UEP-Ozone Depletion Hole Reading Notes PDF

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Section II: THE OZONE DEPLETION PROCESS UEP: Ozone Depletion Hole Reading Notes: -

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Depletion of the Antarctic ozone layer = ozone hole it has occurred as a direct result of the atmospheric and chemical conditions that exist only in this zone Seasonal variations that occur over the Antarctic enhance this ozone hole > low winter temps in the stratosphere cause PSCs [polar stratospheric clouds] reactions between the PSCs with isolation of polar stratospheric air allows chlorine and bromine reactions to essentially develop and produce the hole in the spring (these reactions occur on liquid and solid PSC particles cause the highly reactive chlorine gas ClO to be formed, which catalytically destroys ozone) this depletion occurs relatively more in Antarctic due to the colder temperatures, in the arctic PSC formation temperatures are not always met [depletion does not occur] yet PSC formation temperatures are always present for many months somewhere in the Antarctic, and severe ozone depletion now occurs in each winter season Despite link between ozone/ global warming cold temperatures are still needed for the ozone holes to form essentially as the reactions between the PSCs and the chlorine needs to occur and PSCs only occur as a result of colder atmospheric temps The winter temperatures are low enough for PSCs to form somewhere in the Antarctic for nearly the entire winter (about 5 months) and in the Arctic for only limited periods (10–60 days) in most winters PSCs form in the ozone layer during winters in the Arctic and Antarctic stratospheres wherever low temperatures occur. The particles grow from the condensation of water and nitric acid (HNO3). Reactions on PSCs cause the highly reactive chlorine gas ClO to be formed, which is very effective in the chemical destruction of ozone PSCs are often found near mountain ranges in polar regions because the motion of air over the mountains can cause local cooling of stratospheric air, which increases condensation of water and HNO = orographic When average temperatures begin increasing by late winter, PSCs form less frequently and their surface conversion reactions produce less ClO. Without continued ClO production, ClO amounts decrease and other chemical reactions re-form the reactive reservoirs, ClONO2 and HCl. When PSC temperatures no longer occur, on average, either by late January to early February in the Arctic or by mid-October in the Antarctic, the most intense period of ozone depletion ends (variations in amount of destruction in the hole process can correlate seasonally to temperatures – can ask question on impact of more GHG’s in atmos that could enhance this process? Or even warmer temperatures will impact still be the same?) PSC particles fall to lower altitudes because of gravity. The largest particles can descend several kilometres or more in the stratosphere during the low-temperature winter/spring period that lasts several months in Antarctica. Because PSCs often contain a significant fraction of available HNO3, their descent removes HNO3 from regions of the ozone layer. This process is called denitrification of the stratosphere. With less HNO3, the highly reactive chlorine gas ClO remains chemically active for a longer period, thereby increasing chemical ozone destruction The first decreases in Antarctic total ozone were observed in the early 1980s over research stations located on the Antarctic continent. PSCs form when water vapour enters the stratosphere and here when the temps are cold enough for the w.vap to condense > significantly during winter periods when arctic and Antarctic regions receive little to no solar radiation, the cooling begins = known as ‘polar night’ > under these conditions the PSCs develop. They trap outgoing radiation and reflect most of it back to earth so cooling is reduced in earth thus enhancing warming ....