北京及周边6个城市大气PM2.5中左旋葡聚糖及其异构体的时空分布特征

采集北京及周边6个城市春、夏、秋、冬这4个季节大气PM_2.5样品，用离子色谱法测定其中的左旋葡聚糖（LG）、甘露聚糖（MN）和半乳聚糖（GT），对比这3种脱水聚糖与PM_2.5及有机碳（OC）的浓度水平和时空分布特征，应用SPSS 24.0软件分析了数据间的显著性差异.结果表明，6个城市PM_2.5、OC和LG浓度水平的季节分布规律高度相似，呈现冬季 > 春季 > 秋季 > 夏季，4个季节3种脱水聚糖的浓度水平有显著性差异.从空间角度分析3种脱水聚糖浓度水平，北京与天津、保定、石家庄无显著性差异，但北京与济南、郑州有显著性差异.根据6个城市的LG/MN和LG/（MN+GT）等浓度水平的比较，初步判断该区域PM_2.5中的生物质燃烧源主要来源于农作物秸秆和硬木.春季的PM_2.5污染过程中，北京、天津、石家庄和济南的左旋葡聚糖在PM_2.5中的含量变化基本保持稳定，显示该污染过程受生物质燃烧排放的影响较弱.

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

Air PM_2.5 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 PM_2.5 and organic carbon (OC) were compared. SPSS 24.0 was used to analyze the significant differences. The results indicated that the seasonal distributions of PM_2.5, 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 PM_2.5 mainly came from crop straw and hardwood in this region. During the air pollution process in spring, LG stably existed in PM_2.5 in Beijing, Tianjin, Shijiazhuang, and Ji''nan, indicating that this pollution process was weakly affected by biomass combustion.