Editing Ozone depletion (section)

== Research history ==
{{See also|Ozone–oxygen cycle}}

The basic physical and chemical processes that lead to the formation of an ozone layer in the Earth's stratosphere were discovered by [[Sydney Chapman (mathematician)|Sydney Chapman]] in 1930. Short-wavelength UV radiation splits an oxygen ({{chem|O|2}}) molecule into two oxygen (O) atoms, which then combine with other oxygen molecules to form ozone. Ozone is removed when an oxygen atom and an ozone molecule "recombine" to form two oxygen molecules, i.e. O + {{chem|O|3}} → 2{{chem|O|2}}. In the 1950s, David Bates and Marcel Nicolet presented evidence that various free radicals, in particular hydroxyl (OH) and nitric oxide (NO), could catalyze this recombination reaction, reducing the overall amount of ozone. These free radicals were known to be present in the stratosphere, and so were regarded as part of the natural balance—it was estimated that in their absence, the ozone layer would be about twice as thick as it currently is.

In 1970 [[Paul Crutzen]] pointed out that emissions of [[nitrous oxide]] ({{chem|N|2|O}}), a stable, long-lived gas produced by soil bacteria, from the Earth's surface could affect the amount of [[nitric oxide]] (NO) in the stratosphere. Crutzen showed that nitrous oxide lives long enough to reach the stratosphere, where it is converted into NO. Crutzen then noted that increasing use of [[fertilizers]] might have led to an increase in nitrous oxide emissions over the natural background, which would in turn result in an increase in the amount of NO in the stratosphere. Thus human activity could affect the stratospheric ozone layer. In the following year, Crutzen and (independently) Harold Johnston suggested that NO emissions from [[supersonic transport|supersonic passenger aircraft]], which would fly in the lower stratosphere, could also deplete the ozone layer. However, more recent analysis in 1995 by David W. Fahey, an atmospheric scientist at the [[National Oceanic and Atmospheric Administration]], found that the drop in ozone would be from 1–2 percent if a fleet of 500 supersonic passenger aircraft were operated.<ref>Lipkin, Richard (October 7, 1995). [https://www.questia.com/read/1G1-17639207 SST emissions cut stratospheric ozone. (The introduction of 500 new supersonic transport planes by 2015 could deplete the ozone layer by as much as 1%)] {{Webarchive|url=https://web.archive.org/web/20230107230343/https://www.gale.com/databases/questia |date=2023-01-07 }}. Science News.</ref> This, Fahey expressed, would not be a showstopper for advanced supersonic passenger aircraft development.<ref>{{cite news |url=https://www.baltimoresun.com/1995/10/08/increase-in-supersonic-jets-could-be-threat-to-ozone-u-2-plane-trails-concorde-studies-exhaust-particles/ |title=Increase in supersonic jets could be threat to ozone U-2 plane trails Concorde, studies exhaust particles |newspaper=The Baltimore Sun |agency=Newsday |date=October 8, 1995 |access-date=December 21, 2012 |archive-date=September 1, 2016 |archive-url=https://web.archive.org/web/20160901085907/http://articles.baltimoresun.com/1995-10-08/news/1995281022_1_ozone-sulfur-exhaust-particles |url-status=live }}</ref>

=== Rowland–Molina hypothesis ===
In 1974 [[Frank Sherwood Rowland]], Chemistry Professor at the University of California at Irvine, and his postdoctoral associate [[Mario J. Molina]] suggested that long-lived organic halogen compounds, such as CFCs, might behave in a similar fashion as Crutzen had proposed for nitrous oxide. [[James Lovelock]] had recently discovered, during a cruise in the South Atlantic in 1971, that almost all of the CFC compounds manufactured since their invention in 1930 were still present in the atmosphere. Molina and Rowland concluded that, like {{chem|N|2|O}}, the CFCs would reach the stratosphere where they would be dissociated by UV light, releasing chlorine atoms. A year earlier, [[Richard Stolarski]] and [[Ralph Cicerone]] at the University of Michigan had shown that Cl is even more efficient than NO at catalyzing the destruction of ozone. Similar conclusions were reached by [[Michael McElroy (scientist)|Michael McElroy]] and [[Steven Wofsy]] at [[Harvard University]]. Neither group, however, had realized that CFCs were a potentially large source of stratospheric chlorine—instead, they had been investigating the possible effects of HCl emissions from the [[Space Shuttle]], which are very much smaller.

