric ozone depletion and tropospheric ozone increases drive Southern Ocean interior warming |journal=Nature Climate Change |date=April 2022 |volume=12 |issue=4 |pages=365–372 |bibcode=2022NatCC..12..365L |language=en |issn=1758-6798 |doi=10.1038/s41558-022-01320-w |s2cid=247844868 |url=https://www.researchgate.net/publication/359643522 |url-access=subscription}}<br />Lay summary report: {{cite news |title=Ozone may be heating the planet more than we realize |work=[[University of Reading]] |language=en |url=https://phys.org/news/2022-03-ozone-planet.html |access-date=19 April 2022}}</ref>

== Carbon filtering ==
{{Main article|Carbon filtering}}
Filters containing an [[Adsorption|adsorbent]] or [[catalyst]] such as [[charcoal]] (carbon) may be used to remove [[odour]]s and gaseous pollutants such as volatile organic compounds or ozone.<ref>{{Cite web|url=https://www.arb.ca.gov/research/indoor/acdsumm.pdf|title=California Environmental Protection Agency - Air Cleaning Devices for the Home, Frequently Asked Questions|publisher=California Environmental Protection Agency Air Resources Board|access-date=2016-12-14}}</ref>

==Health effects==
{{See also|Health and environmental impact of the coal industry}}

Ozone is an acutely toxic gas.<ref name="banned">{{Bulleted list|{{cite web | last=Wilson | first=Janet | title=State bans home ozone air purifiers | website=Los Angeles Times | date=28 September 2007 | url=https://www.latimes.com/archives/la-xpm-2007-sep-28-me-purifier28-story.html | access-date=26 July 2025}}|{{cite web | title=Ozone Generators as Indoor Air Cleaners | website=New York State Department of Health | date=7 November 2014 | url=https://www.health.ny.gov/environmental/indoors/air/ozone_generating_air_cleaners.htm | access-date=26 July 2025}}|{{cite web | title=Health Canada Regulates UV and Ozone-emitting Devices | website=College of Alberta Denturists | date=7 June 2021 | url=https://www.abdenturists.ca/blog/health-canada-regulates-uv-and-ozone-emitting-devices/ | access-date=26 July 2025}}|{{cite web | title=Health Canada Regulates UV and Ozone Devices | website=College of Dental Technologists of Ontario | url=https://cdto.ca/health-canada-regulates-uv-and-ozone-devices/ | access-date=26 July 2025}}|{{cite web | title=Ozone generators may be dangerous to your health | website=Publications du gouvernement du Canada | url=https://publications.gc.ca/site/archivee-archived.html?url=https://publications.gc.ca/collections/collection_2014/sc-hc/H46-2-99-230-eng.pdf | language=fr | date=5 March 2001 | access-date=26 July 2025}}}}</ref><ref name="poisonous">{{Bulleted list|{{cite web | title=ICSC 0068 | website=International Chemical Safety Cards (ICSCs) | url=https://chemicalsafety.ilo.org/dyn/icsc/showcard.display?p_lang=en&p_card_id=0068&p_version=2 | access-date=26 July 2025}}|{{cite web | title=Substance Information | website=ECHA | date=19 May 2023 | url=https://echa.europa.eu/substance-information/-/substanceinfo/100.030.051 | access-date=26 July 2025}}|{{cite web | title=Registration Dossier | website=ECHA | date=19 May 2023 | url=https://echa.europa.eu/registration-dossier/-/registered-dossier/22480/2/1 | access-date=26 July 2025}}|{{cite web | title=Ozone | website=pubchem.ncbi.nlm.nih.gov | date=2 June 2025 | url=https://pubchem.ncbi.nlm.nih.gov/compound/Ozone | archive-url=https://web.archive.org/web/20250711122136/https://pubchem.ncbi.nlm.nih.gov/compound/Ozone | archive-date=11 July 2025 | access-date=26 July 2025}}|{{cite web | title=21 CFR 801.415 -- Maximum acceptable level of ozone. | website=eCFR | orig-date=1976 | date=17 July 2025 | url=https://www.ecfr.gov/current/title-21/chapter-I/subchapter-H/part-801/subpart-H/section-801.415 | access-date=26 July 2025}}}}</ref>

For the last few decades, scientists studied the effects of acute and chronic ozone exposure on human health. Hundreds of studies suggest that ozone is harmful to people at levels currently found in urban areas.<ref>{{cite journal |title=Linking Air Quality and Human Health Effects Models: An Application to the Los Angeles Air Basin |journal=Environmental Health Insights |volume=11 |article-number=1178630217737551 |date=13 November 2017 |last1=Stewart |first1=D. R. |last2=Saunders |first2=E. |last3=Perea |first3=R. A. |last4=Fitzgerald |first4=R. |last5=Campbell |first5=D. E. |last6=Stockwell |first6=W. R. |issue=1 |bibcode=2017EnvHI..1173755S |pmid=29162976 |doi=10.1177/1178630217737551 |pmc=5692127}}</ref><ref>{{cite web |last1=US EPA |first1=OAR |title=Health Effects of Ozone Pollution |language=en |date=5 June 2015 |website=US EPA |url=https://www.epa.gov/ground-level-ozone-pollution/health-effects-ozone-pollution}}</ref> Ozone has been shown to affect the respiratory, cardiovascular and central nervous system. Early death and problems in reproductive health and development are also shown to be associated with ozone exposure.<ref>{{cite web |last=US EPA |first=OAR |title=Ground-level Ozone Basics |date=2015-05-29 |language=en |website=US EPA |url=https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics |access-date=2020-11-26}}</ref>

===Vulnerable populations===
The American Lung Association has identified five populations who are especially vulnerable to the effects of breathing ozone:<ref name="Ozone">{{cite web |last1=American Lung Association Scientific and Medical Editorial Review Panel |title=Ozone |website=American Lung Association |url=https://www.lung.org/our-initiatives/healthy-air/outdoor/air-pollution/ozone.html |access-date=24 March 2019}}</ref>
# Children and teens
# People 65 years old and older
# People who work or exercise outdoors
# People with existing lung diseases, such as asthma and chronic obstructive pulmonary disease (also known as COPD, which includes emphysema and chronic bronchitis)
# People with [[cardiovascular disease]]
Additional evidence suggests that women, those with obesity and low-income populations may also face higher risk from ozone, although more research is needed.<ref name="Ozone"/>

===Acute ozone exposure===
Acute ozone exposure ranges from hours to a few days. Because ozone is a gas, it directly affects the lungs and the entire respiratory system. Inhaled ozone causes inflammation and acute—but reversible—changes in lung function, as well as airway hyperresponsiveness.<ref>{{cite journal |last1=Jule |first1=Y. |last2=Michaudel |first2=C. |last3=Fauconnier |first3=L. |last4=Togbe |first4=D. |last5=Riffel |first5=B. |year=2018 |title=Ozone-induced acute and chronic alterations in the lung in mice: a combined digital imaging and functional analysis |journal=European Respiratory Journal |volume=52 |page=4313}}</ref> These changes lead to shortness of breath, wheezing, and coughing which may exacerbate lung diseases, like asthma or chronic obstructive pulmonary disease (COPD) resulting in the need to receive medical treatment.<ref>{{cite journal |last1=Burnett |first1=R. T. |last2=Brook |first2=J. R. |last3=Yung |first3=W. T. |last4=Dales |first4=R. E. |last5=Krewski |first5=D. |year=1997 |title=Association between ozone and hospitalization for respiratory diseases in 16 Canadian cities |journal=Environmental Research |volume=72 |issue=1 |pages=24–31 |bibcode=1997ER.....72...24B |pmid=9012369 |doi=10.1006/enrs.1996.3685}}</ref><ref>{{cite journal |last1=Desqueyroux |first1=H. |last2=Pujet |first2=J. C. |last3=Prosper |first3=M. |last4=Squinazi |first4=F. |last5=Momas |first5=I. |year=2002 |title=Short-term effects of low-level air pollution on respiratory health of adults suffering from moderate to severe asthma |journal=Environmental Research |volume=89 |issue=1 |pages=29–37 |bibcode=2002ER.....89...29D |pmid=12051782 |doi=10.1006/enrs.2002.4357}}</ref> Acute and chronic exposure to ozone has been shown to cause an increased risk of respiratory infections, due to the following mechanism.<ref>{{cite journal |last1=Gent |first1=J. F. |last2=Triche |first2=E. W. |last3=Holford |first3=T. R. |last4=Belanger |first4=K. |last5=Bracken |first5=M. B. |last6=Beckett |first6=W. S. |last7=Leaderer |first7=B. P. |year=2003 |title=Association of low-level ozone and fine particles with respiratory symptoms in children with asthma |journal=JAMA |volume=290 |issue=14 |pages=1859–1867 |pmid=14532314 |doi=10.1001/jama.290.14.1859 |doi-access=free}}</ref>

Multiple studies have been conducted to determine the mechanism behind ozone's harmful effects, particularly in the lungs. These studies have shown that exposure to ozone causes changes in the immune response within the lung tissue, resulting in disruption of both the innate and adaptive immune response, as well as altering the protective function of lung epithelial cells.<ref name="ReferenceA">{{cite journal |last1=Al-Hegelan |first1=M. |last2=Tighe |first2=R. M. |last3=Castillo |first3=C. |last4=Hollingsworth |first4=J. W. |title=Ambient ozone and pulmonary innate immunity |journal=Immunol Res |year=2011 |volume=49 |issue=1–3 |pages=173–91 |pmid=21132467 |doi=10.1007/s12026-010-8180-z |pmc=3747041}}</ref> It is thought that these changes in immune response and the related inflammatory response are factors that likely contribute to the increased risk of lung infections, and worsening or triggering of asthma and reactive airways after exposure to ground-level ozone pollution.<ref name="ReferenceA"/><ref name="ncbi.nlm.nih.gov">Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. The innate and adaptive immune systems. 2010 Dec 7 [Updated 2016 Aug 4]. Available from https://www.ncbi.nlm.nih.gov/books/NBK279396/</ref>

The innate (cellular) immune system consists of various chemical signals and cell types that work broadly and against multiple pathogen types, typically bacteria or foreign bodies/substances in the host.<ref name="ncbi.nlm.nih.gov"/><ref name="Travers P 2001">Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. The components of the immune system. Available from: https://www.ncbi.nlm.nih.gov/books/NBK27092/</ref> The cells of the innate system include phagocytes, neutrophils,<ref name="Travers P 2001"/> both thought to contribute to the mechanism of ozone pathology in the lungs, as the functioning of these cell types have been shown to change after exposure to ozone.<ref name="ncbi.nlm.nih.gov"/> Macrophages, cells that serve the purpose of eliminating pathogens or foreign material through the process of "phagocytosis",<ref name="Travers P 2001"/> have been shown to change the level of inflammatory signals they release in response to ozone, either up-regulating and resulting in an inflammatory response in the lung, or down-regulating and reducing immune protection.<ref name="ReferenceA"/> Neutrophils, another important cell type of the innate immune system that primarily targets bacterial pathogens,<ref name="Travers P 2001"/> are found to be present in the airways within 6 hours of exposure to high ozone levels. Despite high levels in the lung tissues, however, their ability to clear bacteria appears impaired by exposure to ozone.<ref name="ReferenceA"/>

The adaptive immune system is the branch of immunity that provides long-term protection via the development of antibodies targeting specific pathogens and is also impacted by high ozone exposure.<ref name="ncbi.nlm.nih.gov"/><ref name="Travers P 2001"/> Lymphocytes, a cellular component of the adaptive immune response, produce an increased amount of inflammatory chemicals called "cytokines" after exposure to ozone, which may contribute to airway hyperreactivity and worsening asthma symptoms.<ref name="ReferenceA"/>

