Editing Ozone layer

{{Short description|Region of the stratosphere}}
{{pp-semi-indef}}
{{Use mdy dates|date=August 2023}}
[[File:ISS041-E-105277 - View of the Northern Territory.jpg|thumb|The ozone layer visible from space at Earth's horizon as a blue band of [[afterglow]] within the bottom of the large bright blue band that is the [[stratosphere]], with a silhouette of a [[cumulonimbus]] in the orange afterglow of the [[troposphere]].]]

The '''ozone layer''' or '''ozone shield''' is a region of [[Earth]]'s [[stratosphere]] that [[absorption (electromagnetic radiation)|absorbs]] most of the [[Sun]]'s [[ultraviolet]] radiation. It contains a high concentration of [[ozone]] (O<sub>3</sub>) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer peaks at 8 to 15 [[parts per million]] of ozone,<ref>[https://ozonewatch.gsfc.nasa.gov/facts/SH.html NASA Ozone Watch: Ozone facts]</ref> while the average ozone concentration in Earth's atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately {{convert|15|to|35|km|sp=us|0}} above Earth, although its thickness varies seasonally and geographically.<ref>{{cite web |title=Ozone Basics |date=March 20, 2008 |website=NOAA |url=https://www.ozonelayer.noaa.gov/science/basics.htm |access-date=January 29, 2007 |url-status=live |archive-url=https://web.archive.org/web/20171121051325/http://www.ozonelayer.noaa.gov/science/basics.htm |archive-date=November 21, 2017}}</ref>

The ozone layer was discovered in 1913 by French physicists [[Charles Fabry]] and [[Henri Buisson]]. Measurements of the sun showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the [[spectrum]] of a [[black body]] with a temperature in the range of {{convert|5500|–|6000|K|C}}, except that there was no radiation below a [[wavelength]] of about 310&nbsp;nm at the [[ultraviolet]] end of the spectrum. It was deduced that the missing radiation was being absorbed by something in the atmosphere. Eventually the spectrum of the missing radiation was matched to only one known chemical, ozone.<ref>{{cite journal |journal=Atmosphere-Ocean |volume=46 |pages=1–13 |year=2008 |last1=McElroy |first1=C.T. |title=Ozone: From discovery to protection |last2=Fogal |first2=P.F. |issue=1 |bibcode=2008AtO....46....1M |doi=10.3137/ao.460101 |s2cid=128994884}}</ref> Its properties were explored in detail by the British [[meteorologist]] [[G. M. B. Dobson]], who developed a simple [[spectrophotometry|spectrophotometer]] (the [[Dobson spectrometer|Dobsonmeter]]) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson established a worldwide network of ozone monitoring stations, which continue to operate to this day. The "[[Dobson unit]]" (DU), a convenient measure of the [[area density|amount]] of ozone overhead, is named in his honor.

The ozone layer absorbs 97 to 99 percent of the Sun's medium-frequency ultraviolet light (from about 200&nbsp;[[nanometer|nm]] to 315&nbsp;nm wavelength), which otherwise would potentially damage exposed life forms near the surface.<ref name="NASA">{{cite web |title=Ozone layer |url=http://www.nas.nasa.gov/About/Education/Ozone/ozonelayer.html |access-date=September 23, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20210502050928/https://www.nas.nasa.gov/About/Education/Ozone/ozonelayer.html |archive-date=May 2, 2021}}</ref>

In 1985, atmospheric research revealed that the ozone layer was being depleted by chemicals released by industry, mainly [[chlorofluorocarbon]]s (CFCs). Concerns that increased UV radiation due to [[ozone depletion]] threatened life on Earth, including increased skin cancer in humans and other ecological problems,<ref>An Interview with Lee Thomas, EPA's 6th Administrator. [http://www.epaalumni.org/history/video/interview.cfm?id=28 Video], [https://www.epaalumni.org/userdata/pdf/60740780F5ACB3D5.pdf#page=1 Transcript] (see p13). April 19, 2012.</ref> led to bans on the chemicals, and the latest evidence is that ozone depletion has slowed or stopped. The United Nations General Assembly has designated September 16 as the [[International Day for the Preservation of the Ozone Layer]].