The Rowland–Molina hypothesis was strongly disputed by representatives of the aerosol and halocarbon industries. The Chair of the Board of [[DuPont (1802–2017)|DuPont]] was quoted as saying that ozone depletion theory is "a science fiction tale ... a load of rubbish ... utter nonsense".<ref name="greenpeace-ozone">{{cite web|url=http://archive.greenpeace.org/ozone/greenfreeze/moral97/6dupont.html |archive-url=https://web.archive.org/web/20120406093303/http://archive.greenpeace.org/ozone/greenfreeze/moral97/6dupont.html |archive-date=April 6, 2012 |title=Du Pont: A case study in the 3D corporate strategy |publisher=Greenpeace |year=1997 |url-status=unfit}}</ref> [[Robert Abplanalp]], the President of Precision Valve Corporation (and inventor of the first practical aerosol spray can valve), wrote to the Chancellor of [[UC Irvine]] to complain about Rowland's public statements.<ref>Roan, Sharon (1989) ''Ozone crisis: The 15-year evolution of a sudden global emergency'', New York: Wiley, p.&nbsp;56, {{ISBN|0-471-52823-4}}.</ref> Nevertheless, within three years most of the basic assumptions made by Rowland and Molina were confirmed by laboratory measurements and by direct observation in the stratosphere. The concentrations of the source gases (CFCs and related compounds) and the chlorine reservoir species (HCl and {{chem|ClONO|2}}) were measured throughout the stratosphere, and demonstrated that CFCs were indeed the major source of stratospheric chlorine, and that nearly all of the CFCs emitted would eventually reach the stratosphere. Even more convincing was the measurement, by James G. Anderson and collaborators, of chlorine monoxide (ClO) in the stratosphere. ClO is produced by the reaction of Cl with ozone—its observation thus demonstrated that Cl radicals not only were present in the stratosphere but also were actually involved in destroying ozone. McElroy and Wofsy extended the work of Rowland and Molina by showing that bromine atoms were even more effective catalysts for ozone loss than chlorine atoms and argued that the [[Organic compounds|brominated organic compounds]] known as [[Haloalkane|halons]], widely used in fire extinguishers, were a potentially large source of stratospheric bromine. In 1976 the [[United States National Academy of Sciences]] released a report concluding that the ozone depletion hypothesis was strongly supported by the scientific evidence. In response the United States, Canada and Norway banned the use of CFCs in [[Aerosol spray|aerosol spray cans]] in 1978. Early estimates were that, if CFC production continued at 1977 levels, the total atmospheric ozone would after a century or so reach a steady state, 15 to 18 percent below normal levels. By 1984, when better evidence on the speed of critical reactions was available, this estimate was changed to 5 to 9 percent steady-state depletion.<ref name="NAS_report">{{cite book |title=Causes and Effects of Stratospheric Ozone Reduction: An Update |publisher=National Research Council |date=1982 |url=http://www.nap.edu/openbook.php?isbn=0309032482 |isbn=978-0-309-03248-3|page=Summary, 3|doi=10.17226/319 }}</ref>

Crutzen, Molina, and Rowland were awarded the 1995 [[Nobel Prize in Chemistry]] for their work on stratospheric ozone.

