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CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE (1930)

CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE (1930). Odd oxygen family [O x ] = [O 3 ] + [O]. slow. R2. R1. O 2. O O 3. fast. R3. R4. slow. Lifetime of O atoms:. STEADY-STATE ANALYSIS OF CHAPMAN MECHANISM. …is sufficiently short to assume steady state for O:.

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CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE (1930)

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  1. CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE (1930) Odd oxygen family [Ox] = [O3] + [O] slow R2 R1 O2 O O3 fast R3 R4 slow

  2. Lifetime of O atoms: STEADY-STATE ANALYSIS OF CHAPMAN MECHANISM …is sufficiently short to assume steady state for O: …so the budget of O3 is controlled by the budget of Ox. Lifetime of Ox: Ox Steady state for Ox:

  3. SOLAR SPECTRUM AND ABSORPTION X-SECTIONS O3+hv O2+hv

  4. PHOTOLYSIS RATE CONSTANTS: VERTICAL DEPENDENCE quantum yield absorption X-section photon flux

  5. shape determined by k1nO2 CHAPMAN MECHANISM vs. OBSERVATION -3 Chapman mechanism reproduces shape, but is too high by factor 2-3 e missing sink!

  6. non-radical radical + radical RADICAL REACTION CHAINS IN THE ATMOSPHERE photolysis thermolysis oxidation by O(1D) Initiation: bimolecular redox reactions Propagation: radical + non-radical non-radical + radical radical redox reaction Termination: non-radical + non-radical radical + radical non-radical + M 3-body recombination radical + radical + M

  7. H2O mixing ratio WATER VAPOR IN STRATOSPHERE Source: transport from troposphere, oxidation of methane (CH4)

  8. Ozone loss catalyzed by hydrogen oxide (HOx ≡ H + OH + HO2) radicals Initiation: Propagation: Termination: slow H2O OH HO2 fast HOx radical family slow

  9. H2O mixing ratio NITROUS OXIDE IN THE STRATOSPHERE

  10. Ozone loss catalyzed by nitrogen oxide (NOx ≡ NO + NO2) radicals • Initiation N2O + O(1D) 2NO • Propagation NO + O3  NO2 + O2 NO + O3  NO2 + O2 NO2 + h NO + O NO2 + O  NO + O2 O + O2 + M  O3 + M Null cycleNet O3 + O  2O2 • TerminationRecycling NO2 + OH + M  HNO3 + M HNO3 + h NO2 + OH NO2 + O3 NO3 + O2 HNO3 + OH NO3 + H2O NO3 + NO2 + M  N2O5 + M NO3 + h NO2 + O N2O5 + H2O  2HNO3 N2O5 + hNO2 + NO3 O3 loss rate:

  11. ATMOSPHERIC CYCLING OF NOx AND NOy

  12. STRATOSPHERIC OZONE BUDGET FOR MIDLATITUDES CONSTRAINED FROM 1980s SPACE SHUTTLE OBSERVATIONS Gas-phase chemistry only

  13. STRATOSPHERIC DISTRIBUTION OF CF2Cl2 (CFC-12)

  14. Ozone loss catalyzed by chlorine (ClOx≡ Cl + ClO) radicals • Initiation: Cl radical generation from non-radical precursors (e.g., CFC-12) CF2Cl2 + hng CF2Cl + Cl • Propagation: Cl + O3 g ClO + O2 ClO + Og Cl + O2 Net: O3 + O g 2O2 • Termination: Recycling: Cl + CH4g HCl + CH3 HCl + OH gCl + H2O ClO + NO2 + M g ClNO3 + M ClNO3 + hn gCl + NO3 O3 loss rate:

  15. ATMOSPHERIC CYCLING OF ClOx AND Cly

  16. SOURCE GAS CONTRIBUTIONS TOSTRATOSPHERIC CHLORINE (2004)

  17. CHLORINE PARTITIONING IN STRATOSPHERE

  18. OZONE TREND AT HALLEY BAY, ANTARCTICA (OCTOBER) Farman et al. paper published in Nature 1 Dobson Unit (DU) = 0.01 mm O3 STP = 2.69x1016 molecules cm-2

  19. SPATIAL EXTENT OF THE OZONE HOLE Isolated concentric region around Antarctic continent is called the polar vortex. Strong westerly winds, little meridional transport

  20. THE OZONE HOLE IS A SPRINGTIME PHENOMENON

  21. VERTICAL STRUCTURE OF THE OZONE HOLE:near-total depletion in lower stratosphere Argentine Antarctic station southern tip of S. America

  22. ASSOCIATION OF ANTARCTIC OZONE HOLEWITH HIGH LEVELS OF CLO Sept. 1987 ER-2 aircraft measurements at 20 km altitude south of Punta Arenas O3 ClO O3 Sep. 16 Edge of Polar vortex ClO Sep. 2, 1987 20 km altitude Measurements by Jim Anderson’s group (Harvard)

  23. SATELLITE OBSERVATIONS OF ClO IN THE SOUTHERN HEMISPHERE STRATOSPHERE

  24. WHY THE HIGH ClO IN ANTARCTIC VORTEX?Release of chlorine radicals from reactions of reservoir species in polar stratospheric clouds (PSCs)

  25. PSC FORMATION AT COLD TEMPERATURES PSC formation Frost point of water

  26. HOW DO PSCs START FORMING AT 195K?HNO3-H2O PHASE DIAGRAM Antarctic vortex conditions PSCs are not water but nitric acid trihydrate (NAT) clouds

  27. DENITRIFICATION IN THE POLAR VORTEX:SEDIMENTATION OF PSCs

  28. CHRONOLOGY OF ANTARCTIC OZONE HOLE

  29. TRENDS IN GLOBAL OZONE Mt. Pinatubo

  30. LONG-TERM COOLING OF THE STRATOSPHERE Sep 21-30, 25 km, 65-75˚S Increasing CO2 is expected to cool the stratosphere

  31. TRENDS IN POLAR OZONECould greenhouse-induced cooling of stratosphereproduce an Arctic ozone hole over the next decade? Race between chlorine decrease and climate change

  32. SKIN CANCER EPIDEMIOLOGY PREDICTIONS

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