Ozone
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225297484
2008-07-12T23:19:42Z
69.248.33.39
{{Chembox new
| Name = Ozone
| ImageFile = Ozone-1,3-dipole.png
| ImageSize = 150px
| ImageFileL2 = Ozone-3D-vdW.png
| ImageSizeL2 = 125px
| ImageFileR2 = Ozone-elpot-3D-vdW.png
| ImageSizeR2 = 125px
| IUPACName = Trioxygen
| Section1 = {{Chembox Identifiers
| CASNo = 10028-15-6
}}
| Section2 = {{Chembox Properties
| Formula = O<sub>3</sub>
| MolarMass = 47.998 g·mol<sup>−1</sup>
| Appearance = bluish colored gas
| Density = 2.144 g·L<sup>−1</sup> (0 °C), gas
| Solubility = 0.105 g·100mL<sup>−1</sup> (0 °C)
| MeltingPt = 80.7 K, −192.5 °C
| BoilingPt = 161.3 K, −111.9 °C
}}<!--
| [[Triple point]]
| 80.6 K, 0.0114 mbar
|-
|Classification/shape
| AX2E
|-
-->
| Section4 = {{Chembox Thermochemistry
| DeltaHf = +142.3 kJ·mol<sup>−1</sup>
| Entropy = 237.7 J·K<sup>−1</sup>.mol<sup>−1</sup>
}}
| Section7 = {{Chembox Hazards
| EUClass = not listed}}
}}
{{Otheruses}}
'''Ozone''' or '''trioxygen''' ('''O<sub>3</sub>''') is a triatomic [[molecule]], consisting of three [[oxygen]] [[atom]]s. It is an [[allotrope]] of oxygen that is much less stable than the [[diatomic]] O<sub>2</sub>. Ground-level ozone is an [[air pollution|air pollutant]] with harmful effects on the respiratory systems of animals and humans. Ozone in the upper [[atmosphere]] filters potentially damaging [[ultraviolet light]] from reaching the [[Earth]]'s surface. It is present in low concentrations throughout the [[Earth's atmosphere]]. It has many industrial and consumer applications.
Ozone, the first allotrope of a chemical [[element]] to be recognized by science, was proposed as a distinct [[chemical compound]] by [[Christian Friedrich Schönbein]] in 1840, who named it after the [[Greek language|Greek]] word for smell (''ozein''), from the peculiar odor in [[lightning]] storms.<ref name="ozo">{{cite journal |last=Rubin |first=Mordecai B. |authorlink= |coauthors= |year=2001 |month= |title=The History of Ozone. The Schönbein Period, 1839-1868 |journal=Bull. Hist. Chem. |volume=26 |issue= 1|pages= |id= |url=http://www.scs.uiuc.edu/~mainzv/HIST/awards/OPA%20Papers/2001-Rubin.pdf |accessdate= 2008-02-28 |quote= }}</ref><ref>{{cite web | url=http://www.todayinsci.com/10/10_18.htm#Schonbein | title=Today in Science History | accessdate=2006-05-10}}</ref> The 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
| issue =
| pages = 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 | url=http://gcmd.gsfc.nasa.gov/Resources/FAQs/ozone.html | title=Ozone FAQ | publisher=Global Change Master Directory | accessdate=2006-05-10}}</ref>
==Physical properties==
Most people can detect about 0.01 [[Parts-per notation|ppm]] in air. Exposure of 0.1 to 1 ppm produces headaches, burning eyes, and irritation to the respiratory passages.<ref name=brown>{{cite book
|last = Brown
|first = Theodore L.
|coauthors = H. Eugene LeMay Jr., Bruce E. Bursten, Julia R. Burdge
|editor = Nicole Folchetti
|title = Chemistry: The Central Science
|edition = 9th Edition
|origdate = 1977
|date = 2003
|publisher = Pearson Education
|language = English
|isbn = 0-13-066997-0
|pages = pp. 882-883
|chapter = 22
}}</ref>
Ozone is 1.5 times as dense as oxygen. At -112 °C, it forms a dark blue [[liquid]]. At temperatures below -193 °C, it forms a violet-black [[solid]].<ref>{{cite web
|title = Oxygen
|work = WebElements
|url = http://www.webelements.com/webelements/scholar/print/oxygen/key.html
|accessdate = 2006-09-23
}}</ref>
Ozone is [[diamagnetic]], meaning that it will resist formation of a [[magnetic field]] and will decrease the energy stored in the field once the field is established.
