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UW ATMS 211 - Lecture Notes

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1Lecture 4Annoucement: Slides /notes now on class websiteQuestions so far?Last time: Began intro to atmospheric structureOutline of this lecture:• More on atmospheric structure• Start on the ozone layer and ozone depletionTextbook: Leap forward to the beginning of Chapter 17!Goal / Motivation• good example illustrating nature of the Earth-System (including humans)• coupled system...complexityunexpected consequences• global environmental problemdiscoveryexplanationsolution via international agreementsEnvironmental “skeptic” stuffThe following appeals to a sort of folksy common sense andappears to come from a credible source.However, it’s scientific nonsense. Can you work out why?(based on something we’ve covered in lectures)?“Several questions are obvious [problems with the theory of CFCsbeing responsible for ozone depletion]: How does CFC risewhen its molecules are four to eight times heavier than air?”From Environmental Overkill (1993) by Dixy Lee Ray & Louis Guzzo Dixy Lee Ray (Stanford Ph.D. in Zoology (1945), former UW prof., Governor of Washington State (1977-1981), Chairman of Atomic Energy Commission)_____________IgnoranceThe arbiter of truth: ObservationsSource: Scientific Assessment of Ozone Depletion NOAA/ NASA/ WMO/ UN Environment Programhttp://www.al.noaa.gov/WWWHD/Pubdocs/Assessment94/common-questions-q1.htmlThe concentration ofone of the mostcommonchlorofluorocarbons:CFC-11 = freon-11= CCl3FWas used in:- sprays cans-blowing agent formaking Styrofoam- cleaning microchips2A brief history of ozone & CFCs1920s - measurements of the spectrum of ultraviolet lightreaching the ground by Prof. Gordon Dobson (OxfordUniversity) are used to infer the presence of a stratosphericozone layer. (“Dobson units” used today for ozone abundance)1950s - first measurements of the overhead column of ozone are made in Antarctica1930s - CFCs developed; marketed under the trade name“Freon” by Du Pont as a refrigerant. 1973 James Lovelock discovers CFCs are global,persistent, long-lived chemicals in the atmosphere. Noone knew the threat to the O3 layer at the time.history continued…1970s - USA per capita consumption ~ 1 kg CFC/yr1974 - scientists theorize that Cl from CFCs could destroyozone in the stratosphere1978 - US bans CFC use in spray cansLate 70s-early 80s - evidence on ozone depletion inconclusive;some depletion evident but statistical significancequestioned by skeptics1985 - British Antarctic Survey report “ozone hole”.NASA’s Nimbus 7 satellite had been measuring the holefor 6 years at this point, but ozone was so low it wasflagged as “bad” data. In fact, the data was correct.Ozone hole in the newsDU, ozone column depth and geographical distrib."DU" (Dobson Unit)• measure of "ozone column depth"> related to the number of O3molecules overheadÿ1DU = 0.001 cm at surfacepressure• typical value is 300 DU= 0.3 cm layer (3 mm)• geographical distribution due to seasonal winds in stratosphere> thin in the tropics> thicker at high latitudes> thickest in NH high latitudes3 UV notes"UV" ( ultraviolet radiation)• ultraviolet means "beyondviolet"- shorter wavelength thanviolet- not visible to humans• highly energetic- drives photochemicalreactions- causes harm to life(sunburn, genetic damage,cancer)• 3 classes: A, B, C - A not harmful - C extremely harmful, butnone gets to surface- B is the big


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UW ATMS 211 - Lecture Notes

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