Exposure of City Residents to Carbon Monoxide and Monocyclic Aromatic Hydrocarbons during Commuting Trips in the Paris Metropolitan Area

Abstract

A study was conducted from October 1991 to September 1992 in the Paris metropolitan area to assess the exposure of city-dwellers who are directly or indirectly exposed to car exhaust fumes during their daily movements. The study concentrated primarily on trips in automobiles, although other transportation modes were also included: subway, bus, and trips made on foot. Carbon monoxide (CO) and six monocyclic aromatic hydrocarbons (MAHs) were identified as being indicators of automotive exhaust and/or being toxic. The average concentrations collected inside an automobile in central Paris were 12 ppm for carbon monoxide, 46 (ig/m3 for benzene, and 260 μg/m^-3 for toluene. Lesser quantities were recorded for the other modes of transportation: 2-5 ppm of CO, 12-25 μg/m^-3 for benzene, and 80-110 μg/m^-3 for toluene—that is, three times more than in Parisian surrounding air. Further measurements showed that in a moving vehicle, the concentration of pollutants is caused by the exhaust of neighboring vehicles. Consequently, correlations between pollutants are very high, and the relationship between concentrations of CO and MAHs is identical to that found in stationary monitoring stations. From a health standpoint, reference values established by the World Health Organization (WHO) for CO are not exceeded when an individual only travels from home to work. However, if that individual uses a personal car at other times during the day, the reference value for eight hours (10 ppm) may be exceeded. This study shows that in the Paris area, commuting to work in cars contributes an average of 20-30% of the daily inhaled amount of benzene for a nonsmoking city-dweller.