AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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A Study of the Impact of Diesel Buses on Downtown Boulder
Josue Hernandez Pedroza, SHELLY MILLER, CU Boulder
Abstract Number: 535 Working Group: Urban Aerosols
Abstract Many studies have reported the adverse health effects of diesel combustion engine emissions; diesel exhaust is considered carcinogenic to humans. This research examined the major pollutants produced by diesel-powered engines: particulate matter, black carbon, and nitrogen oxides. Ozone was also studied due to its secondary formation from nitrogen oxides. Summer and Winter measurements were taken next to the Boulder Downtown Station in Colorado, for one week in each season. It was not possible to estimate bus emissions due to variability in the number of vehicles and buses traveling in the study corridor. Results showed limited association between pollutant levels and traffic patterns, and followed regional pollution and seasonal trends. Only Winter particle number and nitrogen oxides followed traffic trends. NOx was elevated in winter, and Black carbon contributed 12-34% of the total fine particulate matter.
Bicycle rides were carried out to capture fresh emissions on-road. Black carbon concentration peaked when chasing certain buses, while emissions from other buses were low. Passenger vehicle emissions were not reflected in the black carbon levels. Bicycle ride pollutant averages were lower than averages from stationary measurements, while bicycle ride peak values were higher than peak values in stationary measurements for black carbon and particulate matter. Ozone was always higher on-road.
With the use of MOVES and R-Line, the impact of buses on the concentration of pollutants was analyzed. Emission rates were estimated with MOVES in Summer and Winter by running simulations with and without buses. The R-Line dispersion model was used to estimate the concentration of pollutants at the Boulder Downtown Station and the street right in front of the station. Results showed a concentration ratio without and with buses ranging between 0.55-0.84 without buses and with buses. These values would have been higher if traffic-related emissions from additional surrounding streets would have been included. Bus emissions due to the idling period represented a significant part of pollutants emitted. Therefore, the bus station contributed significantly to the total traffic emissions of Boulder Downtown.