A tracer test shows that exhaust from a diesel school bus engine adds virtually no diesel particulates to the air inside the bus. This new study, which adds a sensitive iridium tracer to the bus diesel fuel, allowed researchers to measure with precision the impact of the bus exhaust on interior air quality.
The study, prepared by California EnSIGHT Inc, an air quality management consulting firm, for IC Corp, found that the bus engine contributed less than 1% of the fine particulate matter inside the bus.
These findings correct an erroneous impression created by a previous report on school bus interior air quality. In 2001, the Natural Resources Defense Council and the Coalition for Clean Air released a report alleging that an extremely high level of diesel particulates occurred inside a tested bus as the result of the exhaust.
In the new study, engine diesel particulates inside a tested bus were 98% less than the NRDC/CAC report indicated. The NRDC/CAC used a less-reliable measurement method that measured black carbon in the bus, without attempting to differentiate the sources of diesel particulates.
Research was conducted on a Los Angeles CA school bus route, using a 1995 school bus with 90,000 miles on it, and regular diesel fuel. The new study involved 12 roadway tests in Los Angeles, using a conventional 1995 model year, front-engine school bus powered by a 190-horsepower International DT466 engine. The bus (which has traveled more than 90,000 miles) used conventional diesel fuel — not the ultra-low-sulfur fuel now increasingly used in new California school buses.
IC Corp, an integrated school bus manufacturer, is a wholly owned subsidiary of International Truck and Engine Corp.