Elevated 3D structures of PM<sub>2.5</sub> and impact of complex terrain-forcing circulations on heavy haze pollution over Sichuan Basin, China

Abstract. Deep basins create uniquely favorable conditions for causing air pollution, and the Sichuan Basin (SCB) in Southwest China is such a basin featuring frequent heavy pollution. A wintertime haze pollution event SCB was studied with conventional intensive observation data WRF-Chem model to explore 3D distribution of PM2.5 understand impact regional pollutant emissions, circulations associated plateaus, downwind transport adjacent areas. It found that vertical structure over characterized by remarkable hollow sandwiched high layers at heights 1.5–3 km highly polluted near-surface layer. The southwesterlies Tibetan Plateau (TP) Yunnan-Guizhou (YGP) resulted lee vortex SCB, which helped form maintain lifted into free troposphere transported outside SCB. At bottom concentrations were mostly located northwestern southern regions. Due blocking effect plateau terrain on northeasterly winds, gradually increased from northeast southwest basin. In lower troposphere, centers distributed southwestern areas, as well central region. For this event, emissions contributed 75.4 %–94.6 % surface major source eastern regions TP northern YGP, contribution rates 72.7 70.5 %, respectively, during dissipation stage regarded affecting atmospheric environment changes China.