Changes in satellite retrievals of atmospheric composition over eastern China during the 2020 COVID-19 lockdowns

Abstract. We examined daily Level-3 satellite retrievals of AIRS CO, OMI SO2 and NO2, and MODIS AOD over eastern China to understand how COVID-19 lockdowns affected atmospheric composition, taking into account trends that have occurred since 2005. Over central east China during the January 23–April 8 lockdown window, CO in 2020 was 12 % lower than the 2005–2019 mean, but only 2 % lower than what would be expected given the decreasing CO trend over that period. Similarly for AOD, 2020 was 30 % lower than the 2011–2019 mean, but not distinct from what would be expected from the trend. NO2 in 2020 was 43 % lower than the 2011–2019 mean, but only 17 % lower than what would be expected given the trend over that period. Over southern China, 2020 NO2 was not significantly different from anticipated, and CO and AOD were significantly higher that what would be expected, which we suggest was partly because of an active fire season in neighbouring countries. Over east central and southern China, SO2 was higher than expected, but the magnitude depended strongly on how daily regional values were calculated from individual retrievals. Future work over China, or other regions, needs to take these trends into account in order to separate the effects of COVID-19 on air quality from recent trends, or from variability in other sources.

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