Characteristics of water soluble inorganic ions in PM2.5 in winter of Beijing in typical urban areas

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.