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[AAS11-17] The global COVID-19 lockdown impacts on secondary aerosol formations
Keywords:Inorganic aerosols, Modeling, Satellite observations
To prevent spreading the 2019 Novel Coronavirus (COVID-19), many countries implemented lockdowns beginning in 2020. The suppressed human activities substantially reduced air pollutants’ emissions. The unprecedented global emission reductions are expected to provide insight on changing human activity impacts on air pollutants’ concentration—emission relationships. Previous studies evaluated the changes in ozone and PM2.5 associated with the COVID-19 lockdowns using combination of satellite observations and modeling (e.g., Miyazaki et al., 2021; Hammer et al., 2021). Nevertheless, changes in aerosol composition on the global scale for different regions of the world remain unclear. In this study, we evaluate impacts of the COVID-19 lockdown on sulfate-nitrate-ammonium (SNA) aerosols based on global chemical data assimilation (DA) of multi-species satellite observations with a resolution of 0.56 degree using an ensemble Kalman filter approach (e.g., Sekiya et al., 2021; Miyazaki et al., 2021), using the TROPOMI for tropospheric NO2 column and total SO2column, the MLS for O3 and HNO3 profiles.
Corresponding to the lockdown measures in many countries, regional NOx emission reductions in April 2020 were estimated to be 20%, 28%, and 23% over East Asia, Europe, and North America, respectively, which recovered to 13%, 12%, and 11% in June 2020, compared with the 2019 emissions estimated using the same DA system. Regional SO2 emissions during April—June 2020 were also reduced by 15%, 20%, and 21% over East Asia, Europe, and North America, respectively. These emission reductions decreased SNA aerosol optical depth (AOD) by 12%, 6%, and 12% over the eastern China, Europe, and the eastern United States (U.S.), respectively, during April 2020. The AOD changes driven by the SNA aerosols account for 62—78% of total AOD reductions observed by Suomi NPP/VIIRS over the eastern China and the eastern U.S. We also find that the SNA aerosols’ response to the emission reductions was influenced by seasonal changes in meteorological conditions: surface nitrate responses over the eastern China, Europe, and the eastern U.S. were 40—65% larger in February than in June, whereas surface sulfate responses were 30—50% smaller. These results suggest that SNA aerosols play an important role in the aerosol changes associated with the COVID-19 lockdown on the regional to global scales, which provides an important implication for assessing impacts of aerosol precursors’ emission control on human health and climate forcing.
Corresponding to the lockdown measures in many countries, regional NOx emission reductions in April 2020 were estimated to be 20%, 28%, and 23% over East Asia, Europe, and North America, respectively, which recovered to 13%, 12%, and 11% in June 2020, compared with the 2019 emissions estimated using the same DA system. Regional SO2 emissions during April—June 2020 were also reduced by 15%, 20%, and 21% over East Asia, Europe, and North America, respectively. These emission reductions decreased SNA aerosol optical depth (AOD) by 12%, 6%, and 12% over the eastern China, Europe, and the eastern United States (U.S.), respectively, during April 2020. The AOD changes driven by the SNA aerosols account for 62—78% of total AOD reductions observed by Suomi NPP/VIIRS over the eastern China and the eastern U.S. We also find that the SNA aerosols’ response to the emission reductions was influenced by seasonal changes in meteorological conditions: surface nitrate responses over the eastern China, Europe, and the eastern U.S. were 40—65% larger in February than in June, whereas surface sulfate responses were 30—50% smaller. These results suggest that SNA aerosols play an important role in the aerosol changes associated with the COVID-19 lockdown on the regional to global scales, which provides an important implication for assessing impacts of aerosol precursors’ emission control on human health and climate forcing.