| Concentrations of polycyclic aromatic hydrocarbons (PAHs) were measured in indoor and outdoor air in Los Angeles, CA, Houston, TX, and Elizabeth, NJ during June 1999—January 2001 as part of the RIOPA study ( Relationships of Indoor, Outdoor, and Personal Air). Integrated 48 hr air samples were collected simultaneously inside and outside 157 non-smokers' residences located close to or farther from identified sources such transportation, oil refineries, gas stations and local businesses. Indoor-to-outdoor (I/O) concentration ratios of individual PAHs showed that indoor sources had a significant effect on the indoor concentrations of 3-ring PAHs and a smaller effect on 4-ring PAHs, and that outdoor sources dominated the indoor concentrations of 5–7 ring PAHs. The contribution of outdoor sources to the indoor concentrations of benzo[g,h,i]perylene, estimated using a single compartment mass balance model, was 63% for all RIOPA homes (69%, 52%, and 59% for Los Angeles homes, Houston homes and Elizabeth homes, respectively). Variations in the distribution of PAHs between the gas and particulate (PM2.5) phases amongst the samples were related to the aerosol characteristics and sampling conditions as shown by stepwise multiple linear regression analysis of the pooled data. Compounds' sub-cooled liquid vapor pressure at 25°C and air temperature are the two most important predictors for partition coefficient, Kp,meas, followed by fractions of elemental (EC) and organic (OC) carbon. Both EC and OC are important predictors of gas/particle partitioning of PAHs, with EC being a better predictor. Because EC is highly correlated with (and is a good tracer of) primary combustion-generated OC, this result suggests that PAHs more readily sorb to combustion-generated aerosol containing EC. Four major sources of PAHs in indoor and outdoor air of the three cities were identified and quantified using factor analysis/multiple linear regression: vehicle exhaust, evaporative emissions, oil combustion, and combustion of natural gas. The source apportionment model developed in this work has demonstrated the existence of indoor non-combustion sources of PAHs. Indoor evaporative emissions contributed, on average, 17–30% to the indoor ΣPAH concentrations, as was estimated by the mass balance model. |
