Modelling the effect of local and regional emissions on PM(2.5) concentrations in Wuhan, China during the COVID-19 lockdown

PM(2.5) concentrations in Wuhan, China decreased by 36.0% between the period prior to the COVID-19 pandemic (1–23 January, 2020) and the COVID-lockdown period (24 January to 29 February, 2020). However, decreases in PM(2.5) concentration due to regional PM(2.5) transport driven by meteorological changes, and the relationship between the PM(2.5) source and receptor, are poorly understood. Therefore, this study assessed how changes in meteorology, local emissions, and regional transport from external source emissions contributed to the decrease in Wuhan's PM(2.5) concentration, using FLEXPART-WRF and WRF-Chem modelling experiments. The results showed that meteorological changes in central China explain up to 22.2% of the total decrease in PM(2.5) concentrations in Wuhan, while the remaining 77.8% was due to air pollutant emissions reduction. Reduction in air pollutant emissions depended on both local and external sources, which contributed alomst equally to the reduction in PM(2.5) concentrations (38.7% and 39.1% of the total reduction, respectively). The key emissions source areas affecting PM(2.5) in Wuhan during the COVID-lockdown were identified by the FLEXPART-WRF modeling, revealing that regional-joint control measures in key areas accounted for 89.3% of the decrease in PM(2.5) concentrations in Wuhan. The results show that regional-joint control can be enhanced by identifying key areas of emissions reduction from the source–receptor relationship of regional PM(2.5) transport driven by meteorology under the background of East Asian monsoon climate change.