The results highlight the problem of "self-pollution," or exhaust from the vehicle leaking into the cabin, particularly among older buses. This also is the first study to specifically look at how much exhaust is breathed in on school buses.
"Although environmental regulators focus on controlling the amount of exhaust emitted by vehicles and other sources, knowing how much of a pollutant is inhaled is a better indicator for related health impacts," said Julian Marshall, a Ph.D. student at the University of California, Berkeley's Energy and Resources Group and lead author of the study, which is scheduled to appear in the April 15 issue of the journal Environmental Science and Technology, but is available now online.
"Diesel is the last big source of air pollution that has yet to be reigned in," said Marshall. "As a policy matter, it seems clear from this analysis that reducing emissions from school buses should be a very high priority."
The researchers noted that children are especially vulnerable to air pollution because, compared with adults, their immune systems are less mature and they inhale more air per body weight per day.
"For every metric ton of pollution emitted by a school bus, the cumulative mass of pollution inhaled by the 40 or so kids on that bus is comparable to, or in many cases larger than, the cumulative mass inhaled by all the other people in an urban area," said Marshall. "That the values were even close was shocking."
The researchers analyzed results from tracer-gas experiments conducted by scientists at UCLA and UC Riverside. They measured the air in six empty school buses traveling through established routes in south-central and suburban Los Angeles, all areas within the
Contact: Sarah Yang
University of California - Berkeley