Molecular Distribution, Seasonal Variations, and Sources of Typical Polar Organics in PM2.5 from Jinzhong, China

Polar organics are essential constituents in atmospheric aerosols, but few studies have analyzed their distribution characteristics and sources. In this study, 42 typical polar organics, including 10 aromatic acids, 9 aliphatic dibasic acids, 3 anhydrosugars, 14 sugars and sterols, and 6 fatty acids in PM2.5 in Jinzhong, China, were analyzed. Their annual average concentrations were 0.07-11.1, 0.24-5.30, 2.33-38.1, 0.06-10.5, and 0.40-22.2 ng/m(3), respectively, with the most abundant compounds being p-phthalic acid, succinic acid, levoglucosan, glycerol, and palmitic acid, respectively. For anhydrosugars, aliphatic dibasic acids, and sugars and sterols, the highest concentrations were found in winter, summer, and spring, respectively. However, the concentrations of aromatic acids from both the primary source and secondary photochemical formation were higher in autumn (36.1%) and winter (35.6%) than in other seasons, whereas fatty acids exhibited no obvious seasonal differences. Two anhydrosugars (mannosan and galactosan), six aromatic acids (m-, p-phthalic acid, and four phenolic acids), and four sugars and sterols (erythritol, glycerol, xylitol, and xylose) were highly correlated with levoglucosan, indicating their association with biomass burning. The levoglucosan/ mannosan and mannosan/galactosan ratios indicated that the types of biomass burning in Jinzhong were crop straw, hardwood, and pine needles. By contrast, three aromatic acids (o-phthalic acid and 1,2,3- and 1,2,4-benzene-tricarboxylic acid), three aliphatic dibasic acids (succinic, glutaric, and adipic acid), and glyceric acid all had a certain correlation with SO42-, indicating their secondary photochemical formation. The values of o-phthalic acid/azelaic acid revealed that the anthropogenic precursor had a higher contribution to secondary formation. Principal component analysis revealed that the potential sources of polar organics in PM2.5 included biomass burning (32.8%), anthropogenic secondary organic aerosols (21.5%), biogenic primary and secondary organic aerosols (18.7%), and soil dust (11.5%).