QUESTIONS 1.Based on the major source of OH described last class where do you expect OH formation to be high? 2.Why don’t reactions of hydrocarbons deplete (or titrate!) all the OH in the troposphere? 3.The Chapman mechanism includes a fifth reaction: O + O + M  O 2 + M What is the effect of this reaction on ozone? Would it be more important in the lower or in the upper stratosphere? 4.On the basis of the lifetimes derived from the Chapman mechanism, would you expect O and O 3 concentrations in the stratosphere to vary with time of day? if so, how?

Initiation N 2 O + O( 1 D)  2NO Propagation NO + O 3  NO 2 + O 2 NO + O 3  NO 2 + O 2 NO 2 + h  NO + O NO 2 + O  NO + O 2 O + O 2 + M  O 3 + M Null cycle Net O 3 + O  2O 2 O 3 loss rate: NO x -CATALYZED OZONE LOSS (NO x  NO + NO 2 ) Day Night NO y  NO x + reservoirs (HNO 3, N 2 O 5,..) Also emitted Termination Recycling NO 2 + OH + M  HNO 3 + M HNO 3 + h  NO 2 + OH NO 2 + O 3  NO 3 + O 2 HNO 3 + OH  NO 3 + H 2 O NO 3 + NO 2 + M  N 2 O 5 + M NO 3 + h  NO 2 + O N 2 O 5 + H 2 O  2HNO 3 N 2 O 5 + h  NO 2 + NO 3

ATMOSPHERIC CYCLING OF NO x AND NO y

NITROUS OXIDE IN THE STRATOSPHERE from CLAES satellite instrument

Gas-phase chemistry only Source of Ox Approximate closure! STRATOSPHERIC OZONE BUDGET FOR MIDLATITUDES CONSTRAINED FROM 1980s SPACE SHUTTLE OBSERVATIONS Paul Crutzen shared 1995 Nobel Prize for his work on the NOx catalyzed destruction of ozone

STRATOSPHERIC DISTRIBUTION OF CFC-12

Initiation: Cl radical generation from non-radical precursors (e.g., CFC-12) CF 2 Cl 2 + h  CF 2 Cl + Cl Propagation: Cl + O 3  ClO + O 2 ClO + O   Cl + O 2 Net: O 3 + O  2O 2 O 3 loss rate: ClO x -CATALYZED OZONE LOSS (ClO x  Cl + ClO) Cl y  ClO x + reservoirs (HCl, ClNO 3 ) Termination:Recycling: Cl + CH 4  HCl + CH 3 HCl + OH  Cl + H 2 O ClO + NO 2 + M  ClNO 3 + MClNO 3 + hn  Cl + NO 3

ATMOSPHERIC CYCLING OF ClO x AND Cl y Molina and Rowland shared 1995 Nobel Prize for their work on the ClOx catalyzed destruction of ozone

SOURCE GAS CONTRIBUTIONS TO STRATOSPHERIC CHLORINE (2004)

CHLORINE PARTITIONING IN STRATOSPHERE

TRENDS IN ATMOSPHERIC CFCs AND HFCs (CFC REPLACEMENTS) Montreal Protocol CFC production is banned [IPCC, 2007]

OZONE TREND AT HALLEY BAY, ANTARCTICA (OCTOBER) Farman et al. paper published in Nature 1 Dobson Unit (DU) = 0.01 mm O 3 STP = 2.69x10 16 molecules cm -2 Stabilization of chlorine?

THE ANTARCTIC OZONE HOLE DU Southern hemisphere ozone column seen from TOMS, October 1 Dobson Unit (DU) = 0.01 mm O 3 STP = 2.69x10 16 molecules cm -2

2006 ANTARCTIC OZONE HOLE: MOST SEVERE OBSERVED Aura OMI – 8 Oct 2006 Minimum of 85 DU on 8 Oct 2006 Ozone Hole Minimum The ozone hole is an austral spring phenomenon – it is not there year-round!

OZONE HOLE IS A SPRING PHENOMENON

VERTICAL STRUCTURE OF THE OZONE HOLE: near-total depletion in lower stratosphere

Sep. 2, 1987 Sep km altitude ASSOCIATION OF ANTARCTIC OZONE HOLE WITH HIGH LEVELS OF ClO Sept ER-2 aircraft measurements at 20 km altitude S of Punta Arenas ClO O3O3 O3O3 Edge of Polar vortex Measurements by Jim Anderson’s group (Harvard)

SATELLITE OBSERVATIONS OF ClO IN THE SOUTHERN HEMISPHERE STRATOSPHERE

O 3 DEPLETION MECHANISM: ClO SELF-REACTION ClO + ClO + M  ClOOCl + M ClOOCl + hv  ClOO + Cl ClOO + M  Cl + O 2 2 x [Cl + O 3  ClO + O 2 ] NET: 2O 3  3O 2  70% of total ozone loss in Antarctic spring An additional catalytic cycle in Antarctic spring involves Br radicals (BrO + ClO)  30% of total ozone loss in Antarctic ozone hole But why are [ClO] so high over Antarctica? Polar stratospheric clouds: conversion of ClOx reservoirs to Cl 2 ClNO 3 + HCl – PSC  Cl 2 + HNO 3 Cl 2 + hv  2Cl

WHY THE HIGH ClO 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

REMINDER: PHASE DIAGRAM FOR WATER Latest Observation for Fort Collins, CO (80523) Site: on CSU campus Time: 8 AM MST 26 AUG 08 Temp: 67.4 F (19.7 C) Dewpt: 54.5 F (12.5 C) Rel Hum: 63% Winds: 2.5 m/s (from SW) Pressure: hPa gas-liquid metastable equilibrium

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

CHRONOLOGY OF ANTARCTIC OZONE HOLE

HYDROLYSIS OF N 2 O 5 IN AEROSOLS INCREASES THE SENSITIVITY OF OZONE TO CHLORINE N 2 O 5 hydrolysis increases HO x -catalyzed ozone loss. Why?

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