Spatial and Temporal Distribution Characteristics of Levoglucosan and Its Isomers in PM2.5 in Beijing and Six Surrounding Cities

Air PM2.5 samples from Beijing and six surrounding cities were collected during spring, summer, autumn, and winter. Levoglucosan (LG), mannosan (MN), and galactosan (GT) contents were analyzed by ion chromatography. The concentrations and distribution characteristics of the three anhydroglucoses with PM2.5 and organic carbon (OC) were compared. SPSS 24.0 was used to analyze the significant differences. The results indicated that the seasonal distributions of PM2.5, OC, and LG in the six cities were highly similar and followed the order winter > spring > autumn > summer. There were significant differences in the concentration levels of the three anhydroglucoses in the four seasons. Between Beijing and Tianjin, Baoding, and Shijiazhuang, there was no significant difference in the three anhydroglucose concentrations. However, significant differences in the three anhydroglucose concentrations appeared between Beijing, Ji'nan, and Zhengzhou. Based on the ratios of LG/MN and LG/(MN+GT) measured in the six cities, it could be determined that the biomass combustion sources in PM2.5 mainly came from crop straw and hardwood in this region. During the air pollution process in spring, LG stably existed in PM2.5 in Beijing, Tianjin, Shijiazhuang, and Ji'nan, indicating that this pollution process was weakly affected by biomass combustion.