==Structure==
The structure of ozone, according to experimental evidence from [[microwave spectroscopy]], is bent, with C<sub>2v</sub> [[molecular symmetry|symmetry]] (similar to the [[water]] molecule), O – O distance of 127.2 pm and O – O – O angle of 116.78°.<ref>Takehiko Tanaka; Yonezo Morino. Coriolis interaction and anharmonic potential function of ozone from the microwave spectra in the excited vibrational states ''Journal of Molecular Spectroscopy'' '''1970''', ''33'', 538–551.</ref> The central atom forms an ''sp''² hybridization with one lone pair. Ozone is a polar molecule with a [[dipole moment]] of 0.5337 [[Debye|D]].<ref>Kenneth M. Mack; J. S. Muenter. Stark and Zeeman properties of ozone from molecular beam spectroscopy. ''Journal of Chemical Physics'' '''1977''', ''66'', 5278–5283. {{doi|10.1063/1.433909}}</ref> The bonding is [[single bond]] on one side and [[double bond]] on the other side, and these bonds are blended to become known as [[resonance structures]]. The [[bond order]] is 1.5 for each side.
==Chemistry==
Ozone is a powerful [[oxidizing]] agent, far better than dioxygen. It is also unstable at high concentrations, decaying to ordinary diatomic oxygen (in about half an hour in atmospheric conditions<ref>[http://gcmd.gsfc.nasa.gov/Resources/FAQs/ozone.html Earth Science FAQ: Where can I find information about the ozone hole and ozone depletion?] ''Goddard Space Flight Center'', National Aeronautics and Space Administration, March 2008.</ref>):
:2 O<sub>3</sub> → 3 O<sub>2</sub>
This reaction proceeds more rapidly with increasing temperature and decreasing pressure. [[Deflagration]] of ozone can be triggered by a spark, and can occur in ozone concentrations of 10 wt%<!--what's this mean?--> or higher.
===Metals===
Ozone will oxidize [[metal]]s (except [[gold]], [[platinum]], and [[iridium]]) to [[oxide]]s of the metals in their highest [[oxidation state]]:
: 2 Cu<sup>1+</sup><sub>(aq)</sub> + 2 H<sub>3</sub>O<sup>+</sup><sub>(aq)</sub> + O<sub>3</sub><sub>(g)</sub> → 2 Cu<sup>2+</sup><sub>(aq)</sub> + 3 H<sub>2</sub>O<sub>(l)</sub> + O<sub>2</sub><sub>(g)</sub>
===Non-metals===
Ozone also increases the oxidation number of oxides:
: [[Nitric oxide|NO]] + O<sub>3</sub> → [[Nitrogen dioxide|NO<sub>2</sub>]] + O<sub>2</sub>
The above reaction is accompanied by [[chemiluminescence]]. The NO<sub>2</sub> can be further oxidized:
: NO<sub>2</sub> + O<sub>3</sub> → NO<sub>3</sub> + O<sub>2</sub>
The NO<sub>3</sub> formed can react with NO<sub>2</sub> to form [[Dinitrogen pentoxide|N<sub>2</sub>O<sub>5</sub>]]:
: NO<sub>2</sub> + NO<sub>3</sub> → N<sub>2</sub>O<sub>5</sub>
Ozone reacts with [[carbon]] to form [[carbon dioxide]], even at room temperature:
: C + 2 O<sub>3</sub> → CO<sub>2</sub> + 2 O<sub>2</sub>
Ozone does not react with ammonium [[salt]]s but it reacts with [[ammonia]] to form [[ammonium nitrate]]:
: 2 [[Ammonia|NH<sub>3</sub>]] + 4 O<sub>3</sub> → NH<sub>4</sub>NO<sub>3</sub> + 4 O<sub>2</sub> + H<sub>2</sub>O
Ozone reacts with [[sulfide]]s to make [[sulfate]]s:
: [[Lead(II) sulfide|PbS]] + 4 O<sub>3</sub> → [[Lead(II) sulfate|PbSO<sub>4</sub>]] + 4 O<sub>2</sub>
[[Sulfuric acid]] can be produced from ozone, starting either from elemental [[sulfur]] or from [[sulfur dioxide]]:
: S + H<sub>2</sub>O + O<sub>3</sub> → H<sub>2</sub>SO<sub>4</sub>
: 3 SO<sub>2</sub> + 3 H<sub>2</sub>O + O<sub>3</sub> → 3 H<sub>2</sub>SO<sub>4</sub>
All three [[atom]]s of ozone may also react, as in the reaction with [[tin]](II) chloride and [[hydrochloric acid]] and NaCl along with Ammonium Nitrate:
: 3 SnCl<sub>2</sub> + 6 HCl + O<sub>3</sub> → 3 SnCl<sub>4</sub> + 3 H<sub>2</sub>O
In the [[gas phase]], ozone reacts with [[hydrogen sulfide]] to form sulfur dioxide:
: H<sub>2</sub>S + O<sub>3</sub> → SO<sub>2</sub> + H<sub>2</sub>O
