Gaseous emissions from vehicles in a traffic tunnel in Vancouver, British Columbia

In August 1995, measurements of CO, NOx, speciated nonmethane hydrocarbons (NMHC), and CO2 were made in Vancouver's Cassiar Connector, a 730-m-long level-grade highway traffic tunnel. Two characteristics of the Vancouver setting are the presence of many propane vehicles and a mandatory inspection and maintenance (I/M) program. Although the driving conditions and vehicle fleets are otherwise outwardly similar to those of recent Tuscarora-tunnel studies, CO/NOx ratios at the Cassiar Connector are significantly lower than those measured at Tuscarora. The Cassiar measurements are consistent with the MOBILE5A mobile emissions model predictions. The Canadian version of MOBILE5A-known as MOBILE5C-gives nearly identical results, indicating that differences in Canadian and U.S. emission standards cannot explain differences between Cassiar and U.S. tunnels. Considering the modeling results as well as measured ethene/acetylene ratios indicative of noncatalyst vehicles, it appears that vehicle deterioration remains the major issue in in-use vehicle emissions-even in Vancouver, where there is a mandatory loaded-mode I/M program. Uncertainties in determining the ages of the vehicles in the tunnel, however, have a significant impact on the model predictions.