Chemical characteristics and regional transport of submicron particulate matter at a suburban site near Lanzhou, China.

Lanzhou, which is a valley city on the Loess Plateau, frequently suffered from aerosol pollution in recent years, especially in winter. However, the lack of understanding of factors governing aerosol pollution limits the implementation of effective emission policies in and around Lanzhou. To help solve this problem, an intensive field campaign was conducted at the SACOL site, which is a suburban site near Lanzhou, in winter 2018. The chemical characteristics and sources of submicron particulate matter (PM) were investigated, and the influence of the topography around Lanzhou on aerosol pollution was examined. In the present study, the average PM mass concentration reached 25.6 ± 12.8 μg m, with 41.0% organics, 16.1% sulfate, 19.7% nitrate, 10.7% ammonium, 3.1% chloride, and 9.4% black carbon (BC). Three organic aerosol (OA) factors were identified with the positive matrix factorization (PMF) algorithm, including a biomass burning OA (BBOA, 13.6%), a coal combustion OA (CCOA, 34.2%), and an oxygenated OA (OOA, 52.2%). The significant relationships between organics, BC, and chloride and wind pattern suggested that the SACOL site was strongly influenced by regionally transported aerosols. Further analysis suggested that these aerosol regional transport events were caused by topography. Due to the limitation of the valley, aerosols accumulated in the valley. These accumulated aerosols were then transported to the SACOL site along the valley by prevailing winds. Our study highlights enhanced aerosol regional transport in valleys, which provides a new perspective for future studies on aerosol pollution in basins and valleys.