In an [[aqueous]] solution, however, two competing simultaneous reactions occur, one to produce elemental sulfur, and one to produce sulfuric acid:
: [[Hydrogen sulfide|H<sub>2</sub>S]] + O<sub>3</sub> → S + O<sub>2</sub> + H<sub>2</sub>O
: 3 H<sub>2</sub>S + 4 O<sub>3</sub> → 3 [[Sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]]
[[Iodine]] [[perchlorate]] can be made by treating iodine dissolved in cold [[anhydrous]] [[perchloric acid]] with ozone:
: I<sub>2</sub> + 6 HClO<sub>4</sub> + O<sub>3</sub> → 2 I(ClO<sub>4</sub>)<sub>3</sub> + 3 H<sub>2</sub>O
Solid [[nitryl]] perchlorate can be made from NO<sub>2</sub>, ClO<sub>2</sub>, and O<sub>3</sub> gases:
: 2 NO<sub>2</sub> + 2 ClO<sub>2</sub> + 2 O<sub>3</sub> → 2 NO<sub>2</sub>ClO<sub>4</sub> + O<sub>2</sub>
===Combustion===
Ozone can be used for [[combustion]] reactions and combusting gases; ozone provides higher temperatures than combusting in [[dioxygen]] (O<sub>2</sub>). Following is a reaction for the combustion of [[carbon subnitride]] which can also cause lower temperatures:
: 3 C<sub>4</sub>N<sub>2</sub> + 4 O<sub>3</sub> → 12 CO + 3 N<sub>2</sub>
Ozone can react at cryogenic temperatures. At 77 K (-196 °C), atomic [[hydrogen]] reacts with liquid ozone to form a hydrogen [[superoxide]] [[radical (chemistry)|radical]], which dimerizes:<ref>Horvath M., Bilitzky L., & Huttner J., 1985. "Ozone." pg 44–49</ref>
: H + O<sub>3</sub> → HO<sub>2</sub> + O
: 2 HO<sub>2</sub> → H<sub>2</sub>O<sub>4</sub>
===Ozonides===
Ozonides can be formed, which contain the [[ozonide]] anion, O<sub>3</sub><sup>-</sup>. These compounds are explosive and must be stored at cryogenic temperatures. Ozonides for all the [[alkali metal]]s are known. KO<sub>3</sub>, RbO<sub>3</sub>, and CsO<sub>3</sub> can be prepared from their respective superoxides:
: KO<sub>2</sub> + O<sub>3</sub> → KO<sub>3</sub> + O<sub>2</sub>
Although KO<sub>3</sub> can be formed as above, it can also be formed from [[potassium hydroxide]] and ozone:<ref>Housecroft & Sharpe, 2005. "Inorganic Chemistry." pg 439</ref>
: 2 KOH + 5 O<sub>3</sub> → 2 KO<sub>3</sub> + 5 O<sub>2</sub> + H<sub>2</sub>O
NaO<sub>3</sub> and LiO<sub>3</sub> must be prepared by action of CsO<sub>3</sub> in liquid NH<sub>3</sub> on an [[ion exchange resin]] containing Na<sup>+</sup> or Li<sup>+</sup> ions:<ref>Housecroft & Sharpe, 2005. "Inorganic Chemistry." pg 265</ref>
: CsO<sub>3</sub> + Na<sup>+</sup> → Cs<sup>+</sup> + NaO<sub>3</sub>
Treatment with ozone of [[calcium]] dissolved in ammonia leads to ammonium ozonide and not calcium ozonide:<ref>Horvath M., Bilitzky L., & Huttner J., 1985. "Ozone." pg 44–49</ref>
: 3 Ca + 10 NH<sub>3</sub> + 6 O<sub>3</sub> → Ca•6NH<sub>3</sub> + Ca(OH)<sub>2</sub> + Ca(NO<sub>3</sub>)<sub>2</sub> + 2 NH<sub>4</sub>O<sub>3</sub> + 2 O<sub>2</sub> + H<sub>2</sub>
===Applications===
Ozone can be used to remove [[manganese]] from the [[water]], forming a [[precipitate]] which can be filtered:
: 2 Mn<sup>2+</sup> + 2 O<sub>3</sub> + 4 H<sub>2</sub>O → 2 MnO(OH)<sub>2 (s)</sub> + 2 O<sub>2</sub> + 4 H<sup>+</sup>
Ozone will also turn [[cyanide]]s to the one thousand times less toxic [[cyanate]]s:
: CN<sup>-</sup> + O<sub>3</sub> → CNO<sup>-</sup> + O<sub>2</sub>
Finally, ozone will also completely decompose [[urea]]:<ref>Horvath M., Bilitzky L., & Huttner J., 1985. "Ozone." pg 259, 269–270</ref>
:(NH<sub>2</sub>)<sub>2</sub>CO + O<sub>3</sub> → N<sub>2</sub> + CO<sub>2</sub> + 2 H<sub>2</sub>O
==Ozone in Earth's atmosphere==
[[Image:Atmospheric ozone.svg|thumb|The distribution of atmospheric ozone in partial pressure as a function of altitude.]][[Image:Nimbus ozone Brewer-Dobson circulation.jpg|thumb|Concentration of ozone as measured by the [[Nimbus program|Nimbus-7]] satellite.]]
