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

In August 1995, measurements of CO, NO(x') 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/NO(x) 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.