Characteristics of water-soluble organic carbon (WSOC) in PM2.5 in inland and coastal cities, China

Water-soluble organic carbon (WSOC) can have direct and indirect impacts on global climate change by absorbing sunlight and altering the hygroscopic properties of aerosols. In this study, PM2.5 samples were collected simultaneously in Jinan (inland city) and Weihai (coastal city) in spring 2018 to examine the optical properties and sources of WSOC. The WSOC concentration in Jinan (9.20 ± 3.04 μg m−3) was significantly higher than that in Weihai (2.95 ± 1.54 μg m−3). The coefficient of divergence (COD) (0.41) showed that the chemical compositions of PM2.5 in Jinan and Weihai had a moderate level of discrepancy. Based on linear regression analysis, biomass burning and secondary formation by liquid phase reactions had important influence on WSOC in Jinan and Weihai, and dust source also made a non-negligible contribution to WSOC in Jinan. Short/regional transport air masses derived from the southern region of the sampling sites were dominant and carried out the most abundant WSOC. The main potential source regions for Jinan covered a larger area than that in Weihai. The absorption Ångstrom exponent (AAE) in Jinan (4.4) was higher than that in Weihai (3.86) but was lower than previous studies. The strong correlation coefficients between light absorption at 365 nm (Abs365) and WSOC indicated water-soluble BrC and WSOC might have similar emission sources. The average mass absorption efficiency at 365 nm (MAE365) in Jinan was 0.65 m2 g−1, which was much lower than that in Weihai (1.18 m2 g−1).