Bus fumes worse for kids on board

Most kids probably think the worst thing about riding a school bus is the bully who sits in the back seat. In fact, the bitter fumes emitted from the buses may be doing them more harm.

Children riding buses in L.A. Unified School District inhale as much, or more, bus exhaust than the rest of the city’s population, a new study has found. The problem is that exhaust from the vehicles, particularly older buses, can leak into the cabin.

The study, published this month in the journal Environmental Science & Technology, is the first to examine how much exhaust is breathed in on school buses.

Researchers are still trying to understand, however, how bus exhaust seeps into the cabin, says Julian Marshall, a doctoral student at UC Berkeley’s Energy and Resources Group and coauthor of the study. “Does it exit the tailpipe and come in through the windows or in through the floor? Is it from the engine? With a little more information, it might be possible to seal buses up a little bit from self-pollution.”

The analysis was conducted in conjunction with researchers from the School of Public Health at UCLA. The researchers analyzed results from tracer-gas experiments in six empty school buses traveling through established routes in South Central and suburban Los Angeles. In some runs, the windows of the buses were left open while other runs were conducted with closed windows. Different buses were compared, such as those powered by diesel fuel and compressed natural gas as well as buses built in various years, from 1975 through 2002.

The experiment revealed that concentrations of key air pollutants were higher inside the bus cabins than outside the cabins. The highest levels of pollutants were found in the older buses. The research on the newer buses produced inconsistent results, but even some of the newer buses had high particle levels. The study also revealed that more particles were found when the bus windows were closed.

The study found that in a single day a child riding a school bus will breathe in anywhere from seven to 70 times more exhaust from his or her bus than a typical L.A. resident will inhale from all school bus emissions combined.

Diesel exhaust particles may contribute to numerous health problems, including cancer. “The current research is finding that it’s not only an issue for the lungs but for the heart as well,” Marshall says.

Children are more vulnerable to air pollution because, compared with adults, they inhale more air per day per body weight.

The new study should encourage policymakers to consider ways to curb school bus pollution, such as by operating newer buses, compressed natural gas buses or by finding methods to seal buses from self-pollution, Marshall says. A survey by School Bus Fleet magazine found that California has the highest percentage of pre-1977 buses in the country, at 10% of the statewide fleet, Marshall says. Officials from L.A. Unified School District were unavailable to comment on the study.

The South Coast Air Quality Management District has tried to reduce exhaust from school buses, using particle traps and other pollution-reducing technology and by purchasing alternative-fuel school buses.

“We need to know the levels of the pollutants these buses are emitting, because our kids ride in them,” says Jean Ospital, health effects officer of South Coast district. “This study shows that a commute can account for a significant, if not the bulk, of our exposures to these particles. It reinforces our efforts to try to reduce emissions from school buses.”

Improving school bus air quality “is something that can be done and should be done,” Marshall says. “But we don’t want to instill fear in parents’ minds over this. Children are safer on school buses [than in cars] -- even knowing this issue.”