AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Characterization of Fine Particulate Matter and Black Carbon Emissions from an Urban Bus Fleet: Emissions Measurements and High Spatial-resolution Inventory Development
Timothy Dallmann, Eric Lipsky, Richa Khosla, Andrea Polli, ALBERT A. PRESTO, Carnegie Mellon University
Abstract Number: 214 Working Group: Urban Aerosols
Abstract This study investigates the air quality impact of diesel-powered urban transit buses in Pittsburgh, PA through near-road emissions measurements and high spatial-resolution emission inventory development. Concentrations of fine particulate matter (PM2.5), black carbon (BC), and carbon dioxide were measured in December 2014 at a near-road site in downtown Pittsburgh as part of the Particle Falls public art installation, an artwork designed to raise awareness of urban air pollution issues through visualization of real-time air quality data. Sampling inlets were located 3 m from a roadway with high levels of bus activity, and pollutant concentrations were measured at a time resolution of 1 s. These high time-resolution measurements supported analysis of the impact of passing diesel buses on near-road air quality and enabled quantification of fuel-specific BC and PM2.5 emission factors for individual buses using a carbon balance method.
Preliminary results show diesel buses contributed to elevated concentrations of BC measured at the near-road sampling site. Weekday diurnal patterns of BC concentrations were well correlated with bus activity, with peaks in each parameter observed from 6-9 AM and 3-6 PM. Short-term (< 30 s) peak events associated with passing buses frequently elevated BC concentrations to levels greater than 20 micrograms per meter-cubed and accounted for between 3 and 30 percent of the daily mean BC concentration measured on weekdays. An initial analysis of 100 individual bus exhaust plumes yielded a fleet-average BC emission factor of approximately 0.40 g/(kg fuel), which is comparable to results from recent real-world measurements of heavy-duty diesel vehicle emissions, though significantly greater than the current PM emission standard for new heavy-duty vehicles. Fleet-average emission factors will be used along with detailed activity data to develop an inventory for BC and PM2.5 emissions from transit buses in the City of Pittsburgh at a spatial resolution of 500 m.