=== Antarctic ozone hole ===
The discovery of the Antarctic "ozone hole" by [[British Antarctic Survey]] scientists [[Joe Farman|Farman]], [[Brian G. Gardiner (meteorologist)|Gardiner]] and [[Jon Shanklin|Shanklin]] (first reported in a paper in ''[[Nature (journal)|Nature]]'' in May 1985<ref>{{Cite journal | last1 = Farman | first1 = J. C. | author-link1 = Joe Farman| last2 = Gardiner | first2 = B. G. | author-link2 = Brian G. Gardiner (meteorologist)| last3 = Shanklin | first3 = J. D. | author-link3 = Jon Shanklin| doi = 10.1038/315207a0 | title = Large losses of total ozone in Antarctica reveal seasonal ClO<sub>x</sub>/NO<sub>x</sub> interaction |journal=Nature |volume=315 |issue=6016 |pages=207–210 |year=1985 |url=https://www.researchgate.net/publication/246650409| bibcode = 1985Natur.315..207F | s2cid = 4346468 }}</ref>) came as a shock to the scientific community, because the observed decline in polar ozone was far larger than had been anticipated.<ref name="Zehr94">{{cite journal |author=Zehr |first=Stephen C. |year=1994 |title=Accounting for the Ozone Hole: Scientific Representations of an Anomaly and Prior Incorrect Claims in Public Settings |journal=The Sociological Quarterly |volume=35 |issue=4 |pages=603–619 |doi=10.1111/j.1533-8525.1994.tb00419.x |jstor=4121521}}</ref> [[Earth observation satellite|Satellite measurements]] ([[TOMS (sensor)|TOMS]] onboard [[Nimbus 7]]) showing massive depletion of ozone around the [[south pole]] were becoming available at the same time.<ref name="Bhartia McPeters 2018 pp. 335–340">{{cite journal | last1=Bhartia | first1=Pawan Kumar | last2=McPeters | first2=Richard D. | title=The discovery of the Antarctic Ozone Hole | journal=Comptes Rendus Geoscience | publisher=Elsevier BV | volume=350 | issue=7 | year=2018 | issn=1631-0713 | doi=10.1016/j.crte.2018.04.006 | pages=335–340| bibcode=2018CRGeo.350..335B | doi-access=free }}</ref> However, these were initially rejected as unreasonable by data quality control algorithms (they were filtered out as errors since the values were unexpectedly low); the ozone hole was detected only in satellite data when the raw data was reprocessed following evidence of ozone depletion in ''in situ'' observations.<ref name="ReferenceA" /> When the [[software]] was rerun without the flags, the ozone hole was seen as far back as 1976.<ref>[http://ozonewatch.gsfc.nasa.gov/facts/history.html History and politics] {{Webarchive|url=https://web.archive.org/web/20161005132113/http://ozonewatch.gsfc.nasa.gov/facts/history.html |date=2016-10-05 }} accessed September 30, 2016.</ref>

[[Susan Solomon]], an atmospheric chemist at the [[National Oceanic and Atmospheric Administration]] (NOAA), proposed that [[chemical reaction]]s on [[polar stratospheric cloud]]s (PSCs) in the cold [[Antarctic]] [[stratosphere]] caused a massive, though localized and seasonal, increase in the amount of [[chlorine]] present in active, ozone-destroying forms. The polar stratospheric clouds in Antarctica are only formed at very low temperatures, as low as −80&nbsp;°C, and early spring conditions. In such conditions the [[ice crystals]] of the cloud provide a suitable surface for conversion of unreactive chlorine compounds into reactive chlorine compounds, which can easily deplete ozone.

Moreover, the [[polar vortex]] formed over [[Antarctica]] is very tight and the reaction occurring on the surface of the cloud crystals is far different from when it occurs in atmosphere. These conditions have led to ozone hole formation in Antarctica. This [[hypothesis]] was decisively confirmed, first by [[laboratory]] measurements and subsequently by direct measurements, from the ground and from high-altitude [[airplane]]s, of very high concentrations of [[chlorine monoxide]] (ClO) in the Antarctic stratosphere.<ref>{{Cite journal | last1 = Solomon | first1 = P. M. | last2 = Connor | first2 = B. | last3 = De Zafra | first3 = R. L. | last4 = Parrish | first4 = A. | last5 = Barrett | first5 = J. | last6 = Jaramillo | first6 = M. | doi = 10.1038/328411a0 | title = High concentrations of chlorine monoxide at low altitudes in the Antarctic spring stratosphere: Secular variation | journal = Nature | volume = 328 | issue = 6129 | pages = 411–413 | year = 1987 | bibcode = 1987Natur.328..411S | s2cid = 4335797 }}</ref>

