成都市重污染期间PM_(2.5)中水溶性离子特征分析

Water-soluble Ions Characteristics of Fine Particulate Matter during Heavy Pollution Period in Chengdu

为了解成都市冬季重污染过程中细颗粒物的水溶性无机离子污染特征,对一次重污染过程进行分析。此次重污染过程中,二次离子NO_3^-、SO_4^(2-)、NH_4^+是PM_(2.5)中主要的水溶性无机离子,且质量浓度大小为NO_3^->SO_4^(2-)>NH_4^+,NO_3^-是首要离子;成都市PM_(2.5)中的阴阳离子基本达到了电荷平衡(C/A值为1.03),呈中性;NH_4^+/SO_4^(2-)比值为0.90,SO_4^(2-)和NO_3^-主要以(NH_4)_2SO_4和NH_4NO_3形式存在,([NO_3^-]+2[SO_4^(2-)])/[NH_4^+]比值小于1,说明此过程中为富氨;重污染期间,SOR和NOR平均值分别为0.46和0.26,与清洁天气相比二次转化更为明显,且硫氧化率大于氮氧化率;NO_3^-/SO_4^(2-)比值为1.49,说明重污染期间研究点处移动源已成为细颗粒物的重要来源。

In order to study the pollution characteristics of the water-soluble inorganic ions of fine particles during heavy pollution in winter in Chengdu,this study analyzed a heavy pollution process in Chengdu. The results showed that during the period of pollution,the secondary inorganic ions in PM2. 5 were mainly NO_3^-,SO_4^(2-)and NH_4^+,the order of the mass concentration of secondary inorganic ions was NO_3^-> SO_4^(2-)> NH_4^+,the NO_3^-is the major ion. The anions and cations basically reached the charge balance( C/A = 1. 03). The ratio of NH_4^+/SO_4^(2-)is 0. 90,which showed SO_4^(2-)and NO_3^-mainly existed in the forms of( NH_4)_2SO_4and NH_4NO_3. The ratio of( [NO_3^-] κ + 2 [SO_4^(2-)] κ)/[NH_4^+] κwas less than 1,indicating that NH_4^+was excess. SOR and NOR were 0. 46 and 0. 26,respectively,which illustrated that the second conversion was more obvious compared with clean process,and sulfur oxygenation rate was greater than nitrogen. NO_3^-/SO_4^(2-)was 1. 49,indicating that the mobile source has become the main source of fine particulate matter during heavy pollution.