北京PM2.5中有机酸的污染特征及来源

采用GC/MS定量分析了2003年9月至2004年7月期间北京市PM2.5中33种脂肪酸(C10～C32)和10种二元酸(diC2～diC11)的含量.研究表明,脂肪酸具有明显的偶数碳优势,4个季节中最丰富的脂肪酸物种都是棕榈酸和硬脂酸(C16、C18).脂肪酸总浓度年均值为493.89ng·m-3,变化范围1.68～2961.70 ng·m-3,季节变化特征不明显.二元酸以草酸(diC2)、丙二酸(diC3)为主,浓度年均值分别为548.13ng·m-3、530.1 ng·m-3;二元酸总浓度呈明显季节变化特征,夏季最高(1539.36 ng·m-3),冬季最低(908.12 ng·m-3).4个季节碳优先指数(CPI)无显著差别,分别是15.3(秋)、12.4(冬)、11.5(春)和13.4(夏);CPI值与植物蜡贡献脂肪酸值呈现出一定的负相关.主成分分析结果表明,油烟、高等植物排放和细菌活动是脂肪酸的主要污染源,二次化学反应转化是二元酸的主要来源.

Concentration characteristics and sources of organic acids in PM2.5 in Beijing

Concentrations of 33 fatty acids (C10~C32) and 10 dicarboxylic acids from PM2.5 samples from September 2003 to July 2004 in Beijing were determined by GC/MS. The fatty acids presented a strong even number predominance, and hexadecanoic acid and stearic acid were the two most abundant species in all seasons. The annual average concentration of the total fatty acids was 493.89 ng·m-3, ranged from 1.68 ng·m-3 to 2961.70 ng·m-3 and showed poor seasonal variation. For dicarboxylic acids, oxalic acid and malonate acid were the two predominant species, with annual average concentrations of 548.13 ng·m-3 and 530.1 ng·m-3, respectively. The total concentration of dicarboxylic acids presented obvious seasonal variation, with the highest in summer (1539.36 ng·m-3) and the lowest in winter (908.12 ng·m-3). The carbon number predominant index (CPI) showed slight seasonal variation, 15.3 (autumn), 12.4 (winter), 11.5 (spring) and 13.4 (summer). The CPI showed negative correlation with the fatty acids contributed by vegetable wax. The principle component analysis (PCA) result indicated that cooking oil, vegetable emission and bacteria activity were the main sources of fatty acids, and secondary chemical reactions were the main source of dicarboxylic acids.