Alternative hypotheses, which had attributed the ozone hole to variations in solar [[Ultraviolet|UV radiation]] or to changes in atmospheric circulation patterns, were also tested and shown to be untenable.<ref>{{cite book |last1=Reddy |first1=Jeevananda |title=Climate Change Myths and Realities |date=4 November 2008 |page=32 |url=https://www.scribd.com/doc/8963733/Climate-Change-Myths-and-Realities |access-date=20 December 2018}}</ref>

Meanwhile, analysis of ozone measurements from the worldwide network of ground-based Dobson spectrophotometers led an international panel to conclude that the ozone layer was in fact being depleted, at all latitudes outside of the tropics.<ref name="epa.gov" /> These trends were confirmed by satellite measurements. As a consequence, the major halocarbon-producing nations agreed to phase out production of CFCs, halons, and related compounds, a process that was completed in 1996.

Since 1981 the [[United Nations Environment Programme]], under the auspices of the World Meteorological Organization, has sponsored a series of technical reports on the [[Scientific Assessment of Ozone Depletion]], based on satellite measurements. The 2007 report showed that the hole in the ozone layer was recovering and the smallest it had been for about a decade.<ref>{{cite news |title=Ozone hole closing up, research shows |url=http://abc.net.au/news/stories/2007/11/16/2092527.htm |archive-url=https://archive.today/20120715114821/http://abc.net.au/news/stories/2007/11/16/2092527.htm |url-status=dead |archive-date=July 15, 2012 |work=[[ABC News (United States)|ABC News]] |publisher=Australian Broadcasting Commission |date=November 16, 2007 }}</ref>

A 2010 report found, "Over the past decade, global ozone and ozone in the Arctic and Antarctic regions is no longer decreasing but is not yet increasing. The ozone layer outside the Polar regions is projected to recover to its pre-1980 levels some time before the middle of this century. In contrast, the springtime ozone hole over the Antarctic is expected to recover much later."<ref>{{cite news |title=New report highlights two-way link between ozone layer and climate change |url=http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=647&ArticleID=6751&l=en&t=long |work=UNEP News Center |date=November 16, 2010 |access-date=September 18, 2010 |archive-date=December 5, 2010 |archive-url=https://web.archive.org/web/20101205143536/http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=647&ArticleID=6751&l=en&t=long |url-status=dead }}</ref>

In 2012, [[NOAA]] and [[NASA]] reported "Warmer air temperatures high above the Antarctic led to the second smallest season ozone hole in 20 years averaging 17.9 million square kilometres. The hole reached its maximum size for the season on Sept 22, stretching to 21.2 million square kilometres."<ref>{{cite web|title=NOAA, NASA: Antarctic ozone hole second smallest in 20 years |url=http://www.noaanews.noaa.gov/stories2012/20121024_antarcticozonehole.html |date=October 24, 2012}}</ref> A gradual trend toward "healing" was reported in 2016<ref name="healing" /> and then in 2017.<ref>{{Cite journal|last1=Kuttippurath|first1=Jayanarayanan|last2=Nair|first2=Prijitha J.|date=2017-04-03|title=The signs of Antarctic ozone hole recovery|journal=Scientific Reports|language=en|volume=7|issue=1|pages=585|doi=10.1038/s41598-017-00722-7|issn=2045-2322|pmc=5429648|pmid=28373709|bibcode=2017NatSR...7..585K}}</ref> It is reported that the recovery signal is evident even in the ozone loss saturation altitudes.<ref>{{Cite journal|last1=Kuttippurath|first1=J.|last2=Kumar|first2=P.|last3=Nair|first3=P. J.|last4=Pandey|first4=P. C.|date=2018-11-21|title=Emergence of ozone recovery evidenced by reduction in the occurrence of Antarctic ozone loss saturation|journal=npj Climate and Atmospheric Science|language=en|volume=1|issue=1|page=42 |doi=10.1038/s41612-018-0052-6|bibcode=2018npCAS...1...42K |issn=2397-3722|doi-access=free}}</ref>

