Level Differences And Transmission Characteristics Between Indoor And Outdoor PM_2.5 Of Residential Buildings In Different Functional Regions In Shanghai

People spend 85%-90%of their time insides,exposed to a long-term threat by indoor air pollution,and the impact of outdoor air pollution on indoor air quality has also drawn public attention.As a center of China's economy,culture and trade,Shanghai has a clear functional region plan.Sources,concentration and chemical compositions of PM2.5 as well as the level of air pollution vary from region to region.In order to know about the interrelation and difference between indoor and outdoor PM2.5 of residential buildings in different functional regions,and to explore the transmission characteristics of particulate matter from outdoor to indoor,12 homes in three kinds of regions were selected as sampling sites for real-time monitoring from Nov.2016 to Sep.2017.And the seasonal,regional,transmission characteristics were obtained through chemical analysis and calculation models.The main research results are as follows:(1)The sequence of the averaged daily mean concentration of indoor and outdoor PM2.5 is:the traffic region>industrial region>the non-characteristic residential region in winter,while industrial region>traffic region>the non-characteristic residential region in summer.The average I/O ratio of residential homes is 0.76±0,14 in winter and 0.75±0.15 in summer,relatively.I/O ratio set approximately obey normal distribution.The maximum,minimum and average values of I/O are lower in summer.However,large gap between I/O ratios of homes in the same regions still exists,which indicates that the structure of building itself might influence the I/O ratio.The infiltration factor of buildings(Finf)calculated by Random Component Superposition(RCS)method is 0.2519?0.7163 in winter and 0.3010?0.8591 in winter;and Finf calculated by External Mixture(EM)are 0.3372 and 0.2867 for winter and summer,respectively.(2)The concentrations of sulfur and metal elements in PM2.5 obey the following sequence:industrial region>traffic region>the non-characteristic residential region.Although S is often regarded as an indicator to trace indoor and outdoor transportation,there is a significant difference between the I/O ratio characterized by S and the I/O ratio characterized by PM2.5 in this study.According to Pearson correlation analysis and ANOVA,Cu might be the best tracer for air transportation between indoor and outdoor in Shanghai residents,and the distinct difference of I/O ratio of Cu was found in in different functional areas.(3)In winter,indoor concentration of PM2.5-bounded As,Cd,Cr,Cu,Pb,S is strongly related to outdoor concentrations while Fe only has moderate correlation;in summer,indoor and outdoor PM2.5-bounded Cd,Cr,Cu have strong correlation while Al,As,Ca,Fe,Pb,Mo,Se,Zn elements are moderately related.The results by Coefficient of Divergence(COD)method show that there is distinctly different between the PM2.5 components in non-characteristic region and those in the traffic region or industrial region.The difference in COD values between different sampling sites implies that chemical components of fine particulate matter in the atmosphere surrounding the residential buildings in Shanghai have distinct regional heterogeneity.In terms of the sources of pollutants,Cd,Zn and Fe are the three elements with the largest Enrichment Factor(EF)value in this study,thus they are most affected by anthropogenic sources.(4)The Time-of-Flight Secondary Ion Mass Spectrometry(ToF-SIMS)was utilized to study the surface components of particulate matter.The results demonstrated that quartz and Teflon filter are suitable for analysis of atomospheric particles byToF-SIMS.During hazy days,more phthalates,heavy metals,aromatics,nitrogen oxides and chlorides are detected from the PM2.5 sample.In addition,according to the two-dimensional element distribution and depth profiles,organic matters are wrapped around the inorganic salts,and the concentration gradually decreased towards the periphery of the particulate matter.During the transmission process of PM2.5 from outdoor to indoor,the concentration of organic matters on the surface of PM2.5 tends to increase while that of inorganic salts tends to decrease,but the concentration of inorganic salts at the core of the particles still remains higher.The results of this study can provide experimental basis for policy-guided decisions of indoor air pollution control,and meanwhile provide data support and method reference for the application of ToF-SIMS to the study of the surface chemistry and transport characteristics of particles.