[[Image:IM ozavg ept 200006.png|thumb|Total ozone concentration in June 2000 as measured by EP-TOMS satellite instrument.]]
The standard way to express total ozone levels (the amount of ozone in a vertical column) in the atmosphere is by using [[Dobson unit]]s. Concentrations at a point are measured in [[Parts-per notation|parts per billion]] (ppb) or in μg/m³.
===Ozone layer===
{{main|Ozone layer}}
The highest levels of ozone in the atmosphere are in the [[stratosphere]], in a region also known as the [[ozone layer]] between about 10 km and 50 km above the surface (or between about 6 and 31 miles). Here it filters out [[photons]] with shorter wavelengths (less than 320 nm) of ultraviolet light, also called UV rays, (270 to 400 nm) from the [[Sun]] that would be harmful to most forms of [[life]] in large doses. These same wavelengths are also among those responsible for the production of [[vitamin D]], a vitamin also produced by the human body. Ozone in the stratosphere is mostly produced from ultraviolet rays reacting with oxygen:
:O<sub>2</sub> + [[photon]](radiation< 240 nm) → 2 O
:O + O<sub>2</sub> → O<sub>3</sub>
It is destroyed by the reaction with [[atomic oxygen]]:
:O<sub>3</sub> + O → 2 O<sub>2</sub>
The latter 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 recent decades the amount of ozone in the stratosphere has been declining mostly because of emissions of [[Haloalkane#Chlorofluoro compounds .28CFC.2C HCFC.29|CFC]]s and similar chlorinated and brominated organic molecules, which have increased the concentration of ozone-depleting catalysts above the natural background. Ozone only makes up 0.00006% of the atmosphere.
{{seealso|Ozone-oxygen cycle|Ozone depletion}}
===Low level ozone===
{{main|Tropospheric ozone|Photochemical smog}}
Low level ozone (or tropospheric ozone) is regarded as a pollutant by the [[World Health Organization]].<ref name=who-Europe>WHO-Europe reports: [http://www.who.dk/document/e79097.pdf Health Aspects of Air Pollution (2003)] (PDF)</ref> It is not emitted directly by [[Internal combustion engine|car engines]] or by industrial operations. It is formed by the reaction of sunlight on air containing [[Volatile organic compound|hydrocarbon]]s and [[nitrogen oxide]]s that react to form ozone directly at the source of the pollution or many kilometers down wind.
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]] OH 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 OH, and by reactions with OH and the peroxy radical HO<sub>2</sub>· (Stevenson et al, 2006).<ref>{{cite web |author =Stevenson et al| year=2006 | url=http://www.agu.org/pubs/crossref/2006/2005JD006338.shtml | title=Multimodel ensemble simulations of present-day and near-future tropospheric ozone| publisher=[[American Geophysical Union]] | accessdate=2006-09-16}}</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 | date=[[2003-07-31]] | url=http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2003/2003073015111.html | title=Rising Ozone Levels Pose Challenge to U.S. Soybean Production, Scientists Say | publisher=NASA Earth Observatory | accessdate=2006-05-10}}</ref><ref>{{cite web | last=Mutters | first=Randall | year=1999 | month=March | url=http://www.arb.ca.gov/research/abstracts/94-345.htm | title=Statewide Potential Crop Yield Losses From Ozone Exposure | publisher=California Air Resources Board | accessdate=2006-05-10}}</ref>
Certain examples of cities with elevated ozone readings are [[Houston, Texas]], and [[Mexico City, Mexico]]. Houston has a reading of around 41 ppb, while Mexico City is far more hazardous, with a reading of about 125 ppb.<ref>{{cite web | last=Mutters | first=Randall | year=1999 | month=March | url=http://www.arb.ca.gov/research/abstracts/94-345.htm | title=Statewide Potential Crop Yield Losses From Ozone Exposure | publisher=California Air Resources Board | accessdate=2006-05-10}}</ref>
====Ozone as a greenhouse gas====
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 | url=http://reports.eea.europa.eu/TOP08-98/en/page004.html | title=Tropospheric Ozone in EU - The consolidated report | publisher=European Environmental Agency | accessdate=2006-05-10}}</ref><ref>{{cite web | title=Atmospheric Chemistry and Greenhouse Gases | url=http://www.grida.no/climate/ipcc_tar/wg1/142.htm | publisher=Intergovernmental Panel on Climate Change | accessdate=2006-05-10}}</ref> This increase in ozone is of further concern because ozone present in the upper [[troposphere]] 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 scientific review on the [[climate change]] (the [[IPCC]] [[Third Assessment Report]]<ref>{{cite web | year=2001 | url=http://www.grida.no/climate/ipcc_tar/ | title=Climate Change 2001 | publisher=Intergovernmental Panel on Climate Change | accessdate=2006-09-12}}</ref>) suggests that the [[radiative forcing]] of tropospheric ozone is about 25% that of [[carbon dioxide]].