The airway epithelial cells also play an important role in protecting individuals from pathogens. In normal tissue, the epithelial layer forms a protective barrier, and also contains specialized ciliary structures that work to clear foreign bodies, mucus and pathogens from the lungs. When exposed to ozone, the cilia become damaged and mucociliary clearance of pathogens is reduced. Furthermore, the epithelial barrier becomes weakened, allowing pathogens to cross the barrier, proliferate and spread into deeper tissues. Together, these changes in the epithelial barrier help make individuals more susceptible to pulmonary infections.<ref name="ReferenceA"/>

Inhaling ozone not only affects the immune system and lungs, but it may also affect the heart as well. Ozone causes short-term autonomic imbalance leading to changes in heart rate and reduction in heart rate variability;<ref>{{cite journal |last1=Gold |first1=D. R. |last2=Litonjua |first2=A. |last3=Schwartz |first3=J. |last4=Lovett |first4=E. |last5=Larson |first5=A. |last6=Nearing |first6=B. |last7=Verrier |first7=R. |year=2000 |title=Ambient pollution and heart rate variability |journal=Circulation |volume=101 |issue=11 |pages=1267–1273 |pmid=10725286 |doi=10.1161/01.cir.101.11.1267 |doi-access=free}}</ref> and high-level exposure for as little as one hour results in a supraventricular arrhythmia in the elderly,<ref>{{cite journal |last1=Sarnat |first1=S. E. |last2=Suh |first2=H. H. |last3=Coull |first3=B. A. |last4=Schwartz |first4=J. |last5=Stone |first5=P. H. |last6=Gold |first6=D. R. |year=2006 |title=Ambient particulate air pollution and cardiac arrhythmia in a panel of older adults in Steubenville, Ohio |journal=Occupational and Environmental Medicine |volume=63 |issue=10 |pages=700–706 |pmid=16757505 |doi=10.1136/oem.2006.027292 |pmc=2078044}}</ref> both increase the risk of premature death and stroke. Ozone may also lead to vasoconstriction resulting in increased systemic arterial pressure contributing to increased risk of cardiac morbidity and mortality in patients with pre-existing cardiac diseases.<ref>{{cite journal |last1=Brook |first1=R. D. |last2=Brook |first2=J. R. |last3=Urch |first3=B. |last4=Vincent |first4=R. |last5=Rajagopalan |first5=S. |last6=Silverman |first6=F. |year=2002 |title=Inhalation of fine particulate air pollution and ozone causes acute arterial vasoconstriction in healthy adults |journal=Circulation |volume=105 |issue=13 |pages=1534–1536 |pmid=11927516 |doi=10.1161/01.cir.0000013838.94747.64 |doi-access=free}}</ref><ref>{{cite journal |last1=Zanobetti |first1=A. |last2=Canner |first2=M. J. |last3=Stone |first3=P. H. |last4=Schwartz |first4=J. |last5=Sher |first5=D. |last6=Eagan-Bengston |first6=E. |last7=Gold |first7=D. R. |year=2004 |title=Ambient pollution and blood pressure in cardiac rehabilitation patients |journal=Circulation |volume=110 |issue=15 |pages=2184–2189 |pmid=15466639 |doi=10.1161/01.cir.0000143831.33243.d8 |doi-access=free}}</ref>

===Chronic ozone exposure===
Breathing ozone for periods longer than eight hours at a time for weeks, months or years defines chronic exposure. Numerous studies suggest a serious impact on the health of various populations from this exposure.

One study finds significant positive associations between chronic ozone and all-cause, circulatory, and respiratory mortality with 2%, 3%, and 12% increases in risk per 10&nbsp;ppb<ref>{{cite journal |last1=Turner |first1=M. C. |last2=Jerrett |first2=M. |last3=Pope |first3=III |last4=Krewski |first4=D. |last5=Gapstur |first5=S. M. |last6=Diver |first6=W. R. |last7=Burnett |first7=R. T. |year=2016 |title=Long-term ozone exposure and mortality in a large prospective study |journal=American Journal of Respiratory and Critical Care Medicine |volume=193 |issue=10 |pages=1134–1142 |pmid=26680605 |doi=10.1164/rccm.201508-1633oc |pmc=4872664}}</ref> and report an association (95% CI) of annual ozone and all-cause mortality with a hazard ratio of 1.02 (1.01–1.04), and with cardiovascular mortality of 1.03 (1.01–1.05). A similar study finds similar associations with all-cause mortality and even larger effects for cardiovascular mortality.<ref>{{cite journal |last1=Crouse |first1=D. L. |last2=Peters |first2=P. A. |last3=Hystad |first3=P. |last4=Brook |first4=J. R. |last5=van Donkelaar |first5=A. |last6=Martin |first6=R. V. |last7=Brauer |first7=M. |year=2015 |title=Ambient PM2. 5, O3, and NO2 exposures and associations with mortality over 16 years of follow-up in the Canadian Census Health and Environment Cohort (CanCHEC) |journal=Environmental Health Perspectives |volume=123 |issue=11 |pages=1180–1186 |pmid=26528712 |doi=10.1289/ehp.1409276 |pmc=4629747|bibcode=2015EnvHP.123.1180C }}</ref> An increased risk of mortality from respiratory causes is associated with long-term chronic exposure to ozone.<ref>{{cite journal |last1=Jerrett |first1=Michael |last2=Burnett |first2=Richard T. |last3=Pope |first3=C. Arden |last4=Ito |first4=Kazuhiko |last5=Thurston |first5=George |last6=Krewski |first6=Daniel |last7=Shi |first7=Yuanli |last8=Calle |first8=Eugenia |last9=Thun |first9=Michael |title=Long-Term Ozone Exposure and Mortality |date=2009-03-12 |journal=The New England Journal of Medicine |volume=360 |issue=11 |pages=1085–1095 |issn=0028-4793 |pmid=19279340 |doi=10.1056/NEJMoa0803894 |pmc=4105969}}</ref>

Chronic ozone has detrimental effects on children, especially those with asthma. The risk for hospitalization in children with asthma increases with chronic exposure to ozone; younger children and those with low-income status are even at greater risk.<ref>{{cite journal |last1=Lin |first1=S. |last2=Liu |first2=X. |last3=Le |first3=L. H. |last4=Hwang |first4=S. A. |year=2008 |title=Chronic exposure to ambient ozone and asthma hospital admissions among children |journal=Environmental Health Perspectives |volume=116 |issue=12 |pages=1725–1730 |pmid=19079727 |doi=10.1289/ehp.11184 |pmc=2599770|bibcode=2008EnvHP.116.1725L }}</ref>

Adults suffering from respiratory diseases (asthma,<ref>{{cite journal |last1=Zu |first1=K. |last2=Shi |first2=L. |last3=Prueitt |first3=R. L. |last4=Liu |first4=X. |last5=Goodman |first5=J. E. |year=2018 |title=Critical review of long-term ozone exposure and asthma development |journal=Inhalation Toxicology |volume=30 |issue=3 |pages=99–113 |bibcode=2018InhTx..30...99Z |pmid=29869579 |doi=10.1080/08958378.2018.1455772 |doi-access=free}}</ref> COPD,<ref>{{cite journal |last1=Malig |first1=B. J. |last2=Pearson |first2=D. L. |last3=Chang |first3=Y. B. |last4=Broadwin |first4=R. |last5=Basu |first5=R. |last6=Green |first6=R. S. |last7=Ostro |first7=B. |year=2015 |title=A time-stratified case-crossover study of ambient ozone exposure and emergency department visits for specific respiratory diagnoses in California (2005–2008) |journal=Environmental Health Perspectives |volume=124 |issue=6 |pages=745–753 |pmid=26647366 |doi=10.1289/ehp.1409495 |pmc=4892911}}</ref> lung cancer<ref>{{cite journal |last1=Vanwinge |first1=C. |last2=Gilles |first2=C. |last3=Gerard |first3=C. |last4=Blacher |first4=S. |last5=Noel |first5=A. |last6=Cataldo |first6=D. |last7=Rocks |first7=N. |year=2017 |title=A Role For Ozone Pollution In Lung Cancer Progression |journal=Am J Respir Crit Care Med |volume=195 |page=A2352}}</ref>) are at a higher risk of mortality and morbidity and critically ill patients have an increased risk of developing acute respiratory distress syndrome with chronic ozone exposure as well.<ref>{{cite journal |last1=Ware |first1=L. B. |last2=Zhao |first2=Z. |last3=Koyama |first3=T. |last4=May |first4=A. K. |last5=Matthay |first5=M. A. |last6=Lurmann |first6=F. W. |last7=Calfee |first7=C. S. |year=2016 |title=Long-term ozone exposure increases the risk of developing the acute respiratory distress syndrome |journal=American Journal of Respiratory and Critical Care Medicine |volume=193 |issue=10 |pages=1143–1150 |pmid=26681363 |doi=10.1164/rccm.201507-1418oc |pmc=4872663}}</ref>

===Ozone produced by air cleaners===
Ozone generators sold as air cleaners intentionally produce the gas ozone.<ref name="EPA-2022"/> These are often marketed to control [[indoor air quality|indoor air pollution]], and use misleading terms to describe ozone. Some examples are describing it as "energized oxygen" or "pure air", suggesting that ozone is a healthy or "better" kind of oxygen.<ref name="EPA-2022"/> However, according to the [[United States Environmental Protection Agency|EPA]], "There is evidence to show that at concentrations that do not exceed public health standards, ozone is not effective at removing many odor-causing chemicals", and "If used at concentrations that do not exceed public health standards, ozone applied to indoor air does not effectively remove viruses, bacteria, mold, or other biological pollutants.".<ref name="EPA-2022"/> Furthermore, another report states that "results of some controlled studies show that concentrations of ozone considerably higher than these [human safety] standards are possible even when a user follows the manufacturer's operating instructions".<ref>[https://web.archive.org/web/19990117032442/http://www.epa.gov/iaq/pubs/ozonegen.html EPA report on consumer ozone air purifiers]. Epa.gov. Retrieved on 2012-02-01.</ref>

The [[California Air Resources Board]] has a page listing air cleaners (many with [[air ioniser|ionizers]]) meeting their indoor ozone limit of 0.050 parts per million.<ref name=CARBlist>[https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-products/california-certified-air-cleaning-devices California Certified Air Cleaning Devices]. From [[California Air Resources Board]].</ref> From that article:

<blockquote>All portable indoor air cleaning devices sold in California must be certified by the California Air Resources Board (CARB). To be certified, air cleaners must be tested for electrical safety and ozone emissions, and meet an ozone emission concentration limit of 0.050 parts per million. For more information about the regulation, visit the [https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-products/air-cleaner-regulation-ab-2276 air cleaner regulation].</blockquote>

===Ozone air pollution===
{{Further|Ground level ozone|Climate change}}
[[File:Alder showing ozone discolouration.jpg|thumb|right|[[Alnus rubra|Red Alder]] leaf, showing discolouration caused by ozone pollution<ref name=EONASA>{{cite web |title=Watching Our Ozone Weather |date=2003-08-22 |author=Jeannie Allen |publisher=NASA Earth Observatory |url=http://earthobservatory.nasa.gov/Features/OzoneWx/ |access-date=2008-10-11}}</ref>]]
[[File:SignboardAirQualityHouston.JPG|thumb|Signboard in [[Gulfton, Houston|Gulfton]], [[Houston]] indicating an ozone watch]]

[[Ozone precursors]] are a group of pollutants, predominantly those emitted during the combustion of [[fossil fuels]]. [[Ground-level ozone]] pollution (tropospheric ozone) is produced near the Earth's surface by the action of daylight [[ultraviolet|UV]] rays on these precursors. The [[ground-level ozone|ozone at ground level]] is primarily from fossil fuel precursors, but [[methane]] is a natural precursor, and the very low natural background level of ozone at ground level is considered safe. This section examines the health impacts of fossil fuel burning, which raises ground level ozone far above background levels.

