REAL-WORLD MEASUREMENTS OF EXHAUST AND EVAPORATIVE EMISSIONS IN THE CASSIAR TUNNEL PREDICTED BY CHEMICAL MASS-BALANCE MODELING

The chemical mass balance model has been used to separate non-methane hydrocarbon emission factors measured in the Cassiar tunnel study into exhaust and evaporative emission factors. The local gasoline composit ion has been used as a real-world surrogate profile for exhaust emissi ons and has been demonstrated to result in vastly improved model perfo rmance compared to the performance obtained with the use of an exhaust profile derived from dynamometer testing. Because of the approach use d, the combustion and unburned gasoline components of exhaust emission gases could be estimated separately. Unburned gasoline was found to c omprise 63.4 +/- 7.0% of exhaust gases for light-duty vehicles operati ng in steady-state driving conditions in this study. On-road benzene e missions were found to split 71%/27%/2% between the combustion, unburn ed gasoline, and evaporative sources. Evaporative non-methane hydrocar bons were found to represent 10.3 +/- 0.8% of the total on-road emissi on rate on average. The apportionment of total NMHC emission factors t o exhaust and evaporative emission factors allowed a detailed comparis on to exhaust and on-road evaporative emission factors predicted by th e MOBILE4.1C and MOBILE5C models.