武汉地区秋冬季清洁与重污染过程的水溶性离子特征研究

利用武汉地区2014年秋、冬季在线离子色谱分析仪Marga监测所得的大气PM_(2.5)中水溶性离子数据和武汉市环境空气质量自动监测的细颗粒物数据,分析了武汉地区秋、冬季重污染和清洁过程的大气污染特征.结果表明,PM_(2.5)是武汉地区秋、冬季大气污染的首要污染物,无论是在清洁还是重污染过程中,NO_3~-、SO_4~(2-)和NH_4~+3种成分都是PM_(2.5)的主要无机成分.重污染过程中PM_(2.5)的平均浓度是清洁过程的4.5倍,而3种主要水溶性离子平均浓度增长至清洁过程的5~6倍,且有着显著的相关性,二次生成水溶性离子的污染已成为武汉秋、冬季大气污染的主要因素.Cl-在重污染过程中的浓度及与PM_(2.5)的相关系数显著增大,表明化石燃料燃烧等过程也对重污染的形成产生了较显著的作用,值得关注的是,K~+在重污染过程中的浓度及与PM_(2.5)的相关系数增大也验证了燃烧过程对重污染起到的贡献.硫氧化率和氮氧化率的分析结果表明,重污染过程中的二次转化要多于清洁过程,可能是非均相反应生成了二次污染的硫酸盐和硝酸盐.线性回归分析的方程系数研究表明,NH_4NO_3和(NH_4)_2SO_4可能是清洁和重污染过程中主要的盐类物质.NO_3~-/SO_4~(2-)的平均质量浓度比说明移动源对武汉地区秋、冬季二次污染的形成和发展已经起到越来越大的作用,特别是重污染过程中的影响更大.

Characteristic analysis of water-soluble ions during clean and heavy pollution processes in autumn and winter in Wuhan

The atmospheric pollution characteristics during clean and heavy air pollution processes in Wuhan was analyzed based on the ion compositions monitored by Marga and PM_2.5 measured by Wuhan environmental air quality automatic monitoring in autumn and winter 2014. During the study period, PM_2.5 was generally the major air pollutant in Wuhan. water-soluble nitrate, sulfate and ammonium were major inorganic components in PM_2.5 during both clean and heavy pollution processes. The average concentration of PM_2.5 during the heavy pollution process was 4.5 times that during clean periods. Three water-soluble ions increased 5~6 times and higher correlations with PM_2.5 were observed. Meanwhile, the secondary inorganic ions in PM_2.5 were the main cause of ambient particle pollution in Wuhan. Chloride concentration and correlation coefficient with PM_2.5 increased remarkably, indicating that fossil fuel burning might have great effect on heavy pollution in Wuhan. Potassium concentration and correlation coefficient with PM_2.5 increased simultaneously, demonstrating that the combustion activities aggravated the pollution process. The analyses of SOR and NOR showed that secondary transformation was enhanced during heavy pollution process, which might be caused by the heterogeneous reactions driving the formation of secondary nitrate and sulfate. Ammonium nitrate and ammonium sulfate were the typical inorganic components during both clean and heavy pollution processes. The average NO₃^-/SO₄^2- ratio implied that mobile source played a major role in particle pollution in Wuhan, especially in heavy pollution process.