Exposure to volatile hydrocarbons in commuter trains and diesel buses

Percentage proportions of 25 C2-C7 hydrocarbons were determined inside both diesel buses and commuter trains in regular traffic. The hydrocarbons originate predominantly from petrol-fuelled vehicles. The total proportion of unburnt petrol components (mainly alkanes and arenes) was considerably larger than the proportion of combustion-formed components (mainly ethene, ethyne and propene). The approximate relative proportions 1 : 1 : 0.4 : 0.1 were observed for the genotoxic species benzene, ethene, propene, and 1,3-butadiene. Isoprene from expired air of the passengers constituted a prominent fraction, particularly in the buses. Samples were taken on triple-layer adsorbent cartridges and were analyzed in the laboratory by thermal desorption and gas chromatography on an aluminium oxide column. Passenger exposure to traffic-emitted volatile hydrocarbons was 2-3 times higher for diesel bus commuters than for train commuters. The presence of road vehicles nearer to the buses explains this difference. Additional pollution in buses from their diesel exhaust strengthens commuter trains as a superior alternative with respect to the exposure of the passengers to hazardous air pollutants.