摘要
于2013年3月9—12日沙尘暴时期,在西安市运用大流量大气采样器进行每小时1次TSP样品采集,对其进行有机碳(OC)、元素碳(EC)、无机离子及吸湿性能分析,同时利用ECOTECH公司EC系列气体监测仪,在线监测NO_x、SO_2及O_3等污染气体,研究沙尘暴期间城市大气颗粒物化学演化特征,探讨硫酸盐、硝酸盐、铵盐及钠盐等主要无机盐的来源、形成机制及其对颗粒物吸湿性能的影响。结果显示:此次沙尘暴期间有两次沙尘峰值过境西安,TSP小时浓度最高分别达到7527μg·m^(-3)和3200μg·m^(-3),同期SO_4^(2-)分别为180μg·m^(-3)和38μg·m^(-3)。沙尘暴初入西安时NO_3^-与NH_4^+浓度较低,其后,二者以1:1的摩尔比同步渐增,至沙尘过后第48小时(即非沙尘期)达最大值(分别为34μg·m^(-3)和8.7μg·m^(-3))。整个观测期间,SO_4^(2-)均与Ca^(2+)、Na^+等强线性相关,沙尘期SO_4^(2-)、Cl^-与Na^+的相关系数大于0.95,NH_4^+与NO_3^-的相关系数沙尘期为0.78。除O_3外,CO、NO_x、SO_2等污染气体的浓度变化趋势均是在沙尘过境后逐渐升高。在沙尘期间Na^+离子主要是以NaCl和Na_2SO_4的形式存在。而在整个观测期,SO_4^(2-)和Cl^-主要以NaCl、Na_2SO_4和CaSO_4的形式存在,其来源是戈壁上的干涸湖泊中的岩盐、芒硝、石膏和钙芒硝等矿物;但NH_4^+和NO_3^-主要来源于沙尘颗粒表面的非均相反应,并以NH_4NO_3的形式存在。由于TSP样品水溶性组分中大部分是无机离子,因此样品水溶性组分显示出了一定的吸湿性,整个观测期其吸湿增长因子变化范围为1.27~1.44。
High-volume TSP samples collected hourly from 9 to 12 March 2013 at an urban site of Xi＇an were analyzed for organic carbon （OC）, elemental carbon （EC）, inorganic ions and hygroscopicity, along with the on-line measurements of CO, NOx, SO2 and o3. The purpose of this work was to investigate the chemistry evolution of urban atmospheric particles during the dust storm period, the main source and formation mechanism of sulfate, nitrate, ammonium and sodium salts and their impact on the hygroscopicity of dust. The results showed that during the sampling period there were two dust storms peaks arriving over Xi＇an with the hourly concentrations of TSP being 7527 μg·m^-3 and 3200μg·m^-3 and SO4^2- being 180 μg·m^-3 and 38 μg·m^-3, respectively. Concentrations of NH4^＋ and NO3^- were almost undetectable at the beginning hour of the dust storm occurring in the city, but both continuously increased with a molar ratio of 1：1 and reached up to 34μg·m^-3 and 8.7 μg·m^-3 within 48 hr after the dust storm leaving Xi＇an. During the whole sampling period, SO4^2- and Cl^- strongly correlated with Ca^2＋ and Na^＋ （r^2〉0.95）, while NH4^＋ correlated well with NO3^- （r^2〉0.78）. Concentrations of CO, NOx and SO2 increased after the dust storm event except O3. During dust storm period, Na^＋ mainly existed as NaCl and Na2SO4. In the whole observation period SO4^2- and Cl in the samples largely existed as the chemical forms of NaCl, Na2SO4 and CaSO4, derived from water-soluble salts in the dried lakes of Gobi desert such as halite, mirabilite, gypsum and glauberite. However, NH4^＋ and NO3^- in the samples were mainly derived from heterogeneous reactions on the dust surface and existed as NH4NO3. Due to the dominant contribution of the salts above to the inorganic ions of the samples, water-soluble fraction of the TSP samples showed a similar hygroscopicity with a hygroscopic growth factor ranging from 1.27-1.44 during the whole campaign.
出处
《地球环境学报》
2015年第1期44-53,共10页
Journal of Earth Environment
基金
国家杰出青年科学基金(4132514)
