Long-Term Trends of High Aerosol Pollution Events and Their Climatic Impacts in North America Using Multiple Satellite Retrievals and Modern-Era Retrospective Analysis for Research and Applications version 2

摘要

abstract_textpMean magnitudes and temporal trends in aerosol optical depth (AOD) from satellite observations and an aerosol reanalysis exhibit a negative-positive east-northwest dipole across the contiguous United States with large magnitude negative trends over the eastern United States while small magnitude positive trends over the northwestern states. Based on analyses of Modern-Era Retrospective Analysis for Research and Applications version 2, the AOD reduction over the eastern United States appears to be largely attributable to reductions in aerosol sulfate, while there have been marked increases in aerosol-organic and elemental carbon over almost all of the contiguous United States and particularly the northwestern states. Long-term trends of high aerosol pollution events (HAPEs; days with AOD over the long-term local 90th daily AOD percentile) during 2000-2017 also indicate that over the eastern United States, both the frequency and spatial scale of summer HAPEs exhibit significant negative trends, while those of moderate aerosol events (days with AOD between the local 30th and 70th AOD percentiles) exhibit weak upward trends. Opposing trends, of smaller magnitude, are derived in the northwestern United States and southwestern Canada. Net and shortwave solar radiation show positive trends at the surface and top of atmosphere under clear-sky conditions over the eastern United States consistent with the reduction in AOD. However, skin temperatures do not indicate significant trends during all days or HAPEs, indicating that the aerosol-induced radiation trends are not sufficient to manifest trends in surface temperature. Precipitation during HAPEs appears to have increased during 2000-2017 over the eastern and central United States, indicating that the reduction in aerosol may already be enhancing the precipitation through aerosol-cloud interactions./p/abstract_text