| 北京夏冬季霾天气下气溶胶水溶性离子粒径分布特征 |
| 摘要点击 3560 全文点击 1897 投稿时间：2012-06-13 修订日期：2012-09-17 |
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| 中文关键词 气溶胶 水溶性离子 二次无机离子 质量浓度谱分布 霾天 |
| 英文关键词 aerosol water-soluble inorganic ions secondary inorganic ions mass size distribution haze days |
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| 中文摘要 |
| 为研究北京夏、冬季霾粒子中水溶性离子的粒径谱分布,并进一步分析其来源及形成机制,于2009年夏季和冬季利用惯性撞击式8级采样器(Andersen)和石英微量振荡天平(TEOM)对北京城区大气气溶胶分别进行了为期2周的连续采样和监测,并用离子色谱(IC)对气溶胶中的水溶性离子进行了分析. 结果表明,夏季霾天PM10和PM2.5的质量浓度分别为(245.5±8.4)μg·m-3和(120.2±2.0)μg·m-3,冬季霾天对应的数值分别为(384.2±30.2)μg·m-3和(252.7±47.1)μg·m-3,无论夏季还是冬季,霾天大气细粒子污染均十分严重. 细粒子中总水溶性离子(TWSS)的浓度霾天远高于对照天,其中霾天浓度上升较快的是SO42-、NO3-和NH4+,二次无机离子 对霾天气的形成过程扮演重要作用. 除NO3-外,其余7种水溶性离子夏、冬季霾天粒径谱分布一致,即,SO42-、NH4+主要分布于PM1.0以下的细粒子模态,Mg2+、Ca2+主要分布于PM2.5以上的粗粒子模态,Na+、Cl-和K+呈双模态分布; 夏季霾天NO3-呈双模态分布,而冬季则主要分布于细粒子中. 夏季霾天SO42-的平均质量中值粒径(MMAD)为0.64 μm,SO42-主要来自远程SO2的云内反应,并且SO2表观转化率(SOR)高于对照天,使得霾天光化学反应生成的细粒子远远高于对照天气过程; 冬季霾天SO42-的MMAD增至0.89 μm,冬季因局地SO2排放并被非均相化学反应过程氧化为SO42-亦为北京大气细粒子的重要来源. 夏、冬季霾天 NO3-的 MMAD分别为 2.85 μm和 0.80 μm,受到温度的影响, NO3-夏、冬季节分别以硝酸钙和硝酸铵的形式存在于粗、细粒子中. |
| 英文摘要 |
| To investigate the size distribution characteristics of water soluble inorganic ions in haze days, the particle samples were collected by two Andersen cascade impactors in Beijing during summer and winter time and each sampling period lasted two weeks. On-line measurement of PM10 and PM2.5 using TEOM were also conducted at the same time. Sources and formation mechanism of water soluble inorganic ions were analyzed based on their size distributions. The results showed that average concentrations of PM10 and PM2.5 were (245.5±8.4)μg·m-3 and (120.2±2.0)μg·m-3 during summer haze days (SHD), and were (384.2±30.2) μg·m-3and (252.7±47.1) μg·m-3 during winter haze days (WHD), which suggested fine particles predominated haze pollution episode in both seasons. Total water-soluble inorganic ions concentrations were higher in haze days than those in non-haze days, especially in fine particles. Furthermore, concentrations of secondary inorganic ions (SO42-, NO3- and NH4+) increased quicker than other inorganic ions in fine particles during haze days, indicating secondary inorganic ions played an important role in the formation of haze pollution. Similar size distributions were found for all Sinorganic water soluble ions except for NO3-, during SHD and WHD. SO42- and NH4+ dominated in the fine mode (PM1.0) while Mg2+ and Ca2+ accumulated in coarse fraction, Na+, Cl- and K+ showed a bimodal distribution. For NO3-, however, it showed a bimodal distribution during SHD and a unimodal distribution dominated in the fine fraction was found during WHD. The average mass median aerodynamic diameter (MMAD) of SO42- was 0.64 μm in SHD, which suggested the formation of SO42- was mainly attributed to in-cloud processes. Furthermore, a higher apparent conversion rate of sulfur dioxide (SOR) was found in SHD, indicating more fine particles were produced by photochemical reaction in haze days than that in non-haze days. The MMAD of SO42- increased to 0.89 μm in WHD, local emission of SO2and the subsequently heterogeneous reaction became the main source of SO42- during winter time. The average MMADs of NO3- were 2.85 μm and 0.80 μm in SHD and WHD, respectively. Influenced by the seasonal temperature difference, NO3- mainly existed in the form of calcium nitrate in coarse mode during SHD while the fine mode nitrate was associated with ammonium during WHD. |
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