Physical and Chemical Characteristics and Volatility of PM in the Proximity of a Light-Duty Vehicle Freeway

摘要

Volatility properties of ultraflne particles were analyzed next to State Route 110(Pasadena freeway CA),a light-duty vehicle freeway where heavy-duty traffic is prohibited.In addition,mass concentration and chemical composition of particulate matter(PM)were measured in coarse,accumulation,and ultrafine modes.On weekdays from 17 May to 4 June 2004,measurements were performed in two locations,one very close to the freeway(within 2.5 m from the curb)and one at a distance of about 50 m from the freeway.For measurement of mass and chemical composition,the study employed in each location a micro-orifice uniform deposit impactor(MOUDI)and a modified high-volume sampler.Both instruments sampled with the same size cut points:a coarse mode from 2.5 to 10 mum,an accumulation mode from 0.18 to 2.5 mum,and an ultra-fine mode of particles less than 0.18 mum in aerodynamic diameter.Alternately,a tandem differential mobility analyzer(TDMA)was used at the two sites.A heater between the two DMAs evaporated volatile material from the monodisperse aerosol,size selected by the first DMA.The second DMA analyzed the losses of volatile components.The ultrafine number concentrations next to the freeway were 46,000 cm~(-3)on average during the sampling period.The MOUDI ultrafine mass concentration,nitrate,and EC were higher next to the freeway than at the background site farther from the freeway.The other components analyzed in the ultrafine mode had similar concentrations next to the freeway and at the background site.Volatility ranged from about 65% volume losses of 120 nm particles heated to 110°C to 95% of 20 nm particles.The 20 nm aerosol was only internally mixed,whereas increasing nonvolatile fractions were found for 40 nm(6% next to the freeway),80 nm(20%),and 120 nm(28%)aerosols.