厦门市大气 PM2.5中水溶性离子污染特征及来源解析

摘要

为探讨厦门市大气 PM2.5水溶性离子污染特征及来源，于2014年8月和12月同步采集了城区和郊区的 PM2.5样品.用离子色谱分析了9种水溶性离子(F-、Cl-、NO3-、SO42-、Na+、K+、NH4+、Ca2+和 Mg2+)的质量浓度.结果表明，厦门大气 PM2.5中水溶性离子浓度处于较低水平，总水溶性离子浓度(µg/m3)顺序为：冬季城区(18.16)>冬季郊区(14.55)>夏季郊区(6.87)>夏季城区(5.33)，降水对水溶性离子有显著的去除作用.观测期间，夏季 PM2.5阴离子相对亏损，冬季反之. SO42-、NO3-、NH4+(简称 SNA)占全部水溶性离子质量浓度之和的比例达79.64%以上，表明厦门市大气 PM2.5二次污染较严重.相关性分析和 SNA 三角图解表明厦门市夏季 NH4+主要以(NH4)2SO4的形式存在，其次为NH NO 43及碱性游离 NH4+；冬季则主要以(NH4)2SO4和 NH4NO3的形式存在，其次为 NH4Cl. N/S 值表明夏季 PM2.5中水溶性离子污染特征以燃煤源排放为主，冬季以交通排放为主，总体呈现出交通源与燃煤污染并存的复合型污染特征，但受海洋源的影响很小.主成分分析进一步表明厦门市大气 PM2.5水溶性离子主要来自燃煤源、交通排放和生物质燃烧源.%The PM2.5 samples were synchronously collected in urban and suburban areas of Xiamen city during August and December in 2014 to investigate the characteristics and sources of water-soluble ions in atmospheric PM2.5. Nine water-soluble ions (F-, Cl-, NO3-, SO42-, Na+, K+, NH4+, Ca2+, Mg2+) were determined by ion chromatography. The level of water-soluble ions in PM2.5 of Xiamen city was relatively lower, and the sum concentrations (µg/m3) of total water-soluble ions showed the order of urban area in winter (18.16) > suburban area in winter (14.55) > suburban area in summer (6.87) >urban area in summer (5.33). Precipitation had a significant effect on the removal of water-soluble ions in PM2.5. Anions in PM2.5 were relative loss in summer, whereas opposite in winter. SO42-, NO3-, NH4+ (SNA) were the major components of water-soluble ions in PM2.5 with a contribution of more than 79.64% to total water-soluble ions, suggesting that the level of secondary ions was relatively high. Correlation analysis and SNA triangular diagram showed that NH4+ in PM2.5 mostly coexisted in the form of (NH4)2SO4 followed by NH4NO3 and alkaline free NH4+ in summer, while mostly in the form of (NH4)2SO4 and NH4NO3 followed by NH4Cl in winter. The mass ratio of N/S demonstrated that the main source to the water-soluble ions in PM2.5 of Xiamen city was coal combustion in summer, while the traffic emissions in winter. Overall, the water-soluble ions in PM2.5 of Xiamen city presented the composite pollution characteristics of traffic source and coal combustion, but barely influenced by marine source. Principal component analysis further indicated that the water-soluble ions in PM2.5 of Xiamen city mainly came from coal combustion, traffic emission and biomass burning.