Roadside and in-vehicle concentrations of monoaromatic hydrocarbons

Airborne concentrations of benzene, toluene and the xylenes have been measured inside passenger cars whilst driven along major roads in the city of Birmingham, UK, as well as immediately outside the car, and at the roadside. A comparison of concentrations measured in the car with those determined from immediately outside showed little difference, with a mean ratio for benzene of 1.17 +/- 0.34 and for toluene 1.11 +/- 0.16 (n = 53). The ratio of in-car to roadside concentration was rather higher at 1.55 +/- 0.68 for benzene and 1.54 +/- 0.72 for toluene (n = 53). The roadside concentrations were typically several-fold higher than those measured at a background suburban monitoring station within Birmingham, although much variation was seen between congested and uncongested roads, with concentrations adjacent to uncongested roads similar to those measured at the background monitoring station. Measurements of benzene and toluene in a car driven on a rural road outside the city showed very comparable in-car and out-of-car concentrations strengthening the conclusion that pollution inside the car is derived from pollutants outside entering with ventilation air. The exceptions were an older car where in-car concentrations appreciably exceeded those outside (in-to out-vehicle ratio = 2.3 for benzene and 2.2 for toluene where n = 5) indicating probable self-contamination, and a very new car which built up increased VOC concentrations when stationary without ventilation (in-to out-vehicle ratio = 2.4 for benzene and 3.3 for toluene where n = 5). A further set of measurements inside London taxi cabs showed concentrations to be influenced by the area within which the taxi was driven, the traffic density and the presence of passengers smoking cigarettes. (C) 1998 Elsevier Science Ltd. All rights reserved.