菏泽市秋冬季PM2.5水溶性离子化学特征分析

Chemical Characteristics of Water-Soluble Ions of PM2.5 in Autumn and Winter in Heze City

为深入研究菏泽市秋冬季PM2.5中水溶性离子污染特征,于2017年10月15日—2018年1月31日对菏泽市3个监测点同步进行PM2.5的采集和分析,分析探讨了不同污染程度下ρ(PM2.5)及水溶性离子化学特征.结果表明:①菏泽市秋冬季PM2.5呈区域污染特征.②整个观测期间,ρ(PM2.5)范围为26.72~284.10μg/m^3,平均值为103.27μg/m^3,其中水溶性离子对ρ(PM2.5)贡献率较大,为44.65%~49.87%;SNA(NO3^-、NH4^+、SO4^2-的统称)的占比较高,SNA占总水溶性离子质量浓度的86.88%,说明二次气溶胶为菏泽市大气PM 2.5中的重要组成部分.③SNA三角图解和水溶性离子相关性结果表明,采样期间大气中NO3^-、SO4^2-可能以NH4NO3、(NH4)2SO4形式存在;ρ(Cl^-)与ρ(K^+)相关性较高(清洁天和污染天的相关系数分别为0.79和0.81),由此推测Cl^-与K^+具有同源性,二者主要源于生物质燃烧.④重度及以上污染天的SOR(硫氧化率)和NOR(氮氧化率)分别为0.54和0.37,分别是清洁天的2.08和2.06倍;轻中污染天的SOR和NOR分别为0.37和0.29,分别是清洁天的1.42和1.61倍.随着污染程度的加重,SO2和NO2向SO4^2-和NO3^-的二次转化增强.重污染日SOR、NOR和相对湿度均大于清洁天和轻中度污染天,而温度则未表现出相似的变化趋势,说明非均相反应是菏泽市秋冬季SO4^2-和NO3^-形成的重要原因.研究显示,菏泽市污染呈区域性污染特征,二次气溶胶是菏泽市大气PM 2.5的重要组成部分,污染天ρ(NO3^-)、ρ(SO4^2-)、ρ(NH4^+)均与相对湿度呈显著正相关(P<0.05),均与温度呈负相关,表明在污染天高湿低温对SO2、NO2转化为SO4^2-、NO3^-有推动作用.

In order to study the characteristics of water-soluble ions in PM2.5 in autumn and winter in Heze City,PM2.5 samples were collected simultaneously at 3 monitoring sites from October 15 th,2017 to January 31 st,2018.The chemical characteristics of water-soluble ions in PM2.5 were analyzed at different pollution levels.The results showed that:(1)PM2.5 shows regional pollution characteristics in autumn and winter in Heze City.(2)ρ(PM2.5)was 26.72-284.10μg/m^3,with an average value of 103.27μg/m^3.The contribution rate of water-soluble ions to(PM2.5)was 44.65%-49.87%;Secondary inorganic ions(NO3^-,NH4^+and SO4^2-)have a large proportion of water-soluble ions,accounting for 86.88%.The results show that secondary inorganic aerosols are an important part of PM2.5 in Heze City.(3)NO3^-and SO4^2-in the atmosphere may exist in the form of NH 4NO 3 and(NH4)2SO4 during sampling period.The correlation between Cl-and K+was relatively high(r is about 0.79 and 0.81 on clean days and polluted days,respectively),indicating that Cl-and K+has same sources,which was mainly derived from biomass combustion.(4)sulful oxidation rate(SOR)and nitrogen oxidation rate(NOR)were 0.54 and 0.37 on heavy-polluted days,respectively,which were 2.08 and 2.06 times than that on clean days.The SOR and NOR of light moderate-polluted days were 0.37 and 0.29,respectively,which were 1.42 and 1.61 times than that on clean days.The results showed that the secondary transformation of SO2 and NO2 to SO4^2-and NO3^-was enhanced with the increase of pollution level.The values of SOR,NOR and relative humidity on heavy pollution days are larger than clean days and light moderate pollution days,while temperature show no similar change trend,indicating that heterogeneous reactions are an important reason for the formation of SO4^2-and NO3^-in autumn and winter in Heze City.The research shows that there is regional pollution in Heze City,secondary aerosols are an important part of atmospheric PM2.5 in Heze City.NO3^-,SO4^2-and NH4^+on polluted days have significant positive correlation with relative humidity(P<0.05)and shows negative correlation with temperature,indicating that high humidity and low temperature on polluted days may promote the conversion of SO2 and NO2 to SO4^2-and NO3^-.