December 2009
On-Road, In-Use Gaseous Emission Measurements by Remote Sensing of School Buses Equipped with Diesel Oxidation Catalysts and Diesel Particulate Filters
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Daniel A. Burgard and Melissa N. Provinsal,
Chemistry Department, University of Puget Sound, Tacoma, WA
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AbstractA remote sensing device was used to obtain on-road and in-use gaseous emission measurements from three fleets of schools buses at two locations in Washington State. This paper reports each fleet’s carbon monoxide (CO), hydrocarbon (HC), nitric oxide (NO), and nitrogen dioxide (NO2) mean data. The fleets represent current emission retrofit technologies, such as diesel particulate filters and diesel oxidation catalysts, and a control fleet. This study shows that CO and HC emissions decrease with the use of either retrofit technology when compared with control buses of the same initial emission standards. The CO and HC emission reductions are consistent with published U.S. Environmental Protection Agency verified values. The total oxides of nitrogen (NOx), NO, and the NO2/NOx ratio all increase with each retrofit technology when compared with control buses. As was expected, the diesel particulate filters emitted significantly higher levels of NO2 than the control fleet because of the intentional conversion of NO to NO2 by these systems. Most prior research suggests that NOx emissions are unaffected by the retrofits; however, these previous studies have not included measurements from retrofit devices on-road and after nearly 5 yr of use. Two 2006 model-year buses were also measured. These vehicles did not have retrofit devices but were built to more stringent new engine standards. Reductions in HCs and NOx were observed for these 2006 vehicles in comparison to other non-retrofit earlier model-year vehicles.
ImplicationsNew diesel vehicles are required to meet the stringent particulate matter standards enacted in 2007 and will soon have to meet the new 2010 NOx standards. To clean up pre-2007 model-year vehicles, many public and private entities are installing diesel oxidation catalysts or diesel particulate filters. This on-road study measures the gaseous emissions from these retrofit devices used on school buses after 5 yr of use. Reductions of CO and HCs are apparent, but a significant increase in NOx emissions is seen for the driving modes associated with bus traffic near the entrance and exit of schools.
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