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Study Shows School Bus Pollution 'Shocking'

Pollution Found Inside Buses, but Industry Official Says Test Used Older Buses
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WebMD Health News

April 19, 2005 -- Pollution from school buses can turn up inside the buses, according to a study from Los Angeles in Environmental Science & Technology.

About 90% of school bus fuel consumption is diesel, say the researchers. They note that diesel particle matter "has been estimated to cause a majority of the ambient air pollution" in the area studied (California's south coast air basin).

Children are believed to be especially susceptible to air pollution, the researchers say. As a major form of children's transportation, school bus emissions represent a potentially important source of children's exposure to vehicle pollution.

Scientists monitored the air inside six empty school buses while driving the buses on routes in and around Los Angeles. The highest pollution levels inside the buses were seen with the oldest models (circa 1975) with high diesel emissions and closed windows.

"Self-pollution is substantial for all six buses," write the researchers, who included Julian Marshall, a PhD candidate with the Energy and Resources Group at the University of California, Berkeley.

"The school bus microenvironment contributes significantly to children's estimated total inhalation intake of DPM [diesel particulate matter]," says the report. Primary data came from a study sponsored by the California Air Resources Board, says the journal.

John Corr, president-elect of the National School Transportation Association, says, "The average age of school buses is much newer than some of the extremes that were used in that test." Corr is also president of The Trans Group, a school bus fleet contracting company based in Spring Valley, N.Y.

Corr says the average age of buses in privately owned fleets is closer to eight years. Buses built from 1995 have significantly improved diesel engines that use electronics to help the engines burn more cleanly and efficiently.

The researchers studied six buses on nine routes in and around Los Angeles. No students were aboard during the experiment.

School bus pollution was checked with a tracer gas while the windows were open and closed. The test included buses built in 1975, 1985, 1993, 1998, and 2002. They included an older model with high diesel emissions, a more recent bus with more typical diesel emissions, a bus outfitted with particle traps, and another powered by compressed natural gas.

The scientists calculated the fraction of each bus's emissions that someone in the bus would inhale. The average for all of the buses was 27 grams inhaled per million grams emitted. The highest total was about 94 grams inhaled per million grams emitted.

Researcher's Perspective

This may not sound like a lot," says Marshall in a news release. "But intake fraction values for vehicle emissions are 5-15 per million in a typical U.S. urban area, and about 50 per million in a large urban area like Los Angeles."

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