[[Venus]] also has a thin ozone layer at an altitude of 100 kilometers above the planet's surface.<ref name="venus ozone">{{cite web |title=Scientists discover Ozone Layer on Venus |publisher=Purch |work=SPACE.com |date=October 11, 2011 |author=SPACE.com staff |url=https://www.space.com/13244-venus-atmosphere-ozone-layer.html |access-date=October 3, 2015}}</ref>

==Sources==
{{Main|Ozone–oxygen cycle}}
[[File:Ozone cycle.svg|thumb|upright=1.5|[[Ozone-oxygen cycle]] in the ozone layer]]
The Earth's ozone layer formed about 500 million years ago, when the [[neoproterozoic oxygenation event]] brought the fraction of oxygen in the atmosphere to about 20%.<ref>{{cite web|url=https://www.discovermagazine.com/environment/how-the-ozone-layer-evolved-and-why-its-important|title=How the Ozone Layer Evolved and Why It's Important |author=Paul M. Sutter |date=July 20, 2023 |publisher=Discover Magazine}}</ref>

The [[photochemical]] mechanisms that give rise to the ozone layer were discovered by the British physicist [[Sydney Chapman (mathematician)|Sydney Chapman]] in 1930. Ozone in the Earth's stratosphere is created by ultraviolet light striking ordinary [[oxygen]] [[molecule]]s containing two oxygen [[atom]]s (O<sub>2</sub>), splitting them into individual oxygen atoms ([[atomic oxygen]]); the atomic oxygen then combines with unbroken O<sub>2</sub> to create ozone, O<sub>3</sub>. The ozone molecule is unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O<sub>2</sub> and an individual atom of oxygen, a continuing process called the [[ozone–oxygen cycle]]. Chemically, this can be described as:
: <chem>O2{} + \mathit{h}\nu_{uv} -> 2O </chem>
: <chem>O + O2 <-> O3</chem>
About 90% of the ozone in the atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about {{convert|20|and|40|km|ft}}, where they range from about 2 to 8 parts per million. If all of the ozone were compressed to the pressure of the air at sea level, it would be only {{convert|3|mm|in|abbr=off|frac=8}} thick.<ref>{{cite web |title=NASA Facts Archive |url=http://www.nasa.gov/facts/Earth/earth_facts_archives.html |access-date=June 9, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20130406065500/http://www.nasa.gov/facts/Earth/earth_facts_archives.html |archive-date=April 6, 2013}}</ref>

==Ultraviolet light==
[[File:Ozone solar UV absorb DNA action.jpg|thumb|300px|UV-B energy levels at several altitudes. Blue line shows DNA sensitivity. Red line shows surface energy level with 10 percent decrease in ozone]]
[[File:Ozone altitude UV graph.svg|thumb|300px|Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UV-C (100–280&nbsp;nm) is blocked by dioxygen (from 100–200&nbsp;nm) or else by ozone (200–280&nbsp;nm) in the atmosphere. The shorter portion of the UV-C band and the more energetic UV above this band 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 also blocks most, but not quite all, of the sunburn-producing [[UV-B]] (280–315&nbsp;nm) band, which lies in the wavelengths longer than UV-C. The band of UV closest to visible light, [[UV-A]] (315–400&nbsp;nm), is hardly affected by ozone, and most of it reaches the ground. UV-A does not primarily cause skin reddening, but there is evidence that it causes long-term skin damage.]]

Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the Sun. Extremely short or vacuum UV (10–100&nbsp;nm) is screened out by nitrogen. UV radiation capable of penetrating nitrogen is divided into three categories, based on its wavelength; these are referred to as UV-A (400–315&nbsp;nm), [[UV-B]] (315–280&nbsp;nm), and [[UV-C]] (280–100&nbsp;nm).

UV-C, which is very harmful to all living things, is entirely screened out by a combination of dioxygen (< 200&nbsp;nm) and ozone (> about 200&nbsp;nm) by around {{convert|35|km|ft}} altitude. UV-B radiation can be harmful to the skin and is the main cause of [[sunburn]]; excessive exposure can also cause cataracts, immune system suppression, and genetic damage, resulting in problems such as [[skin cancer]]. The ozone layer (which absorbs from about 200&nbsp;nm to 310&nbsp;nm with a maximal absorption at about 250&nbsp;nm)<ref>{{cite journal |title=Photolysis of Atmospheric Ozone in the Ultraviolet Region |author1=Matsumi, Y. |author2=Kawasaki, M. |journal=Chem. Rev. |date=2003 |volume=103 |issue=12 |pages=4767–4781 |pmid=14664632 |doi=10.1021/cr0205255 |url=http://yly-mac.gps.caltech.edu/N2O/Prasad/Matsumi_O3_cr0205255%20copy.pdf |access-date=March 14, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20120617123007/http://yly-mac.gps.caltech.edu/N2O/Prasad/Matsumi_O3_cr0205255%20copy.pdf |archive-date=June 17, 2012}}</ref> is very effective at screening out UV-B; for radiation with a wavelength of 290&nbsp;nm, the intensity at the top of the atmosphere is 350 million times stronger than at the Earth's surface. Nevertheless, some UV-B, particularly at its longest wavelengths, reaches the surface, and is important for the skin's production of [[vitamin D]] in [[mammals]].

