Chemical Compositions Of Fine Particulate Matter And Submicron Particulate Matter Near An Urban Freeway

With the rapid increase of vehicle counts, vehicle emission has become a major source of atmospheric particulate matter. It is very improtant to carry out research on mass concentration and chemical compositions of PM2.5and PM1near the urban freeway and this can help with the the pollution control of motor vehicles, the environmental impacts assessment and human health risks evaluation.In this study, the North Fourth Ring Road, a typical urban freeway in Beijing was chosen. A sampling campaign was performed to characterize submicron particulate matter (i.e., PM1) including semi-volatile composition using annular denuder-filter pack sampler. This field study was carried out during December2011and August2012. The samples were used to analyze mass concentration and major chemical composition of PM1and calculate correction factor of semi-volatile composition. This study also used he correction factor of semi-volatile composition to adjust mass concentration of PM2.5samples collected between2008and2012and get the mass contration and temporal profile of PM2.5.Optimized results of annular denuder-filter pack sampler shows that the appropriate concentration of Na2CO3was2%and7%for citric acid, a considerable volatile fraction of total nitrate mass and organic carbon was lost from original PMi samples, which were35±13%and3.4%±1.3%in winter, and increased to68±15%and6.8%±3.7%in summer. In normal days, our results showed that average PM1concentrations were52.5±29.9μg/m3in summer and59.6±32.5μg/m3in winter, but increased to154.2±36.3μg/m3in haze days in summer. Chemical composition with the highest concentrations are OC、SO42-、NO3-、NH4+and EC。Vehicle emission, coal combustion, biomass burning, and industrial emission are the major source of PMi. During haze days, the concentrations of OC、EC and water soluble ions were much higher than those in non-haze days. Mass concentration of PM2.5decreased slowly from2008to2012. The mass concentration of PM0.2-1accounts for as much as70%of PM0.2-2.5. OC/EC decreased year by year while NO3-/SO42-showed the opposite trend. The contribution of vehicle emission in particulate matter is increasing.