Impact of the Tibetan Topography on Downwind Spatial Distribution of Fine Particulate Matter in Winter

The Tibetan Plateau (TP) with a large landmass serves as an obstacle that hinders westerly flows and alters climate downwind. Here, we investigate the TP influence on the magnitude and spatial distribution of wintertime fine particulate matter (PM_2.5) concentrations downwind and associated underlying mechanisms. Based on simulations using an Earth system model, we show that the removal of the TP would reduce surface PM_2.5 concentrations by 230.4% in the Sichuan basin (SC) and by 212.4% in the North China Plain (NCP), but increase the concentrations by 18.1% in eastern China (EC), suggesting that the TP could naturally intensify PM_2.5 pollution in SC and NCP. If the TP were absent, more meridional circulations would turn into zonal ones and the East Asian winter monsoon would become weaker. There would be less precipitation and lower humidity over SC and EC in the south, while the opposite occurs over NCP in the north. Consequently, the changes in circulations would result in a net outflow of PM_2.5 from SC and NCP, but a net inflow of PM_2.5 to EC. In response to the spatial changes in precipitation, wet deposition would decrease in SC and EC but increase in NCP. PM_2.5 production would reduce in SC and EC but amplify in NCP, following the changes in humidity. In magnitude, the changes in transport and wet deposition would be dominant in SC and NCP, while in EC, transport, wet deposition, and chemical production would be equally important. This study illustrates significant and heterogeneous impacts of the TP on air quality downwind.