Publication Date:
2013-03-31
Description:
[1] Anderson et al . [2012] ( A2012 ) report in situ observations of convectively injected water vapor (H 2 O) in the North American (NA) summer lowermost stratosphere (LMS), occasionally exceeding 12 ppmv. They contend that, in such cold/wet conditions, heterogeneous chemistry on binary water-sulfate aerosols can activate chlorine, leading to catalytic ozone destruction. Aura Microwave Limb Sounder 100-hPa and 82.5-hPa H 2 O measurements show that, indeed, the NA LMS is unusually wet, both in mean values and in outliers reaching 18 ppmv. Using A2012 ’s threshold, 4% (0.03%) of 100-hPa (82.5-hPa) NA July–August observations are cold/wet enough for activation. Cold parcels, whether wet or dry, typically have much less HCl to activate and O 3 to destroy than A2012 ’s initial conditions. Slightly lower concentrations of HCl and O 3 in cold/wet parcels are attributable, at least in part, to dilution by tropospheric air. Alarming reductions in NA summer column O 3 suggested by A2012 are not seen in the current climate.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
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