Wintertime characteristics of water-soluble organic carbon in PM2.5 during haze and non-haze days in Jinan in the North China Plain

Abstract

Water-soluble organic carbon (WSOC) makes up a substantial proportion of organic carbon (OC) in fine particles that can disrupt aerosol hygroscopicity, influence global climate change, and harm human health. In the winter of 2014, carbonaceous species and water-soluble inorganic ions (WSII) were analyzed in PM2.5 samples collected from Jinan in the North China Plain. According to the results, the primary components of PM2.5 include SO42−, NO3−, NH4+ (SNA) and organic carbonaceous aerosol. Except for Ca2+, the average concentration of each chemical component was higher on hazy days than on clear days. Secondary aerosol generation probably played a vital role in haze production, as the relative abundance of secondary inorganic ions and secondary organic carbon was higher on haze days compared to non-haze days. The average WSOC concentration during the sampling period was 10.89 ± 4.66 μg m−3, accounting for 0.47 ± 0.14 of OC. The level of WSOC increased from 9.60 ± 3.32 μg m−3 on days without haze to 16.94 ± 5.43 μg m−3 on haze days. Analyses of linear regression and quantitative calculations demonstrated that burning of biomass and the generation of secondary aerosols were essential contributors to WSOC. WSOC increased with relative humidity/aqueous water content, suggesting that secondary WSOC (WSOCsec) may originate from reactions in the aqueous phase, particularly on haze days. The absorption Ångstrom exponents (AAE) were 6.55 ± 1.79 on non-haze days and 6.59 ± 0.90 on haze days. The average mass absorption efficiency (MAE) at 365 nm on haze days (1.07 ± 0.21 m2 g−1) was higher than on non-haze days (0.88 ± 0.33 m2 g−1), indicating the slightly stronger WSOC's light absorption ability during haze times. Four quantitative sources of WSOC were identified using positive matrix factorization modeling: (i) a mixed primary source (21.78%), (ii) biomass burning (22.14%), (iii) a process comparable to NO3− formation (33.17%) and (iv) a process similar to SO42− formation (22.91%). Comparatively, secondary sources (factors 3 and 4) contributed more to WSOC (56.08%) than primary sources (43.92%, factors 1 and 2). Secondary formation contributed more to WSOC during haze conditions.