Comparing emission rates derived from a model with those estimated using a plume-based approach and quantifying the contribution of vehicle classes to on-road emissions and air quality

A comparison of fleet average emission factor(s) derived from a traffic emission model with emission factors (EF) estimated using plume-based measurements, including an investigation of the contribution of vehicle classes to CO, NO_x, and elemental carbon (EC) along an urban corridor. A field campaign was conducted over one week in June 2016 on an arterial road in Toronto, Canada. A traffic simulation model was calibrated and validated, and second-by-second speed profiles for all vehicle trajectories were extracted to model emissions. Dispersion modeling was carried out to identify the extent to which differences in emissions translate to differences in near-road concentrations. The results indicate that modeled EF for CO and NO_x are twice as high as plume-based EF. Modeled results indicate that transit bus emissions accounted for 60% and 70% of the total emissions of NO_x and EC, respectively. Transit bus emission rates in g/passenger-km for NO_x and EC were up to 8 and 22 times, respectively, the emission rates of passenger cars. Meanwhile, electrically fueled-street cars in Toronto improved near-road air quality despite their negative impact on traffic speeds. The difference in estimated concentrations derived from the two methods was not as large as the difference in estimated emissions due to the influence of meteorology and of the urban background.