Hydrocarbon emissions in a highway tunnel in the Paris area

The present study was carried out in the Thiais tunnel, which is situated close to Paris. The aim of the study was to determine the hydrocarbon speciation of vehicle emissions and to measure the emission rates of non-methane hydrocarbons (NMHCs) and carbon monoxide (CO). The major compounds observed, and expressed in terms of % w/w of total hydrocarbons, were isoC(2)H(12) (25%), and C2H4(21.4%),with other major hydrocarbons, C2H2, C3H6 and n-C4H10 each accounting for about 10%. Other measured NMHCs were emitted in very low amounts of about 1% or less. The NMHC composition in the Thiais Tunnel was consistent both with other tunnel distributions (Gertler et al., 1996. Atmospheric Environment 30(12), 2297-2365; Duffy and Nelson, 1996. Atmospheric Environment 30(15), 2759-2768) and with modeling predictions made by Ahlvik et al. (1997) based on the European fleet distribution. Expressed in terms of a mixing ratio percentage, alkenes, alkanes and alkynes accounted for 46, 35 and 19%, respectively of the total identified NMHCs. The evolution of this composition was followed over a 24 h period under OH oxidation in order to determine the respective changes in the relative levels of each group of hydrocarbons. Considering the contribution of light-duty (LD) and heavy-duty (HD) NMHC vehicle emissions, our results were compared with other tunnel experiments. The major compounds measured in the present study were the same as for measurements made in other tunnels. However, the CO and NMHC emission factors more than two times higher in the Thiais tunnel, can be explained by the differences in catalyst-equipped fleets. (C) 2000 Elsevier Science Ltd. All rights reserved.