AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Bridging Model Estimates of Vehicular Emissions with Near-Roadway Ambient Measurements
AYLA MORETTI, David R. Cocker III, Matthew Barth, University of California, Riverside
Abstract Number: 587 Working Group: Urban Aerosols
Abstract Currently, vehicle emissions are measured using dynamometers and/or portable emissions measurement systems (PEMS); however, these systems operate at temperature and dilution ratios not representative of the ambient atmosphere. Estimates of near-roadway particulate matter (PM) concentrations using these emission factors within emission models, such as the EPA’s Motor Vehicle Emission Simulator (MOVES), underpredicts measured near-roadway PM concentrations. A majority of differences between the near-road ambient studies and MOVES could be due to the changes in PM that occur immediately after the emissions rapidly dilute and cool in the ambient atmosphere. Evolution of engine technology, emissions control technology, and fuel composition further motivates the need to revisit effects of dilution and cooling on engine exhaust.
Organic aerosol (OA) formation from gasoline vehicle emissions were measured with a temperature controlled dilution sampler to account for additional OA formation during the dilution and cooling process, on the timescale of near-roadway emissions. The dilution sampler simulates the rapid dilution and cooling that occurs as the vehicle exhaust mixes with the ambient atmosphere following the original approach of Hildemann et al. (1989). The emission factor of a small gasoline engine was measured as a function of dilution and residence time to assess the sensitivity of the emission factors to near-roadway meteorology. A new module within MOVES was developed using ratios of measured (after dilution) emission factor to chassis and PEMS emission factors to identify the sensitivity of the near-roadway PM estimation from tailpipe to dilution processes. Characterization of the diluted aerosol include aerosol sizing (SMPS), aerosol shape and density (APM-SMPS), volatility (v-TDMA), and bulk chemical composition (HR-ToF-AMS).