Ealuation of a Denuder-MOUDI-PUF Sampling System to Measure the Size Distrbution of Semi-Volatile Polycyclic Aromaic Hydrocarons in the Atmosphere

摘要

This study describes a field comparison conducted between 2 methods employing diferent MOUDI impactor configurations to evaluae their performance n sampling and measurement of the size distriution of 15 priority pollutant polycyclic aromatic hydrocarbons(PAHs).samples were collected during 24h periods approximately every 7th day,beginning at 8:00 AM,in 2 different sites of the Los Angeles Basin.one site was near Central Los Angeles n an area impacted by high vehicular traffic,whereas the other ste was located about 60 km down wind of central Los Angeles (receptor site).Particle samples from about 43 m~3 of air were collected using collocated MOUDI impactos and classified in 3 aerodynamic diameter size intervales:0-0.18 mum (ultrafine mode I),0.18-2.5 mumm(accumulation mode II),and 2.5-10mm(coarse model III).One MOUDI operated in teh conventonal mode,the other with a vapor trapping system that included an SAD-4 coated annular denueder placed upstream of the impactor an da polyurethane foam plug (PUF) placed in series behind the impactor.PAHs were separated and quantified by HPLC with fluorescence detection optimized for the highest sensitivity.The results showed tha for both sites,using either sampling system,the size distributons obtained are similar for the less volatile PAHs (logpL=-.206).In the central Los Angeles site,the largest PAH fraction was found in the 0-0.18 mum(modeI)size range,typical of primary emissions.At the downwind location,the largest fraction was in the 0.18-2.5 mum(modelII) size range,consistent with an "aged" aerosol.At both sites,albeit not statistically sinificant,the mean reular to denuded MOUDI mass ratios were 33-36 and 11-16 higher,respectively,for the more volatile and the less volatile PAH groups.Sampling with the regular MOUFDI coniguration is simpler and thus recommender for measurement of the size distribution of PAHs in either group.