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The Wheels on the Bus

Moreover, the kids on buses were breathing a higher percentage of the buses' exhaust than the outside population

By Novella Carpenter

The wheels on the bus go round and round, round and round. Ever think about school buses? Nah, me neither, except when I'm stuck behind one, huffing the diesel smoke that spews out of their tailpipes. If you do consider the yellow-orange fleet as a whole, though, it is really mass transit that only runs twice a day and caters to the under-18 crowd--or I should say under-16 crowd, because what self-respecting high school junior would ride the bus?

Now that I'm older, I'd like the school bus to take me to work. Wouldn't that be great? Free bus, all your friends and some lady with press-on fingernails driving. Heaven. What's not heavenly is a new study put out by the School of Public Health at UCLA that shows that school buses are more effective than an average vehicle at "delivering" emissions to children's lungs. Oh, dear.

Two scientists, Julian Marshall and Eduardo Behrentz, tried to answer the question of how much exhaust schoolchildren are getting exposed to while riding the bus. Their studies took place in South-Central Los Angeles, arguably a place with some of the worst air quality in the country. The researchers devised a mobile monitoring unit that took readings of emissions inside the buses--also known as self-pollution. A tracer gas, sodium hexafluoride, was fed into the buses' engines, which could then be measured by the machines in the front and the back of the buses. The buses drove along their normal routes in order to monitor the emissions during a regular day of driving. Of the nine buses they did runs with, all had substantial levels of self-pollution. Moreover, the kids on buses were breathing a higher percentage of the buses' exhaust than the outside population, more if the bus was older than 1990, and more still if the windows were closed. In addition, exhaust from surrounding traffic also entered the bus.

"Children are especially susceptible to emissions because they are smaller and therefore breathe more rapidly," Julian Marshall, an air-pollution expert, told me in a recent interview, "They have narrow lung airways, low lung-clearance rates and immature immune systems. But the answer isn't to pull your kids off the buses." The reason is the increased likelihood of being involved in a car accident. If all parents drove their kids to school, their cars still wouldn't as safe as a stinky but solid bus. What's to be done? One thing is obvious--reduce emissions. Marshall explained, "The take-home message is if we want to reduce emissions of diesel in general, and you care about kids, then reduce school-bus emissions." For example, the compressed natural gas (CNG) bus had a significantly lower self-pollution level. Using particle traps or fuels like ultralow-sulfur diesel can help, too. "The second idea is to directly address the issue of self-pollution," Julian explained. "If you change the engine technology, you still have the same fraction of self-pollution, the shape of the bus is still the same."

The study didn't show how the exhaust gets into the bus---it might leave the tailpipe and get in through a window or maybe it leaks in through cracks in the floor or the exhaust manifold. UCLA is working on that right now by testing emissions with vents on top of the bus, placing the tailpipes in different directions. The researchers have a positive outlook, noting that by reducing the self-pollution levels in buses, you get more benefit than trying to lower emissions of passenger cars. The impact would be immediate, and it is more cost-effective to retrofit buses than passenger cars. Also, simple fixes (not having caravans of buses lined up) would make a significant change in emissions breathed by children. To my mind, the bus manufacturers need to act. School-bus design hasn't evolved like car design has. School buses have retained their basic design, and now, in the face of this new research, they need some major overhauls. A call to arms then: Design better buses, damn it.

Email Novella at [email protected].

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From the June 15-22, 2005 issue of Metro Santa Cruz.

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