Chem5151_strat2

Chem5151_strat2 - 1 Stratospheric Chemistry – Part 2...

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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 ν O O 3 O 2 O O 2 h ν h ν Odd oxygen 2 O 2 + h υ ¡ O + O O + O 2 + M ¡ O 3 + M O 3 + h υ ¡ 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 υ ¡ 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 ν → + O 2 → + h ν.... → 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) • Can’t be too soluble in water (e.g. HCl, NaCl) • Can’t react rapidly with OH or O 3 • Can’t have large cross sections at visible λ 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 ν ¡ CFCl 2 + Cl CF 2 Cl 2 h ν ¡ CF 2 Cl + Cl O 2 + h υ ¡ O + O O + O 2 + M ¡ O 3 + M O 3 + h υ ¡ 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” ‘un’reactivity release “flame” destruction source 4 Which one is it?...
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Chem5151_strat2 - 1 Stratospheric Chemistry – Part 2...

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