Clean School Bus Initiative Reduces VOC and Fine Particle Emissions

The U.S. Environmental Protection Agency has concluded that breathing diesel exhaust over a number of years poses a lung cancer hazard and exacerbates asthma symptoms. Diesel engines are more efficient than gasoline engines and so use less fuel and emit less carbon dioxide (the main global warming gas) than gasoline engines. On the other hand, diesel engines emit more nitrogen oxides, and diesel exhaust is a significant contributor to fine particle pollution. Diesel engine manufacturers and new  federal rules have significantly lowered these polluting emissions through engine technology and controls.

Diesel engines, however, are durable and long-lived, which means that older, dirtier vehicles may be on the road for another 20 to 30 years. Dane County Clean Air Coalition designed a project to address concerns about the familiar black smoke that comes from the tailpipes of older diesel trucks, buses and non-road equipment. Using diesel retrofit emission control programs for school buses and off-road construction equipment DCCAC demonstrated two cost-effective strategies that hold promise for statewide implementation.

According to EPA, the installation of diesel oxidation catalysts can reduce VOCs (volatile organic compounds) by 50%, carbon monoxide by 40% and particulate matter by 20%. The Clean School Bus project involved a consortium of partners, including 14 Wisconsin school districts (six in Dane County) and five private bus companies in southern and central Wisconsin, that installed diesel oxidation catalysts in 253 school buses. The Madison Metropolitan School District (MMSD) was the project leader in partnership with DCCAC and the EPA's Clean School Bus USA program.

DCCAC and EPA also partnered with the Middleton-Cross Plains School District to provide the same retrofit service to its publicly-owned school bus fleet and to Denmark School District's fleet in Brown County.

DCCAC is also demonstrating how biodiesel fuel can be used to reduce diesel emissions including VOC emissions. For  example, DCCAC partners MGE and UW–Madison are using a 20% biodiesel blend in their diesel vehicles. Biodiesel requires no engine alteration and also reduces VOC emissions.