Ozone is transparent to most UV-A, so most of this longer-wavelength UV radiation reaches the surface, and it constitutes most of the UV reaching the Earth. This type of UV radiation is significantly less harmful to [[DNA]], although it may still potentially cause physical damage, premature aging of the skin, indirect genetic damage, and skin cancer.<ref>{{cite journal |title=Review: Ultraviolet radiation and skin cancer |author1=Narayanan, D.L. |author2=Saladi, R.N. |author3=Fox, J.L. |journal=International Journal of Dermatology |volume=49 |issue=9 |pages=978–986 |date=2010 |pmid=20883261 |doi=10.1111/j.1365-4632.2010.04474.x |doi-access=free |s2cid=22224492}}</ref>

==Distribution in the stratosphere==
{{More citations needed section|date=February 2013}}
[[File:Atmosphere20Layers 2018.jpg|thumb|Ozone layer within Earth's atmosphere by altitude]]

The thickness of the ozone layer varies worldwide and is generally thinner near the equator and thicker near the poles.<ref name="APH">{{cite book |title=Global Warming: The Effect Of Ozone Depletion |author=Tabin, Shagoon |publisher=APH Publishing |year=2008 |isbn=9788131303962 |page=194 |url=https://books.google.com/books?id=QFBmUu1lwzAC |access-date=January 12, 2016}}</ref> Thickness refers to how much ozone is in a column over a given area and varies from season to season. The reasons for these variations are due to atmospheric circulation patterns and solar intensity.<ref>{{cite web |title=Nasa Ozone Watch: Ozone facts |website=ozonewatch.gsfc.nasa.gov |url=https://ozonewatch.gsfc.nasa.gov/facts/SH.html |access-date=September 16, 2021}}</ref>

The ozone layer ends gradually, but in general its upper limit is where air becomes too thin for UV light to generate much ozone, and its lower limit is where generated ozone blocks enough UV light to stop most ozone production.

In the [[homosphere]], wind-driven movement is more important than relative gas weight. The majority of ozone is produced over the [[tropics]] and is transported toward the poles by stratospheric wind patterns. In the northern hemisphere these patterns, known as the [[Brewer–Dobson circulation]], make the ozone layer thickest in the spring and thinnest in the fall.<ref name="APH"/> When ozone is produced by solar UV radiation in the tropics, it is done so by circulation lifting ozone-poor air out of the troposphere and into the stratosphere where the sun [[photolyzes]] oxygen molecules and turns them into ozone. Then, the ozone-rich air is carried to higher latitudes and drops into lower layers of the atmosphere.<ref name="APH"/>

Research has found that the ozone levels in the United States are highest in the spring months of April and May and lowest in October. While the total amount of ozone increases moving from the tropics to higher latitudes, the concentrations are greater in high northern latitudes than in high southern latitudes, with spring ozone columns in high northern latitudes occasionally exceeding 600 DU and averaging 450 DU whereas 400 DU constituted a usual maximum in the Antarctic before anthropogenic ozone depletion. This difference occurred naturally because of the weaker polar vortex and stronger Brewer–Dobson circulation in the northern hemisphere owing to that hemisphere's large mountain ranges and greater contrasts between land and ocean temperatures.<ref>{{cite journal |author=Douglass |first1=Anne R. |last2=Newman |first2=Paul A. |last3=Solomon |first3=Susan |title=The Antarctic ozone hole: An update |journal=Physics Today |year=2014 |volume=67 |issue=7 |pages=42–48 |publisher=American Institute of Physics |bibcode=2014PhT....67g..42D |doi=10.1063/PT.3.2449 |hdl=1721.1/99159 |hdl-access=free |url=https://physicstoday.scitation.org/doi/pdf/10.1063/PT.3.2449}}</ref> The difference between high northern and southern latitudes has increased since the 1970s due to the [[ozone hole]] phenomenon.<ref name="APH"/> The highest amounts of ozone are found over the Arctic during the spring months of March and April, but the Antarctic has the lowest amounts of ozone during the summer months of September and October,

