lec19 - ATM 6, Lecture #19 Stratospheric Ozone Depletion or...

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1 1 ATM 6, Lecture #19 Cort Anastasio Atmospheric Science Program University of California - Davis Stratospheric Ozone Depletion or “The Ozone Hole” Part III: PSCs, History of O 3 Depletion, and Prognosis for Stratospheric Ozone 2 A History of Stratospheric O 3 Loss (I) 1930s: CFCs developed. Used widely by end of WWII: propellants in aerosol cans, refrigerants, solvents. 1971: Lovelock – made first measurements of CFCs in troposphere. 1973/74: Rowland and Molina (UC Irvine) posed question: What is fate of CFCs? Their answer: CFCs are broken down by UV radiation in stratosphere The produced Cl atoms can destroy stratospheric O 3 ! Predicted 7-14% global loss of O 3 . 1976: U.S. announces schedule to ban CFCs in aerosol sprays (~3/4 of CFC use at time), effective 1978. Similar bans announced in a few other countries. 1984/85: Farman et al. measure spectacular decreases in O 3 at Antarctic during spring (October). Column O 3 amounts are 33% lower than they should be (Fig. 13.22 at right)! Observations are confirmed with satellite (TOMS). This shocking loss of O 3 was much higher than thought possible by chemists. What key feature was missing in these early models of stratospheric O 3 chemistry?
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2 3 The Missing Piece: PSCs Introduction to Polar Stratospheric Clouds • PSCs are stratospheric particles made of sulfuric and nitric acids and ice • PSCs form only under very cold conditions (approximately -110 °F) – In the stratosphere, these cold temperatures are found over poles in winter • Temperatures get so low in part because of “polar vortex” – Vortex isolates poles during dark winter, keeping warming air out Arctic PSCs over Sweden in Jan. 2000 Minimum Temperatures in Polar Stratosphere Fig. 13.24 Cartoon of polar vortex over Antarctic 4 PSC Chemistry How Do PSCs Accelerate Ozone Loss? • Remember that there are
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This note was uploaded on 04/22/2008 for the course ATM 006 taught by Professor Anastasio during the Fall '07 term at UC Davis.

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lec19 - ATM 6, Lecture #19 Stratospheric Ozone Depletion or...

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