Hydrocarbon emissions in a highway tunnel in the Paris area

The present study was carried out in the Thiais tunnel, which is situated c lose to Paris. The aim of the study was to determine the hydrocarbon specia tion 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-C4H1 0 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. Atmosphe ric Environment 30(15), 2759-2768) and with modeling predictions made by Ah lvik et al. (1997) based on the European fleet distribution. Expressed in t erms of a mixing ratio percentage, alkenes, alkanes and alkynes accounted f or 46, 35 and 19%, respectively of the total identified NMHCs. The evolutio n 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 g roup of hydrocarbons. Considering the contribution of light-duty (LD) and h eavy-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 NM HC emission factors more than two times higher in the Thiais tunnel, can be explained by the differences in catalyst-equipped fleets. (C) 2000 Elsevie r Science Ltd. All rights reserved.