====Ozone cracking====
[[Image:Ozone cracks in tube1.jpg|thumb|left|200px|Ozone cracking in [[Natural rubber]] tubing]]
Ozone gas attacks any [[polymer]] possessing olefinic or [[double bond]]s within its chain structure, such materials including [[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 product and the concentration of ozone in the atmosphere. Such materials can be protected by adding anti-ozonants, 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 tires for example, but the problem is now seen only in very old tires. 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 are often made from reinforced rubber tubing and may also be susceptible to attack, especially within engine compartments where low levels of ozone are produced from electrical equipment.
==Health effects==
===Air pollution===
[[Image:US-ozone-non-attainment-2007-06.png|thumb|right|300px]]
There is a great deal of evidence to show that high concentrations of ozone, created by high concentrations of pollution and daylight UV rays at the earth's surface, 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)] (PDF)</ref> A connection has also been shown to exist between increased ozone caused by thunderstorms and hospital admissions of [[asthma]] sufferers..<ref> {{cite journal|first=W. |last =Anderson |coauthors = G.J. Prescott, S. Packham, J. Mullins, M. Brookes, and 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 | publisher = Oxford Journals |date=August 2001 |doi= 10.1093/qjmed/94.8.429| pmid = 11493720}}</ref> Air quality guidelines such as those from the World Health Organization are based on detailed studies of what levels can cause measurable [[health effect]]s.
A common British folk myth dating back to the [[Victorian era]] holds that the smell of the sea is caused by ozone, and that this smell has "bracing" health benefits.<ref>Ashfield District Council: [http://www.ashfield-dc.gov.uk/ccm/navigation/environment/pollution/air-pollution/monitored-air-pollutants/ Monitored Air Pollutants], downloaded [[February 2]], [[2007]]</ref> Neither of these is true. The characteristic "smell of the sea" is not caused by ozone but by the presence of [[dimethyl sulfide]] generated by [[phytoplankton]], and dimethyl sulfide, like ozone, is toxic in high concentrations.<ref>University of East Anglia press release, [http://comm.uea.ac.uk/press/release.asp?id=720 Cloning the smell of the seaside], [[February 2]], [[2007]]</ref>
The [[United States Environmental Protection Agency]] (EPA) has developed an Air Quality index to help explain air pollution levels to the general public. Eight-hour average ozone concentrations of 85 to 104 [[parts per notation|ppbv]] are described as "Unhealthy for Sensitive Groups", 105 ppbv to 124 ppbv as "unhealthy" and 125 ppb to 404 ppb as "very unhealthy".<ref>{{cite web | work = AIRNow.gov | title = Smog - Who does it hurt? What You Need to Know About Ozone and Your Health | url = http://www.airnow.gov/index.cfm?action=health2.smog1#4 | accessdate = 2007-07-10 }}</ref> The EPA has designated over 300 counties of the [[United States]], clustered around the most heavily populated areas (especially in [[California]] and the [[Northeastern United States|Northeast]]), as failing to comply with the [[National Ambient Air Quality Standards]].
Ozone can also be present in [[indoor air pollution]].
===Physiology===
{{seealso|trioxidane}}
Ozone, along with reactive forms of oxygen such as [[superoxide]], [[singlet oxygen]], [[hydrogen peroxide]], and [[hypochlorite]] ions, is naturally produced by [[white blood cell]]s and other biological systems (such as the roots of [[marigold]]s) 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]]. Ozone has been found to convert [[cholesterol]] in the [[Blood|blood stream]] to plaque (which causes hardening and narrowing of arteries). 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. A team headed by Dr. [http://www.iupac.org/organ/members/w/wentworth.html Paul Wentworth Jr]. of the Department of Chemistry at the [[Scripps Research Institute]] has shown 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| first=Roald |last=Hoffmann| journal=American Scientist | volume=92 | issue= 1|pages=23| date=January 2004 | url=http://www.americanscientist.org/template/AssetDetail/assetid/29647?&print=yes| doi=10.1511/2004.1.23 |accessdate=2006-10-11}}</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 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 | publisher = [[Elsevier]] | date = 1 August 2004
| url = http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+toxline:@term+@mh+%22+5,6-secosterol+%22+@OR+@na+%22+5,6-secosterol+%22+@OR+@ab+%22+5,6-secosterol+%22+@OR+@kw+%22+5,6-secosterol+%22
| doi = 10.1016/j.freeradbiomed.2004.04.024 | accessdate = 2008-05-17}}</ref> as well as a secondary condensation product via aldolization.<ref>{{cite web|title=Evidence for Ozone Formation in Human Atherosclerotic Arteries|url=http://www.sciencemag.org/cgi/content/full/302/5647/1053|author=Paul Wentworth|year=2003|month=November|accessdate=2006-08-03}}</ref>
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. | coauthors = Ángeles Calatayuda, Eva Barrenob, Eduardo Primo-Milloa and 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 | publisher = [[Elsevier]] | date = February-March 2006 | url = http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VRD-4JSF4VY-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=088005a9f3bd83a2de1605ca93f9461a] | doi = 10.1016/j.plaphy.2006.03.007 | accessdate = 2008-05-17 }}</ref>
==Production==
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 g/Nm³ or weight percent. The regime of applied concentrations ranges from 1 to 5 weight percent in air and from 6 to 14 weight percent in oxygen.
