The Characteristic Of Water-soluble Ions And Source Apportionment Of PM_2.5 In Dormitories Of An University

In recent years,the airborne fine particulate matter(especially PM2.5)has caused great air pollution in China.PM2.5 can penetrates into indoors and has serious impact on indoor environment where people spend most of their time.Therefore,it is necessary to achieve better understanding of the characteristics of the indoor PM2.5.In this paper,field experiments were conducted in dormitories of an university in Nanjing to collect both indoor and outdoor PM2.5.The water-soluble ions of PM2.5 were analyzed with ion chromatography,Nessler's reagent spectrophotometry and inductively coupled plasma optical emission spectrometry.Furthermore,the source of PM2.5 was apportioned by PMF method.The key findings are as follows:The average indoor and outdoor PM2.5 concentrations in winter were significant higher than that in summer.The average PM2.5 concentrations during hot summer days were also higher than that in plum rainy season.In winter the concentrations of total water-soluble ions were higher than that in summer,and water-soluble ions were more easily enriched in PM2.5 in winter.The indoor average concentrations of total water-soluble ions in winter and summer were 40.84±18.47 and 12.23±6.86?g/m3,respectively.The total water-soluble ions in winter and summer accounted approximately for about 50%and 28%of PM2.5 mass concentrations.In summer and winter,NO3-,SO42-and NH4+ were the main components of water-soluble ions in PM2.5 collected from indoor and ambient air.Meanwhile,for both indoor and outdoor PM2.5 samplers,the highest component in winter and summer was SO42-and NO3-,respectively.The values of atmospheric C/A in winter and summer for PM2.5 from the ambient air were 1.03 and 1.31,respectively,while the corresponding values from dormitories were 1.15 and 1.43,respectively.The acidity of atmospheric PM2.5 was higher than that in dormitories.[NO3-]/[SO42-]ratio of atmospheric PM2.5 in winter and summer were 1.41 and 0.56,respectively.And the corresponding values of PM2.5 in dormitories were 1.13 and 0.48,respectively.The influence of mobile sources on indoor and outdoor PM2.5 in winter was larger than that in summer.On the contrary,indoor and outdoor PM2.5 in summer were impacted greatly by stationary sources.The results of source apportionment indicated that four major source factors of indoor and outdoor PM2.5 were included:mixed sources,soil dust,vehicle exhaust and fossil fuels combustion.The contribution of four source factors to outdoor PM2.5 were 42.5%,21.1%,18.2%and 18.1%,respectively.The four major source factors contributed 37.4%,21.5%,24.5%and 16.7%to indoor PM2.5,respectively.The pollution of secondary aerosol was more serious in dormitories in winter.The mixed sources containing secondary aerosols contributed 40.6%to dormitory indoor PM2.5 in summer which is lower than that in winter(54.7%).Compared with dormitory,PM2.5 in office had higher acidity and lower value of C/A(1.39).[NO3-]/[SO42-]ratio of PM2.5 in office during summer were 0.30 which was lower than the value in dormitory.It indicated that the mobile sources contributed more to dormitory than to office.Furthermore,the mixed sources containing secondary aerosols contributed 29.5%to office indoor PM2.5 in summer which was much lower than that to dormitory(40.6%).