Characterization of vehicle emissions in Vancouver BC during the 1993 Lower Fraser Valley Oxidants Study

As part of the 1993 Lower Fraser Valley Oxidants Study, measurements of mobile source emission factors were performed in the Cassiar Tunnel on the Trans-Canada Highway to measure the on-road contribution to the ozone-forming precursors (NOx and speciated hydrocarbons) along with CO. Observed emission factors were compared to the Canadian versions of the U.S. Environmental Protection Agencyʹs MOBILE models, MOBILE4.1C and MOBILE5C, to assess uncertainty in the predicted mobile source contributions to the Vancouver emissions inventory. A total of 16 1-h runs were made. The timing of the individual runs was designed to encompass different traffic volumes, driving conditions, and times of day. A total of 24,513 vehicles traversed the tunnel during the study, with approximately 91% light-duty vehicles, 4% heavy-duty spark ignition vehicles, and 5% heavy-duty diesel vehicles. MOBILE5C overpredicted the observed value of CO by 2%, NMHC by 24%, and NOx by 13%, while MOBILE4.1C underpredicted the observed values by 36, 29, and 23% for CO, NMHC, and NOx respectively.