[[File:Nimbus ozone Brewer-Dobson circulation.jpg|thumb|300px|Brewer–Dobson circulation in the ozone layer]]

==Depletion==
{{Main|Ozone depletion}}
[[File:Future ozone layer concentrations.gif|thumb|300px|NASA projections of stratospheric ozone concentrations if [[chlorofluorocarbon]]s had not been banned]]

The ozone layer can be depleted by [[free radical]] [[catalysis|catalysts]], including [[nitric oxide]] (NO), [[nitrous oxide]] (N<sub>2</sub>O), [[hydroxyl]] (OH), atomic [[chlorine]] (Cl), and atomic [[bromine]] (Br). While there are natural sources for all of these [[chemical species|species]], the concentrations of chlorine and bromine increased markedly in recent decades because of the release of large quantities of man-made [[organohalogen]] compounds, especially [[chlorofluorocarbon]]s (CFCs) and [[bromofluorocarbons]].<ref>{{cite book |chapter-url=http://www.eia.doe.gov/oiaf/1605/archive/gg97rpt/chap5.html |chapter=Halocarbons and Other Gases |publisher=Energy Information Administration |title=Emissions of Greenhouse Gases in the United States 1996 |date=1997 |access-date=June 24, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080629032506/http://www.eia.doe.gov/oiaf/1605/archive/gg97rpt/chap5.html |archive-date=June 29, 2008}}</ref> Atmospheric components are not sorted out by weight in the [[homosphere]] because of wind-driven mixing that extends to an altitude of about 90 km, well above the ozone layer. So despite being heavier than diatomic nitrogen and oxygen, these highly stable compounds rise into the [[stratosphere]], where Cl and Br [[radical (chemistry)|radicals]] are liberated by the action of ultraviolet light. Each radical is then free to initiate and catalyze a chain reaction capable of breaking down over 100,000 ozone molecules. By 2009, nitrous oxide was the largest ozone-depleting substance (ODS) emitted through human activities.<ref>{{cite web |title=NOAA Study Shows Nitrous Oxide Now Top Ozone-Depleting Emission |publisher=NOAA |date=August 27, 2009 |url=http://www.noaanews.noaa.gov/stories2009/20090827_ozone.html |access-date=November 8, 2011}}</ref>

The breakdown of ozone in the stratosphere results in reduced absorption of ultraviolet radiation. Consequently, unabsorbed and dangerous ultraviolet radiation reaches the Earth's surface at a higher intensity. Ozone levels have dropped by a worldwide average of about 4 percent since the late 1970s. For approximately 5 percent of the Earth's surface, around the north and south poles, much larger seasonal declines have been seen, and are described as "ozone holes". "Ozone holes" are actually patches in the ozone layer in which the ozone is thinner. The thinnest parts of the ozone are at the [[polar regions of Earth|polar points of Earth's axis]].<ref>{{cite web |title=ozone layer {{!}} National Geographic Society |url=https://education.nationalgeographic.org/resource/ozone-layer |access-date=May 30, 2022 |website=education.nationalgeographic.org}}</ref> The discovery of the annual depletion of ozone above the Antarctic was first announced by [[Joe Farman]], [[Brian G. Gardiner (meteorologist)|Brian Gardiner]], and [[Jonathan Shanklin]], in a paper which appeared in ''[[Nature (journal)|Nature]]'' on May 16, 1985.

