北京市门头沟区大气降尘污染特征及其化学组分特征与质量重构

Characteristics of Atmospheric Dust Fall Pollution and Its Chemical Composition and Mass Reconstruction in Mentougou District of Beijing

为研究北京市门头沟区大气降尘污染特征,收集了20182022年门头沟区2个国控环境空气站57个大气降尘量月平均监测结果,分析了门头沟区大气降尘污染状况及其时间变化特征.为探究大气降尘化学组分特征与质量重构结果及其来源,在三家店国控环境空气站,使用主动抽滤法模拟采集降尘样品57个,测定了降尘的质量浓度及其化学组分的质量浓度,研究了大气降尘中的化学组分特征,并利用颗粒物质量重构技术对大气降尘主要组分进行质量重构,探讨了质量重构的结果可靠性及其未确定成分的原因.结果表明,20182022年,北京市门头沟区月降尘量呈周期性变化,最大值在春季4、5月,最小值在秋季10、11月,且最大月降尘量是最小月降尘量的3.28.4倍.季度平均月降尘量大小表现为:春季>夏季>秋季>冬季,且降尘主要来自于春季和夏季,其降尘量分别占全年总降尘量的40.1%43.0%和23.8%37.5%.北京市门头沟区大气降尘年平均月降尘量下降趋势明显,2022年较2018年降尘量下降了52.8%,年均下降了13.2%,与近年来北京市城市环境保护精细化管理水平的提高有关;2021年沙尘对门头沟区降尘量的影响显著,实际贡献率达44.2%.门头沟区大气降尘中化学组分以水溶性离子、地壳元素、有机碳(OC)和元素碳(EC)为主,所测化学组分质量总和所占降尘的质量分数为65.0%,二次有机碳(SOC)也是大气降尘的重要组成部分,其质量浓度为13.5μg·m^(-3),所占OC的质量分数达96.4%.大气降尘质量重构的主要组分为地壳元素扬尘、有机物(OM)、SO_(4)^(2-)、NO_(3)^(-)、NH_(4)^(+)、微量元素、EC和Cl-,质量浓度分别为34.8、28.0、20.6、15.0、5.6、4.3、3.2和2.2μg·m^(-3),所占降尘的质量分数分别为25.5%、20.6%、15.1%、11.1%、4.1%、3.2%、2.3%和1.6%;大气降尘主要来源于土壤风沙扬尘、建筑水泥尘、生物质燃烧、垃圾焚烧和二次转化过程等.大气降尘实测质量浓度与化学组分质量重构质量浓度相关性良好,可决系数R2为0.8173.质量重构结果中未确定组分占降尘质量的16.5%,其中降尘中的结合水(PBW)占降尘的质量分数为6.2%,其余未鉴别组分可能与未测量组分、选用的OM与地壳元素扬尘估算系数、颗粒物粒径组成、选择的化学组分分析方法及其测量误差有关.

To study the characteristics of atmospheric dust fall pollution in Mentougou District of Beijing,the monthly average monitoring results of 57 atmospheric dust fall samples from two state-controlled ambient air stations in Mentougou District from 2018 to 2022 were collected,and the atmospheric dust fall pollution status and its time variation characteristics in Mentougou District were analyzed.In order to explore the characteristics of chemical components of atmospheric dust fall and the results of quality mass reconstruction and their sources,57 dust fall samples were collected using the active suction method at the Sanjiadian State-controlled Ambient Air Station.The mass concentration of dust fall and its chemical components were measured,the characteristics of chemical components in atmospheric dust fall were studied,and the mass reconstruction of the main components of atmospheric dust fall was performed using particle mass reconstruction technology.The reliability of the mass reconstruction results and the reasons for its undetermined components were also discussed.The results showed that from 2018 to 2022,the monthly dust fall in Mentougou District of Beijing changed periodically,being the maximum in April or May in spring and the minimum in October or November in autumn,and the maximum monthly dust fall was 3.2 to 8.4 times the minimum monthly dust fall.The order of the quarterly average monthly dust fall was as follows:spring>summer>autumn>winter,and the dust fall mainly came from spring and summer,accounting for 40.1%-43.0%and 23.8%-37.5%of the total annual dust fall,respectively.The annual average monthly dust fall in Mentougou District of Beijing showed a significant downward trend.The dust fall in 2022 had decreased by 52.8%compared with that in 2018,with an average annual decline of 13.2%,which was related to the improvement in the fine management level of urban environmental protection in Beijing in recent years.In 2021,soil dust had a significant impact on dust fall in Mentougou District,with an actual contribution of 44.2%.The chemical components in the atmospheric dust fall in Mentougou District were mainly water-soluble ions,crustal elements,organic carbon(OC),and elemental carbon(EC).The total mass of the measured chemical components accounted for 65.0%of the mass fraction of the dust fall.The secondary organic carbon(SOC)was also an important component of the atmospheric dust fall,and its mass concentration was 13.5μg·m^(-3),accounting for 96.4%of the mass fraction of OC.The main components of atmospheric dust fall mass reconstruction were crust element fugitive dust,organic matter(OM),SO_(4)^(2-),NO_(3)^(-),NH_(4)^(+),trace elements,EC,and Cl-,with mass concentrations of 34.8,28.0,20.6,15.0,5.6,4.3,3.2,and 2.2μg·m^(-3),accounting for 25.5%,20.6%,15.1%,11.1%,4.1%,3.2%,2.3%,and 1.6%of the dust fall quality,respectively.The atmospheric dust fall mainly came from the soil dust,construction cement dust,biomass combustion,waste incineration,and secondary transformation process.The measured mass concentration of atmospheric dust fall had a good correlation with the reconstructed mass concentration of chemical components,and the determination coefficient R2 was 0.8173.The undetermined components in the mass reconstruction results accounted for 16.5%of the dust fall mass,of which the particle bound water(PBW)in the dust fall accounted for 6.2%of the dust fall mass,and the remaining undetermined components might have been related to the unmeasured components,the selected estimation coefficient of OM and crustal elemental dust,the particle size composition,the selected chemical component analysis method,and its measurement error.