There is a great deal of evidence to show that ground-level ozone can harm lung function and irritate the [[respiratory system]].<ref name="who-Europe"/><ref>[http://www.euro.who.int/document/E82790.pdf Answer to follow-up questions from CAFE (2004)] {{webarchive|url=https://web.archive.org/web/20050909162153/http://www.euro.who.int/document/E82790.pdf |date=2005-09-09}} (PDF)</ref> Exposure to ozone (and the pollutants that produce it) is linked to premature [[death]], [[asthma]], [[bronchitis]], [[heart attack]], and other cardiopulmonary problems.<ref>{{cite web |last1=[[EPA]] Course Developers |title=Health Effects of Ozone in the General Population |publisher=[[EPA]] |date=2016-03-21 |url=https://www.epa.gov/ozone-pollution-and-your-patients-health/health-effects-ozone-general-population}}</ref><ref name="pmid18629332">{{cite journal |author=Weinhold B |title=Ozone nation: EPA standard panned by the people |journal=Environ. Health Perspect. |volume=116 |issue=7 |pages=A302–A305 |year=2008 |pmid=18629332 |doi=10.1289/ehp.116-a302 |pmc=2453178 |bibcode=2008EnvHP.116.a302W }}</ref>

Long-term exposure to ozone has been shown to increase risk of death from [[respiratory illness]].<ref name="EPA-2022"/> A study of 450,000 people living in U.S. cities saw a significant correlation between ozone levels and respiratory illness over the 18-year follow-up period. The study revealed that people living in cities with high ozone levels, such as Houston or Los Angeles, had an over 30% increased risk of dying from lung disease.<ref>{{cite journal |last1=Jerrett |first1=Michael |last2=Burnett |first2=Richard T. |last3=Pope |first3=C. Arden III |last4=Ito |first4=Kazuhiko |last5=Thurston |first5=George |last6=Krewski |first6=Daniel |last7=Shi |first7=Yuanli |last8=Calle |first8=Eugenia |last9=Thun |first9=Michael |journal=N. Engl. J. Med. |volume=360 |pages=1085–1095 |date=March 12, 2009 |issue=11 |title=Long-Term Ozone Exposure and Mortality |pmid=19279340 |doi=10.1056/NEJMoa0803894 |pmc=4105969}}</ref><ref>{{cite journal |last=Wilson |first=Elizabeth K. |title=Ozone's Health Impact |date=March 16, 2009 |volume=87 |issue=11 |page=9 |journal=Chemical & Engineering News |doi=10.1021/cen-v087n011.p009a}}</ref>

Air quality guidelines such as those from the [[World Health Organization]], the [[U.S. Environmental Protection Agency]] (EPA), and the [[European Union]] are based on detailed studies designed to identify the levels that can cause measurable ill [[health effect]]s.

According to scientists with the EPA, susceptible people can be adversely affected by ozone levels as low as 40&nbsp;nmol/mol.<ref name="pmid18629332"/><ref>{{cite journal |title=Ozone Overload: Current Standards May Not Protect Health |journal=Environ. Health Perspect. |year=2006 |volume=114 |issue=4 |pages=A240 |last=Dahl |first=R |doi=10.1289/ehp.114-a240a |pmc=1440818}}</ref><ref>{{cite journal |volume=114 |issue=4 |title=The exposure-response curve for ozone and risk of mortality and the adequacy of current ozone regulations |year=2006 |journal=Environ. Health Perspect. |pages=532–6 |last1=Bell |first1=ML |last2=Peng |first2=RD |last3=Dominici |first3=F |pmid=16581541 |doi=10.1289/ehp.8816 |pmc=1440776|bibcode=2006EnvHP.114..532B }}</ref> In the EU, the current target value for ozone concentrations is 120&nbsp;μg/m<sup>3</sup> which is about 60&nbsp;nmol/mol. This target applies to all member states in accordance with Directive 2008/50/EC.<ref>[http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32008L0050:en:NOT Directive 2008/50/EC]. Eur-lex.europa.eu. Retrieved on 2013-01-17.</ref> Ozone concentration is measured as a maximum daily mean of 8 hour averages and the target should not be exceeded on more than 25 calendar days per year, starting from January 2010. While the directive requires in the future a strict compliance with 120&nbsp;μg/m<sup>3</sup> limit (i.e. mean ozone concentration not to be exceeded on any day of the year), there is no date set for this requirement and this is treated as a long-term objective.<ref>{{cite web |publisher=EC |title=DIRECTIVE 2008/50/EC on ambient air quality and cleaner air for Europe |date=2008-06-11 |url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:152:0001:0044:EN:PDF |access-date=2010-08-23}}</ref>

In the US, the [[Clean Air Act (United States)|Clean Air Act]] directs the EPA to set [[National Ambient Air Quality Standards]] for several pollutants, including ground-level ozone, and counties out of compliance with these standards are required to take steps to reduce their levels. In May 2008, under a court order, the EPA lowered its ozone standard from 80&nbsp;nmol/mol to 75&nbsp;nmol/mol. The move proved controversial, since the Agency's own scientists and advisory board had recommended lowering the standard to 60&nbsp;nmol/mol.<ref name="pmid18629332"/> Many public health and environmental groups also supported the 60&nbsp;nmol/mol standard,<ref>{{cite web |title=Comments of the American Lung Association, Environmental Defense, Sierra Club on the U.S. Environmental Protection Agency's Proposed Revisions to the National Ambient Air Quality Standards for Ozone July 11, 2007 – 72 FR 37818 |publisher=Lungusa.org |url=http://www.lungusa.org/get-involved/advocate/advocacy-documents/Comments-to-the-Environmental-Protection-Agency-re-National-Ambient-Air-Quality-Standard-for-Ozone.PDF  |archive-url=https://web.archive.org/web/20100710051224/http://www.lungusa.org/get-involved/advocate/advocacy-documents/Comments-to-the-Environmental-Protection-Agency-re-National-Ambient-Air-Quality-Standard-for-Ozone.PDF |archive-date=July 10, 2010}}</ref> and the [[World Health Organization]] recommends 100&nbsp;μg/m<sup>3</sup> (51&nbsp;nmol/mol).<ref>{{cite web |title=Ambient (outdoor) air pollution |language=en |website=who.int |url=https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health |access-date=2020-07-31}}</ref>

On January 7, 2010, the U.S. Environmental Protection Agency (EPA) announced proposed revisions to the National Ambient Air Quality Standard (NAAQS) for the pollutant ozone, the principal component of smog:

<blockquote>... EPA proposes that the level of the 8-hour primary standard, which was set at 0.075&nbsp;μmol/mol in the 2008 final rule, should instead be set at a lower level within the range of 0.060 to 0.070&nbsp;μmol/mol, to provide increased protection for children and other ''at risk'' populations against an array of {{Chem|O|3}} – related adverse health effects that range from decreased lung function and increased respiratory symptoms to serious indicators of respiratory morbidity including emergency department visits and hospital admissions for respiratory causes, and possibly cardiovascular-related morbidity as well as total non- accidental and cardiopulmonary mortality&nbsp;...<ref>[https://web.archive.org/web/20100402134306/http://www.epa.gov/air/ozonepollution/fr/20100119.pdf National Ambient Air Quality Standards for Ozone]. Environmental Protection Agency (EPA). Proposed rule</ref></blockquote>

On October 26, 2015, the EPA published a final rule with an effective date of December 28, 2015, that revised the 8-hour primary NAAQS from 0.075&nbsp;ppm to 0.070&nbsp;ppm.<ref>{{cite web |title=Federal Register {{!}} National Ambient Air Quality Standards for Ozone |date=2015-10-26 |website=federalregister.gov |url=https://www.federalregister.gov/articles/2015/10/26/2015-26594/national-ambient-air-quality-standards-for-ozone |access-date=2016-05-16}}</ref>

The EPA has developed an [[air quality index]] (AQI) to help explain air pollution levels to the general public. Under the current standards, eight-hour average ozone mole fractions of 85 to 104&nbsp;nmol/mol are described as "unhealthy for sensitive groups", 105&nbsp;nmol/mol to 124&nbsp;nmol/mol as "unhealthy", and 125&nbsp;nmol/mol to 404&nbsp;nmol/mol as "very unhealthy".<ref>[http://www.airinfonow.org/html/ed_ozone.html What is Ozone?] airinfonow.org</ref>

Ozone can also be present in [[indoor air pollution]], partly as a result of electronic equipment such as photocopiers. A connection has also been known to exist between the increased pollen, fungal spores, and ozone caused by thunderstorms and hospital admissions of [[asthma]] sufferers.<ref>{{cite journal |last=Anderson |first=W. |author2=G.J. Prescott |author3=S. Packham |author4=J. Mullins |author5=M. Brookes |author6=A. Seaton |title=Asthma admissions and thunderstorms: a study of pollen, fungal spores, rainfall, and ozone |journal=QJM: An International Journal of Medicine |volume=94 |issue=8 |pages=429–433 |year=2001 |pmid=11493720 |doi=10.1093/qjmed/94.8.429 |doi-access=free}}</ref>

In the [[Victorian era]], one British folk myth held that the smell of the sea was caused by ozone. In fact, the characteristic "smell of the sea" is caused by [[dimethyl sulphide]], a chemical generated by [[phytoplankton]]. Victorian Britons considered the resulting smell "bracing".<ref>University of East Anglia press release, [http://www.uea.ac.uk/env/research/reshigh/cloning Cloning the smell of the seaside] {{Webarchive|url=https://web.archive.org/web/20121031132419/http://www.uea.ac.uk/env/research/reshigh/cloning |date=2012-10-31}}, February 2, 2007</ref>

====Heat waves====
An investigation to assess the joint mortality effects of ozone and heat during the European [[heat wave]]s in 2003, concluded that these appear to be additive.<ref>{{cite journal
|author=Kosatsky T.
|title=The 2003 European heat waves
|date=July 2005
|journal=Eurosurveillance
|volume=10
|issue=7
|pages=3–4
|pmid=29208081
|doi=10.2807/esm.10.07.00552-en
|doi-access=free
|url=http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=552
|access-date=January 14, 2014
}}</ref>

===Physiology===
{{See also|Trioxidane}}
Ozone, along with reactive forms of oxygen such as [[superoxide]], [[singlet oxygen]], [[hydrogen peroxide]], and [[hypochlorite]] ions, is produced by [[white blood cell]]s and other biological systems (such as the roots of [[tagetes|marigolds]]) as a means of destroying foreign bodies. Ozone reacts directly with organic double bonds. Also, when ozone breaks down to dioxygen it gives rise to oxygen [[free radical]]s, which are highly reactive and capable of damaging many [[organic compound|organic molecules]]. Moreover, it is believed that the powerful oxidizing properties of ozone may be a contributing factor of [[inflammation]]. The cause-and-effect relationship of how the ozone is created in the body and what it does is still under consideration and still subject to various interpretations, since other body chemical processes can trigger some of the same reactions. There is evidence linking the antibody-catalyzed water-oxidation pathway of the human [[immune system|immune response]] to the production of ozone. In this system, ozone is produced by antibody-catalyzed production of [[trioxidane]] from water and neutrophil-produced singlet oxygen.<ref>{{cite journal |title=The Story of O |last=Hoffmann |first=Roald |journal=American Scientist |volume=92 |issue=1 |page=23 |date=January 2004 |doi=10.1511/2004.1.23 |url=http://www.americanscientist.org/template/AssetDetail/assetid/29647?&print=yes |access-date=2006-10-11 |archive-url=https://web.archive.org/web/20060925011907/http://www.americanscientist.org/template/AssetDetail/assetid/29647?&print=yes |archive-date=2006-09-25}}</ref>