===Corona discharge method===
This is the most popular type of ozone generator for most industrial and personal uses. While variations of the "hot spark" coronal 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]].<ref>Organic Syntheses, Coll. Vol. 3, p.673 (1955); Vol. 26, p.63 (1946). ([http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0673 Article])</ref> They are typically very cost-effective and do not require an oxygen source other than the ambient air. 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 vapor and increase ozone production. 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 vapor, but also the bulk of the nitrogen.
===Ultraviolet light===
UV 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. |authorlink= |coauthors=W. J. Masschelein |year=1987 |journal=Ozone Sci. Eng. |month= |title=Photochemical Generation of Ozone: Present State-of-the-Art |volume=9 |issue= |pages=315–334 }}</ref>
While standard UV ozone generators tend to be less expensive, they usually produce ozone with a concentration of about 0.5% or lower. Another disadvantage of this method is that it requires the 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)|sterilization]], for example).
===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.
Cold plasma machines utilize pure oxygen as the input source and produce a maximum concentration of about 5% ozone. They produce far greater quantities of ozone in a given space of time compared to ultraviolet production. However, because cold plasma ozone generators are very expensive, they are found less frequently than the previous two types.
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.
Some cold plasma units also have the capability of producing short-lived allotropes of oxygen which include O<sub>4</sub>, O<sub>5</sub>, O<sub>6</sub>, O<sub>7</sub>, etc. These anions are even more reactive than ordinary O<sub>3</sub>.
===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 kg per hour, a gas/water tube heat-exchanger may be utilized as ground electrode and assembled with tubular high-voltage electrodes on the gas-side. The regime of typical gas pressures is around 2 [[Bar (unit)|bar]] absolute in oxygen and 3 bar absolute in air. Several megawatts of [[electric power|electrical power]] may be installed in large facilities, applied as one phase AC [[Electric current|current]] at 50 to 8000 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 few materials may be used like [[stainless steel]] (quality 316L), [[titanium]], [[aluminum]] (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 come 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 ageing of rubber samples.
===Incidental production===
Ozone may be formed from O<sub>2</sub> by electrical discharges and by action of high energy [[electromagnetic radiation]]. 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, and [[arc welding|arc welders]]. [[Electric motor]]s using [[brush (electric)|brush]]es can generate ozone from repeated [[spark gap|spark]]ing inside the unit. Large motors that use brushes, such as those used by elevators or hydraulic pumps, will generate more ozone than smaller motors.
===Laboratory production===
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 3M [[sulfuric acid]] [[electrolyte]].<ref>{{cite journal | last=Ibanez | first=Jorge G. | coauthors=Rodrigo Mayen-Mondragon and M. T. Moran-Moran | year=2005 | month=October | title=Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 7: Microscale Production of Ozone | journal=Journal of Chemical Education | volume=82 | number=10 | pages=1546 | url=http://jchemed.chem.wisc.edu/Journal/Issues/2005/Oct/abs1546.html | accessdate=2006-05-10}}</ref> The [[half cell]] reactions taking place are
: 3 H<sub>2</sub>O → O<sub>3</sub> + 6 H<sup>+</sup> + 6 e<sup>−</sup>; [[Table of standard electrode potentials|ΔE<sup>o</sup>]] = −1.53 [[Volt|V]];
: 6 H<sup>+</sup> + 6 e<sup>−</sup> → 3 H<sub>2</sub>; [[Table of standard electrode potentials|ΔE<sup>o</sup>]] = 0 [[Volt|V]];
: 2 H<sub>2</sub>O → O<sub>2</sub> + 4 H<sup>+</sup> + 4 e<sup>−</sup>; [[Table of standard electrode potentials|ΔE<sup>o</sup>]] = −1.23 [[Volt|V]];
so that 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 prepared by passing 10,000-20,000 [[volts]] [[Direct current|DC]] through dry O<sub>2</sub>. This can be done with an apparatus consisting of two concentric glass tubes sealed together at the top, with in and out spigots 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. Dry O<sub>2</sub> should be run through the tube in one spigot. As the O<sub>2</sub> is run through one spigot into the apparatus and 10,000-20,000 [[volts]] [[Direct current|DC]] are applied to the foil leads, [[electricity]] will discharge between the dry dioxygen in the middle and form O<sub>3</sub> in O<sub>2</sub> out the other spigot. The reaction can be summarized as follows:<ref name=brown />
: 3 O<sub>2</sub> — ''electricity'' → 2 O<sub>3</sub>
==Applications==
===Industry===
The largest use of ozone is in the preparation of [[pharmaceuticals]], [[synthetic lubricants]], as well as 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)|bleach]]ing substances and for killing microorganisms in air and water sources. Many municipal drinking water systems kill bacteria with ozone instead of the more common [[chlorine]].<ref>{{cite book |last=Hoigné |first= J.|authorlink= |coauthors= |title=Handbook of Environmental Chemistry, Vol. 5 part C, p83-141|year=1998 |publisher=Springer-Verlag |location=Berlin|isbn=
}}</ref> Ozone has a very high [[oxidation potential]].<ref>{{Cite web |url=http://www.ozone-information.com/Oxidation_Potential_Ozone.html | title=Oxidation Potential of Ozone| work= Ozone-Information.com| accessdate=2008-05-17}}</ref> Ozone does not form [[organochlorine]] compounds, nor does it remain in the water after treatment, so some systems introduce a small amount of chlorine to prevent [[bacterial growth]] in the pipes, or may use chlorine intermittently, based on results of periodic 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 odor in drinking water.
