Aerosol chemical compositions in the North China Plain and the impact on the visibility in Beijing and Tianjin
Aerosol chemical compositions in the North China Plain and the impact on the visibility in Beijing and Tianjin
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DOI：
10.1016/j.atmosres.2017.09.014
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发表时间：
2018-03
影响因子：
5.5
通讯作者：
Jianan Zou;Zirui Liu;B. Hu;Xiaojuan Huang;T. Wen;D. Ji;Jing-Yuan Liu;Yang Yang-Yang;Q. Yao
中科院分区：
文献类型：
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作者：
Jianan Zou;Zirui Liu;B. Hu;Xiaojuan Huang;T. Wen;D. Ji;Jing-Yuan Liu;Yang Yang-Yang;Q. Yao
为了更好地了解由水溶性离子和碳质气溶胶组成的气溶胶的化学组成特征及其对北中国平原能见度的影响，在2013年6月至2014年5月期间进行了4次实验采样。采样点分布在北京、香山、天津、石家庄和秦皇岛。大气污染事件主要发生在北半球的秋冬季。对于不同的粒度分布，NCP中细颗粒的阴阳离子比(0.64)大于粗颗粒(0.54)。散度系数表明，北半球5个城市的气溶胶污染具有相似的特征，污染物具有相互影响和区域性迁移的特点。在不同的相对湿度(RH)条件下，PM2.5的能见度与质量浓度之间存在不同的非线性相关关系。当相对湿度为70%时，能见度为5千米；这表明，由于相对湿度较高时的吸湿增长，PM2.1的增加导致能见度降低。使用机构间受保护视觉环境监测(ENPROVE)方法从测量的化学物质浓度估计消光系数(LEC)。有机质(OM)、硝酸铵(AN)和硫酸铵(AS)是北京地区夏季LEC的主要贡献者，分别占总贡献率的32.2%、25.9%和24.4%。全年海盐LEC变化不大，北京占4.1-5.3%，天津占4.8-7.4%。根据《环境空气质量标准》，天数分为污染天数(PD)和达标天数(AD)。AN、As和OM浓度的增加导致NCP中LEC的增加，导致秋冬季低能见度事件的发生。北京、天津和天津的NH_4+、NO_3-−和SO_4~(2-)−主要以细小颗粒形式存在(粒径分别为73.5%、80.7%和78.0%，PD分别为63.3%、79.4%和72.5%)和天津(PD分别为81.0%、80.6%和82.1%，AD分别为71.5%、44.3%和69.7%)。然而，主要来自燃料燃烧的CA在粗尺寸(2.1g；直径和9.0gμm)的能见度损害中也发挥了重要作用。根据正矩阵分解(PMF)模型，北京和天津的LEC分别有37.1%和26.5%来自PD的二次气溶胶。此外，生物质燃烧、燃料燃烧和扬尘也是NCP中LEC的重要来源。
To better understand the characteristics of the chemical compositions of aerosols comprised of water soluble ions (WSIs) and carbonaceous aerosol (CA) and their impacts on the visibility throughout the North China Plain (NCP), four experimental sampling campaigns were carried out between June 2013 and May 2014. The sampling sites were located in Beijing, Xiangshan, Tianjin, Shijiazhuang, and Qinhuangdao. The air pollution episodes mainly occurred during the autumn and winter in the NCP. With regard to different particle size distributions, the ratio of anions to cations in the fine size (0.64) was greater than that in the coarse size (0.54) in the NCP. Coefficients of divergence indicate that aerosol pollution had similar characteristics in the five cities of the NCP and that the pollutants were characterized by mutual influences and regional transfer processes. There were different non-linear correlations between the visibility and mass concentrations of PM2.5at different relative humidity (RH) conditions. When the RH was > 70%, the visibility was < 5 km; this shows that, due to hygroscopic growth in a higher RH, the increase in PM2.1resulted in a decrease in the visibility. The Interagency Monitoring of Protected Visual Environments (IMPROVE) method was used to estimate the light extinction coefficients (LEC) from the measured concentrations of chemical species. Organic matter (OM), ammonium nitrate (AN), and ammonium sulfate (AS) were the three dominant species that contributed to the LEC in Beijing and had the highest proportions of total contributions to the LEC in the summer, accounting for 32.2%, 25.9%, and 24.4%, respectively. The LEC of sea salts did not change much throughout the year and accounted for 4.1–5.3% in Beijing and 4.8–7.4% in Tianjin. According to the Ambient Air Quality Standard, the days were divided into pollutional days (PD) and attained days (AD). The increasing concentrations of AN, AS and OM resulted in an increase in the LEC in the NCP, which led to the occurrences of low visibility events during the autumn and winter. NH4+, NO3−, and SO42 −mainly existed as fine size particles (diameter < 2.1 μm) in Beijing (73.5%, 80.7%, and 78.0% on PD and 63.3%, 79.4%, and 72.5% on AD, respectively) and Tianjin (81.0%, 80.6%, and 82.1% on PD and 71.5%, 44.3%, and 69.7% on AD, respectively). However, the CA originating mainly from fuel combustion also played an important part in the visibility impairment in the coarse size (2.1 < diameter < 9.0 μm). According to a positive matrix factorization (PMF) model, 37.1% and 26.5% of the LEC came from secondary aerosols on PD in Beijing and in Tianjin, respectively. In addition, biomass burning, fuel combustion and fugitive dust were also important contributing sources of the LEC in the NCP.