2020—2022年呼和浩特市城区大气PM_(2.5)中5种水溶性离子污染特征分析

Analysis on pollution characteristics of five water-soluble ions in atmospheric PM_(2.5)in urban areas of Hohhot from 2020 to 2022

目的了解2020—2022年呼和浩特城区大气中5种水溶性细颗粒物(fine particulate matter,PM_(2.5))离子NO_(3)^(-)、NH_(4)^(+)、F^(-)、Cl^(-)及SO_(4)^(2-)的污染水平,根据污染来源特征评价污染治理综合状况。方法以2020—2022年每月10—16日所采集的252天的大气PM_(2.5)样品为研究对象,测定2020—2022年呼和浩特市城区5种大气PM_(2.5)标志性无机离子NO_(3)^(-)、NH_(4)^(+)、F^(-)、Cl^(-)及SO_(4)^(2-)的平均质量浓度。结果2020—2022年呼和浩特市5种大气PM_(2.5)标志性无机离子平均浓度:NO_(3)^(-)为4.56μg/m^(3),NH_(4)^(+)为2.83μg/m^(3),F^(-)为0.10μg/m^(3),Cl^(-)为0.86μg/m^(3),SO_(4)^(2-)为4.05μg/m^(3)。Cl^(-)、NH_(4)^(+)及NO_(3)^(-)质量浓度的年度差异均有统计学意义(χ^(2)=8.13、10.24、9.79,均P<0.05),NO_(3)^(-)、SO_(4)^(2-)、NH_(4)^(+)和Cl^(-)质量浓度的季节性差异均有统计学意义(χ^(2)=26.34、29.88、27.65和68.01,均P<0.05)。NO_(3)^(-)、SO_(4)^(2-)及NH_(4)^(+)具有高度相关性,趋于二次结合产生NH4NO3、(NH4)2SO4及(NH4)HSO4。并且,SO_(4)^(2-)及NO_(3)^(-)能够被NH_(4)^(+)完全中和,其中SO_(4)^(2-)较NO_(3)^(-)更易发生二次氧化反应。结论2020—2022年呼和浩特市大气PM_(2.5)及水溶性离子浓度水平状况良好,废气排放综合状况压力较大,环境大气PM_(2.5)治理状况优秀。

Objective To investigate the pollution levels of five water-soluble fine particulate matter(PM_(2.5))ions,including NO_(3)^(-),NH_(4)^(+),F^(-),Cl^(-)and SO_(4)^(2-),in the atmosphere of Hohhot urban area from 2020 to 2022,evaluate the comprehensive status of pollution control according to the characteristics of pollution sources.Methods The 252 days of atmospheric PM_(2.5)samples collected from the 10th to the 16th of each month from 2020 to 2022 were taken as the research object.The average mass concentrations of NO_(3)^(-),NH_(4)^(+),F^(-),Cl^(-)and SO_(4)^(2-)were measured,which are the five typical inorganic ions in atmospheric PM_(2.5)in urban areas of Hohhot from 2020 to 2022.Results The average concentrations of five typical inorganic ions in atmospheric PM_(2.5)in Hohhot from 2020 to 2022 were 4.56μg/m^(3)for NO_(3)^(-),2.83μg/m^(3)for NH_(4)^(+),0.10μg/m^(3)for F^(-),0.86μg/m^(3)for Cl^(-)and 4.05μg/m^(3)for SO_(4)^(2-).There were statistically significant differences in the mass concentration of Cl^(-),NH_(4)^(+)and NO_(3)^(-)among years(χ^(2)=8.13,10.24,9.79,all P<0.05),and there were statistically significant differences in the mass concentration of NO_(3)^(-),SO_(4)^(2-),NH_(4)^(+)and Cl^(-)among seasons(χ^(2)=26.34,29.88,27.65,68.01,all P<0.05).NO_(3)^(-),SO_(4)^(2-)and NH_(4)^(+)were highly correlated and tend to bind to produce NH4NO3,(NH4)2SO4 and(NH4)HSO4.Moreover,SO_(4)^(2-)and NO_(3)^(-)could be completely neutralized by NH_(4)^(+),and SO_(4)^(2-)was more prone to secondary oxidation than NO_(3)^(-).Conclusion From 2020 to 2022,Hohhot has a good atmospheric PM_(2.5)and water-soluble ion concentration level,a large pressure on the comprehensive status of exhaust emissions,and excellent environmental atmospheric control.