The Stratospheric Chemistry and The Ozone Layer

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Presentation transcript:

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

Temperature Structure of the Atmosphere

Height/km Latitude Mesosphere Stratopause Stratosphere Tropopause Troposphere Latitude

Black region is troposphere Eruption of Mt Pinatubo, Phillipine Is, 5ON, June 1991 Satellite measurements of aerosol as a tracer for stratospheric circulation

Mesosphere Stratosphere Upper troposphere

MEAN (11yr) ATMOSPHERIC WINDS AT 20 km ALTITUDE (NOAA Analysis)

MEAN (11yr) ATMOSPHERIC TEMPERATURE AT 20 km ALTITUDE (NOAA Analysis)

Potential Vorticity At ~20 km in the S.Polar Vortex

30 km Altitude 16 km 1950 The QBO In equatorial regions 1978

Variations in mean O3 column(DU) due to QBO (from satellite observations)

Climatology of Global O3 column (after Dutsch, 1971) In Dobson units, i.e. mmHgx100 at STP

Chemical Kinetics I

Chemical Kinetics II

Chemical Kinetics III

O(3P) O3 O2 O3

O2 + hn  O + O Window region where UV radiation penetrates into the lower stratosphere giving: O2 + hn  O + O

Chemical lifetime of O3:calculated daily averaged photodissociation rate of molecular oxygen

Release of catalysts by Photolysis in the lower Stratosphere

O2 + hn(l<243nm)  O + O oxygen photolysis O + O2 + M  O3 + M ozone formation O + O3  O2 + O2 ozone destruction O3 + hn(l<310nm)  O(1D) + O2 O3 + hn(l<1180nm)  O + O2 oxygen photolysis NO2 + hn(l<243nm)  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]

Interconversion of Cl & ClO Formation and release from reservoirs of Cl & ClO

STRATOSPERE  heterogeneous reactions on sulphate aerosol

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.

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

 heterogeneous reactions on sulphate aerosol