Regulation attempts have included but not have been limited to the [[Clean Air Act (United States)|Clean Air Act]] implemented by the [[United States Environmental Protection Agency]]. The Clean Air Act introduced the requirement of [https://www.epa.gov/criteria-air-pollutants/naaqs-table National Ambient Air Quality Standards (NAAQS)] with ozone pollutions being one of six criteria pollutants. This regulation has proven to be effective since counties, cities, and tribal regions must abide by these standards and the EPA also provides assistance for each region to regulate contaminants.<ref>{{cite web |last=US EPA |first=OAR |title=Ozone Implementation Regulatory Actions |date=December 14, 2016 |language=en |website=epa.gov |url=https://www.epa.gov/ground-level-ozone-pollution/ozone-implementation-regulatory-actions |access-date=May 30, 2022}}</ref> Effective presentation of information has also proven to be important in order to educate the general population of the existence and regulation of ozone depletion and contaminants. A scientific paper was written by Sheldon Ungar in which the author explores and studies how information about the depletion of the ozone, [[climate change]], and various related topics. The ozone case was communicated to lay persons "with easy-to-understand bridging metaphors derived from the popular culture" and related to "immediate risks with everyday relevance".<ref>{{cite journal |last=Ungar |first=Sheldon |title=Knowledge, ignorance and the popular culture: climate change versus the ozone hole |date=July 2000 |journal=Public Understanding of Science |language=en |volume=9 |issue=3 |pages=297–312 |issn=0963-6625 |doi=10.1088/0963-6625/9/3/306 |s2cid=7089937 |url=https://journals.sagepub.com/doi/10.1088/0963-6625/9/3/306|url-access=subscription }}</ref> The specific metaphors used in the discussion (ozone shield, ozone hole) proved quite useful and, compared to global climate change, the ozone case was much more seen as a "hot issue" and imminent risk. Lay people were cautious about a depletion of the ozone layer and the risks of skin cancer.

[[Satellite]]s burning up upon re-entry into Earth's atmosphere produce [[aluminum oxide]] (Al<sub>2</sub>O<sub>3</sub>) [[nanoparticle]]s that endure in the atmosphere for decades.<ref name=GeophysResearchLtrs_20240611/> Estimates for 2022 alone were ~17 metric tons (~30{{nbsp}}kg of nanoparticles per ~250{{nbsp}}kg satellite).<ref name=GeophysResearchLtrs_20240611/> Increasing populations of [[satellite constellation]]s can eventually lead to significant ozone depletion.<ref name=GeophysResearchLtrs_20240611>{{cite journal |last1=Ferreira |first1=Jose P. |last2=Huang |first2=Ziyu |last3=Nomura |first3=Ken-ichi |last4=Wang |first4=Joseph |title=Potential Ozone Depletion From Satellite Demise During Atmospheric Reentry in the Era of Mega-Constellations |journal=Geophysical Research Letters |date=11 June 2024 |volume=51 |issue=11 |doi=10.1029/2024GL109280 |doi-access=free|bibcode=2024GeoRL..5109280F }}</ref>

"Bad" ozone{{Clarification needed|date=January 2025}} can cause adverse health risks respiratory effects (difficulty breathing) and is proven to be an aggravator of respiratory illnesses such as [[asthma]], [[chronic obstructive pulmonary disease|COPD]], and [[emphysema]].<ref>{{cite journal |last1=Zhang |first1=Junfeng (Jim) |last2=Wei |first2=Yongjie |last3=Fang |first3=Zhangfu |title=Ozone Pollution: A Major Health Hazard Worldwide |date=2019 |journal=Frontiers in Immunology |volume=10 |page=2518 |issn=1664-3224 |pmid=31736954 |doi=10.3389/fimmu.2019.02518 |doi-access=free |pmc=6834528}}</ref> That is why many countries have set in place regulations to improve "good" ozone{{Clarification needed|date=January 2025}} and prevent the increase of "bad" ozone in urban or residential areas. In terms of ozone protection (the preservation of "good" ozone) the [[European Union]] has strict guidelines on what products are allowed to be bought, distributed, or used in specific areas.<ref>{{cite web |title=Ozone Regulation |language=en |website=ec.europa.eu |url=https://ec.europa.eu/clima/eu-action/protection-ozone-layer/ozone-regulation_en |access-date=May 30, 2022}}</ref> With effective regulation, the ozone is expected to heal over time.<ref>{{cite web |last=US EPA |first=OAR |title=International Treaties and Cooperation about the Protection of the Stratospheric Ozone Layer |date=July 15, 2015 |language=en |website=epa.gov |url=https://www.epa.gov/ozone-layer-protection/international-treaties-and-cooperation-about-protection-stratospheric-ozone |access-date=May 30, 2022}}</ref>
[[File:TOMS Global Ozone 65N-65S.png|thumb|Levels of atmospheric ozone measured by satellite show clear seasonal variations and appear to verify their decline over time.]]

