Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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2.1.4. Indirect Effects Involving Atmospheric CO and CH 4
Other reports in this collection
The tropospheric modeling tools detailed in Section 2.2.1 produce an increased global inventory of OH radicals in response to subsonic aircraft injection of NO x . This
characteristic model response to increased NO x levels in air traffic corridors arises through the reaction sequence:
HO 2 + NO NO 2 + OH (3)
so that increased ozone production is accompanied by an increase in the OH radical concentration and the concentration ratio of OH to HO 2 . Increased OH levels in
air traffic corridors then lead to decreased CO concentrations through the following reaction series:
OH + CO H + CO 2 (1)
H + O 2 + M HO 2 + M (2)
CO lifetimes may approach 2 months and are therefore much longer than NO x lifetimes. As a result, a region of decreased CO concentrations spreads out from air
traffic corridors toward lower altitudes and toward the Equator. Ultimately, as a result of subsonic aircraft NO x emissions, decreased CO levels are found in tropical and
sub-tropical regions where much of the CH 4 is oxidized. Because CO levels are lower, OH levels are higher; hence CH 4 concentrations decrease slightly, so the total
flux through the OH + CH 4 reaction (35) remains in balance with CH 4 emissions:
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