The Stratospheric Chemistry and The Ozone Layer

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The Stratospheric Chemistry and The Ozone Layer

• Stratospheric circulation
• Stratospheric photochemistry
• Gas phase reactions
• Ozone and Catalytic cycles

Dr Tony Cox ERCA 2004 -Lecture 2
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Temperature Structure of the Atmosphere
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Mesosphere
Stratopause
Height/km
Stratosphere
Tropopause
Troposphere
Latitude
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Black region is troposphere
Eruption of Mt Pinatubo, Phillipine Is, 5ON, June
1991
Satellite measurements of aerosol as a tracer for
stratospheric circulation
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Mesosphere
Stratosphere
Upper troposphere
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MEAN (11yr) ATMOSPHERIC WINDS AT 20 km ALTITUDE
(NOAA Analysis)
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MEAN (11yr) ATMOSPHERIC TEMPERATURE AT 20 km
ALTITUDE (NOAA Analysis)
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Potential Vorticity At 20 km in the S.Polar
Vortex
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30 km Altitude 16 km
1950
The QBO In equatorial regions
1978
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Variations in mean O3 column(DU) due to QBO (from
satellite observations)
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Climatology of Global O3 column (after Dutsch,
1971) In Dobson units, i.e. mmHgx100 at STP
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Chemical Kinetics I
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Chemical Kinetics II
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Chemical Kinetics III
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O(3P)
O3
O2
O3
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Window region where UV radiation penetrates into
the lower stratosphere giving O2 hn ? O O
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Chemical lifetime of O3calculated daily averaged
photodissociation rate of molecular oxygen
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Release of catalysts by Photolysis in the
lower Stratosphere
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O2 hn(llt243nm) ? O O oxygen
photolysis O O2 M ? O3 M
ozone formation O O3 ? O2 O2
ozone destruction O3 hn(llt310nm) ? O(1D)
O2 O3 hn(llt1180nm) ? O O2 oxygen
photolysis
NO2 hn(llt243nm) ? NO O NO2 photolysis O
O2 M ? O3 M ozone formation
X O3 ? XO O2 XO O ? X O2 Net O O3
? O2 O2 ozone destruction X H, OH, NO,
Cl, Br, etc
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Interconversion of Cl ClO
Formation and release from reservoirs of Cl ClO
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STRATOSPERE
???? heterogeneous reactions on sulphate aerosol
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OZONE DEPLETION CYCLES IN THE LOWER STRATOSPHERE
Concentration of O atoms fall off in lower
stratosphere as photolysis of O2 and O3 reduces.
Catalytic destruction through cycles involving
participation of atomic O is less important.
Other cycles not involving O(3P) can occur.
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OZONE DEPLETION CYCLES INVOLVING HALOGENS THE
LOWER STRATOSPHERE
Involving ClOx/NOx coupling ClO NO2
ClONO2 ClONO2 hn Cl NO3 NO3 hn
NO O2 NO O3 NO2 O2 Cl O3
ClO O2 net O3 O3 3O2 Involving
NOx/Halogen (X Br or I) coupling XO HO2
HOX O2 HOX hn X HO OH O3 HO2
O2 X O3 XO O2 net O3 O3 3O2
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???? heterogeneous reactions on sulphate aerosol
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