Beyond the lockdowns: satellite observations of aerosol optical depth through 2020, the first year of the COVID-19 pandemic

Abstract

Anticipated future reductions in aerosol emissions are expected to accelerate warming and substantially change precipitation characteristics. Therefore, it is vital to identify the existing patterns and possible future pathways of anthropogenic aerosol reductions. The COVID-19 pandemic prompted abrupt, global declines in transportation and industrial activities, providing opportunities to study the aerosol effects of pandemic-driven emissions changes. Here, measurements of aerosol optical depth (AOD) from two satellite instruments were used to characterize aerosol burdens throughout 2020 in four Northern Hemisphere source regions (Eastern & Central China, the United States, India, and Europe). In most regions, record-low measures of AOD persisted beyond the earliest ‘lockdown’ periods of the pandemic. Record-low values were most concentrated during the boreal spring and summer months, when 56% to 72% of sampled months showed record-low AOD values for their respective regions. However, in India and Eastern & Central China, the COVID-19 AOD signature was eclipsed by sources of natural variability (dust) and a multi-year trend, respectively. In the United States and Europe, a likely COVID-19 signal peaks in the summer of 2020, contributing as much as −.01 to −.03 AOD units to observed anomalies.

Footprint of the 2020 COVID-19 Lockdown on Column-Integrated Aerosol Parameters in Spain

“…The main results indicate that AOD increased in the lockdown period and decreased in the post-lockdown period. This result is in line with Barragán et al [53] for the particular case of Madrid and with satellite studies that found an increase in AOD in the southwest of Europe during the 2020 lockdown [10][11][12][13].…”

“…Moreover, Ibrahim et al [11] analysed MODIS data over Europe and confirmed a 10% increase in AOD over Spain. This positive anomaly in AOD over Spain during March and April 2020 was also reported in the global studies performed by Sanap [12] and Smith et al [13] using MODIS and CALIPSO satellites.…”

“…Moreover, Ibrahim et al[11] analysed MODIS data over Europe and confirmed a 10% increase in AOD over Spain. This positive anomaly in AOD over Spain during March and April 2020 was also reported in the global studies performed by Sanap[12] and Smith et al[13] using MODIS and CALIPSO satellites.Several sources may have contributed to this increase in AOD such as the Saharan events detected in Madrid[53] and Barcelona[49] during this period, advecting desert dust and causing high AOD levels. These events can be clearly identified in Figure3as very high AOD measurements measured by several stations.…”

“…Their results indicate a substantial reduction in primary air pollutants [6,7] and, specifically, an overall reduction in PM2.5 in the most polluted capital cities of the world [7][8][9]. The effect on the column aerosol has also been observed at the global scale by several satellites such as MODIS and CALIOP, with wide areas of the world being covered [10][11][12][13].…”