Low levels of ozone have been advertised to be of some disinfectant use in residential homes, however 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 where asthma patients start to have issues.
Industrially, ozone is used to:
* Disinfect laundry in hospitals, food factories, care homes etc;<ref>{{cite web | date=2007-04-01 | url=http://www.hdmagazine.co.uk/story.asp?storyCode=2043080 | title=Decontamination: Ozone scores on spores| work= Hospital Development | publisher=Wilmington Media Ltd. | accessdate=2007-05-30}}</ref>
* Disinfect water in place of chlorine<ref name=brown />
* Deodorize air and objects, such as after a fire. This process is extensively used in [[Fabric Restoration]];
* Kill bacteria on food or on contact surfaces;<ref name="food"/>
* Sanitize swimming pools and spas
* Scrub yeast and mold spores from the air in food processing plants;
* Wash fresh fruits and vegetables to kill yeast, mold and bacteria;<ref name="food"/>
* Chemically attack contaminants in water ([[iron]], [[arsenic]], [[hydrogen sulfide]], [[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 |url=http://www.ozone-information.com/Chemical_Synthesis_Ozone.html | title=Chemical Synthesis with Ozone| work= Ozone-Information.com| accessdate=2008-05-17}}</ref>
* Clean and bleach fabrics (the former use is utilized in Fabric Restoration; the latter use is patented);
* 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 in the U.S. and 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 | last =de Boer | first = Hero E. L. | coauthors = Carla M. van Elzelingen-Dekker, BSc; Cora M. F. van Rheenen-Verberg, BSc; Lodewijk Spanjaard, MD, PhD
| 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 | publisher = [[The University of Chicago Press]] | location = [[Chicago]] | date = October 2006 | url = http://www.journals.uchicago.edu/doi/abs/10.1086/507966 | doi = 10.1086/507966 | accessdate = 2008-05-17}}</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|authorlink= |coauthors= |title=Wood Chemistry: Fundamentals and Applications |year=1993 |publisher=Academic Press, Inc. |location=San Diego, CA |isbn=0-12-64748 }}</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> {{Citation
| last = Su
| first =Yu-Chang
| author-link =
| last2 =Chen
| first2 =Horng-Tsai
| author2-link =
| title =Enzone Bleaching Sequence and Color Reversion of Ozone-Bleached Pulps
| journal =Taiwan Journal of Forest Science
| volume =16
| issue =2
| pages =93–102
| date =
| year =2001
| url =http://www.tfri.gov.tw/enu/pub_science_in.aspx?pid=339&catid0=37&catid1=64&pg0=&pg1=1
| doi =
| id = }}
</ref>
Ozone can be used to detoxify [[cyanide]] wastes (for example from [[gold]] and [[silver]] [[mining]]) by oxidizing cyanide to [[cyanate]] and eventually to [[carbon dioxide]].<ref>{{cite book |last=Bollyky |first= L. J.|authorlink= |coauthors= |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>
===Consumers===
Devices generating high levels of ozone, some of which use ionization, are used to sanitize and deodorize uninhabited buildings, rooms, ductwork, woodsheds, and boats and other vehicles.
In the U.S., [[air purifier]]s emitting lower levels of ozone have been sold. This kind of air purifier is sometimes claimed to imitate nature's way of purifying the air<ref>{{cite web|url=http://www.youtube.com/watch?v=Ydb2_pyZeJk|title =The Unknown Truth Regarding Ozone!|accessdate =2006-09-16}}</ref> without filters and to sanitize both it and household surfaces. The [[United States Environmental Protection Agency]] has declared that 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" or "viruses, bacteria, mold, or other biological pollutants." Furthermore, its 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>[http://www.epa.gov/iaq/pubs/ozonegen.html EPA report on consumer ozone air purifiers]</ref> The government successfully sued one company in 1995, ordering it to stop repeating health claims without supporting scientific studies.
