Characteristics of airborne water-soluble organic carbon (WSOC) at a background site of the North China Plain

摘要

Water-soluble organic carbon (WSOC), a significant part of organic carbon (OC) in fine particles, can alter the hygroscopic properties of aerosols and affect global climate change. In this study, PM2.5 filter samples were collected in 2017 winter and summer to investigate the secondary formation, sources and light absorption properties of WSOC. The average WSOC/OC was 66% with the higher value in summer (74%). There are strong correlations between WSOC and secondary components like secondary organic carbon (SOC) and inorganic ions while the correlation between WSOC and EC was weak, indicating secondary formation contributed a dominant portion to WSOC at this site. Moreover, high aerosol liquid water (ALW) and particle acidity were found to enhance the secondary formation of WSOC. The sources of WSOC investigated with Positive Matrix Factorization model (PMF) demonstrated that secondary formation was dominated with 59.9% in winter and 77.9% in summer. The absorption Angstrom exponents (AAE) were 6.88 in winter and 9.15 in summer. The MAE(365) in winter (1.32m(2) g(-1)) was higher than that in summer (0.38m(2) g(-1)), indicating the stronger light absorption ability of WSOC in winter. The radiative forcing of WSOC by light absorption corresponded to only 1-10% of that caused by EC. The potential source contribution function (PSCF) identified inland cities in Shandong province, eastern Henan and Jiangsu province as major source regions of WSOC. The findings from this study imply a critical role of secondary formation characteristics of WSOC at the regional background site of the North China Plain.