PM1 chemical composition and light absorption properties in urban and rural areas within Sichuan Basin, southwest China.

Sichuan Basin is encircled by high mountains and plateaus with the heights ranging from 1 km to 3 km, and is one of the most polluted regions in China. However, the dominant chemical species and light absorption properties of aerosol particles is still not clear in rural areas. Chemical composition in PM1 (airborne particulate matter with an aerodynamic diameter less than 1 μm) and light-absorbing properties were determined in Chengdu (urban) and Sanbacun (rural) in western Sichuan Basin (WSB), Southwest China. Carbonaceous aerosols and secondary inorganic ions (NH4+, NO3- and SO42-) dominate PM1 pollution, contributing more than 85% to PM1 mass at WSB. The mean concentrations of organic and elemental carbon (OC, EC), K+ and Cl- are 19.69 μg m-3, 8.00 μg m-3, 1.32 μg m-3, 1.16 μg m-3 at the rural site, which are 26.2%, 65.3%, 34.7% and 48.7% higher than those at the urban site, respectively. BrC (brown carbon) light absorption coefficient at 405 nm is 63.90 ± 27.81 M m-1 at the rural site, contributing more than half of total absorption, which is about five times higher than that at urban site (10.43 ± 4.74 M m-1). Compared with secondary OC, rural BrC light absorption more depends on primary OC from biomass and coal burning. The rural MAEBrC (BrC mass absorption efficiency) at 405 nm ranges from 0.6 to 5.1 m2 g-1 with mean value of 3.5 ± 0.8 m2 g-1, which is about three times higher than the urban site.