Aggravation effect of regional transport on wintertime PM2.5 over the middle reaches of the Yangtze River under China's air pollutant emission reduction process

Abstract

The contributions of emission reduction and meteorological changes to air quality improvement in Hubei Province (HB) have required assessment in recent years. In this study, the WRF-Chem scenario tests were conducted to evaluate the effect of both the emission and meteorological changes on the winter PM2.5 from 2015 to 2019, especially that of regional transport and local emissions on the PM2.5 variations in HB. The results showed that meteorological changes in January 2019 increased the PM2.5 by 24% relative to January 2015, whereas emissions reduced it by 36%, indicating that emission reduction was vital in improving the air quality in HB. However, the meteorological changes increased the concentration of air pollutants by 10–25% relative to January 2018. This led to a rebound of the observed pollutant concentrations in January 2019, highlighting the importance of meteorological conditions on air pollution. Regional transport of air pollutants contributed to the inter-annual increase of wintertime PM2.5 by 78%, driven purely by meteorology from 2015 to 2019. This indicated that regional PM2.5 transport could aggravate PM2.5 levels in winter over HB with the reduction of air pollutant emissions in China. Additionally, the regional transport of air pollutants contributed to the decrease in PM2.5 in HB by 42%, resulting from the non-local emission reduction during COVID-19 lockdown in winter. This indicates the importance of the regional transport of air pollutants in driving regional changes in the atmospheric environment over China.