Children’s School Bus Exposure Study

This page updated April 26, 2004

The Children's School Bus Exposure Study was conducted to characterize the range of children's exposures to diesel vehicle-related pollutants and other vehicle pollutants during their commutes to school by school buses. It was the most comprehensive school bus exposure study ever conducted. Researchers at the University of California's Riverside and Los Angeles campuses, measured pollutant concentrations inside five conventional diesel school buses while driving actual school bus routes in Los Angeles. For comparison, a diesel bus equipped with a particulate trap and a bus powered by natural gas were also included.

Buses were outfitted with dual sets of real-time instruments, which allowed front versus back and inside versus outside comparisons. The researchers measured multiple diesel vehicle-related pollutants, including black carbon and particle-bound PAHs, as well as many other exhaust pollutants. A tracer gas was used to determine the bus's own contributions to on-board concentrations. The study measured exposures inside the buses and did not include tail-pipe emissions tests.
           
Major Findings:
Measurements indicated that for some buses, significantly higher exposures of vehicle-related pollutants occurred during the bus commutes than roadway pollutant concentrations alone would indicate. The high commute concentrations were a function of several influences:
  • the high concentrations of pollutants already present on roadways, especially if traffic was heavy;
  • the direct influence of other vehicles being followed; and
  • the contribution of the bus’s own emissions. The extent of a bus’s own contribution to these high concentrations appeared to be highest when windows were closed for the older diesel buses, but bus-to-bus variability was high.
           

Recommendations from this report include:

  • Reducing school bus-related exposures by assigning the newest and cleanest buses to the longest routes.
  • Avoiding caravanning of buses through staggered departure times.
  • Replacing conventional (uncontrolled) diesel school buses with natural gas-powered or particulate trap-equipped buses.
  • Maintaining diesel school buses to reduce visible exhaust.
           

Downloadable Documents
           

Other ARB School Bus Programs

  • School Bus Idling ATCM Program - The California Air Resources Board has approved an airborne toxic control measure (ATCM) that limits school bus idling and idling at or near schools to only when necessary for safety or operational concerns.
  • Lower-Emission School Bus Program - This program is for the acquisition of clean, safe, school buses.
           

Conference Presentations
           
For more information about the Children's School Bus Exposure Study, you may contact Kathleen Kozawa at (916) 323-2999
           

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