chapman mechanism for stratospheric ozone (1930)
DESCRIPTION
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:. - PowerPoint PPT PresentationTRANSCRIPT
CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE CHAPMAN MECHANISM FOR STRATOSPHERIC OZONE (1930)(1930)
2
2 3
3 2
3 2
(R1) O O + O ( < 240 nm)
(R2) O + O M O M
(R3) O O O ( 320 nm)
(R4) O O 2O
h
h
O O3O2
slow
slow
fast
Odd oxygen family [Ox] = [O3] + [O]
R2
R3
R4
R1
STEADY-STATE ANALYSIS OF CHAPMAN MECHANISMSTEADY-STATE ANALYSIS OF CHAPMAN MECHANISMLifetime of O atoms:
O 22 2 4 3 2 O2
[O] 11 s
[O][O ][M]+ [O ][O] ak k k C n
…is sufficiently short to assume steady state for O:
3 O2 2 3 3 2
3 2 2 3
x 3
[O]2 3 [O][O ][M]= [O ] 1
[O ]
[O ] [O ]O a O
kR R k k
k C n
…so the budget of O3 is controlled by the budget of Ox.
Lifetime of Ox:
xOx
4 3 4
[O ] 1
2 [O ][O] 2 [O]k k
Steady state for Ox:1
321 2 2
3 O23
1 2 44
3 [O2 1 2 4 [O ] [O O] ]][ aR R kk k
C nk k
k
Ox
SOLAR SPECTRUM AND ABSORPTION X-SECTIONSSOLAR SPECTRUM AND ABSORPTION X-SECTIONS
O2+hv O3+hv
PHOTOLYSIS RATE CONSTANTS: VERTICAL DEPENDENCEPHOTOLYSIS RATE CONSTANTS: VERTICAL DEPENDENCE
0X+ ... ( ) ( )X Xh k q I d
quantumyield
absorptionX-section
photonflux
2 2 3 3optical depth ( ( ) ( ))O O O Od n z n z dz
( )I z dz
( )I z
2 2 3 3
( ) ( ) e
( ( ') ( ')) 'O O O Oz
I z I
n z n z dz
CHAPMAN MECHANISM vs. OBSERVATIONCHAPMAN MECHANISM vs. OBSERVATION
-3
shapedeterminedby k1nO2
Chapman mechanism reproduces shape, but is too high by factor 2-3missing sink!
RADICAL REACTION CHAINS IN THE ATMOSPHERERADICAL REACTION CHAINS IN THE ATMOSPHERE
non-radical radical + radicalInitiation:photolysisthermolysisoxidation by O(1D)
radical + non-radical non-radical + radicalPropagation: bimolecularredox reactions
non-radical + non-radicalTermination: radical redox reaction
radical + radical
non-radical + M radical + radical + M 3-body recombination
WATER VAPOR IN STRATOSPHEREWATER VAPOR IN STRATOSPHERE
Source: transport from troposphere, oxidation of methane (CH4)
H2O mixing ratio
Initiation:1
2H O + O( ) 2OHD
Propagation: 3 2 2
2 3
3
2
2
OH + O HO O
HO +
Net:
O OH +
2O
2O
3O
Termination:2 2 2OH + HO H O + O
OH HO2H2Oslow
slow
fast HOx radical family
Ozone loss catalyzed by hydrogen oxide (HOOzone loss catalyzed by hydrogen oxide (HOxx ≡ H + OH + HO ≡ H + OH + HO22) )
radicalsradicals
NITROUS OXIDE IN THE STRATOSPHERENITROUS OXIDE IN THE STRATOSPHERE
H2O mixing ratio
• 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 cycle Net O3 + O 2O2
• Termination RecyclingNO2 + 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:
32
[O ]2 [NO ][O]
dk
dt
Ozone loss catalyzed by nitrogen oxide (NOOzone loss catalyzed by nitrogen oxide (NOxx ≡ NO + NO ≡ NO + NO22) )
radicalsradicals
ATMOSPHERIC CYCLING OF NOATMOSPHERIC CYCLING OF NOxx AND NO AND NOyy
STRATOSPHERIC OZONE BUDGET FOR MIDLATITUDES STRATOSPHERIC OZONE BUDGET FOR MIDLATITUDES CONSTRAINED FROM 1980s SPACE SHUTTLE OBSERVATIONSCONSTRAINED FROM 1980s SPACE SHUTTLE OBSERVATIONS
Gas-phasechemistryonly
