期刊
GEOPHYSICAL RESEARCH LETTERS
卷 44, 期 1, 页码 455-464出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2016GL070695
关键词
sulfate aerosl; seasonal trend; castnet; cloud chemistry; CMIP; air quality
资金
- NOAA Climate Program Office's Atmospheric Chemistry, Carbon Cycle, and Climate program
Stringent controls have reduced U.S. SO2 emissions by over 60% since the late 1990s. These controls have been more effective at reducing surface SO42- in summer (June, July, and August) than in winter (December, January, and February (DJF)), a seasonal contrast that is not robustly captured by Climate Model Intercomparison Project 5 global models. We use the Geophysical Fluid Dynamics Laboratory AM3 chemistry-climate model to show that oxidant limitation during winter causes SO42- (DJF) to be sensitive to primary SO42- emissions, in-cloud titration of H2O2, and in-cloud oxidation by O-3. The observed contrast in the seasonal response of SO42- to decreasing SO2 emissions is best explained by the O-3 reaction, whose rate coefficient has increased over the past decades as a result of increasing NH3 emissions and decreasing SO2 emissions, both of which lower cloud water acidity. The fraction of SO2 oxidized to SO42- is projected to keep increasing in future decades, delaying improvements in wintertime air quality.
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