Sources and light absorption characteristics of water-soluble organic carbon (WSOC) of atmospheric particles at a remote area in inner Himalayas and Tibetan Plateau

Abstract

Water-soluble organic carbon (WSOC) is an important component of carbonaceous aerosols. Increasing evidences show that WSOC absorbs and scatters sunlight in the atmosphere, which is one of the key components of climate change. Despite numbers of related studies, understanding of basic characteristics of WSOC is limited at remote region, such as the Himalayas and Tibetan Plateau (HTP), one of the remotest regions in the world with weak local anthropogenic activities. In this study, we conducted a year-round investigation of multiple aerosol species at Nam Co, a pristine station in inner part of the HTP. The results showed that the annual mean concentrations of PM2.5 and its WSOC were 8.9 ± 5.4 μg m−3 and 249 ± 111 ng m−3, respectively, which was among the lowest values in the HTP, representing a clean environment. WSOC of PM2.5 and total suspended particle (TSP) samples were mainly derived from combustion emissions and fine particle of local surface soil, respectively, indicating significant contribution of local sources of the HTP to TSP samples. Similarly, due to the influence of surface soil, respective absorption per mass of WSOC at 365 nm (α/ρWSOC) of TSP (1.74 ± 0.94 m2 g−1) was significantly higher than that of PM2.5 (1.22 ± 0.43 m2 g−1). Seasonally, high and low WSOC concentrations and α/ρWSOC values appeared at non-monsoon and monsoon periods, respectively. This study provides observational constraints for related researches such as modelling of the environmental impact of WSOC in the HTP.