When inhaled, ozone reacts with compounds lining the lungs to form specific, cholesterol-derived metabolites that are thought to facilitate the build-up and pathogenesis of [[atherosclerotic plaques]] (a form of [[heart disease]]). These metabolites have been confirmed as naturally occurring in human atherosclerotic arteries and are categorized into a class of secosterols termed ''[[atheronals]]'', generated by [[ozonolysis]] of cholesterol's double bond to form a [[atheronals|5,6 secosterol]]<ref>{{cite journal |last=Smith |first=LL |title=Oxygen, oxysterols, ouabain, and ozone: a cautionary tale |journal=Free Radical Biology & Medicine |volume=37 |issue=3 |pages=318–24 |year=2004 |pmid=15223065 |doi=10.1016/j.freeradbiomed.2004.04.024}}</ref> as well as a secondary condensation product via aldolization.<ref>{{cite journal |title=Evidence for Ozone Formation in Human Atherosclerotic Arteries |author=Paul Wentworth |year=2003 |journal=Science |volume=302 |last2=Nieva |first2=J |last3=Takeuchi |first3=C |last4=Galve |first4=R |last5=Wentworth |first5=AD |last6=Dilley |first6=RB |last7=Delaria |first7=GA |last8=Saven |first8=A |last9=Babior |first9=BM |last10=Janda |first10=K. D. |last11=Eschenmoser |first11=A |last12=Lerner |first12=R. A. |issue=5647 |pages=1053–6 |display-authors=8 |bibcode=2003Sci...302.1053W |pmid=14605372 |doi=10.1126/science.1089525 |s2cid=11099904}}</ref>

===Impact on plant growth and crop yields===
Ozone has been implicated to have an adverse effect on plant growth: "... ozone reduced total chlorophylls, carotenoid and carbohydrate concentration, and increased [[1-aminocyclopropane-1-carboxylic acid]] (ACC) content and ethylene production. In treated plants, the ascorbate leaf pool was decreased, while lipid peroxidation and solute leakage were significantly higher than in ozone-free controls. The data indicated that ozone triggered protective mechanisms against oxidative stress in citrus."<ref>{{cite journal |last=Iglesias |first=Domingo J. |author2=Ángeles Calatayuda |author3=Eva Barrenob |author4=Eduardo Primo-Milloa |author5=Manuel Talon |title=Responses of citrus plants to ozone: leaf biochemistry, antioxidant mechanisms and lipid peroxidation |journal=Plant Physiology and Biochemistry |volume=44 |issue=2–3 |pages=125–131 |year=2006 |bibcode=2006PlPB...44..125I |pmid=16644230 |doi=10.1016/j.plaphy.2006.03.007|hdl=20.500.11939/5370 }}</ref> Studies that have used pepper plants as a model have shown that ozone decreased fruit yield and changed fruit quality.<ref name="Bortolin-2014">{{cite journal |last1=Bortolin |first1=Rafael Calixto |last2=Caregnato |first2=Fernanda Freitas |last3=Divan |first3=Armando Molina |last4=Reginatto |first4=Flávio Henrique |last5=Gelain |first5=Daniel Pens |last6=Moreira |first6=José Cláudio Fonseca |title=Effects of chronic elevated ozone concentration on the redox state and fruit yield of red pepper plant Capsicum baccatum |date=2014-02-01 |journal=Ecotoxicology and Environmental Safety |volume=100 |pages=114–121 |bibcode=2014EcoES.100..114B |issn=0147-6513 |pmid=24238720 |doi=10.1016/j.ecoenv.2013.09.035}}</ref><ref name="Bortolin-2016">{{cite journal |last1=Bortolin |first1=Rafael Calixto |last2=Caregnato |first2=Fernanda Freitas |last3=Divan Junior |first3=Armando Molina |last4=Zanotto-Filho |first4=Alfeu |last5=Moresco |first5=Karla Suzana |last6=de Oliveira Rios |first6=Alessandro |last7=de Oliveira Salvi |first7=Aguisson |last8=Ortmann |first8=Caroline Flach |last9=de Carvalho |first9=Pâmela |title=Chronic ozone exposure alters the secondary metabolite profile, antioxidant potential, anti-inflammatory property, and quality of red pepper fruit from Capsicum baccatum |date=2016-07-01 |journal=Ecotoxicology and Environmental Safety |volume=129 |pages=16–24 |bibcode=2016EcoES.129...16B |issn=0147-6513 |pmid=26970882 |doi=10.1016/j.ecoenv.2016.03.004}}</ref> Furthermore, it was also observed a decrease in chlorophylls levels and antioxidant defences on the leaves, as well as increased the [[reactive oxygen species]] (ROS) levels and lipid and protein damages.<ref name="Bortolin-2014"/><ref name="Bortolin-2016"/>

A 2022 study concludes that East Asia loses 63&nbsp;billion dollars in crops per year due to ozone pollution, a byproduct of fossil fuel combustion. China loses about one-third of its potential wheat production and one-fourth of its rice production.<ref>{{cite news |last=Dickie |first=Gloria |author-link=Gloria Dickie |title=Ozone harms East Asian crops, costing $63 bln a year, scientists say |date=2022-01-17 |language=en |work=Reuters |url=https://www.reuters.com/business/environment/ozone-harms-east-asian-crops-costing-63-bln-year-scientists-say-2022-01-17/ |access-date=2022-01-23}}</ref><ref>{{cite journal |title=Air pollution takes a bite out of Asia's grain crops |date=2022-01-21 |journal=Nature |volume=601 |issue=7894 |page=487 |language=en |bibcode=2022Natur.601R.487. |pmid=35064229 |doi=10.1038/d41586-022-00117-3 |s2cid=246165555 |url=https://www.nature.com/articles/d41586-022-00117-3}}</ref>

===Safety regulations===
Because of the strongly oxidizing properties of ozone, ozone is a primary irritant, affecting especially the eyes and respiratory systems and can be hazardous at even low concentrations. The Canadian Centre for Occupation Safety and Health reports that:

<blockquote>Even very low concentrations of ozone can be harmful to the upper respiratory tract and the lungs. The severity of injury depends on both the concentration of ozone and the duration of exposure. Severe and permanent lung injury or death could result from even a very short-term exposure to relatively low concentrations."<ref>[http://www.the-o-zone.cc/research/abstracts/OSHC.pdf What are the main health hazards associated with breathing in ozone?], Canadian Centre for Occupational Health and Safety</ref></blockquote>

To protect workers potentially exposed to ozone, [[U.S. Occupational Safety and Health Administration]] has established a permissible exposure limit (PEL) of 0.1&nbsp;μmol/mol ([[29 CFR]] 1910.1000 table Z-1), calculated as an 8-hour time weighted average. Higher concentrations are especially hazardous and [[NIOSH]] has established an [[Immediately dangerous to life or health]] limit (IDLH) of 5&nbsp;μmol/mol.<ref>[https://www.cdc.gov/niosh/idlh/intridl4.html Documentation for Immediately Dangerous to Life or Health Concentrations (IDLH)]: NIOSH Chemical Listing and Documentation of Revised IDLH Values (as of 3/1/95)</ref> Work environments where ozone is used or where it is likely to be produced should have adequate ventilation and it is prudent to have a monitor for ozone that will alarm if the concentration exceeds the OSHA PEL. Continuous monitors for ozone are available from several suppliers.

Elevated ozone exposure can occur on [[passenger aircraft]], with levels depending on altitude and atmospheric turbulence.<ref name="portfolio">Lai, Jennifer (2008-05-08). "[http://www.portfolio.com/views/blogs/daily-brief/2008/05/08/airplane-air-heavy-on-the-ozone Airplane Air Heavy On The Ozone – Daily Brief]". Portfolio.com. Retrieved on 2012-02-01.</ref> U.S. [[Federal Aviation Administration]] regulations set a limit of 250&nbsp;nmol/mol with a maximum four-hour average of 100&nbsp;nmol/mol.<ref>[https://www.sciencedaily.com/releases/2007/09/070905140105.htm Air Quality In Airplanes: Blame Ozone And Natural Oils On Skin]. Sciencedaily.com (2007-09-05). Retrieved on 2012-02-01.</ref> Some planes are equipped with ozone converters in the ventilation system to reduce passenger exposure.<ref name="portfolio"/>

==Production==
[[File:THC 2003.902.021 E. H. Johnston Ozone Production.jpg|thumb|Ozone production demonstration, Fixed Nitrogen Research Laboratory, 1926]]

'''Ozone generators''', or '''ozonators''',<ref>{{cite web |title=Visual Encyclopedia of Chemical Engineering |website=encyclopedia.che.engin.umich.edu |url=http://encyclopedia.che.engin.umich.edu/Pages/TransportStorage/Ozonators/Ozonators.html |access-date=2020-04-19 |archive-date=2021-06-19 |archive-url=https://web.archive.org/web/20210619081113/https://encyclopedia.che.engin.umich.edu/Pages/TransportStorage/Ozonators/Ozonators.html |url-status=dead }}</ref> are used to produce ozone for cleaning air or removing smoke odours in unoccupied rooms. These ozone generators can produce over 3&nbsp;g of ozone per hour. Ozone often forms in nature under conditions where O<sub>2</sub> will not react.<ref name=brown/> Ozone used in industry is measured in μmol/mol (ppm, parts per million), nmol/mol (ppb, parts per billion), μg/m<sup>3</sup>, mg/h (milligrams per hour) or weight percent. The regime of applied concentrations ranges from 1% to 5% (in air) and from 6% to 14% (in oxygen) for older generation methods. New electrolytic methods can achieve up 20% to 30% dissolved ozone concentrations in output water.

Temperature and humidity play a large role in how much ozone is being produced using traditional generation methods (such as corona discharge and ultraviolet light). Old generation methods will produce less than 50% of nominal capacity if operated with humid ambient air, as opposed to very dry air. New generators, using electrolytic methods, can achieve higher purity and dissolution through using water molecules as the source of ozone production.

===Corona discharge method===
[[File:Shkarkese elektrike.jpg|thumb|Homemade [[Tesla coil]]. Ozone is produced in the [[corona discharge]].]]
This is the most common type of ozone generator for most industrial and personal uses. While variations of the "hot spark" corona discharge method of ozone production exist, including medical grade and industrial grade ozone generators, these units usually work by means of a [[corona discharge|corona discharge tube]] or ozone plate.<ref>{{cite web |title=Ozone Cell vs Ozone Plate – A2Z Ozone |work=A2Z Ozone |url=https://www.a2zozone.com/blogs/news/ozone-tube-vs-ozone-plate |access-date=2020-01-10 |archive-url=https://web.archive.org/web/20200110211607/https://www.a2zozone.com/blogs/news/ozone-tube-vs-ozone-plate |archive-date=2020-01-10}}</ref><ref>{{OrgSynth|last1=Smith|first1=L. I.|last2=Greenwood|first2=F. L.|last3=Hudrlik|first3=O. |collvol=3|collvolpages=673 |volume=26|pages=63|year=1946|title=A laboratory ozonizer|prep=cv3p0673}}</ref> They are typically cost-effective and do not require an oxygen source other than the ambient air to produce ozone concentrations of 3–6%. Fluctuations in ambient air, due to weather or other environmental conditions, cause variability in ozone production. However, they also produce [[nitrogen oxide]]s as a by-product. Use of an [[air dryer]] can reduce or eliminate nitric acid formation by removing water vapour and increase ozone production. At room temperature, nitric acid will form into a vapour that is hazardous if inhaled. Symptoms can include chest pain, shortness of breath, headaches and a dry nose and throat causing a burning sensation. Use of an [[oxygen concentrator]] can further increase the ozone production and further reduce the risk of nitric acid formation by removing not only the water vapour, but also the bulk of the nitrogen.

