无锡冬季和春季大气中细粒子化学组分及其特性分析

Characteristic analysis of chemical species in atmospheric fine particles in Wuxi during winter & spring sampling campaigns

本研究对无锡冬(2011年1月)春(2011年5月)两季PM2.5、PM10颗粒物浓度进行了传统的膜采样及离线检测分析,并运用大气气体/气溶胶水溶性离子在线收集及分析(GAC-IC)系统对PM2.5颗粒物中水溶性无机离子(WSII)进行了在线检测,时间分辨率为30 min.无锡冬、春两季PM2.5的浓度分别为108.15±41.76μg·m-3和84.40±26.74μg·m-3,其PM2.5/PM10比值分别为0.81±0.07和0.78±0.07,有较强的二次气溶胶生成过程.铵可用性指数(J冬季=101.2%±22.3%,J春季=79.5%±20.2%)分析表明冬季无锡大气颗粒物中铵(NH+4)相对比较富余,而春季则出现铵(NH+4)亏损现象,春季光化学反应更为活跃,硫氧化率(SOR)由冬季的0.15±0.05增至春季的0.35±0.13,硫酸盐(SO2-4)浓度增加明显,导致铵(NH+4)相对不足.硫氧化率(SOR)没有明显的季节变化,冬、春两季均为0.15.细粒子中的WSII与气态污染物、气象因子、硫氧化率(SOR)和氮氧化率(NOR)等的主成分分析表明无锡大气光化学反应与污染物的其他来源,例如工业源、交通移动源、生物质燃烧源等,有很好的协同作用,共同推高了大气中颗粒物的浓度.观测期间同时测得冬季PM2.5颗粒中有机碳(OC)与元素碳(EC)浓度之间有较好的相关性(R2=0.839),两者有一个共同的主导源,而春季来源则比较复杂,两者相关性较差;二次有机碳(SOC)的半定量分析表明春季大气中有机气溶胶的形成有较强的二次转化过程.

Daily PM2. 5and PM10 mass concentration were analyzed using traditional filter samplers located at three sampling sites in Wuxi during winter（ 2011） and spring（ 2011） sampling campaigns. Water soluble inorganic ions（ WSII） in PM2. 5were also continuously measured using gases and aerosol collector coupled with ion chromatography on-line detecting（ GAC-IC） system with a time resolution of 30 mins. The average mass concentrations of PM2. 5during winter and spring observation periods were 108. 15±41. 76 μg·m-3and 84. 40±26. 74 μg·m-3,and PM2. 5/PM10 mass concentration ratio were 0. 81±0. 07 and 0. 78±0. 07,respectively,indicating a process of secondaryaerosols transformation. Analysis of ammonium availability index（ Jwinter= 101. 2% ±22. 3%,Jspring=79. 5% ±20. 2%） suggests that the ambient air was ammonia-rich in winter. By contrast,Wuxi had an ammonia-deficient atmosphere in spring. Sulfur oxidation ratio（ SOR） increased significantly from 0. 15±0. 05 in winter to 0. 35±0. 13 in spring. Comparatively,nitrogen oxidation ratio（ NOR）was essentially unchanged with a value of 0. 15,making it clear that the atmosphere of Wuxi was photochemically much more active in spring. Principal component analysis（ PCA） of PM2. 5aerosol chemical components,meteorological factors,gaseous pollutants（ SO2,CO,O3,NO,NO2）,SOR and NOR at Caozhang site showed that photochemical reaction with other pollutants sources,such as industrial sources,vehicle exhaust,biomass domestic and open burning etc.,had a positive synergisitc effect during sampling campaigns,pushing up the mass concentration of particulate matters in atmosphere in Wuxi,especially fine particles. Meanwhile,during sampling campaigns,the concentration of OC and EC had a positive correlation（ R2= 0. 839） in winter,revealing a common source which dominated the emission of OC and EC. The spring showed different sources of OC and EC. Secondary organic carbon（ SOC） was semi-quantitatively estimated,and it implied that the formation of secondary organic aerosol was mainly due to a secondary transformation.