Seasonal and Spatial Variation of Polycyclic Aromatic Hydrocarbons in Vapor-Phase and PM_2.5in Southern California Urban and Rural Communities

Abstract

Fifteen priority polycyclic aromatic hydrocarbons (PAHs) were measured in two rural communities (Atascadero and Lompoc) located several hundred km northwest of Los Angeles and in four urban communities 40–100 km downwind of Los Angeles (San Dimas, Upland, Mira Loma, and Riverside), during all seasons, from May 2001 to July 2002. PM2.5 and vapor-phase PAHs were collected, on prebaked quartz fiber filters and PUF-XAD-4 resin, respectively, at 113 LPM, during 24 h periods, every eighth day, and quantified by HPLC-Fluorescence. At all sites vapor-phase PAHs contained > 99.9% of the total PAH mass and were dominated by naphthalene (NAP), which varied from about 60 ng m − 3 in Lompoc, a community with light traffic, to ∼580 ng m − 3 in Riverside, a community traversed by ∼200,000 vehicles day− 1. During summer pollution episodes in urban sites, NAP concentrations reached 7–30 times annual averages. Except for summer episodes, concentrations of low MW PAHs showed small seasonal variations (∼2 times higher in winter). Similar concentrations of particle-phase PAHs were observed at all sites except for Lompoc. Benzo[ghi]perylene (BGP), a marker of gasoline exhaust emissions, showed the highest concentration among particle-phase PAHs, varying from 23.3 pg m−3 in Lompoc to 193 pg m−3 in Mira Loma. Benzo[a]pyrene and indeno[1,2,3-cd]pyrene, found exclusively in the particle phase, were much higher in urban sites (∼40–100 pg m−3), than in Lompoc (∼12 pg m−3). Winter particle-phase PAHs were 2 to 14 times higher than summer levels. Particle-phase PAHs were negatively correlated with mean air temperature in urban sites (r = −0.50 to −0.75), probably resulting from surface inversions occurring during winter. The data suggest that in Southern California vehicular exhaust emissions are a major contributor to particle-phase PAHs.