===Ultraviolet light===
{{See also|Photochemistry}}
UV ozone generators, or vacuum-ultraviolet (VUV) ozone generators, employ a light source that generates a narrow-band ultraviolet light, a subset of that produced by the Sun. The Sun's UV sustains the ozone layer in the stratosphere of Earth.<ref>{{cite journal |last=Dohan |first=J. M. |author2=W. J. Masschelein |year=1987 |journal=Ozone Sci. Eng. |title=Photochemical Generation of Ozone: Present State-of-the-Art |volume=9 |pages=315–334 |issue=4 |bibcode=1987OzSE....9..315D |doi=10.1080/01919518708552147}}</ref>

UV ozone generators use ambient air for ozone production, no air prep systems are used (air dryer or oxygen concentrator), therefore these generators tend to be less expensive. However, UV ozone generators usually produce ozone with a concentration of about 0.5% or lower which limits the potential ozone production rate. Another disadvantage of this method is that it requires the ambient air (oxygen) to be exposed to the UV source for a longer amount of time, and any gas that is not exposed to the UV source will not be treated. This makes UV generators impractical for use in situations that deal with rapidly moving air or water streams (in-duct air [[sterilization (microbiology)|sterilisation]], for example). Production of ozone is one of the [[ultraviolet germicidal irradiation#Potential dangers|potential dangers]] of [[ultraviolet germicidal irradiation]]. VUV ozone generators are used in swimming pools and [[spa]] applications ranging to millions of gallons of water. VUV ozone generators, unlike corona discharge generators, do not produce harmful nitrogen by-products and work extremely well in humid air environments. There is also not normally a need for expensive off-gas mechanisms, and no need for air driers or oxygen concentrators which require extra costs and maintenance.

===Cold plasma===
In the cold plasma method, pure oxygen gas is exposed to a [[plasma (physics)|plasma]] created by [[dielectric barrier discharge]]. The diatomic oxygen is split into single atoms, which then recombine in triplets to form ozone.

It is common in the industry to mislabel some DBD ozone generators as CD Corona Discharge generators. Typically all solid flat metal electrode ozone generators produce ozone using the dielectric barrier discharge method. Cold plasma machines use pure oxygen as the input source and produce a maximum concentration of about 24% ozone. They produce far greater quantities of ozone in a given time compared to ultraviolet production that has about 2% efficiency. The discharges manifest as filamentary transfer of electrons (micro discharges) in a gap between two electrodes. In order to evenly distribute the micro discharges, a dielectric [[electrical insulation|insulator]] must be used to separate the metallic electrodes and to prevent arcing.

===Electrolytic===
Electrolytic ozone generation (EOG) splits water molecules into H<sub>2</sub>, O<sub>2</sub>, and O<sub>3</sub>.

In most EOG methods, the hydrogen gas will be removed to leave oxygen and ozone as the only reaction products. Therefore, EOG can achieve higher [[dissolution (chemistry)|dissolution]] in water without other competing gases found in corona discharge method, such as nitrogen gases present in ambient air. This method of generation can achieve concentrations of 20–30% and is independent of air quality because water is used as the source material. Production of ozone electrolytically is typically unfavourable because of the high [[overpotential]] required to produce ozone as compared to oxygen. This is why ozone is not produced during typical water electrolysis. However, it is possible to increase the overpotential of oxygen by careful catalyst selection such that ozone is preferentially produced under electrolysis. Catalysts typically chosen for this approach are [[lead dioxide]]<ref>{{cite journal |author1=Foller, Peter C. |author2=Tobias, Charles W. |title=The Anodic Evolution of Ozone |journal=Journal of the Electrochemical Society |volume=129 |issue=3 |page=506 |year=1982 |bibcode=1982JElS..129..506F |doi=10.1149/1.2123890}}</ref> or boron-doped diamond.<ref>{{cite journal |author1=Arihara, Kazuki |author2=Terashima, Chiaki |author3=Fujishimam Akira |title=Electrochemical Production of High-Concentration Ozone-Water Using Freestanding Perforated Diamond Electrodes |journal=Journal of the Electrochemical Society |volume=154 |issue=4 |pages=E71 |year=2007 |bibcode=2007JElS..154E..71A |doi=10.1149/1.2509385}}</ref>

The ozone-to-oxygen ratio is improved by increasing current density at the anode, cooling the electrolyte around the anode close to 0&nbsp;°C, using an acidic electrolyte (such as dilute sulphuric acid) instead of a basic solution, and by applying pulsed current instead of DC.<ref name="Hale1919">{{cite book |last=Hale |first=Arthur J. |title=The Manufacture of Chemicals by Electrolysis |year=1919 |publisher=D. Van Nostrand Co. |pages=15, 16 |url=https://books.google.com/books?id=eDNDAAAAIAAJ |access-date=12 September 2019}}</ref>

===Special considerations===
Ozone cannot be stored and transported like other industrial gases (because it quickly decays into diatomic oxygen) and must therefore be produced on site. Available ozone generators vary in the arrangement and design of the high-voltage electrodes. At production capacities higher than 20&nbsp;kg per hour, a gas/water tube heat-exchanger may be utilised as ground electrode and assembled with tubular high-voltage electrodes on the gas-side. The regime of typical gas pressures is around {{convert|2|bar|lk=on}} absolute in oxygen and {{convert|3|bar}} absolute in air. Several megawatts of [[electric power|electrical power]] may be installed in large facilities, applied as single phase AC [[electric current|current]] at 50 to 8000&nbsp;Hz and peak [[voltage]]s between 3,000 and 20,000 volts. Applied voltage is usually inversely related to the applied frequency.

The dominating parameter influencing ozone generation efficiency is the gas temperature, which is controlled by cooling water temperature and/or gas velocity. The cooler the water, the better the ozone synthesis. The lower the gas velocity, the higher the concentration (but the lower the net ozone produced). At typical industrial conditions, almost 90% of the effective power is dissipated as heat and needs to be removed by a sufficient cooling water flow.

Because of the high reactivity of ozone, only a few materials may be used like [[stainless steel]] (quality 316L), [[titanium]], [[aluminium]] (as long as no moisture is present), [[glass]], [[polytetrafluorethylene]], or [[polyvinylidene fluoride]]. [[Viton]] may be used with the restriction of constant mechanical forces and absence of humidity (humidity limitations apply depending on the formulation). [[Hypalon]] may be used with the restriction that no water comes in contact with it, except for normal atmospheric levels. [[Embrittlement]] or shrinkage is the common mode of failure of elastomers with exposure to ozone. Ozone cracking is the common mode of failure of elastomer seals like [[O-rings]].

[[Silicone rubber]]s are usually adequate for use as [[gaskets]] in ozone concentrations below 1 wt%, such as in equipment for accelerated aging of rubber samples.

===Incidental production===
Ozone may be formed from {{chem|O|2}} by electrical discharges and by action of high energy [[electromagnetic radiation]]. [[Arc suppression|Unsuppressed arcing]] in electrical contacts, motor brushes, or mechanical switches breaks down the chemical bonds of the atmospheric oxygen surrounding the contacts [{{chem|O|2}} -> 2O]. Free radicals of oxygen in and around the arc recombine to create ozone [{{chem|O|3}}].<ref>{{cite web |title=Lab Note #106 ''Environmental Impact of Arc Suppression'' |publisher=Arc Suppression Technologies |date=April 2011 |url=http://www.arcsuppressiontechnologies.com/arc-suppression-facts/lab-app-notes/ |access-date=October 10, 2011}}</ref> Certain [[electrical equipment]] generate significant levels of ozone. This is especially true of devices using [[high voltage]]s, such as [[air ioniser|ionic air purifiers]], [[laser printer]]s, [[photocopier]]s, [[electroshock weapon|tasers]], and [[arc welding|arc welders]]. [[Electric motor]]s using [[brush (electric)|brushes]] can generate ozone from repeated [[spark gap|sparking]] inside the unit. Large motors that use brushes, such as those used by elevators or hydraulic pumps, will generate more ozone than smaller motors.

Ozone is similarly formed in the [[Catatumbo lightning|Catatumbo lightning storms]] phenomenon on the [[Catatumbo River]] in [[Venezuela]], though ozone's instability makes it dubious that it has any effect on the ozonosphere.<ref name="Zulia">[http://www.agenciadenoticias.luz.edu.ve/index.php?option=com_content&task=view&id=4965&Itemid=151 ¿Relámpagos del Catatumbo regeneran la capa de ozono?] {{Webarchive|url=https://web.archive.org/web/20160305205225/http://agenciadenoticias.luz.edu.ve/index.php?id=4965&itemid=151&option=com_content&task=view |date=2016-03-05}}. Agencia de noticias de la [[Universidad del Zulia]].</ref>
It is the world's largest single natural generator of ozone, lending calls for it to be designated a [[UNESCO World Heritage Site]].<ref name="meteo">{{cite web |title=Fire in the Sky |url=http://www.meteogroup.co.uk/uk/home/weather/weather_news/news_archive/archive/2007/november/ch/f540146dcc/article/fire_in_the_sky.html |access-date=2008-08-16 |archive-url=https://web.archive.org/web/20110721215231/http://www.meteogroup.co.uk/uk/home/weather/weather_news/news_archive/archive/2007/november/ch/f540146dcc/article/fire_in_the_sky.html |archive-date=2011-07-21}}</ref>

===Laboratory production===
[[File:Siemen's Ozoniser.jpg|thumb|A laboratory method for the preparation of ozone by using a Siemen's ozoniser]]
In the laboratory, ozone can be produced by [[electrolysis]] using a [[9 volt battery]], a pencil graphite rod [[cathode]], a [[platinum]] wire [[anode]], and a 3 [[molar (concentration)|molar]] sulphuric acid [[electrolyte]].<ref>{{cite journal |last=Ibanez |first=Jorge G. |author2=Rodrigo Mayen-Mondragon |author3=M. T. Moran-Moran |year=2005 |title=Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 7: Microscale Production of Ozone |journal=Journal of Chemical Education |volume=82 |issue=10 |page=1546 |bibcode=2005JChEd..82.1546A |doi=10.1021/ed082p1546}}</ref> The [[half cell]] reactions taking place are:
:<math chem>\begin{align}
& \ce{3 H2O -> O3 + 6 H+ + 6 e-} && (\Delta E^\circ=-\text{1.53 V}) \\
& \ce{6 H+ + 6 e- -> 3 H2} && (\Delta E^\circ=\text{0 V}) \\
& \ce{2 H2O -> O2 + 4 H+ + 4 e-} && (\Delta E^\circ=\text{1.23 V})
\end{align}</math>

where {{mvar|E°}} represents the [[standard electrode potential (data page)|standard electrode potential]].

In the net reaction, three equivalents of water are converted into one equivalent of ozone and three equivalents of [[hydrogen]]. Oxygen formation is a competing reaction.