The hole in the Earth's ozone layer over the South Pole has affected atmospheric circulation in the Southern Hemisphere all the way to the equator.<ref>{{cite web |url=http://www.earth.columbia.edu/articles/view/2802 |title=Study Links Ozone Hole to Weather Shifts |publisher=The Earth Institute – Columbia University |date=April 22, 2011 |access-date=December 21, 2012}}</ref> The ozone hole has influenced atmospheric circulation all the way to the tropics and increased rainfall at low, subtropical latitudes in the Southern Hemisphere.<ref>{{Cite web |title=Study Links Ozone Hole to Weather Shifts – The Earth Institute – Columbia University |url=https://www.earth.columbia.edu/articles/view/2802 |access-date=2022-07-13 |website=www.earth.columbia.edu}}</ref>

=== Arctic ozone "mini-hole" ===
On March 3, 2005, the journal ''Nature''<ref>{{Cite journal|url=http://www.nature.com/news/2005/050228/full/news050228-12.html|title=Solar wind hammers the ozone layer|journal=Nature|access-date=May 28, 2016|doi=10.1038/news050228-12|year=2005|last1=Schiermeier|first1=Quirin|pages=news050228–12}}</ref> published an article linking 2004's unusually large Arctic ozone hole to solar wind activity.

On March 15, 2011, a record ozone layer loss was observed, with about half of the ozone present over the Arctic having been destroyed.<ref>{{cite magazine |author=Dell'Amore, Christine |url=http://news.nationalgeographic.com/news/2011/03/110321-ozone-layer-hole-arctic-north-pole-science-environment-uv-sunscreen/ |archive-url=https://web.archive.org/web/20110324184811/http://news.nationalgeographic.com/news/2011/03/110321-ozone-layer-hole-arctic-north-pole-science-environment-uv-sunscreen/ |url-status=dead |archive-date=March 24, 2011 |title=First North Pole Ozone Hole Forming? |magazine=National Geographic |date=March 22, 2011 |access-date=April 6, 2011}}</ref><ref name=verge/><ref>{{cite web|url=http://scienceblogs.com/deanscorner/2011/03/the_arctic_ozone_sieve_more_gl.php |title=The Arctic Ozone Sieve: More Global Weirding? |publisher=Scienceblogs.com |date=March 25, 2011 |access-date=April 6, 2011 |url-status=unfit |archive-url=https://web.archive.org/web/20110404141912/http://scienceblogs.com/deanscorner/2011/03/the_arctic_ozone_sieve_more_gl.php |archive-date=April 4, 2011 }}</ref> The change was attributed to increasingly cold winters in the Arctic stratosphere at an altitude of approximately {{convert|20|km|mi|abbr=on}}, a change associated with global warming in a relationship that is still under investigation.<ref name=verge>{{cite web|url=https://www.sciencedaily.com/releases/2011/03/110314100835.htm |title=Arctic on the verge of record ozone loss |author=Helmholtz Association of German Research Centres |website=Science Daily |date=March 14, 2011 |access-date=April 6, 2011}}</ref> By March 25, the ozone loss had become the largest compared to that observed in all previous winters with the possibility that it would become an ozone hole.<ref name="euractiv1">{{cite web|url=http://www.euractiv.com/en/climate-environment/developing-ozone-hole-approaches-europe-news-503504 |title=Developing ozone hole approaches Europe |publisher=EurActiv |access-date=April 6, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110404023940/http://www.euractiv.com/en/climate-environment/developing-ozone-hole-approaches-europe-news-503504 |archive-date=April 4, 2011 }}</ref> This would require that the quantities of ozone to fall below 200 Dobson units, from the 250 recorded over central Siberia.<ref name="euractiv1" /> It is predicted that the thinning layer would affect parts of Scandinavia and Eastern Europe on March 30–31.<ref name="euractiv1" />

