Abstract
The outbreak of the COVID-19 virus in Wuhan, China, in January 2020 just before the Spring Festival and subsequent country-wide measures to contain the virus, effectively resulted in the lock-down of the country. Most industries and businesses were closed, traffic was largely reduced, and people were restrained to their homes. This resulted in the reduction of emissions of trace gases and aerosols, the concentrations of which were strongly reduced in many cities around the country. Satellite imagery from the TROPOspheric Monitoring Instrument (TROPOMI) showed an enormous reduction of tropospheric NO2 concentrations, but aerosol optical depth (AOD), as a measure of the amount of aerosols, was less affected, likely due to the different formation mechanisms and the influence of meteorological factors. In this study, satellite data and ground-based observations were used together to estimate the separate effects of the Spring Festival and the COVID-19 containment measures on atmospheric composition in the winter of 2020. To achieve this, data were analyzed for a period from 30 days before to 60 days after the Spring Festivals in 2017–2020. This extended period of time, including similar periods in previous years, were selected to account for both the decreasing concentrations in response to air pollution control measures, and meteorological effects on concentrations of trace gases and aerosols. Satellite data from TROPOMI provided the spatial distributions over mainland China of the tropospheric vertical column density (VCD) of NO2, and VCD of SO2 and CO. The MODerate resolution Imaging Spectroradiometer (MODIS) provided the aerosol optical depth (AOD). The comparison of the satellite data for different periods showed a large reduction of, e.g., NO2 tropospheric VCDs due to the Spring Festival of up to 80% in some regions, and an additional reduction due to the COVID-19 containment measures of up to 70% in highly populated areas with intensive anthropogenic activities. In other areas, both effects are very small. Ground-based in situ observations from 26 provincial capitals provided concentrations of NO2, SO2, CO, O3, PM2.5, and PM10. The analysis of these data was focused on the situation in Wuhan, based on daily averaged concentrations. The NO2 concentrations started to decrease a few days before the Spring Festival and increased after about two weeks, except in 2020 when they continued to be low. SO2 concentrations behaved in a similar way, whereas CO, PM2.5, and PM10 also decreased during the Spring Festival but did not trace NO2 concentrations as SO2 did. As could be expected from atmospheric chemistry considerations, O3 concentrations increased. The analysis of the effects of the Spring Festival and the COVID-19 containment measures was complicated due to meteorological influences. Uncertainties contributing to the estimates of the different effects on the trace gas concentrations are discussed. The situation in Wuhan is compared with that in 26 provincial capitals based on 30-day averages for four years, showing different effects across China.
Highlights
As the world’s largest developing country, China has achieved enormous economic development since the 1980s, to become the second-largest economy in the world, after the USA, with a gross domestic product (GDP) of 99.1 trillion RMB (14.41 trillion US$) in 2019
For 2020, we looked at the extended period after the Spring Festival to see the effect of the measures to contain the COVID-19 outbreak from the comparison with the previous year
The Spring Festival resulted in an overall reduction of the NO2 tropospheric vertical column density (VCD) by about a factor of 2
Summary
As the world’s largest developing country, China has achieved enormous economic development since the 1980s, to become the second-largest economy in the world, after the USA, with a gross domestic product (GDP) of 99.1 trillion RMB (14.41 trillion US$) in 2019. The Chinese government has attached great importance to environmental issues and has adopted a series of policy measures to reduce China’s air pollution (e.g., [2,3]). The effects of these measures are visible in satellite measurements of trace gases and aerosols. For the confirmation of these satellite observations, as well as to quantify the trends near the surface, long-term ground-based measurements of concentrations of aerosols and trace gases are needed. For NO2, the changes during that period were variable with no overall trend across China [8,9]
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