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

Robert D Field,Jonathan E Hickman,Kostas Tsigaridis,Igor V Geogdzhayev,Susanne E Bauer

doi:10.5194/acp-21-18333-2021

Robert D Field, Jonathan E Hickman + Show 3 more

Open Access

https://doi.org/10.5194/acp-21-18333-2021

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Abstract

Abstract. We examined daily level-3 satellite retrievals of Atmospheric Infrared Sounder (AIRS) CO, Ozone Monitoring Instrument (OMI) SO2 and NO2, and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) over eastern China to understand how COVID-19 lockdowns affected atmospheric composition. Changes in 2020 were strongly dependent on the choice of background period since 2005 and whether trends in atmospheric composition were accounted for. Over central east China during the 23 January–8 April lockdown window, CO in 2020 was between 3 % and 12 % lower than average depending on the background period. The 2020 CO was not consistently less than expected from trends beginning between 2005 and 2016 and ending in 2019 but was 3 %–4 % lower than the background mean during the 2017–2019 period when CO changes had flattened. Similarly for AOD, 2020 was between 14 % and 30 % lower than averages beginning in 2005 and 14 %–17 % lower compared to different background means beginning in 2016. NO2 in 2020 was between 30 % and 43 % lower than the mean over different background periods and between 17 % and 33 % lower than what would be expected for trends beginning later than 2011. Relative to the 2016–2019 period when NO2 had flattened, 2020 was 30 %–33 % lower. Over southern China, 2020 NO2 was between 23 % and 27 % lower than different background means beginning in 2013, the beginning of a period of persistently lower NO2. CO over southern China was significantly higher in 2020 than what would be expected, which we suggest was partly because of an active fire season in neighboring countries. Over central east and southern China, 2020 SO2 was higher than expected, but this depended strongly on how daily regional values were calculated from individual retrievals and reflects background values approaching the retrieval detection limit. Future work over China, or other regions, needs to take into account the sensitivity of differences in 2020 to different background periods and trends in order to separate the effects of COVID-19 on air quality from previously occurring changes or from variability in other sources.

Highlights

In an effort to control the spread of COVID-19, the Chinese government implemented a range of restrictions on movement
Observations by the Tropospheric Monitoring Instrument (TROPOMI) showed large decreases in tropospheric NO2 column densities over Chinese cities, on the order of 40 % for 11 February to March 2020 compared to the same period in 2019, ranging from roughly % for cities not affected by lockdown to 60 % for Wuhan and Xi’an (Bauwens et al, 2020)
There was a decrease in Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) (Fig. 2d) in central east China coincident with the decreases in carbon monoxide (CO) and NO2 but smaller in magnitude

Summary

Introduction

In an effort to control the spread of COVID-19, the Chinese government implemented a range of restrictions on movement. These led to reductions in industrial and other workrelated and personal activities starting 23 January 2020 in Wuhan, Hubei province, and extending to other cities and regions in the days that followed. On 8 April 2020, Wuhan was the last city to reopen after a complete lockdown that prevented most people from leaving their homes. These measures have been linked to changes in air quality. Prospective simulations suggested that meteorology may limit the effect of reduced emissions on PM2.5 concentrations, with Chinese cities experiencing less than 20 % reductions (Wang et al, 2020)

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