On October 2, 2011, a study was published in the journal ''[[Nature (journal)|Nature]]'', which said that between December 2010 and March 2011 up to 80 percent of the ozone in the atmosphere at about {{convert|20|km|mi}} above the surface was destroyed.<ref name="bbc">{{cite news|title=Arctic ozone loss at record level|url=https://www.bbc.co.uk/news/science-environment-15105747|work=[[BBC News]] Online|access-date=October 3, 2011|archive-url=https://web.archive.org/web/20111002225339/http://www.bbc.co.uk/news/science-environment-15105747|archive-date=October 2, 2011|url-status=live|date=October 2, 2011}}</ref> The level of ozone depletion was severe enough that scientists said it could be compared to the ozone hole that forms over Antarctica every winter.<ref name="bbc" /> According to the study, "for the first time, sufficient loss occurred to reasonably be described as an Arctic ozone hole."<ref name="bbc" /> The study analyzed data from the [[Aura (satellite)|Aura]] and [[CALIPSO]] satellites, and determined that the larger-than-normal ozone loss was due to an unusually long period of cold weather in the Arctic, some 30 days more than typical, which allowed for more ozone-destroying chlorine compounds to be created.<ref name="press release" /> According to Lamont Poole, a co-author of the study, cloud and aerosol particles on which the chlorine compounds are found "were abundant in the Arctic until mid March 2011—much later than usual—with average amounts at some altitudes similar to those observed in the Antarctic, and dramatically larger than the near-zero values seen in March in most Arctic winters".<ref name="press release">{{cite press release |title=Unprecedented Arctic Ozone Loss in 2011, Says NASA-Led Study |url=http://www.nasa.gov/centers/langley/news/releases/2011/11-085.html |publisher=NASA |access-date=July 1, 2016 |date=October 2, 2011 |archive-date=July 9, 2023 |archive-url=https://web.archive.org/web/20230709105936/https://www.nasa.gov/centers/langley/news/releases/2011/11-085.html |url-status=dead }}</ref>

In 2013, researchers analyzed the data and found the 2010–2011 Arctic event did not reach the ozone depletion levels to classify as a true hole. A hole in the ozone is generally classified as 220 Dobson units or lower;<ref>{{Cite journal|last1=Millan|first1=Luis|last2=Manney|first2=Gloria|date=2017-05-02|title=An assessment of Ozone Mini-holes Representation in Reanalyses Over the Northern Hemisphere|url=https://www.researchgate.net/publication/316632591|journal=Atmospheric Chemistry and Physics Discussions|volume=17|issue=15|page=9277|doi=10.5194/acp-2017-341|bibcode=2017ACP....17.9277M |doi-access=free }}</ref> the Arctic hole did not approach that low level.<ref>{{Cite journal|last1=Strahan|first1=S. E.|last2=Douglass|first2=A. R.|last3=Newman|first3=P. A.|date=2013|title=The contributions of chemistry and transport to low arctic ozone in March 2011 derived from Aura MLS observations|journal=Journal of Geophysical Research: Atmospheres|language=en|volume=118|issue=3|pages=1563–1576|doi=10.1002/jgrd.50181|bibcode=2013JGRD..118.1563S|issn=2169-8996|hdl=2060/20120011691|s2cid=128447261|hdl-access=free}}</ref><ref>{{Cite web|url=http://www.nasa.gov/topics/earth/features/2011-ozone-hole.html|title=NASA Pinpoints Causes of 2011 Arctic Ozone Hole|last=Zell|first=Holly|date=2013-06-07|website=NASA|language=en|access-date=2019-10-03|archive-date=2019-09-07|archive-url=https://web.archive.org/web/20190907014502/https://www.nasa.gov/topics/earth/features/2011-ozone-hole.html|url-status=dead}}</ref> It has since been classified as a "mini-hole."<ref>{{Cite web|url=https://www.livescience.com/27824-arctic-ozone-loss-nasa.html|title=Cause of Odd Arctic Ozone 'Hole' Found|last=Earth|first=Stephanie Pappas 2013-03-11T23:38:39Z Planet|website=livescience.com|date=11 March 2013|language=en|access-date=2019-10-03}}</ref>

