Abstract
Abstract. Due to the coronavirus disease 2019 (COVID-19) pandemic, human activities and industrial productions were strictly restricted during January–March 2020 in China. Despite the fact that anthropogenic aerosol emissions largely decreased, haze events still occurred. Characterization of aerosol transport pathways and attribution of aerosol sources from specific regions are beneficial to air quality and pandemic control strategies. This study establishes source–receptor relationships in various regions covering all of China during the COVID-19 outbreak based on the Community Atmosphere Model version 5 with Explicit Aerosol Source Tagging (CAM5-EAST). Our analysis shows that PM2.5 burden over the North China Plain between 30 January and 19 February is mostly contributed by local emissions (40 %–66 %). For other regions in China, PM2.5 burden is largely contributed from nonlocal sources. During the most polluted days of the COVID-19 outbreak, local emissions within the North China Plain and eastern China contributed 66 % and 87 % to the increase in surface PM2.5 concentrations, respectively. This is associated with the anomalous mid-tropospheric high pressure at the location of the climatological East Asia trough and the consequently weakened winds in the lower troposphere, leading to the local aerosol accumulation. The emissions outside China, especially those from South Asia and Southeast Asia, contribute over 50 % to the increase in PM2.5 concentration in southwestern China through transboundary transport during the most polluted day. As the reduction in emissions in the near future is desirable, aerosols from long-range transport and unfavorable meteorological conditions are increasingly important to regional air quality and need to be taken into account in clean-air plans.
Highlights
The coronavirus disease 2019 (COVID-19) has spread worldwide since December 2019 and resulted in more than a million cases within the first 4 months (Sharma et al, 2020; Dong et al, 2020)
The estimated NOx emissions in eastern China were reduced by 60 %–70 %, of which 70 %– 80 % were related to the reduced road traffic and 20 %–25 % from industrial enterprises shutdown during the COVID-19 lockdown period
Our study provides source apportionment of aerosols covering all of China and quantifies the contribution from foreign transport for the first time in the case of COVID-19 emission reductions, which is beneficial to the investigation of policy implications for future air pollution control
Summary
The coronavirus disease 2019 (COVID-19) has spread worldwide since December 2019 and resulted in more than a million cases within the first 4 months (Sharma et al, 2020; Dong et al, 2020). By applying the WRF-CAMx model together with air quality monitoring data, Li et al (2020) revealed that primary particle emissions were reduced by 15 %–61 % during the COVID-19 lockdown over the Yangtze River Delta region, the daily mean concentration of PM2.5 was still relatively high, reaching up to 79 μg m−3. By applying particulate source apportionment technology in the CAMx model, Xue et al (2014) found that the contributions of regional transport to annual average PM2.5 concentrations in Hainan, Shanghai, Jiangsu, Zhejiang, Jilin and Jiangxi provinces of China are more than 45 %. Our study provides source apportionment of aerosols covering all of China and quantifies the contribution from foreign transport for the first time in the case of COVID-19 emission reductions, which is beneficial to the investigation of policy implications for future air pollution control
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