Source proximity and outdoor-residential VOC concentrations: results from the RIOPA study.

Ambient volatile organic compound concentrations outside residences were measured in Elizabeth, New Jersey as part of the Relationship of Indoor, Outdoor, and Personal Air (RIOPA) study to assess the influence of proximity of the residences to known ambient emissions sources. The closest distances between the outdoor samplers and emission sources were determined using Geographic Information Systems (GIS) techniques. Multiple regression models were developed for residential ambient concentrations of aromatic hydrocarbons (BTEX), methyl tert butyl ether (MTBE), and tetrachloroethylene (PCE). The natural log transformed ambient concentrations of BTEX were inversely associated with distances to major roadways with high traffic densities and gasoline stations, atmospheric stability, temperature, and wind speed. Ambient MTBE levels were associated with inverse distance to gas stations and interstate highways. Residential ambient PCE concentration was inversely associated with distance to dry cleaning facilities, atmospheric stability, temperature, wind speed, and relative humidity. The linear regression models that include proximity to emission sources and meteorological variables explained 16-45% of the overall variation of ambient residential VOC concentrations. Meteorological conditions, especially atmospheric stability and temperature, explained 60-90% of the total variation in the regression models. The residential ambient air concentrations were 1.5-4 times higher than the urban background levels outside homes very close (< 50 m) to ambient emission sources where similar to 7% of the population live. However, the relative increase of risk for disease is small and variations in air concentration in the background urban atmosphere are greater than those from the proximity to roadways.