It can also be generated by a [[high voltage]] [[electric arc|arc]]. In its simplest form, high voltage AC, such as the output of a [[neon-sign transformer]] is connected to two metal rods with the ends placed sufficiently close to each other to allow an arc. The resulting arc will convert atmospheric oxygen to ozone.

It is often desirable to contain the ozone. This can be done with an apparatus consisting of two concentric glass tubes sealed together at the top with gas ports at the top and bottom of the outer tube. The inner core should have a length of metal foil inserted into it connected to one side of the power source. The other side of the power source should be connected to another piece of foil wrapped around the outer tube. A source of dry {{chem|O|2}} is applied to the bottom port. When high voltage is applied to the foil leads, [[electricity]] will discharge between the dry dioxygen in the middle and form {{chem|O|3}} and {{chem|O|2}} which will flow out the top port. This is called a Siemen's ozoniser. The reaction can be summarized as follows:<ref name=brown/>
: <chem>3O2 ->[\text{electricity}] 2O3</chem>

==Applications==

===Industry===
The largest use of ozone is in the preparation of [[pharmaceuticals]], [[synthetic lubricants]], and many other commercially useful [[organic compounds]], where it is used to sever [[carbon]]-carbon bonds.<ref name=brown/> It can also be used for [[bleach (chemical)|bleaching]] substances and for killing microorganisms in air and water sources.<ref>{{cite web |work=Ozone Information |title=Ozone and Color Removal |url=http://www.ozonesolutions.com/Ozone_Color_Removal.html |access-date=2009-01-09 |archive-url=https://web.archive.org/web/20110715031645/http://www.ozonesolutions.com/Ozone_Color_Removal.html |archive-date=2011-07-15}}</ref> Many municipal drinking water systems kill bacteria with ozone instead of the more common [[chlorine]].<ref>{{cite book |last=Hoigné |first=J. |title=Handbook of Environmental Chemistry, Vol. 5 part C |pages=83–141 |year=1998 |publisher=Springer-Verlag |location=Berlin}}</ref> Ozone has a very high [[oxidation potential]].<ref>{{cite web |title=Oxidation Potential of Ozone |work=Ozone-Information.com |url=http://www.ozone-information.com/Oxidation_Potential_Ozone.html |access-date=2008-05-17 |archive-url=https://web.archive.org/web/20080419034421/http://www.ozone-information.com/Oxidation_Potential_Ozone.html |archive-date=2008-04-19}}</ref> Ozone does not form [[organochlorine]] compounds, nor does it remain in the water after treatment. Ozone can form the suspected carcinogen [[bromate]] in source water with high [[bromide]] concentrations. The U.S. [[Safe Drinking Water Act]] mandates that these systems introduce an amount of chlorine to maintain a minimum of 0.2&nbsp;μmol/mol residual [[free chlorine]] in the pipes, based on results of regular testing. Where [[electric power|electrical power]] is abundant, ozone is a cost-effective method of treating water, since it is produced on demand and does not require transportation and storage of hazardous chemicals. Once it has decayed, it leaves no taste or odour in drinking water.

Although low levels of ozone have been advertised to be of some disinfectant use in residential homes, the concentration of ozone in dry air required to have a rapid, substantial effect on airborne pathogens exceeds safe levels recommended by the U.S. [[Occupational Safety and Health Administration]] and [[United States Environmental Protection Agency|Environmental Protection Agency]]. Humidity control can vastly improve both the killing power of the ozone and the rate at which it decays back to oxygen (more humidity allows more effectiveness). [[Spore]] forms of most pathogens are very tolerant of atmospheric ozone in concentrations at which asthma patients start to have issues.

In 1908 artificial ozonisation of the [[Central line (London Underground)|Central Line]] of the [[London Underground]] was introduced for aerial disinfection. The process was found to be worthwhile, but was phased out by 1956. However the beneficial effect was maintained by the ozone created incidentally from the electrical discharges of the train motors (see above: [[#Incidental production|Incidental production]]).<ref>{{cite book |last1=Postgate |first1=J. R. |title=Microbes and man |date=1992 |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-41259-9 |page=97 |edition=3rd}}</ref>

Ozone generators were made available to schools and universities in Wales for the Autumn term 2021, to disinfect classrooms after [[COVID-19]] outbreaks.<ref>{{cite news |last1=Weaver |first1=Matthew |title=Concerns over plan to use ozone to disinfect classrooms in Wales |work=[[The Guardian]] |date=30 August 2021 |language=en |url=https://www.theguardian.com/uk-news/2021/aug/30/concerns-over-plan-to-disinfect-classrooms-in-wales-with-ozone}}</ref>

Industrially, ozone is used to:
* Disinfect laundry in hospitals, food factories, care homes, etc.<ref>{{cite web |title=Decontamination: Ozone scores on spores |date=2007-04-01 |work=Hospital Development |publisher=Wilmington Media Ltd. |url=http://www.hdmagazine.co.uk/story.asp?storyCode=2043080 |access-date=2007-05-30 |archive-url=https://web.archive.org/web/20070929000438/http://www.hdmagazine.co.uk/story.asp?storyCode=2043080 |archive-date=2007-09-29}}</ref>
* Disinfect water in place of chlorine<ref name=brown/>
* Deodorise air and objects, such as after a fire
* Kill bacteria on food or on contact surfaces<ref name="food"/>
* Replace chemical sanitizers such as [[peracetic acid]], [[hypochlorite]] or heat in water-intense industries such as [[breweries]] and [[dairy]] plants
* Disinfect [[cooling tower]]s and control [[Legionella]] with reduced chemical consumption and water bleed-off, and increased performance
* Sanitise swimming pools and spas
* Kill insects in stored grain<ref>{{cite news |title=Ozone may provide environmentally safe protection for grains |date=January 30, 2003 |publisher=Purdue News |author=Steeves, Susan A. |url=http://news.uns.purdue.edu/UNS/html4ever/030130.Mason.ozone.html}}</ref>
* Scrub yeast and mould spores from the air in food processing plants
* Wash fresh fruits and vegetables to kill yeast, mould, and bacteria<ref name="food"/>
* Chemically attack contaminants in water: ([[iron]], [[arsenic]], [[hydrogen sulphide]], [[nitrite]]s, and complex organics lumped together as "colour")
* Provide an aid to [[flocculation]] (agglomeration of molecules, which aids in filtration, where the iron and arsenic are removed)
* Manufacture chemical compounds via chemical synthesis<ref>{{cite web |title=Chemical Synthesis with Ozone |work=Ozone-Information.com |url=http://www.ozone-information.com/Chemical_Synthesis_Ozone.html |access-date=2008-05-17 |archive-url=https://web.archive.org/web/20080410114619/http://www.ozone-information.com/Chemical_Synthesis_Ozone.html |archive-date=2008-04-10}}</ref>
* Clean and bleach fabrics (the former use is utilised in [[fabric restoration]]; the latter use is patented)<ref>{{cite web |title=Clean and bleach fabrics by ozone |url=http://www.ifatcc.org/wp-content/uploads/2017/12/E13.-PERINCEK.pdf}}</ref>
* Act as an [[antichlor]] in chlorine-based bleaching
* Assist in processing plastics to allow adhesion of inks
* Age rubber samples to determine the useful life of a batch of rubber
* Eradicate water-borne parasites such as ''[[Giardia lamblia]]'' and ''[[Cryptosporidium]]'' in surface water treatment plants.

Ozone is a [[reagent]] in many [[organic reactions]] in the laboratory and in industry. [[Ozonolysis]] is the cleavage of an [[alkene]] to [[carbonyl]] compounds.

Many hospitals around the world use large ozone generators to decontaminate operating rooms between surgeries. The rooms are cleaned and then sealed airtight before being filled with ozone which effectively kills or neutralizes all remaining bacteria.<ref>{{cite journal |last1=de Boer |first1=Hero E. L. |last2=van Elzelingen-Dekker |first2=Carla M. |last3=van Rheenen-Verberg |first3=Cora M. F. |last4=Spanjaard |first4=Lodewijk |title=Use of Gaseous Ozone for Eradication of Methicillin-Resistant ''Staphylococcus aureus'' From the Home Environment of a Colonized Hospital Employee |journal=Infection Control and Hospital Epidemiology |volume=27 |issue=10 |pages=1120–1122 |date=October 2006 |jstor=507966 |pmid=17006820 |doi=10.1086/507966 |s2cid=11627160}}</ref>

Ozone is used as an alternative to [[chlorine]] or [[chlorine dioxide]] in the [[bleaching of wood pulp]].<ref>{{cite book |last=Sjöström |first=Eero |title=Wood Chemistry: Fundamentals and Applications |year=1993 |publisher=Academic Press, Inc. |location=San Diego, CA |isbn=978-0-12-647481-7 |url=https://books.google.com/books?id=Sv3xcS6eS5QC&pg=PA187}}</ref> It is often used in conjunction with oxygen and hydrogen peroxide to eliminate the need for chlorine-containing compounds in the manufacture of high-quality, white [[paper]].<ref>{{cite journal
|last1=Su
|first1=Yu-Chang
|last2=Chen
|first2=Horng-Tsai
|title=Enzone Bleaching Sequence and Color Reversion of Ozone-Bleached Pulps
|journal=Taiwan Journal of Forest Science
|volume=16
|issue=2
|pages=93–102
|year=2001
|url=http://www.tfri.gov.tw/enu/pub_science_in.aspx?pid=339&catid0=37&catid1=64&pg0=&pg1=1
|access-date=2007-08-31
|archive-url=https://web.archive.org/web/20101014002621/http://www.tfri.gov.tw/enu/pub_science_in.aspx?pid=339&catid0=37&catid1=64&pg0=&pg1=1
|archive-date=2010-10-14
}}</ref>

Ozone can be used to detoxify [[cyanide]] wastes (for example from [[gold]] and [[silver]] [[mining]]) by oxidising cyanide to [[cyanate]] and eventually to [[carbon dioxide]].<ref>{{cite book |last=Bollyky |first=L. J. |title=Ozone Treatment of Cyanide-Bearing Wastes, EPA Report 600/2-77-104 |year=1977 |publisher=U.S. Environmental Protection Agency |location=Research Triangle Park, N.C.}}</ref>

