Chapman Mechanism (~1930, Sidney Chapman) O 2 + h O + O (
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Transcript of Chapman Mechanism (~1930, Sidney Chapman) O 2 + h O + O (
Chapman Mechanism(~1930, Sidney Chapman)
O2 + h O + O (<242.4 nm)
O + O2 + M O3 + M
O3 + h O + O2 (<280 nm)
O + O3 2O2
O + O + M O2 + M
http://www.epa.gov/indicators/roe/html/roeAirInfo.htmUnited States Environmental Protection AgencyEPA Report on the Environment (ROE)
http://www.atm.ch.cam.ac.uk/tour/part2.html“The Ozone Tour”Centre for Atmospheric Science, University of Cambridge
“The Ozone Tour” -- http://www.atm.ch.cam.ac.uk/tour/part3.htmlCentre for Atmospheric Science, University of Cambridge
Paul J. CrutzenThe NetherlandsMax-Planck InstitutMainz, Germany
Mario J. MolinaUSAM.I.T.Cambridge, Mass.
F. Sherwood RowlandUSAUniversity of CaliforniaIrvine, California
NobelPrize1995
(1/3 each)
Catalytic Decompositionof Ozone
X + O3 XO + O2
XO + O X + O2________________________________
O3 + O 2O2X = HOx (H, OH, HOO) NOx (NO, NO2) ClOx (Cl, ClO)
N2O from troposphere:N2O + O* 2NO in middle & upper stratosphere
NO + O3 NO2 + O2
NO2 + O NO + O2________________________________
O3 + O 2O2
HO + O3 HOO + O2
HOO + O HO + O2________________________________
O3 + O 2O2
Above 45 km, OH dominates, from:O* + H2O OH + OH and
O* + CH4 OH + CH3
X + O3 XO + O2
X + O3 XO + O2
XO + XO X + X+ O2________________________________
2O3 3O2
In lower stratosphere (~15-25 km), [O] is relatively low:
UV-C absorbed by ozone.[O2] is high (so most O quickly reacts with it).
Therefore, the dominant ozone loss mechanism is:
Reaction goes by:
XO + XO [XOOX] X + X+ O2
Rate of O3 production depends on [O2], [O3], h (UV-C)
Destruction is more complex, but depends on [X], UV-B.
If something changes, generally [O3] increases or decreasesuntil it reaches a steady state.
Self-healing: [O3], UV-C, more O3 forms below.
Next: Atomic Cl and Br as X.
Atomic Cl and Br as X:
Cl can destroy tens of thousands of O3 molecules each, butis mainly in inactive forms (HCl, ClONO2) in stratosphere.
ClO + NO2 ClONO2
Cl + CH4 HCl + CH3
CH3 does not operate as an X catalyst, since it combineswith O2 to give CO2.
On crystals:
ClONO2g + HCls Cl2g + HNO3aq
Cl2 + h 2Cl
or:
ClONO2g + HsOaq HOClaq + HNO3aq
HClg H+aq + Cl-
aq
Cl -aq + HOClaq Cl2g + OH-
aq
Crystals bind NO2 that would normally deactivateCl, removing it to the troposphere (denitrification).
Conditions in the Arctic are similar to those in theAntarctic, but not as severe, because the temperatureis not as low there as in the Antarctic.