Following the ozone depletion in 1997 and 2011, a 90% drop in ozone was measured by [[weather balloons]] over the Arctic in March 2020, as they normally recorded 3.5 parts per million of ozone, compared to only around 0.3 parts per million lastly, due to the coldest temperatures ever recorded since 1979, and a strong polar [[vortex]] which allowed chemicals, including chlorine and bromine, to reduce ozone.<ref>{{cite journal|url=https://www.nature.com/articles/d41586-020-00904-w|title=Rare ozone hole opens over Arctic — and it's big|journal=Nature|date=27 March 2020|doi=10.1038/d41586-020-00904-w|last1=Witze|first1=Alexandra|volume=580|issue=7801|pages=18–19|pmid=32221510|bibcode=2020Natur.580...18W|s2cid=214694393}}</ref>

A rare hole, the result of unusually low temperatures in the atmosphere above the North Pole, was studied in 2020.<ref>{{Cite news |last=Harvey |first=Fiona |author-link=Fiona Harvey |date=2020-04-07 |title=Record-size hole opens in ozone layer above the Arctic |url=https://www.theguardian.com/environment/2020/apr/07/record-size-hole-opens-in-ozone-layer-above-the-arctic |access-date=2020-04-08 |work=[[The Guardian]] |language=en-GB |issn=0261-3077}}</ref><ref>{{cite news |last1=Lubben |first1=Alex |title=Now There's Another Hole in the Ozone Layer. Great. |url=https://www.vice.com/en/article/now-theres-another-hole-in-the-ozone-layer-great/ |work=[[Vice (magazine)|Vice]]|date=8 April 2020 |language=en}}</ref>

=== Tibet ozone hole ===
As winters that are colder are more affected, at times there is an ozone hole over Tibet. In 2006, a 2.5&nbsp;million [[square kilometer]] ozone hole was detected over Tibet.<ref>{{cite web|url=http://elainemeinelsupkis.typepad.com/earth_news/2006/05/chinese_scienti.html |title=Earth news: Chinese Scientists Find New Ozone Hole Over Tibet |publisher=Elainemeinelsupkis.typepad.com |date=May 4, 2006 |access-date=April 6, 2011}}</ref> Again in 2011, an ozone hole appeared over mountainous regions of [[Tibet]], [[Xinjiang]], [[Qinghai]] and the [[Hindu Kush]], along with an unprecedented hole over the Arctic, though the Tibet one was far less intense than the ones over the Arctic or Antarctic.<ref>{{cite web|last=Schiermeier |first=Quirin |url=http://blogs.nature.com/news/thegreatbeyond/2011/04/arctic_ozone_hole_causes_conce.html |title=The Great Beyond: Arctic ozone hole causes concern |publisher=Blogs.nature.com |date=February 22, 1999 |access-date=April 6, 2011}}</ref>

=== Potential depletion by storm clouds ===
Research in 2012 showed that the same process that produces the ozone hole over Antarctica, occurs over summer storm clouds in the United States, and thus may be destroying ozone there as well.<ref>{{cite web |url=http://www.livescience.com/21882-storm-clouds-deplete-ozone.html |title=Storm Clouds May Punch Holes in Ozone |first=Becky |last=Oskin |publisher=LiveScience |date=July 26, 2012 |access-date=March 13, 2015}}</ref><ref>{{cite news |first=Henry |last=Fountain |url=https://www.nytimes.com/2012/07/27/science/earth/strong-storms-threaten-ozone-layer-over-us-study-says.html?pagewanted=all |title=Storms Threaten Ozone Layer Over U.S., Study Says |date=July 27, 2012 |newspaper=[[The New York Times]] |page=A1 |access-date=March 13, 2015}}</ref>

