北京市典型城区PM_2.5中正构烷烃的污染特征与来源

Distribution Characteristics and Source Identification of n-Alkanes in PM_(2. 5) in Typical Urban Area of Beijing

2013年6月在北京及华北平原大城市空气污染联合观测期间,使用大流量PM2.5采样仪分昼、夜采集北京市典型城区环境空气中PM2.5样品,利用GC-MS技术对PM2.5中正构烷烃的污染水平、分布特征与来源进行分析,并且结合后向轨迹分析了远距离传输的影响.结果表明：观测期间ρ（PM2.5）为29.73~275.30μgm3,PM2.5中ρ（总正构烷烃）为50.33~143.49 ngm3.PM2.5中正构烷烃质量浓度随碳数分布呈单峰-后峰型和双峰-后高型2种;Cmax（主峰碳数）为C29或C31;CPI（碳优势指数）为1.34~6.66;LMWHMW〔ρ（C14~C24正构烷烃）ρ（C25~C36正构烷烃）〕为0.10~0.31.观测期间PM2.5中正构烷烃主要来自高等植物蜡,并且主要来自温带植物;其次来自化石燃料和生物质的不完全燃烧.观测期间来自北京市南向气团轨迹出现概率最高,影响最为突出,其次为来自东南沿海方向和内蒙古中西部方向的气团轨迹.

Atmospheric fine particle （PM2.5） samples were collected in June 2013 during the period of CAREBEIJING-NCP campaign in a typical urban area of Beijing, and the ambient particulate n-alkanes were determined by using GC-MS technique. The influence of the long-range transport of air mass on the pollution characteristics of n-alkanes in PM25 was investigated on the basis of studies on ambient level, distribution characteristics and source identification combined with backward trajectory analysis. The results showed that p（ PM2.5 ） ranged from 29.73 to 275.30 μg/m3 , while p （ total n-alkanes） ranged from 50.33 to 143.49 ng/m3. Carbon number distribution of n-alkanes in PM2.5 presented two kinds of peak shapes that were unimodal and bimodal. The maximum carbon number （Cmax ） was C29 orC31. The carbon preference index （CPI） ranged from 1.34 to 6.66, and the ratios of p （C14-C24.n-alkanes） and p （ C25-C36 n-alkanes） （ LMW/HMW ） ranged from 0. 10 to 0. 31. The n-alkanes in PM25 during the observation period were mainly from higher plants wax dominated by those from temperate regions, with additional contributions from incomplete combustion of fossil fuels and biomass. The air mass mainly originated from the southern direction, followed by southeast coast and the mid-west Inner Mongolian direction. The air mass from the south made the most important influence on the distribution characteristics of n-alkanes in PM2.5.