AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Linking High Time Resolution Particle Size Distribution Measurements to Real-world Emission Factors: Variability in Pollutant Emissions Relating to Particle Characteristics
JON M WANG, Naomi Zimmerman, Cheol-Heon Jeong, Robert Healy, Nathan Hilker, Greg J. Evans, SOCAAR, University of Toronto
Abstract Number: 476 Working Group: Urban Aerosols
Abstract On-road motor vehicles are one of the largest sources of air pollutants in urban environments. Regulatory test protocols have included particle number concentration emissions from vehicles, however the protocols typically include thermodilution to remove volatile particles in vehicle exhaust. Although this facilitates reproducibility and repeatability of the method, it excludes particles smaller than 23 nm and the volatile fraction that may otherwise exist in real-world urban exposure environments.
Five month-long campaigns in 2013-2015 were conducted at a near-road field sampling site located 15 m from a major roadway in downtown Toronto, Canada. A Fast Mobility Particle Sizer and photoacoustic soot spectrometer were utilized for high time resolution measurements of particle size distribution, and particle absorption and scattering, respectively, in addition to typical pollutant measurements (i.e., CO, NOx, CO2, BTEX, particle-bound PAH). These pollutant emission factors (EFs), which were measured on an individual plume basis were categorized depending on the mean mode diameter of each plume so as to classify different emission types. Coincident total particle number concentration measurements were made before and after a thermodenuder operating at 250 °C as a simple method to test for particle loss due to the removal of the volatile particle fraction.
Results show five general categories based on size distribution of plumes, with substantial differences in BC, NOx, and BTEX EFs influenced by different vehicle types. It was found that for the majority of plumes only a small fraction of the particles make it through the thermodenuder. Plumes where few to no particles made it through the thermodenuder had higher particle scattering coefficients on average, inferring the presence of non-refractory material. On average, the use of a thermodenuder resulted in a 90% lower particle number EF vs. when including the volatile fraction.