UC Study Breaks Down School Bus Self-Pollution

Acknowledging school buses as the safest vehicles on the road, researchers conclude that safety inside the bus is another matter - the culprit, diesel exhaust.

Part 1 in a series

By Ryan Gray | Senior Editor

BERKELEY, Calif. - The pupil transportation industry is calling for further studies and an increase in sample size after published research by the University of California found that onboard school bus pollution in the Los Angeles area affects children's lungs more adversely than the outside general population

Researchers said 80 percent of children's lung tissue is still developing.

The new analysis of an onboard school bus pollution study, conducted April through June of 2002, appeared in the April 15, 2005 issue of "Environmental Science and Technology" and recommended that school districts purge high emitting school buses from their fleets and that they more stringently adhere to idling guidelines. The California Air Resource Board provided the majority of funding at a clip of $450,000, with the South Coast Air Quality Management District contributing $59,000 and the U.S. EPA funding $72,000.

An original 2001 study by the Natural Resource Defense Council (NRDC) and the Coalition for Clean Air that said school bus diesel fumes that leak into the cabin could cause cancer in children, according to EPA and federal guidelines.

But the report was criticized by the American Council on Science and Health because the NRDC is not a scientific organization and their research was not open to peer review.

The new analysis out of the UC system, however, has been published in four other scientific journals, including the widely respected "Journal of Exposure Analysis and Environmental Epidemiology." The School Bus Information Council "wholeheartedly" agreed with a conclusion that calls for additional research using additional buses, bus types and operating conditions when addressing the issue of onboard diesel pollution. However, SBIC officials question one aspect of the research methodology.

"The sample size upon which the study was premised was so small that it is not necessarily representative of the entire nationwide bus fleet," it wrote a few days in advance of the article's publication.

But that is difficult, short of testing each of the nation's 500,000 school buses, explained one of the study's co-authors.

"Even if you test 50 buses you can always say 50 buses are not representative enough. We were looking for the worse case scenario," said Eduardo Behrentz, a post-doctorate research associate at UCLA's Environmental Science and Engineering Program and the School of Public Health .

Diesel exhaust is at least as much or more damaging to students - no matter their age - than to the rest of the local population, found the joint research teams from UCLA and UC Riverside. They conducted experiments onboard six school buses on regular morning and afternoon routes from South Central Los Angeles to the West Los Angeles enclave of Brentwood . Meanwhile, the Environmental Working Group, a Washington, D.C.-based non-profit, released on April 20 that smog-related absences cost California school districts a total of $82 million a year because state support of local schools is based on attendance. Meanwhile, parental costs could be three times that. The University of California research indicates that school bus self-pollution could be at least a contributing factor.

During morning and afternoon commutes for year-1975 and newer and buses that totaled several hours a day, the UC study said that students riding school buses have 34 percent and 70 percent higher intakes of diesel particulate matter than car commuters, respectively. The daily inhalation intake by a child of emissions from the one school bus on which they commute is between seven and 70 times greater than the average daily inhalation intake by a typical South Coast resident of emissions from all school buses.

While recognizing school buses as the safest, most effective way to transport children to school, the American Lung Association said the study proves there is much to be done to make the air on school buses safer for student passengers to breathe.

"Where they can be fixed and where they can have devices to clean up (diesel emissions), that needs to be done as soon as possible," said spokesperson Janice Nolan, adding that the EPA's Clean School Bus USA program and requirements for the manufacture of ultra low sulfur diesel by next year are only the tip of the iceberg.

The American Lung Association said that nearly 1.3 million children with asthma live in counties with unhealthy levels of year-round particle pollution.

The Data

For every metric ton of pollution emitted by a school bus, the study found, the cumulative mass of pollution inhaled by a school bus with 40 children onboard is comparable to and in many cases larger than the cumulative mass inhaled by all other people in that same urban area. Researchers said the study is the first of its kind that highlights "self pollution," or the instance of emissions leaking into the cabin of older school buses, and that specifically analyzes how much exhaust is breathed on school buses.

"Diesel is the last big source of air pollution yet to be reigned in," said Julian Marshall , a doctorate student at the University of California , Berkeley and lead author of the study. "As a policy matter, it seems clear from this analysis that reducing emissions from school buses should be a very high priority."

The researchers analyzed results from onboard experiments that measured tracer gases, black carbon and PM 2.5 levels on four conventional school buses, one fitted with a particulate matter trap and one CNG bus with only 1,000 miles on the odometer. The vehicles and engines tested were: high-emitting 1975 and 1985 Crown Supercoach buses with midship engines, the former with a Cummins 290 and the latter with a Detroit Diesel 671; a 1993 Thomas Built Bus Saf-T-Liner with a Cat 3116; two 1998 Thomas Saf-T-Liners with Cummins 250 HP 8.3L engines; and a 2002 Thomas Saf-T-Liner with a John Deere 8.1L CNG engine. The Thomas engines were all rear located.

No engine tuning was performed prior to the tests.

Researchers ran the buses on established morning and afternoon routes supplied by the Los Angeles Unified School District . Nine runs were made with the bus windows open and seven with the windows closed.

"We determined that concentrations of key air pollutants were higher inside the bus cabins than outside the cabins," said Behrentz. "While the conditions inside the cabin were affected by the emissions of other vehicles on the road, our tracer gas measurements revealed that a significant amount of the pollutants found inside the buses originated from the buses' own exhaust systems, especially when the windows are closed."

The researchers added that, although environmental regulators focus on controlling the amount of exhaust by vehicle and other sources, knowing how much pollutants are inhaled is a better indicator of the related health impacts. Because their immune systems are less mature, the group found that children are more vulnerable to air pollution than are adults because, per body weight, children inhale more air.

"(Children) breathe at a faster rate so more air is inside their lungs," said Behrentz.

In the August 2005 issue, School Transportation News will further gauge the pupil transportation industry's reaction to the new analysis, and recommendations made by researchers to lower the incidence of onboard pollution.