Spatiotemporal characteristics and socioeconomic factors of PM heterogeneity in mainland China during the COVID-19 epidemic.

Spatiotemporal variation of PM in 2018 and 2020 were compared to analyze the impacts of COVID-19, the spatial heterogeneity of PM, and meteorological and socioeconomic impacts of PM concentrations heterogeneity in China in 2020 were investigated. The results showed that the annual average PM concentration in 2020 was 32.73 μg/m existing a U-shaped variation pattern, which has decreased by 6.38 μg/m compared to 2018. A consistent temporal pattern was found in 2018 and 2020 with significant high values in winter and low in summer. PM declined dramatically in eastern and central China, where are densely populated and economically developed areas during the COVID-19 epidemic compared with previous years, indicating that the significantly decline of social activities had an important effect on the reduction of PM concentrations. The lowest PM was found in August because that precipitation had a certain dilution effect on pollutants. January was the most polluted due to centralized coal burning for heating in North China. Overall, the PM concentrations in China were spatially agglomerated. The highly polluted contiguous zones were mainly located in northwest China and the central plains city group, while the coastal area and Inner Mongolia were areas with good air quality. Negative correlations were found between natural factors (temperature, precipitation, wind speed and relative humidity) and PM concentrations, with precipitation has the greatest impact on PM, which are beneficial for reducing PM concentrations. Among the socio-economic factors, proportion of the secondary industry, number of taxis, per capita GDP, population, and industrial nitrogen oxide emissions have positive correlation effects on PM, while the overall social electricity consumption, industrial sulfur dioxide emissions, green coverage in built-up areas, and total gas and liquefied gas supply have negative correlation effects on the PM.