{{Main|Ozone depletion and climate change}}

In 1978, the United States, Canada, and [[Norway]] enacted bans on [[chlorofluorocarbon|CFC]]-containing [[aerosol spray]]s that damage the ozone layer but the European Community rejected a similar proposal. In the U.S., chlorofluorocarbons continued to be used in other applications, such as refrigeration and industrial cleaning, until after the discovery of the Antarctic ozone hole in 1985. After negotiation of an international treaty (the [[Montreal Protocol]]), CFC production was capped at 1986 levels with commitments to long-term reductions.<ref>{{cite journal |title=The Evolution of Policy Responses to Stratospheric Ozone Depletion |journal=Natural Resources Journal |date=1989 |last=Morrisette |first=Peter M. |volume=29 |pages=793–820 |url=http://www.ciesin.org/docs/003-006/003-006.html |access-date=April 20, 2010}}</ref> This allowed for a ten-year phase-in for developing countries<ref>An Interview with Lee Thomas, EPA's 6th Administrator. [http://www.epaalumni.org/history/video/interview.cfm?id=28 Video], [https://www.epaalumni.org/userdata/pdf/60740780F5ACB3D5.pdf#page=1 Transcript] (see p15). April 19, 2012.</ref> (identified in Article 5 of the protocol). Since then, the treaty was amended to ban CFC production after 1995 in developed countries, and later in developing countries.<ref>{{cite web |title=Amendments to the Montreal Protocol |publisher=EPA |date=August 19, 2010 |url=http://www.epa.gov/ozone/intpol/history.html |access-date=March 28, 2011}}</ref> All of the world's 197 countries have signed the treaty. Beginning January 1, 1996, only recycled or stockpiled CFCs were available for use in developed countries like the US. The production phaseout was possible because of efforts to ensure that there would be substitute chemicals and technologies for all ODS uses.<ref>{{cite web |title=Brief Questions and Answers on Ozone Depletion |publisher=EPA |date=June 28, 2006 |url=http://www.epa.gov/ozone/science/q_a.html |access-date=November 8, 2011}}</ref>

On August 2, 2003, scientists announced that the global depletion of the ozone layer might be slowing because of the international regulation of ozone-depleting substances. In a study organized by the [[American Geophysical Union]], three satellites and three ground stations confirmed that the upper-atmosphere ozone-depletion rate slowed significantly over the previous decade. Some breakdown was expected to continue because of ODSs used by nations which have not banned them, and because of gases already in the stratosphere. Some ODSs, including CFCs, have very long atmospheric lifetimes ranging from 50 to over 100 years. It has been estimated that the ozone layer will recover to 1980 levels near the middle of the 21st century.<ref name="wmo2010">{{cite book |title=Scientific Assessment of Ozone Depletion: 2010 |date=2011 |publisher=WMO |chapter=Stratospheric Ozone and Surface Ultraviolet Radiation |chapter-url=http://acdb-ext.gsfc.nasa.gov/Documents/O3_Assessments/Docs/WMO_2010/Chapter_2.pdf |access-date=March 14, 2015}}</ref> A gradual trend toward "healing" was reported in 2016.<ref name=healing>{{cite journal |title=Emergence of healing in the Antarctic ozone layer |vauthors=Solomon, Susan etal |journal=Science |volume=353 |issue=6296 |pages=269–74 |date=June 30, 2016 |bibcode=2016Sci...353..269S |pmid=27365314 |doi=10.1126/science.aae0061 |doi-access=free |hdl=1721.1/107197 |hdl-access=free}}</ref>

Compounds containing [[carbon–hydrogen bond|C–H bonds]] (such as [[hydrochlorofluorocarbon]]s, or HCFCs) have been designed to replace CFCs in certain applications. These replacement compounds are more reactive and less likely to survive long enough in the atmosphere to reach the stratosphere where they could affect the ozone layer. While being less damaging than CFCs, HCFCs can have a negative impact on the ozone layer, so they are also being phased out.<ref>{{cite web |title=Ozone Depletion Glossary |publisher=EPA |url=http://www.epa.gov/ozone/defns.html#hcfc |access-date=September 3, 2008}}</ref> These in turn are being replaced by [[hydrofluorocarbon]]s (HFCs) and other compounds that do not destroy stratospheric ozone at all.

