【摘要】 为了探讨西安市春季大气细粒污染物的污染水平及水溶性组分的特征及来源,2005年3—5月对西安大气PM2.5进行了观测,并应用离子色谱对其中的水溶性组分进行了分析。结果显示,西安市春季大气PM2.5的质量浓度为159.9μg·m-3。分析的11种阴阳离子(Na+、NH4+、K+、Mg2+、Ca2+、F-、Cl-、Br-、NO2-、NO3-和SO42-)质量浓度占PM2.5的30%,表明水溶性组分是大气细粒子的主要组成之一。NH4+、SO42-和NO3-为水溶性离子的主要组分,其平均质量浓度分别为6.6、20.1和7.6μg·m-3,在总水溶性离子中的百分比分别为12.4%、47.4%和16.9%,SO42-和NO3-质量浓度与能见度有较好的负相关性,表明细粒子中二次气溶胶组分对能见度有显著的影响。阴阳离子的平衡和pH值的测定结果显示,西安市大气细粒子污染物为弱酸性。离子间的相关性分析揭示水溶性离子在颗粒物中主要结合方式为(NH4)2SO4、NH4HSO4、NH4NO3、KHSO4和K2SO4。Mg2+和Ca2+的相关性也较好,其摩尔比率为0.07,小于中国北方沙漠和黄土的平均值(0.15),揭示二次扬尘和建筑扬尘等过程对Ca2+的质量浓度影响较大。计算的NO3-/SO42-质量浓度比值的均值为0.38,说明固定排放源(燃煤)对细粒子中水溶性组分的贡献大于移动排放源(机动车)。更多还原

【Abstract】 The purpose of this study was to investigate the mass concentration of PM2.5 and water-soluble components over Xi’an during spring. Daily PM2.5 samples were collected from March to May in 2005,and 11 kinds of water-soluble ions (Na+,NH4+,K+,Mg2+,Ca2+,F-,Cl-,Br-,NO2-,NO3-and SO42-) were determined by an ion chromatography. The results showed that mean mass concentration of PM2.5 in spring was 159.9 μg·m-3,and 11 kinds of ions occupied about 30% in PM mass. NH4+,SO42-and NO3-were major species in water-soluble ions with mean concentrations of 6.6 μg·m-3,20.1 μg·m-3,and 7.6 μg·m-3,respectively,which occupied 14.3%,47.9% and 18.0% in the total ions,respectively. SO42-and NO3-had good negative relationship with visibility,suggested that secondary aerosol species had a strong influence on the urban visibility. The ions balance between total cations and total anions showed airborne PM2.5 at Xi’an was just a little acid,which was consistent with the results of pH measurement. The relationships for different ions suggested that water-soluble ions mainly existed in the forms of (NH4)2SO4,NH4HSO4 ,NH4NO3,KHSO4,and K2SO4. The molar ratios of Mg2+/Ca2+ averaged 0.07,which was lower than that of eolian dust from desert regions (0.15),implied that Ca2+ was strong impacted on local re-suspended dust or construction dust. The concentration mean ratio of NO3-/SO42-was 0.38,indicating that coal burning,which represent the stationary source compared to the mobile source of vehicle emission,was the main pollution sources of water-soluble species in Xi’an.更多还原