STRATOSPHERIC DISTRIBUTION OF CFSTRATOSPHERIC DISTRIBUTION OF CF22ClCl22 (CFC-12) (CFC-12)
Ozone loss catalyzed by chlorine (ClOOzone loss catalyzed by chlorine (ClOxx ≡≡ Cl + ClO) radicals Cl + ClO) radicals
• Initiation: Cl radical generation from non-radical precursors (e.g., CFC-12)
CF2Cl2 + h CF2Cl + Cl
• Propagation:
Cl + O3 ClO + O2
ClO + OCl + O2
Net: O3 + O 2O2
• Termination: Recycling:
Cl + CH4 HCl + CH3 HCl + OH Cl + H2O
ClO + NO2 + M ClNO3 + M ClNO3 + hCl + NO3
O3 loss rate: 3[O ]2 [ClO][O]
dk
dt
ATMOSPHERIC CYCLING OF ClOATMOSPHERIC CYCLING OF ClOxx AND Cl AND Clyy
SOURCE GAS CONTRIBUTIONS TOSOURCE GAS CONTRIBUTIONS TOSTRATOSPHERIC CHLORINE (2004)STRATOSPHERIC CHLORINE (2004)
CHLORINE PARTITIONING IN STRATOSPHERECHLORINE PARTITIONING IN STRATOSPHERE
OZONE TREND AT HALLEY BAY, ANTARCTICA (OCTOBER)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
SPATIAL EXTENT OF THE OZONE HOLESPATIAL 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 PHENOMENONTHE OZONE HOLE IS A SPRINGTIME PHENOMENON
VERTICAL STRUCTURE OF THE OZONE HOLE:VERTICAL STRUCTURE OF THE OZONE HOLE:near-total depletion in lower stratospherenear-total depletion in lower stratosphere
Argentine Antarctic station southern tip of S. America
Sep. 2, 1987
Sep. 16
20 km altitude
ASSOCIATION OF ANTARCTIC OZONE HOLEASSOCIATION OF ANTARCTIC OZONE HOLEWITH HIGH LEVELS OF CLOWITH HIGH LEVELS OF CLO
Sept. 1987 ER-2 aircraft measurements at 20 km altitude south of Punta Arenas
ClO
ClO
O3
O3
Edge ofPolar vortex
Measurements by Jim Anderson’s group (Harvard)
SATELLITE OBSERVATIONS OF ClO SATELLITE OBSERVATIONS OF ClO IN THE SOUTHERN HEMISPHERE STRATOSPHERE IN THE SOUTHERN HEMISPHERE STRATOSPHERE
WHY THE HIGH ClO IN ANTARCTIC VORTEX?WHY THE HIGH ClO IN ANTARCTIC VORTEX?Release of chlorine radicals from reactions of reservoir species in Release of chlorine radicals from reactions of reservoir species in
polar stratospheric clouds (PSCs)polar stratospheric clouds (PSCs)
PSC FORMATION AT COLD TEMPERATURESPSC FORMATION AT COLD TEMPERATURES
PSC formation
Frost point of water
HOW DO PSCs START FORMING AT 195K?HOW DO PSCs START FORMING AT 195K?HNOHNO33-H-H22O PHASE DIAGRAMO PHASE DIAGRAM
Antarcticvortexconditions
PSCs are not water but nitric acid trihydrate (NAT) clouds
DENITRIFICATION IN THE POLAR VORTEX:DENITRIFICATION IN THE POLAR VORTEX:SEDIMENTATION OF PSCsSEDIMENTATION OF PSCs
CHRONOLOGY OF ANTARCTIC OZONE HOLECHRONOLOGY OF ANTARCTIC OZONE HOLE
TRENDS IN GLOBAL OZONETRENDS IN GLOBAL OZONE
Mt. Pinatubo
LONG-TERM COOLING OF THE STRATOSPHERELONG-TERM COOLING OF THE STRATOSPHERE
Sep 21-30, 25 km, 65-75˚S
Increasing CO2 is expected to cool the stratosphere
TRENDS IN POLAR OZONETRENDS IN POLAR OZONECould greenhouse-induced cooling of stratosphereCould greenhouse-induced cooling of stratosphereproduce an Arctic ozone hole over the next decade?produce an Arctic ozone hole over the next decade?
Race between chlorine decrease and climate change
SKIN CANCER SKIN CANCER EPIDEMIOLOGY EPIDEMIOLOGY PREDICTIONSPREDICTIONS