Water-soluble organic carbon (WSOC) and its temperature-resolved carbon fractions in atmospheric aerosols in Beijing

Investigation of temperature-resolved carbon fractions of water-soluble organic carbon (WSOC) can improve our understanding of the chemical properties, formation processes and sources of WSOC in aerosols. We developed a method that can examine different temperature-resolved carbon fractions of WSOC and used this method to characterize aerosol samples (n = 102) collected from an urban site in Beijing in 2010-2011. The aerosol composition data including inorganic ions, elements and temperature-resolved carbon fractions of WSOC were used as input of positive matrix factorization (PMF) model to investigate the sources of WSOC. The results showed that the mean concentrations of WSOC were 10.2 μg m− 3 with increased values in winter and decreased values in summer, while WSOC/OC ratios (mean: 51.7%) were higher in spring and summer than in fall and winter. The sampling artifacts of WSOC (18.2%) were higher than those of OC (13.4%). Though WSOC was significantly influenced by biomass burning in spring and winter, the strong correlations between WSOC and other secondary components suggested that WSOC was secondary in nature. Results of temperature-resolved carbon fractions of OC and WSOC showed that WSOC/OC ratios for different carbon fractions had the highest value of 0.92 and lowest value of 0.30. PMF analysis identified four factors, three of which were associated with three organic polar compounds groups (low, medium, and high molecular weight compounds) based on their thermal evolution features, and one of which was attributed to inorganic secondary formation processes. Annually, the contributions of four factors were 20.5%, 46.2%, 12.4% and 20.9%, respectively.