摘要:
为了全面了解北京市煤改气后冬季大气细颗粒 PM2.5中无机水溶性离子及其来源,于 2017年冬季供暖期间在北京市海淀区连续采集了41个PM2.5 样品,采用离子色谱分析了其中10 种水溶性离子(Na+、NH4+、K+、Ca2+、Mg2+、F-、Cl-、NO2-、NO3-、SO42-)的浓度。 结果表明:采样期 间北京市 PM2.5 的日均质量浓度范围为(94.28±52.49)μg/m3,相较于2016 年,2017 年冬季 PM2.5 日均质量浓度降低了29μg/m3,减少幅度达28.2% ,污染天数明显降低;污染期颗粒物中 NO3-、SO42-、NH4+显著高于优良期;质量浓度比 ρ(NO3-)/ρ(SO42-)大于1,移动源贡献相对较 大,反映出“煤改气”政策实施引起燃煤等固定源排放硫酸盐减少。 采用飞行时间二次离子质谱 (TOF-SIMS)结合质量高分辨模式与正负离子成像模式表征了PM2.5。 结果显示NH4+在污染期 倾向以分子硫酸铵或硫酸氢铵的形态存在。
Abstract:
Inordertofullyunderstandtheinorganicwater-solubleionsandtheirsourcesintheatmosphericfineparticlesPM2.5inBeijingaftercoal-to-gasconversion,41PM2.5 sampleswerecontinuously collectedinHaidianDistrictofBeijingduringthewinterheatingperiodin2017.Theconcentrationsof 10kindsofwater-solubleions(Na+,NH4+,K+,Ca2+,Mg2+,F-,Cl-,NO2-,NO3-,SO42-)wereanalyzed byionchromatography.TheresultsshowthatthedailyaveragemassconcentrationofPM2.5 inBeijing duringthesamplingperiodis(94.28±52.49)μg/m3.Comparedwiththewinterof2016,theaverage dailyPM2.5concentrationinBeijingin2017decreasedby29μg/m3,withadecreaseof28.2%,and thenumber of pollution days decreased significantly.During the pollution period,NO3-,SO42-,and NH4+intheparticulatematterweresignificantlyhigherthanthecleanperiod.Theratiooftheconcentrationofρ(NO3-)/ρ(SO42-) isgreaterthan1,andthecontributionofthemobilesourceisrelatively large,reflectingthattheimplementationofthe“coaltogas”policyhascontributedtothereductionof sulfateemissionsfromfixedsourcessuchascoal.Time-of-flightsecondaryionmassspectrometry(TOFSIMS)wascombinedwithmasshighresolutionmodeandpositiveandnegativeionimagingmodeto characterizePM2.5.TheresultsshowthatNH4+tendstoexistintheformofmolecularammoniumsulfate orammoniumhydrogensulfateduringthepollutionperiod.
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