===Water disinfection===
Since the invention of [[dielectric barrier discharge]] (DBD) plasma reactors, it has been employed for water treatment with ozone.<ref>{{cite journal |last1=Siemens |first1=Werner |title=About the electrostatic induction and the delay of the current in bottle wires. |date=1857 |journal=Annals of Physics |volume=178 |issue=9 |page=66 |doi=10.1002/andp.18571780905}}</ref> However, with cheaper alternative disinfectants like chlorine, such applications of DBD ozone water decontamination have been limited by high power consumption and bulky equipment.<ref name="auto">{{cite news |last1=US Environmental Protection Agency. |title=Drinking Water Treatability Database.|date=2009 }}</ref><ref name="Trihalomethane formation during che">{{cite journal |last1=Sorlini |first1=Sabrina |last2=Collivignarelli |first2=Carlo |title=Trihalomethane formation during chemical oxidation with chlorine, chlorine dioxide and ozone of ten Italian natural waters |date=2005 |journal=Desalination |volume=176 |issue=1–3 |pages=103–111 |bibcode=2005Desal.176..103S |doi=10.1016/j.desal.2004.10.022}}</ref> Despite this, with research revealing the negative impacts of common disinfectants like chlorine with respect to toxic residuals and ineffectiveness in killing certain micro-organisms,<ref>{{cite journal |last1=Gallard |first1=Hervé |last2=Gunten |first2=Urs von |title=Chlorination of natural organic matter: kinetics of chlorination and of THM formation. |date=2002 |journal=Water Research |volume=36 |issue=1 |pages=65–74 |bibcode=2002WatRe..36...65G |pmid=11766819 |doi=10.1016/S0043-1354(01)00187-7|url=http://infoscience.epfl.ch/record/167307 }}</ref> DBD plasma-based ozone decontamination is of interest in current available technologies. Although ozonation of water with a high concentration of bromide does lead to the formation of undesirable brominated disinfection byproducts, unless drinking water is produced by desalination, ozonation can generally be applied without concern for these byproducts.<ref name="Trihalomethane formation during che"/><ref>{{cite news |last1=Croué |first1=J. P. |last2=Koudjonou |first2=B. K. |last3=Legube |first3=B. |title=Parameters affecting the formation of bromate ion during ozonation.|date=1996 }}</ref><ref>{{cite journal |last1=Siddiqui |first1=Mohamed S. |last2=Amy |first2=Gary L. |title=Factors affecting DBP formation during ozone–bromide reactions. |date=1993 |journal=American Water Works Association |volume=85 |issue=1 |pages=63–72 |bibcode=1993JAWWA..85a..63S |doi=10.1002/j.1551-8833.1993.tb05922.x}}</ref><ref>{{cite news |last1=World Health Organization. |title=Atrazine in drinking-water: background document for development of WHO guidelines for drinking-water quality|date=2003 }}</ref> Advantages of ozone include high thermodynamic oxidation potential, less sensitivity to organic material and better tolerance for pH variations while retaining the ability to kill bacteria, fungi, viruses, as well as spores and cysts.<ref>{{cite journal |last1=Khadre |first1=M. A. |last2=Yousef |first2=A. E. |last3=Kim |first3=J-G. |title=Microbiological aspects of ozone applications in food: a review. |date=2001 |journal=Journal of Food Science |volume=66 |issue=9 |pages=1242–1252 |doi=10.1111/j.1365-2621.2001.tb15196.x}}</ref><ref>{{cite journal |last1=Mujovic |first1=Selman |last2=Foster |first2=John E. |title=Plasma Physics and Chemistry for Water Reuse: Scaling the Plasma-Water Interface as an AOP Alternative |date=2018 |journal=Proceedings of the Water Environment Federation 2018 |volume=15 |pages=1969–1983}}</ref><ref>{{cite journal |last1=Guzel-Seydim |first1=Zeynep B. |last2=Greene |first2=Annel K. |last3=Seydim |first3=A. C. |title=Use of ozone in the food industry |date=2004 |journal=LWT - Food Science and Technology |volume=37 |issue=4 |pages=453–460 |doi=10.1016/j.lwt.2003.10.014}}</ref> Although, ozone has been widely accepted in Europe for decades, it is sparingly used for decontamination in the U.S. due to limitations of high-power consumption, bulky installation and stigma attached with ozone toxicity.<ref name="auto"/><ref>{{cite journal |last1=Weschler |first1=Charles J. |title=Ozone in indoor environments: concentration and chemistry. |date=2000 |journal=Indoor Air |volume=10 |issue=4 |pages=269–288 |bibcode=2000InAir..10..269W |pmid=11089331 |doi=10.1034/j.1600-0668.2000.010004269.x |doi-access=free}}</ref> Considering this, recent research efforts have been directed toward the study of effective ozone water treatment systems.<ref>{{cite journal |last1=Choudhury |first1=Bhaswati |last2=Portugal |first2=Sherlie |last3=Mastanaiah |first3=Navya |last4=Johnson |first4=Judith A. |last5=Roy |first5=Subrata |title=Inactivation of ''Pseudomonas aeruginosa'' and Methicillin-resistant ''Staphylococcus aureus'' in an open water system with ozone generated by a compact, atmospheric DBD plasma reactor. |date=2018 |journal=Scientific Reports |volume=8 |issue=1 |page=17573 |bibcode=2018NatSR...817573C |pmid=30514896 |doi=10.1038/s41598-018-36003-0 |pmc=6279761}}</ref> Researchers have looked into lightweight and compact low power surface DBD reactors,<ref>{{cite journal |last1=Choudhury |first1=Bhaswati |last2=Portugal |first2=Sherlie |last3=Johnson |first3=Judith A. |last4=Roy |first4=Subrata |title=Performance evaluation of fan and comb shaped plasma reactors for distribution of generated ozone in a confined space. |date=2020 |journal=AIAA Scitech 2020 Forum |page=1165}}</ref><ref>{{cite patent |country=US |number=10,651,014 |status=Issued |title=Compact portable plasma reactor |gdate=May 12, 2020. |fdate=05/12/2020 |invent1=Subrata Roy |invent2=Sherlie Portugal}}</ref> energy efficient volume DBD reactors<ref>{{cite journal |last1=Draou |first1=Abdelkader |last2=Nemmich |first2=Said |last3=Nassour |first3=Kamel |last4=Benmimoun |first4=Youcef |last5=Tilmatine |first5=Amar |title=Experimental analysis of a novel ozone generator configuration for use in water treatment applications. |date=2019 |journal=International Journal of Environmental Studies |volume=76 |issue=2 |pages=338–350 |bibcode=2019IJEnS..76..338D |doi=10.1080/00207233.2018.1499698 |s2cid=105285760}}</ref> and low power micro-scale DBD reactors.<ref>{{cite journal |last1=Zito |first1=Justin C. |last2=Durscher |first2=Ryan J. |last3=Soni |first3=Jignesh |last4=Roy |first4=Subrata |last5=Arnold |first5=David P. |title=Flow and force inducement using micron size dielectric barrier discharge actuators. |date=2012 |journal=Applied Physics Letters |volume=100 |issue=19 |page=193502 |bibcode=2012ApPhL.100s3502Z |doi=10.1063/1.4712068}}</ref><ref>{{cite journal |last1=Kuvshinov |first1=Dmitriy |last2=Lozano-Parada |first2=Jaime |last3=Siswanto |first3=Anggun |last4=Zimmerman |first4=William |title=Efficient compact micro DBD plasma reactor for ozone generation for industrial application in liquid and gas phase systems |date=2014 |journal=International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering |volume=8 |issue=1}}</ref> Such studies can help pave the path to re-acceptance of DBD plasma-based ozone decontamination of water, especially in the U.S.

===Consumers===
{{See also|Air purifier#Potential ozone hazards}}

Ozone levels which are safe for people are ineffective at killing fungi and bacteria.<ref name="CARB">{{cite web |title=An Investigation of Ozone Emissions From Consumer Products |author=CARB Indoor Air Quality Group |date=January 5, 2021 |url=https://ww2.arb.ca.gov/resources/fact-sheets/ozone-emissions-consumer-products-study}}</ref> Some consumer disinfection and cosmetic products emit ozone at levels harmful to human health.<ref name="CARB"/>

Devices generating high levels of ozone, some of which use ionisation, are used to sanitise and deodorise uninhabited buildings, rooms, ductwork, woodsheds, boats, and other vehicles.

Ozonated water is used to launder clothes and to sanitise food, drinking water, and surfaces in the home. According to the [[U.S. Food and Drug Administration]] (FDA), it is "amending the [[food additive]] regulations to provide for the safe use of ozone in gaseous and aqueous phases as an [[antimicrobial|antimicrobial agent]] on food, including meat and poultry." Studies at [[California Polytechnic State University|California Polytechnic University]] demonstrated that 0.3&nbsp;μmol/mol levels of ozone dissolved in filtered tapwater can produce a reduction of more than 99.99% in such food-borne microorganisms as salmonella, ''E. coli'' 0157:H7 and ''Campylobacter''. This quantity is 20,000 times the [[World Health Organization|WHO]]-recommended limits stated above.<ref name="food">{{cite web |last=Montecalvo |first=Joseph |author2=Doug Williams |title=Application of Ozonation in Sanitizing Vegetable Process Washwaters |publisher=California Polytechnic State University |url=http://www.cwtozone.com/files/articles/Food_Produce/Article%20-%20Veg.%20Process%20washwater.pdf |access-date=2008-03-24  |archive-url=https://web.archive.org/web/20080528140629/http://www.cwtozone.com/files/articles/Food_Produce/Article%20-%20Veg.%20Process%20washwater.pdf |archive-date=May 28, 2008}}</ref><ref>{{cite web |last=Long |first=Ron |year=2008 |title=POU Ozone Food Sanitation: A Viable Option for Consumers & the Food Service Industry |url=http://www.purityintl.com/Article%20POU.pdf |url-status=usurped |archive-url=https://web.archive.org/web/20110715132442/http://www.purityintl.com/Article%20POU.pdf |archive-date=2011-07-15}} (the report also shows that tapwater removes 99.95% of pathogens from lettuce; samples were inoculated with pathogens before treatment)</ref>

Ozone can be used to remove [[pesticide]] residues from [[fruit]]s and [[vegetable]]s.<ref>{{cite web |last=Tersano Inc |year=2007 |title=lotus Sanitises Food without Chemicals |url=http://www.tersano.com/sanitizing_system_food.shtml |access-date=2007-02-11 |archive-url=https://web.archive.org/web/20070211025555/http://www.tersano.com/sanitizing_system_food.shtml |archive-date=2007-02-11}}</ref><ref name="fruit">{{cite book |title=Improving the Safety of Fresh Fruit and Vegetables |last=Jongen |first=W |year=2005 |publisher=Woodhead Publishing Ltd |location=Boca Raton |isbn=978-1-85573-956-7}}</ref>

Ozone is used in homes and [[hot tub]]s to kill bacteria in the water and to reduce the amount of chlorine or bromine required by reactivating them to their free state. Since ozone does not remain in the water long enough, ozone by itself is ineffective at preventing cross-contamination among bathers and must be used in conjunction with [[halogens]]. Gaseous ozone created by ultraviolet light or by corona discharge is injected into the water.<ref>{{cite web |title=Alternative Disinfectants and Oxidant Guidance Manual |date=April 1999 |publisher=[[United States Environmental Protection Agency]] |url=http://water.epa.gov/lawsregs/rulesregs/sdwa/mdbp/upload/2001_07_13_mdbp_alternative_disinfectants_guidance.pdf |archive-url=https://web.archive.org/web/20110212093610/http://water.epa.gov/lawsregs/rulesregs/sdwa/mdbp/upload/2001_07_13_mdbp_alternative_disinfectants_guidance.pdf |archive-date=February 12, 2011 |access-date=2008-01-14}}</ref>

Ozone is also widely used in the treatment of water in aquariums and fishponds. Its use can minimise bacterial growth, control parasites, eliminate transmission of some diseases, and reduce or eliminate "yellowing" of the water. Ozone must not come in contact with fishes' gill structures. Natural saltwater (with life forms) provides enough "instantaneous demand" that controlled amounts of ozone activate bromide ions to [[hypobromous acid]], and the ozone entirely decays in a few seconds to minutes. If oxygen-fed ozone is used, the water will be higher in dissolved oxygen and fishes' gill structures will atrophy, making them dependent on oxygen-enriched water.

