AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Characterization of Exhaust Emissions from In-Use Motor Vehicles
TIMOTHY DALLMANN, Steven DeMartini, Thomas Kirchstetter, David Worton, Edward Fortner, Scott Herndon, Timothy Onasch, Ezra Wood, Robert Harley, University of California, Berkeley
Abstract Number: 255 Working Group: Urban Aerosols
Abstract Detailed measurements of particle emissions from motor vehicles driving in a highway tunnel in the San Francisco Bay area in July 2010 are reported. This study features highly time-resolved measurements of pollutant concentrations in the exhaust plumes of individual diesel trucks. Emission factors for individual trucks were calculated using a carbon balance method, in which emissions of pollutants in each exhaust plume were normalized to emissions of carbon dioxide. Pollutants considered include PM$_(2.5) and BC mass, particle optical properties (b$_(abs), b$_(scat), b$_(ext)), and gaseous species including CO, NO, and NO$_2. Fleet-average emission factors and emissions distributions were characterized for each species. Results indicate the average BC emission factor decreased 35 ± 11% relative to levels measured at the same location in 2006. Emissions distributions for all species were skewed with a small fraction of trucks contributing disproportionately to total emissions. For example, the dirtiest 10% of trucks emitted half of total PM$_(2.5) and BC emissions. Emission rates for NO$_2 were found to be anti-correlated with all other species considered here, likely due to the use of catalyzed diesel particle filters to help control exhaust emissions. Absorption and scattering cross-section emission factors were used to calculate the aerosol single scattering albedo (SSA, at 532 nm) for individual truck exhaust plumes, which averaged 0.14 ± 0.04.
A soot particle mass spectrometer (SP-AMS) was used to characterize the emitted fine particles from gasoline and diesel vehicles. This instrument provides a unique and selective method for measuring the mass, chemical composition, and size distribution of fine particles including refractory components such as black carbon. SP-AMS measurements will be used to develop emission profiles that describe the organic aerosol and black carbon emitted by gasoline vehicles, and separately, diesel trucks, and to investigate variations in emission signatures for individual diesel exhaust plumes.