Molecular distributions of dicarboxylic acids, oxocarboxylic acids, and α-dicarbonyls in aerosols over Tuoji Island in the Bohai Sea: Effects of East Asian continental outflow

Field measurements of the concentrations of dicarboxylic acids and related compounds (oxocarboxylic acids and α-dicarbonyls) in PM2.5 were conducted on a background island (Tuoji Island, China) over the Bohai Sea to better understand the effects of pollution downwind of the East Asian continental outflow. Air mass backward trajectory calculations demonstrated that the distributions of dicarboxylic acids and related compounds at Tuoji Island depended strongly on the East Asian continental outflow and correlated with the hours spent by an air parcel in the polluted boundary layer. Based on the data analysis, the sampling period was categorized into heavy aerosol pollution periods (HAPPs) and light aerosol pollution periods (LAPPs). The average concentration of dicarboxylic acids and related compounds during HAPPs (1280 ± 503 ng m−3) was approximately seven times higher than that during LAPPs (189 ± 90.8 ng m−3). The order of the major species of dicarboxylic acids and related compounds, ranked by concentrations, was oxalic acid (C2) > glyoxylic acid (ωC2) > succinic acid (C4) > terephthalic acid (tPh) during HAPPs, and C2 > malonic acid (C3) > ωC2 > C4 during LAPPs. Results of positive matrix factorization (PMF) showed that secondary sources were the dominant source of dicarboxylic acids and related compounds, with contributions of 38% and 57% during HAPPs and LAPPs, respectively. Primary sources of biomass burning and plastic waste burning were also significant during HAPPs (contributions: 26% and 20%, respectively) and LAPPs (contributions: 18% and 12%, respectively). The concentration ratios of C3 to C4 (C3/C4), C2 to C4 (C2/C4), fumaric acid to maleic acid (F/M), phthalic acid to azelaic acid (Ph/C9), adipic acid to azelaic acid (C6/C9), and the positive correlations of Ph or tPh with dicarboxylic acids, and levoglucosan with dicarboxylic acids and related compounds further support the PMF results.