Chem5151_strat2

Chem5151_strat2 - 1 Stratospheric Chemistry Part 2 Darin...

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Unformatted text preview: 1 Stratospheric Chemistry Part 2 Darin Toohey CU PAOS Quick summary from last time The controversy The Big Surprise of 1985 Heterogeneous chemistry Chlorine and NO y Why Antarctica and the Arctic? The story continues O+O 3 O + catalysts O 2 h O O 3 O 2 O O 2 h h Odd oxygen 2 O 2 + h O + O O + O 2 + M O 3 + M O 3 + h O 2 + O O 3 + O O 2 + O 2 Chapman chemistry (in steady state) Fast and approx. balance Slow and exactly balance ] [ ] ][ [ 2 4 3 2 O k J O O O = ] [ ~ ] ][ ][ [ 3 2 2 3 O J M O O k O ] ][ [ 1 ~ ] [ ] [ 2 2 3 3 M O k J O O O ] ][ [ ] [ 3 4 2 2 O O k O J O = 2 3 2 1 2 1 4 2 3 ] [ 21 . ~ ] [ 3 2 M J J k k O O O X + O 3 XO + O 2 XO + O X + O 2 O 3 + O O 2 + O 2 Catalysts O 3 + h O 2 + O( 1 D) N 2 O + O( 1 D) NO + NO (about 4% of all N 2 O oxidation) H 2 O + O( 1 D) OH + OH CF x Cl y + h + O 2 + h .... CO 2 + xF + yCl SSTs H 2 O, NO x Chlorine volcanoes, space shuttle N 2 O from fertilizing H 2 O from CH 4 oxidation CFCs refrigerants, propellants, foam blowing, etc. 3 are unusually stable chemically and only slightly soluble in water and might therefore persist and accumulate in the atmosphere The presence of these compounds constitutes no conceivable hazard. (Lovelock) Must have reasonably long lifetimes in troposphere (~years or more) Cant be too soluble in water (e.g. HCl, NaCl) Cant react rapidly with OH or O 3 Cant have large cross sections at visible s Examples N 2 O hundreds of years F-11 (CFCl 3 ) 50 years F-12 (CF 2 Cl 2 ) 100 years HCFCs (CHFCl 2 ) year CH 3 Br - ~1-2 years CF 3 Cl (ppt) lat The pieces come together! Brewer-Dobson circulation 2 CFCl 3 + h CFCl 2 + Cl CF 2 Cl 2 h CF 2 Cl + Cl O 2 + h O + O O + O 2 + M O 3 + M O 3 + h O 2 + O O 3 + O O 2 + O 2 Cl + O 3 ClO + O 2 ClO + O Cl + O 2 Net - O 3 + O O 2 + O 2 transport spark unreactivity release flame destruction source 4 Which one is it?...
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Chem5151_strat2 - 1 Stratospheric Chemistry Part 2 Darin...

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