===Aquaculture===
{{Redirect|Ozonation|the chemical reaction|ozonolysis}}
Ozonation – a process of infusing water with ozone&nbsp;– can be used in aquaculture to facilitate organic breakdown. Ozone is also added to recirculating systems to reduce [[nitrite]] levels<ref name="Noble">{{cite journal |last1=Noble |first1=A.C. |last2=Summerfelt |first2=S.T. |year=1996 |title=Diseases encountered in rainbow trout cultured in recirculating systems |journal=Annual Review of Fish Diseases |volume=6 |pages=65–92 |doi=10.1016/S0959-8030(96)90006-X |bibcode=1996AnFD....6...65N |doi-access=free}}</ref> through conversion into [[nitrate]]. If nitrite levels in the water are high, nitrites will also accumulate in the blood and tissues of fish, where it interferes with oxygen transport (it causes oxidation of the heme-group of [[haemoglobin]] from ferrous ({{chem|Fe|2+}}) to ferric ({{chem|Fe|3+}}), making haemoglobin unable to bind {{chem|O|2}}).<ref name="Ferreira">{{cite journal |last1=Ferreira |first1=O |last2=de Costa |first2=O.T. |last3=Ferreira |first3=Santos |last4=Mendonca |first4=F. |year=2004 |title=Susceptibility of the Amazonian fish, Colossoma macropomum (Serrasalminae), to short-term exposure to nitrite |journal=Aquaculture |volume=232 |issue=1–4 |pages=627–636 |bibcode=2004Aquac.232..627F |doi=10.1016/S0044-8486(03)00524-6}}</ref> Despite these apparent positive effects, ozone use in recirculation systems has been linked to reducing the level of bioavailable iodine in salt water systems, resulting in iodine deficiency symptoms such as goitre and decreased growth in Senegalese sole (''[[Solea senegalensis]]'') larvae.<ref>{{cite journal |last1=Ribeiro |first1=A.R.A. |last2=Ribeiro |first2=L. |last3=Saele |first3=Ø. |last4=Hamre |first4=K. |last5=Dinis |first5=M.T. |last6=Moren |first6=M. |title=Iodine-enriched rotifers andArtemiaprevent goitre in Senegalese sole (Solea senegalensis) larvae reared in a recirculation system |journal=Aquaculture Nutrition |year=2009 |volume=17 |issue=3 |pages=248–257 |doi=10.1111/j.1365-2095.2009.00740.x}}</ref>

Ozonate seawater is used for surface disinfection of [[haddock]] and [[Atlantic halibut]] eggs against nodavirus. Nodavirus is a lethal and vertically transmitted virus which causes severe mortality in fish. Haddock eggs should not be treated with high ozone level as eggs so treated did not hatch and died after 3–4 days.<ref>{{cite journal |last1=Buchan |first1=K. |last2=Martin-Robinchaud |first2=D. |last3=Benfey |first3=T.J. |last4=MacKinnon |year=2006 |first4=A |last5=Boston |first5=L |title=The efficacy of ozonated seawater for surface disinfection of haddock (Melanogrammus aeglefinus) eggs against piscine nodavirus |journal=Aquacultural Engineering |volume=35 |issue=1 |pages=102–107 |bibcode=2006AqEng..35..102B |doi=10.1016/j.aquaeng.2005.10.001}}</ref>

===Agriculture===
Ozone application on freshly cut pineapple and banana shows increase in flavonoids and total phenol contents when exposure is up to 20 minutes. Decrease in [[ascorbic acid]] (one form of [[vitamin C]]) content is observed but the positive effect on total phenol content and flavonoids can overcome the negative effect.<ref>{{cite journal |last1=Alothman |first1=M. |last2=Kaur |first2=B. |last3=Fazilah |first3=A. |last4=Bhat |year=2010 |first4=Rajeev |last5=Karim |first5=Alias A. |title=Ozone-induced changes of antioxidant capacity of fresh-cut tropical fruits |journal=Innovative Food Science and Emerging Technologies |volume=11 |issue=4 |pages=666–671 |doi=10.1016/j.ifset.2010.08.008}}</ref> Tomatoes upon treatment with ozone show an increase in β-carotene, lutein and lycopene.<ref>{{cite journal |last1=Tzortzakis |first1=N. |last2=Borland |first2=A. |last3=Singleton |first3=I. |year=2007 |last4=Barnes |first4=J |title=Impact of atmospheric ozone-enrichment on quality-related attributes of tomato fruit |journal=Postharvest Biology and Technology |volume=45 |issue=3 |pages=317–325 |doi=10.1016/j.postharvbio.2007.03.004 |bibcode=2007PosBT..45..317T }}</ref> However, ozone application on strawberries in pre-harvest period shows decrease in ascorbic acid content.<ref>{{cite journal |last1=Keutgen |first1=A.J. |last2=Pawelzik |first2=E. |year=2008 |title=Influence of pre-harvest ozone exposure on quality of strawberry fruit under simulated retail conditions |journal=Postharvest Biology and Technology |volume=49 |issue=1 |pages=10–18 |doi=10.1016/j.postharvbio.2007.12.003|bibcode=2008PosBT..49...10K |url=https://resolver.sub.uni-goettingen.de/purl?gro-2/15685 }}</ref>

Ozone facilitates the extraction of some heavy metals from soil using [[EDTA]]. EDTA forms strong, water-soluble coordination compounds with some heavy metals ([[lead|Pb]] and [[zinc|Zn]]) thereby making it possible to dissolve them out from contaminated soil. If contaminated soil is pre-treated with ozone, the extraction efficacy of [[lead|Pb]], [[americium|Am]], and [[plutonium|Pu]] increases by 11.0–28.9%,<ref>{{cite journal |last1=Lestan |first1=D. |last2=Hanc |first2=A. |last3=Finzgar |first3=N. |year=2005 |title=Influence of ozonation on extractability of Pb and Zn from contaminated soils |journal=Chemosphere |volume=61 |issue=7 |pages=1012–1019 |bibcode=2005Chmsp..61.1012L |pmid=16257321 |doi=10.1016/j.chemosphere.2005.03.005}}</ref> 43.5%<ref name="Plaue">{{cite journal |last1=Plaue |first1=J.W. |last2=Czerwinski |first2=K.R. |year=2003 |title=The influence of ozone on ligand-assisted extraction of 239Pu and 241Am from rocky flats soil |journal=Radiochim. Acta |volume=91 |issue=6–2003 |pages=309–313 |doi=10.1524/ract.91.6.309.20026 |s2cid=96019177}}</ref> and 50.7%<ref name="Plaue"/> respectively.

===Effect on pollinators===
Crop pollination is an essential part of an ecosystem. Ozone can have detrimental effects on plant-pollinator interactions.<ref>{{cite journal |last=Otieno |first=Mark |title=Interactive effects of ozone and carbon dioxide on plant-pollinator interactions and yields in a legume crop |date=October 2022 |journal=Environmental Advances |volume=9 |article-number=100285 |bibcode=2022EnvAd...900285O |doi=10.1016/j.envadv.2022.100285 |doi-access=free}}</ref> Pollinators carry pollen from one plant to another. This is an essential cycle inside of an ecosystem. Causing changes in certain atmospheric conditions around pollination sites or with xenobiotics could cause unknown changes to the natural cycles of pollinators and flowering plants. In a study conducted in North-Western Europe, crop pollinators were negatively affected more when ozone levels were higher.<ref name="Rollin-2022">{{cite journal |last=Rollin |first=Orianne |title=Effects of ozone air pollution on crop pollinators and pollination |date=July 2022 |journal=Global Environmental Change |volume=75 |article-number=102529 |bibcode=2022GEC....7502529R |via=Elsevier Science Direct |doi=10.1016/j.gloenvcha.2022.102529 |s2cid=249086005 |url=https://www.sciencedirect.com/science/article/abs/pii/S095937802200067X}}</ref>

===Alternative medicine===
{{See also|Ozone therapy}}
The use of ozone for the treatment of medical conditions is not supported by high quality evidence, and is generally considered [[alternative medicine]].<ref name=ACS>{{cite web |title=Oxygen Therapy |publisher=[[American Cancer Society]] |url=http://www.cancer.org/Treatment/TreatmentsandSideEffects/ComplementaryandAlternativeMedicine/PharmacologicalandBiologicalTreatment/oxygen-therapy |access-date=29 November 2012 |url-status=unfit |archive-url=https://web.archive.org/web/20120321213742/http://www.cancer.org/Treatment/TreatmentsandSideEffects/ComplementaryandAlternativeMedicine/PharmacologicalandBiologicalTreatment/oxygen-therapy |archive-date=March 21, 2012}}</ref>

==See also==
* [[Chappuis absorption]]
* [[Cyclic ozone]]
* [[Global Ozone Monitoring by Occultation of Stars]] (GOMOS)
* [[International Day for the Preservation of the Ozone Layer]] (September 16)
* [[Lightning]]
* [[NOx|Nitrogen oxides]]
* [[Ozone depletion]], including the phenomenon known as the [[Vienna Convention for the Protection of the Ozone Layer|ozone hole]].
* [[Ozone monitor]]
* [[Ozone monitoring instrument]]
* [[Ozone therapy]]
* [[Ozoneweb]]
* [[Ozonide]] (ion)
* [[Ozonolysis]]
* [[Polymer degradation]]
* [[Sterilization (microbiology)]]

==References==
'''Footnotes'''
{{Notelist}}

'''Citations'''
{{Reflist}}

==Further reading==
* {{Greenwood&Earnshaw2nd}}
* Becker, K. H., U. Kogelschatz, K. H. Schoenbach, R. J. Barker (ed.). ''Non-Equilibrium Air Plasmas at Atmospheric Pressure''. Series in Plasma Physics. Bristol and Philadelphia: Institute of Physics Publishing Ltd; {{ISBN|0-7503-0962-8}}; 2005
* United States Environmental Protection Agency. Risk and Benefits Group. (August 2014). ''[https://purl.fdlp.gov/GPO/gpo54607 Health Risk and Exposure Assessment for Ozone: Final Report]''.

==External links==
{{External links|section|date=June 2023}}
{{Commons category}}
* [https://ioa-pag.org/ International Ozone Association]
* [http://www.eea.europa.eu/maps/ozone/welcome European Environment Agency's near real-time ozone map (ozoneweb)]
* [http://www.nasa.gov/vision/earth/environment/ozone_resource_page.html NASA's Ozone Resource Page] {{Webarchive|url=https://web.archive.org/web/20130406111342/http://www.nasa.gov/vision/earth/environment/ozone_resource_page.html |date=2013-04-06}}
* [https://www.osha.gov/dts/chemicalsampling/data/CH_259300.html OSHA Ozone Information] {{Webarchive|url=https://web.archive.org/web/20160120052750/https://www.osha.gov/dts/chemicalsampling/data/CH_259300.html |date=2016-01-20}}
* [http://www.vega.org.uk/video/programme/111 Paul Crutzen Interview]—Video of Nobel Laureate Paul Crutzen talking to Nobel Laureate Harry Kroto by the Vega Science Trust
* [https://web.archive.org/web/19991013075147/http://earthobservatory.nasa.gov/Library/Ozone/ozone.html NASA's Earth Observatory article on Ozone]
* [http://www.inchem.org/documents/icsc/icsc/eics0068.htm International Chemical Safety Card 0068]
* [https://www.cdc.gov/niosh/npg/npgd0476.html NIOSH Pocket Guide to Chemical Hazards]
* [https://web.archive.org/web/20071029172649/http://www.niehs.nih.gov/health/topics/agents/ozone/ National Institute of Environmental Health Sciences, Ozone Information]
* [http://www.giss.nasa.gov/research/news/20060314/ NASA Study Links "Smog" to Arctic Warming]—[[Goddard Space Flight Center|NASA Goddard]] Institute for Space Studies (GISS) study shows the warming effect of ozone in the Arctic during winter and spring.
* [https://web.archive.org/web/20080913213217/http://ownyourair.org/ozone.html Ground-level ozone information from the American Lung Association of New England]

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