CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE 1930 slow O

CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE (1930) slow O 2 R 1 O R 2 fast R 3 R 4 slow Odd oxygen family [Ox] = [O 3] + [O] O 3

STEADY-STATE ANALYSIS OF CHAPMAN MECHANISM Lifetime of O atoms: …is sufficiently short to assume steady state for O: …so the budget of O 3 is controlled by the budget of Ox. Lifetime of Ox: Steady state for Ox: Ox

SOLAR SPECTRUM AND ABSORPTION X-SECTIONS O 2+hv O 3+hv

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

CHAPMAN MECHANISM vs. OBSERVATION shape determined by k 1 n. O 2 -3 Chapman mechanism reproduces shape, but is too high by factor 2 -3 e missing sink!

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

WATER VAPOR IN STRATOSPHERE H 2 O mixing ratio Source: transport from troposphere, oxidation of methane (CH 4)

Ozone loss catalyzed by hydrogen oxide (HOx ≡ H + OH + HO 2) radicals Initiation: Propagation: Termination: slow H 2 O OH fast HO 2 slow HOx radical family

NITROUS OXIDE IN THE STRATOSPHERE H 2 O mixing ratio

Ozone loss catalyzed by nitrogen oxide (NOx ≡ NO + NO 2) radicals • Initiation N 2 O + O(1 D) 2 NO • Propagation NO + O 3 NO 2 + O 2 NO 2 + h NO + O NO 2 + O NO + O 2 + M O 3 + M O 3 loss rate: Null cycle Net O 3 + O 2 O 2 • Termination NO 2 + OH + M HNO 3 + M NO 2 + O 3 NO 3 + O 2 NO 3 + NO 2 + M N 2 O 5 + M N 2 O 5 + H 2 O 2 HNO 3 Recycling HNO 3 + h NO 2 + OH HNO 3 + OH NO 3 + H 2 O NO 3 + h NO 2 + O N 2 O 5 + h NO 2 + NO 3

ATMOSPHERIC CYCLING OF NOx AND NOy

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

STRATOSPHERIC DISTRIBUTION OF CF 2 Cl 2 (CFC-12)

Ozone loss catalyzed by chlorine (Cl. Ox ≡ Cl + Cl. O) radicals • Initiation: Cl radical generation from non-radical precursors (e. g. , CFC-12) CF 2 Cl 2 + h g CF 2 Cl + Cl • Propagation: Cl + O 3 g Cl. O + O 2 Cl. O + O g Cl + O 2 Net: O 3 + O g 2 O 2 • Termination: Cl + CH 4 g HCl + CH 3 Cl. O + NO 2 + M g Cl. NO 3 + M O 3 loss rate: Recycling: HCl + OH g. Cl + H 2 O Cl. NO 3 + h g. Cl + NO 3

ATMOSPHERIC CYCLING OF Cl. Ox AND Cly

SOURCE GAS CONTRIBUTIONS TO STRATOSPHERIC CHLORINE (2004)

CHLORINE PARTITIONING IN STRATOSPHERE

OZONE TREND AT HALLEY BAY, ANTARCTICA (OCTOBER) Farman et al. paper published in Nature 1 Dobson Unit (DU) = 0. 01 mm O 3 STP = 2. 69 x 1016 molecules cm-2

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

THE OZONE HOLE IS A SPRINGTIME PHENOMENON

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

ASSOCIATION OF ANTARCTIC OZONE HOLE WITH HIGH LEVELS OF CLO Sept. 1987 ER-2 aircraft measurements at 20 km altitude south of Punta Arenas O 3 Cl. O O 3 Sep. 16 Sep. 2, 1987 Cl. O 20 km altitude Measurements by Jim Anderson’s group (Harvard) Edge of Polar vortex

SATELLITE OBSERVATIONS OF Cl. O IN THE SOUTHERN HEMISPHERE STRATOSPHERE

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

PSC FORMATION AT COLD TEMPERATURES PSC formation Frost point of water

HOW DO PSCs START FORMING AT 195 K? HNO 3 -H 2 O PHASE DIAGRAM Antarctic vortex conditions PSCs are not water but nitric acid trihydrate (NAT) clouds

DENITRIFICATION IN THE POLAR VORTEX: SEDIMENTATION OF PSCs

CHRONOLOGY OF ANTARCTIC OZONE HOLE

TRENDS IN GLOBAL OZONE Mt. Pinatubo

LONG-TERM COOLING OF THE STRATOSPHERE Sep 21 -30, 25 km, 65 -75˚S Increasing CO 2 is expected to cool the stratosphere

TRENDS IN POLAR OZONE Could greenhouse-induced cooling of stratosphere produce an Arctic ozone hole over the next decade? Race between chlorine decrease and climate change

SKIN CANCER EPIDEMIOLOGY PREDICTIONS