The residual effects of CFCs accumulating within the atmosphere lead to a concentration gradient between the atmosphere and the ocean. This organohalogen compound dissolves into the ocean's surface waters and acts as a [[chlorofluorocarbon|time-dependent tracer]]. This tracer helps scientists study ocean circulation by tracing biological, physical, and chemical pathways.<ref>{{cite journal |title=Observations of CFCs and SF6 as Ocean Tracers |last=Fine |first=Rana A. |date=2011 |journal=Annual Review of Marine Science |volume=3 |pages=173–95 |bibcode=2011ARMS....3..173F |pmid=21329203 |doi=10.1146/annurev.marine.010908.163933 |url=http://yyy.rsmas.miami.edu/groups/cfc/pubs/Fine_AnnRevMarineSci3_2011.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150210212306/http://yyy.rsmas.miami.edu/groups/cfc/pubs/Fine_AnnRevMarineSci3_2011.pdf |archive-date=February 10, 2015}}</ref>

==Implications for astronomy==
As ozone in the atmosphere prevents most energetic ultraviolet radiation reaching the surface of the Earth, astronomical data in these wavelengths have to be gathered from satellites orbiting above the atmosphere and ozone layer. Most of the light from young hot stars is in the ultraviolet and so study of these wavelengths is important for studying the origins of galaxies. The Galaxy Evolution Explorer, [[GALEX]], is an orbiting ultraviolet space telescope launched on April 28, 2003, which operated until early 2012.<ref>{{cite web |title=ozone layer |date=May 9, 2011 |language=en |website=National Geographic Society |url=http://www.nationalgeographic.org/encyclopedia/ozone-layer/ |access-date=September 16, 2021}}</ref>

<gallery class="center" widths="300" heights="260">
File:Ultraviolet image of the Cygnus Loop Nebula crop.jpg|This [[GALEX]] image of the [[Cygnus Loop|Cygnus Loop nebula]] could not have been taken from the surface of the Earth because the ozone layer blocks the ultra-violet radiation emitted by the nebula.
</gallery>

==See also==
*[[Cambrian explosion]]
*[[Nuclear winter]]
*[[Oxygen]]
*[[Short-lived climate pollutants]]
*[[United Nations Environment Programme]]

==References==
{{Reflist|33em}}

==Further reading==
; Science

* {{cite journal |authorlink=Stephen O. Andersen |last=Andersen |first=S. O. |title=Lessons from the stratospheric ozone layer protection for climate |journal=Journal of Environmental Studies and Sciences |year=2015 |volume=5 |issue=2 |pages=143–162 |bibcode=2015JEnSS...5..143A |doi=10.1007/s13412-014-0213-9 |s2cid=129725437 |url=https://link.springer.com/article/10.1007/s13412-014-0213-9|url-access=subscription }}
* {{cite book |last1=Andersen |first1=S.O. |last2=Sarma |first2=K.M. |last3=Sinclair |first3=L. |title=Protecting the Ozone Layer: The United Nations History |publisher=Taylor & Francis |year=2012 |isbn=978-1-84977-226-6 |url=https://books.google.com/books?id=zuesUPcIOq8C}}
* [[Hannah Ritchie|Ritchie, Hannah]], "What We Learned from Acid Rain: By working together, the nations of the world can solve climate change", ''[[Scientific American]]'', vol. 330, no. 1 (January 2024), pp.&nbsp;75–76. "[C]ountries will act only if they know others are willing to do the same. With [[acid rain]], they did act collectively.... We did something similar to restore Earth's protective ozone layer.... [T]he cost of technology really matters.... In the past decade the price of [[solar energy]] has fallen by more than 90 percent and that of [[wind energy]] by more than 70 percent. [[Electric battery|Battery]] costs have tumbled by 98 percent since 1990, bringing the price of [[electric car]]s down with them....[T]he stance of [[elected official]]s matters more than their [[political party|party]] affiliation.... Change can happen – but not on its own. We need to drive it." (p.&nbsp;76.)
* [[United Nations Environment Programme]] (2010). ''Environmental Effects of Ozone Depletion and its Interactions with Climate Change: 2010 Assessment''. Nairobi: UNEP.
* {{cite journal |title=The large contribution of projected HFC emissions to future climate forcing |year=2009 |last1=Velders |first1=G. J. M. |last2=Fahey |first2=D. W. |last3=Daniel |first3=J. S. |last4=McFarland |first4=M. |last5=Andersen |first5=S. O. |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=27 |pages=10949–10954 |bibcode=2009PNAS..10610949V |pmid=19549868 |doi=10.1073/pnas.0902817106 |doi-access=free |pmc=2700150 |s2cid=3743609}}
* {{cite journal |last1=Velders |first1=Guus J.M. |last2=Andersen |first2=Stephen O. |last3=Daniel |first3=John S. |last4=Fahey |first4=David W. |last5=McFarland |first5=Mack |year=2007 |title=The Importance of the Montreal Protocol in Protecting Climate |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=104 |issue=12 |pages=4814–4819 |bibcode=2007PNAS..104.4814V |pmid=17360370 |doi=10.1073/pnas.0610328104 |doi-access=free |pmc=1817831}}

