Editing Ozone depletion (section)

=== Percentage of human-made chlorine ===
[[File:Sources stratospheric chlorine.png|right|thumb|upright=1.7|Sources of stratospheric chlorine]]

Another misconception is that natural sources of chlorine are several times larger than human-made ones. While this statement is true for tropospheric chlorine, that is irrelevant to ozone depletion, which is only affected by stratospheric chlorine. Chlorine from [[salt spray|ocean spray]] is soluble and thus is washed by rainfall before it reaches the stratosphere. CFCs, in contrast, are insoluble and long-lived, allowing them to reach the stratosphere. In the lower atmosphere, there is much more chlorine from CFCs and related [[haloalkane]]s than there is in HCl from salt spray, and in the stratosphere halocarbons are dominant.<ref>[http://www.faqs.org/faqs/ozone-depletion/stratcl ozone-depletion FAQ, Part II] {{Webarchive|url=https://web.archive.org/web/20090203032254/http://www.faqs.org/faqs/ozone-depletion/stratcl/ |date=2009-02-03 }}, section 4.3</ref> Only methyl chloride, which is one of these halocarbons, has a mainly natural source,<ref>{{Cite journal
| last1 = Yokouchi | first1 = Y.
| last2 = Noijiri | first2 = Y.
| last3 = Barrie | first3 = L. A.
| last4 = Toom-Sauntry | first4 = D.
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| title = A strong source of methyl chloride to the atmosphere from tropical coastal land
| journal = Nature
| volume = 403
| issue = 6767
| pages = 295–298
| doi = 10.1038/35002049
| year = 2000
| pmid = 10659845
| bibcode = 2000Natur.403..295Y
| s2cid = 4318352
}}</ref> and it is responsible for about 20 percent of the chlorine in the stratosphere; the remaining 80 percent comes from human-made sources.

Very violent volcanic eruptions can inject HCl into the stratosphere, but researchers have shown that the contribution is not significant compared to that from CFCs.<ref name="O3F4_4">[http://www.faqs.org/faqs/ozone-depletion/stratcl ozone-depletion FAQ, Part II] {{Webarchive|url=https://web.archive.org/web/20090203032254/http://www.faqs.org/faqs/ozone-depletion/stratcl/ |date=2009-02-03 }}, section 4.4</ref> A similar erroneous assertion is that soluble halogen compounds from the volcanic plume of [[Mount Erebus]] on Ross Island, Antarctica are a major contributor to the Antarctic ozone hole.<ref name="O3F4_4" />

Nevertheless, a 2015 study showed that the role of [[Mount Erebus]] volcano in the Antarctic ozone depletion was probably underestimated. Based on the [[NCEP/NCAR reanalysis]] data over the last 35 years and by using the NOAA [[HYSPLIT]] trajectory model, researchers showed that gas emissions from the volcano (including [[hydrogen chloride]] (HCl)) can reach the Antarctic stratosphere via high-latitude cyclones and then the [[polar vortex]]. Depending on the level of its volcanic activity, the additional annual HCl mass entering the stratosphere from Erebus varies from 1.0 to 14.3 kt.<ref>{{cite journal |last1=Zuev |first1=V. V. |last2=Zueva |first2=N. E. |last3=Savelieva |first3=E. S. |last4=Gerasimov |first4=V. V. |year=2015 |title=The Antarctic ozone depletion caused by Erebus volcano gas emissions |journal=[[Atmospheric Environment]] |volume=122 |pages=393–399 |bibcode=2015AtmEn.122..393Z |doi=10.1016/j.atmosenv.2015.10.005 |doi-access=free}}</ref>