Ozonated water is used to launder clothes and to sanitize food, drinking water, and surfaces in the home. According to the [[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 University]] demonstrated that 0.3 ppm 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.<ref>{{Citation| last=Long| first=Ron| year=2008| url=http://www.purityintl.com/Article%20POU.pdf| format=pdf| title=POU Ozone Food Sanitation: A Viable Option for Consumers & the Food Service Industry}} (report also shows tapwater removes 99.95% of pathogens from lettuce; samples were first innoculated with pathogens before treatment)</ref><ref name="food">{{cite web
| last = Montecalvo
| first = Joseph
| authorlink =
| coauthors = Doug Williams
| title = Application of Ozonation in Sanitizing Vegetable Process Washwaters
| work =
| publisher = California Polytechnic State University
| date =
| url = http://www.cwtozone.com/files/articles/Food_Produce/Article%20-%20Veg.%20Process%20washwater.pdf
|accessdate=2008-03-24}}</ref>
Ozone can be used to remove [[pesticide]] residues from [[fruit]]s and [[vegetable]]s.<ref>{{Citation| last=Tersano Inc | year=2007| url=http://web.archive.org/web/20070211025555/http://www.tersano.com/sanitizing_system_food.shtml| title=lotus Sanitises Food without Chemicals| accessdate=2007-02-11}}</ref><ref name="fruit">{{cite book |title=Improving the Safety of Fresh Fruit and Vegetables |last=Jongen |first=W |authorlink= |coauthors= |year=2005 |publisher=Woodhead Publishing Ltd |location=Boca Raton |isbn=1855739569 |pages= }}</ref>
New, patented technology uses ozone to disinfect and deodorize protective sports gear by blowing it directly into the equipment to destroy bacteria within the padding. This has proven particularly useful in battling the spread of [[MRSA]].<ref>[http://www.freshgear.ca/ozone Fresh Gear C40 uses ozone to disinfect and deodorize sports gear.] (2005). Retrieved [[October 15]], [[2007]].</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 these halogens. Gaseous ozone created by ultraviolet light or by corona discharge is injected into the water.<ref>{{cite web |url=http://www.epa.gov/OGWDW/mdbp/alternative_disinfectants_guidance.pdf |title=Alternative Disinfectants and Oxidant Guidance Manual | publisher = [[United States Environmental Protection Agency]] |accessdate=2008-01-14 |format= |work= }}</ref>
Ozone is also widely used in treatment of water in aquariums and fish ponds. Its use can minimize bacterial growth, control parasites, eliminate transmission of some diseases, and reduce or eliminate "yellowing" of the water. Ozone must not come in contact with fish's gill structures. Natural salt water (with life forms) provides enough "instantaneous demand" that controlled amounts of ozone activate bromide ion 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, fish's gill structures will atrophy and they will become dependent on higher dissolved oxygen levels.
==See also==
* [[Global Ozone Monitoring by Occultation of Stars]] (GOMOS)
* [[International Day for the Preservation of the Ozone Layer]] ([[September 16]])
* [[Ozone Action Day]]
* [[Ozone depletion]], including the phenomenon known as the ozone hole.
*[[Ozone therapy]]
* [[Ozoneweb]]
* [[Polymer degradation]]
==Notes and references==
{{reflist|2}}
* {{Greenwood&Earnshaw}}
* Series in Plasma Physics: Non-Equilibrium Air Plasmas at Atmospheric Pressure. Edited by K.H. Becker, U. Kogelschatz, K.H. Schoenbach, R.J. Barker; Bristol and Philadelphia: Institute of Physics Publishing Ltd; ISBN 0-7503-0962-8; 2005
</div>
==External links==
* [http://www.int-ozone-assoc.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]
* [http://www.vega.org.uk/video/programme/111 Paul Crutzen Interview] Freeview video of Paul Crutzen Nobel Laureate for his work on decomposition of ozone talking to Harry Kroto Nobel Laureate by the Vega Science Trust.
* [http://earthobservatory.nasa.gov/Library/Ozone/ozone.html NASA's Earth Observatory article on Ozone]
* [http://internet12.eapps.com/countme/CMICampaigns.nsf/UNIDs/70DD73E27B24746D85256D7F00331B23 International Day for the Preservation of the Ozone Layer]
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0068.htm International Chemical Safety Card 0068]
* [http://www.cdc.gov/niosh/npg/npgd0476.html NIOSH Pocket Guide to Chemical Hazards]
* [http://www.niehs.nih.gov/health/topics/agents/ozone/ National Institute of Environmental Health Sciences, Ozone Information]
* [http://www.greenfacts.org/air-pollution/ozone-o3/index.htm Ground-level Ozone Air Pollution]
* [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.
* [http://www.epa.gov/iaq/pubs/ozonegen.html EPA Assessment of Effectiveness and Health Consequences of Ozone Generators that are Sold as Air Cleaners]
* [http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id=PC39189 Pesticides Database; Ozone]
{{oxygenallotropes}}
[[Category:Environmental chemistry]]
[[Category:Oxygen compounds]]
[[Category:Ozone depletion]]
[[Category:Oxidizing agents]]
[[Category:Disinfectants]]
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