; Policy
* {{cite journal |title=The importance of phasing down hydrofluorocarbons and other short-lived climate pollutants |year=2015 |last1=Zaelke |first1=Durwood |last2=Borgford-Parnell |first2=Nathan |journal=Journal of Environmental Studies and Sciences |volume=5 |issue=2 |pages=169–175 |bibcode=2015JEnSS...5..169Z |doi=10.1007/s13412-014-0215-7 |s2cid=128974741 |url=https://link.springer.com/article/10.1007%2Fs13412-014-0215-7|url-access=subscription }}
* {{cite journal |title=The role of HFCS in mitigating 21st century climate change |year=2013 |last1=Xu |first1=Y. |last2=Zaelke |first2=D. |last3=Velders |first3=G. J. M. |last4=Ramanathan |first4=V. |journal=Atmospheric Chemistry and Physics |volume=13 |issue=12 |pages=6083–6089 |bibcode=2013ACP....13.6083X |doi=10.5194/acp-13-6083-2013 |doi-access=free |url=https://acp.copernicus.org/articles/13/6083/2013/acp-13-6083-2013.html}}
* {{cite journal |title=Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions |year=2009 |last1=Molina |first1=M. |last2=Zaelke |first2=D. |last3=Sarma |first3=K. M. |last4=Andersen |first4=S. O. |last5=Ramanathan |first5=V. |last6=Kaniaru |first6=D. |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=49 |pages=20616–20621 |pmid=19822751 |doi=10.1073/pnas.0902568106 |doi-access=free |pmc=2791591 |s2cid=13240115}}
* {{cite book |last1=Anderson |first1=S. O. |last2=Sarma |first2=M. K. |last3=Taddonio |first3=K. |year=2007 |title=Technology Transfer for the Ozone Layer: Lessons for Climate Change |location=London |publisher=Earthscan |isbn=9781849772846 |url=https://books.google.com/books?id=OvgA-hZrPOcC}}
* {{cite book |last1=Benedick |first1=Richard Elliot |author2=World Wildlife Fund (U.S.) |author3=Institute for the Study of Diplomacy. Georgetown University. |title=Ozone Diplomacy: New Directions in Safeguarding the Planet |edition=2nd |year=1998 |publisher=Harvard University Press |isbn=978-0-674-65003-9 |url=https://books.google.com/books?id=4yM9uPRUvi4C}} (Ambassador Benedick was the Chief U.S. Negotiator at the meetings that resulted in the Montreal Protocol.)
* {{cite book |last1=Chasek |first1=P. S. |last2=Downie |first2=David L. |last3=Brown |first3=J. W. |year=2013 |title=Global Environmental Politics |edition=6th |location=Boulder |publisher=Westview Press |isbn=9780813348971 |url=https://books.google.com/books?id=Ju41zgEACAAJ}}
* {{cite book |last=Grundmann |first=Reiner |title=Transnational Environmental Policy: Reconstructing Ozone |year=2001 |publisher=Psychology Press |isbn=978-0-415-22423-9 |url=https://books.google.com/books?id=FYyVDlRhBvEC}}
* {{cite book |last=Parson |first=E. |year=2003 |title=Protecting the Ozone Layer: Science and Strategy |location=Oxford |publisher=Oxford University Press |isbn=9780190288716 |url=https://books.google.com/books?id=VNkJCAAAQBAJ}}

==External links==
{{Commons category|Ozone layer}}
{{Wikisource}}
*[http://www.ccpo.odu.edu/SEES/ozone/oz_class.htm Stratospheric ozone: an electronic textbook]
*[https://archive.today/20040702045343/http://www.unep.org/ozone/Public_Information/4Aii_PublicInfo_Facts_OzoneLayer.asp Ozone Layer Info] (archived July 2, 2004)
*The [http://www.copernicus-stratosphere.eu/ CAMS stratospheric ozone service] delivers maps, datasets, and validation reports about the past and current state of the ozone layer.

{{Earth's atmosphere}}

{{Authority control}}
[[Category:Ozone depletion|Layer]]
[[Category:Ultraviolet radiation]]