摘要:
用离子色谱法对11种无机水溶性离子(Na+,NH4+,K+,Mg2+,Ca2+,F-,Cl-,Br-,NO2-,NO3-和SO42-)进行分析,探讨大气颗粒物中水溶性无机组分的季节变化与典型污染(灰霾、浮尘、燃烧秸秆和燃放烟花)的理化特性.结果表明,西安市大气中PM2.5和TSP的日均质量浓度分别为167.1和382.0μg·m-3,PM2.5占TSP总质量浓度的44%.PM2.5和TSP中无机水溶性离子组分的年均值分别为75.2μg·m-3和101.7μg·m-3.PM2.5中水溶性离子组分占PM2.5总质量浓度的45%左右,TSP中水溶性离子组分占TSP总质量浓度的30%左右.各种水溶性离子的来源和形成机理不同,其季节变化趋势和粒径分布也不同.典型污染事件期间,颗粒物污染特征与平时相比有很大差异:雾霾时PM2.5和TSP的质量浓度都显著增加,主要污染组分为二次污染离子NH4+,NO3-和SO42-;浮尘发生时,大气颗粒物中人为污染组分会大大减少,而来自沙尘传输和地面扬尘等的地壳物质显著增加;燃烧秸秆对大气颗粒物中K+和Cl-的影响最大;燃放烟花时K+,Mg2+和Ca2+的质量浓度显著增加.
Abstract:
PM2.5 and TSP samples were simultaneously collected from October 2006 to October 2007 in Xi'an,and to investigate seasonal variations of water-soluble inorganic ions(Na+,NH4+,K+,Mg2+,Ca2+,F-,Cl-,Br-,NO2-,NO3- and SO42-)and their characteristics of typical pollution episodes(haze,dust,straw combustion,and fireworks).The result showed that the mean value of PM2.5 and TSP mass concentration were 167.1 μg·m-3 and 382.0 μg·m-3.PM2.5 occupied 44% of TSP mass.The annual mean mass concentration for total water-soluble ions in PM2.5 and TSP were 75.2μg·m-3 and 101.7μg·m-3,respectively,which occupied nearly 45% of PM2.5 mass and nearly 30% of TSP mass.The size distribution and seasonal variation of water-soluble ions were diverse when considering different sources and formation mechanism.Characteristics of aerosol particles and ionic species in typical pollution episodes were disparity than ordinary days.In haze days,the mass concentration of PM2.5 and TSP increased significantly compared to normal days,and major ions were secondary species such as NH4+,NO3-,and SO42-.In floating dusty days,anthropogenic components were greatly reduced while the concentration of Na+,Mg2+,and Ca2+,which represent fugitive dust,increased fast.Straw combustion had a remarkable influence on K+ and Cl-in particulate matter.Fireworks brought more K+,Mg2+ and Ca2+.
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