摘要
利用离子色谱分析北京市大气气溶胶中的水溶性无机离子,结果表明,北京城乡结合部TSP中水溶性离子的年均浓度为54.97μg.m-3,其中SO42-、NO3-、C a2+、NH4+4种组分占总离子浓度的85%。TSP中总离子浓度冬季最高、夏季最低。K+浓度夏季最高,C a2+和M g2+秋季浓度明显比其他季节高。NH4+和SO42-的浓度变化趋势相似,相关系数为0.97。大气气溶胶中水溶性离子的粒径分布各不相同,F-、M g2+和C a2+呈粗模态分布,NH4+是细模态分布,其余离子呈双模态分布。F-、NH4+、M g2+和C a2+4种离子粒径分布的季节变化不明显,冬季NO3-在细颗粒中的比例最大,春季N a+在粗颗粒中的比例最大,采暖期前后SO42-的粒径分布有明显变化。
Concern about air pollution has led to numerous studies on the chemical composition and sources of atmospheric aerosols. Atmospheric aerosols influence many atmospheric processes including cloud formation, visibility variation and solar radiation transfer, and play a major role in acidification of clouds, rain and fog. Also, they have been found to be associated with health problems, such as mortality and asthma. To understand their sources, behaviors and forming mechanisms, it is important to measure both size distribution and chemical composition of atmospheric aerosols. The aim of this study was to investigate the size distribution and seasonal variation of the water-soluble ion species in atmospheric aerosols. The sampling site was chosen on the roof of a five-story building （about 15 m above the ground level） in Research Center for Eco-Environmental Sciences, located in northwestern semi-urban area of Beijing city. Size fractionated atmospheric aerosols were sampled two times per month from January to December, 2003. In each sampling, a four-stage cascade particulate separator （DFJ-1） was used at a flow rate of 566 L min ^-1 with nominal size cuts of 〈1.1, 1.1-2.0, 2.0-3.3, 3.3-7.0 and 7.0 μm aerodynamic diameter. Sampling duration was about 24 h starting from 10 a.m. Once sampling was finished, sampler filter was folded face to face and placed in a plastic bag. Sampled filters were ultrasonically extracted for 45 min using 50 ml of deionized water, the extracts were filtered and analyzed for major ions （i. e. anions： F^-, Cl^- , NO3^- and SO4^2- ; and cations ： Na^＋ , NH^＋ , K^＋ , Mg^2＋ and Ca^2＋ ） using Dionex DX-120 ion chromatograph. Data showed that average concentration of total water-soluble ions in TSP was 54. 97 μg/m^3, with a maximal value in winter and a minimum in summer. Composition of the collected aerosols indicated that the highest ion was SO4^2-, followed by Ca^2＋ , NO3^- and NH4^＋. These four ions accounted for more than 85% of total ionic concentration. The maximum concentration of K^＋ was observed in summer, while the highest concentrations of Ca^2＋ and Mg^2＋ occurred in autumn. The total nitrate was greater in autumn and winter than that in spring and summer, suggesting that part of ammonium nitrate might be vaporized at high temperature due to the equilibrium between gas phase and solid phase. The concentrations of NH4^＋ and SO4^2- had similar trend of variation with a correlation coefficient （r） of 0.97. The distributions of water-soluble ions in atmospheric aerosols were different among different sizes. The mass size distributions of Cl^-, NO3^-, SO4^2-, Na^＋ and K^＋ were bimodal while that of F^-, Mg^2＋, Ca^2＋ and NH4^＋ were unimodal. F^-, Mg^2＋ and Ca^2＋ were mainly enriched in the coarse fractions, while NH4^＋ was abundant in fine fractions. Seasonal variations of F^-, NH4^＋ , Mg^2＋ and Ca^2＋ in different size particulates remained constant. Size distribution of NO3^- was different in different seasons, with the highest concentration in fine particles （〈 1. 1 μm） in winter and coarse particles （〉7.0 μm） in other seasons. Na^＋ was dominant in coarse particulates （〉7.0 μm） in spring, suggesting that Na^＋ was largely soil derived. Because K^＋ was mainly enriched in particulates less than 1.1μm, it was believed that K^＋ was mainly originated from biomass burning. The size distribution of SO4^2- was significantly different between heating and non-heating periods. SO4^2- in coarse particle had been ascribed to contribution from re-suspension of soil and formation by heterogeneous oxidation of SO2 on particulates derived from soil.
出处
《生态学报》
CAS
CSCD
北大核心
2005年第12期3231-3236,共6页
Acta Ecologica Sinica
基金
中国科学院知识创新资助项目(KZCX3-SW-424)
国家973资助项目(2003CB415003)~~
关键词
气溶胶
水溶性离子
粒径分布
北京
aerosol
water-soluble ion
size distribution
Beijing