=== Ozone hole over tropics ===
Physicist Qing-Bin Lu, of the University of Waterloo, claimed to have discovered a large, all-season ozone hole in the lower stratosphere over the tropics in July 2022.<ref>{{Cite web |last=American Institute of Physics |date=2022-07-05 |title=Discovery reveals large, year-round ozone hole over tropics: 'New' ozone hole much larger than Antarctic ozone hole |url=https://www.sciencedaily.com/releases/2022/07/220705112242.htm |access-date=2022-07-06 |website=ScienceDaily |language=en}}</ref> However, other researchers in the field refuted this claim, stating that the research was riddled with "serious errors and unsubstantiated assertions."<ref>{{cite web | url=https://www.sciencemediacentre.org/expert-reaction-to-research-claiming-ozone-hole-over-tropics/ | title=Expert reaction to research claiming ozone hole over tropics &#124; Science Media Centre }}</ref> According to Dr Paul Young, a lead author of the 2022 WMO/UNEP Scientific Assessment of Ozone Depletion, "The author's identification of a 'tropical ozone hole' is down to him looking at percentage changes in ozone, rather than absolute changes, with the latter being much more relevant for damaging UV reaching the surface." Specifically, Lu's work defines "ozone hole" as "an area with O3 loss in percent larger than 25%, with respect to the undisturbed O3 value when there were no significant CFCs in the stratosphere (~ in the 1960s)"<ref>{{Citation |author=Lu |first=Qing-Bin |title=Observation of large and all-season ozone losses over the tropics |journal=AIP Advances |volume=12 |issue=7 |pages=075006 |year=2022 |arxiv=2112.14977 |bibcode=2022AIPA...12g5006L |doi=10.1063/5.0094629 |s2cid=251643894}}.</ref> instead of the general definition of 220 Dobson units or lower. Dr Marta Abalos Alvarez has added "Ozone depletion in the tropics is nothing new and is mainly due to the acceleration of the Brewer-Dobson circulation."

=== Depletion caused by wildfire smoke ===

Analyzing the atmospheric impacts of the [[2019–20 Australian bushfire season|2019–2020 Australian bushfire season]], scientists led by MIT researcher Susan Solomon found the smoke destroyed 3–5% of ozone in affected areas of the Southern Hemisphere. Smoke particles absorb [[hydrogen chloride]] and act as a catalyst to create chlorine radicals that destroy ozone.<ref>
{{cite news |author=Gramling |first=Carolyn |date=March 8, 2023 |title=How wildfires deplete the Earth's ozone layer |url=https://www.sciencenews.org/article/wildfire-ozone-layer-chemical-reaction-smoke |publisher=ScienceNews}}</ref><ref>
{{cite news |author=Chu |first=Jennifer |date=February 28, 2022 |title=Study reveals chemical link between wildfire smoke and ozone depletion |url=https://news.mit.edu/2022/wildfire-smoke-ozone-depletion-0228}}</ref><ref>
{{cite journal |last1=Solomon |first1=Susan |last2=Stone |first2=Kane |last3=Yu |first3=Pengfei |last4=Murphy |first4=D. M. |last5=Kinnison |first5=Doug |last6=Ravishankara |first6=A. R. |last7=Wang |first7=Peidong |date=March 8, 2023 |title=Chlorine activation and enhanced ozone depletion induced by wildfire aerosol |journal=Nature |volume=615 |issue=7951 |pages=259–264 |bibcode=2023Natur.615..259S |doi=10.1038/s41586-022-05683-0 |pmid=36890371}}</ref><ref>
{{cite journal |last1=Solomon |first1=Susan |last2=Dube |first2=Kimberlee |last3=Stone |first3=Kane |last4=Yu |first4=Pengfei |last5=Kinnison |first5=Doug |last6=Toon |first6=Owen B. |last7=Strahan |first7=Susan E. |last8=Rosenlof |first8=Karen H. |last9=Portmann |first9=Robert |last10=Davis |first10=Sean |last11=Randel |first11=William |last12=Bernath |first12=Peter |last13=Boone |first13=Chris |last14=Bardeen |first14=Charles G. |last15=Bourassa |first15=Adam |date=March 1, 2022 |title=On the stratospheric chemistry of midlatitude wildfire smoke |journal=PNAS |volume=119 |issue=10 |pages=e2117325119 |bibcode=2022PNAS..11917325S |doi=10.1073/pnas.2117325119 |pmc=8915979 |pmid=35238658 |doi-access=free |author16=Daniel Zawada |author17=Doug Degenstein}}</ref>