Air Date: Week of January 7, 2000

Some school districts in California are switching from diesel buses to those powered by cleaner-burning natural gas. Many of the oldest and most polluting diesel engines are in school bus fleets. And health experts say that diesel exhaust contributes to lung cancer, asthma and other respiratory problems, putting school children at an especially high risk. Cheryl Colopy (CAHL-o-py) reports.

Transcript

CURWOOD: Compared to gasoline-powered cars, there are far fewer diesel trucks and buses on the road. But there is a reason people react so strongly to the stink of diesel exhaust. The small particles it contains are particularly deadly. Indeed, the particulates from diesel engines and coal-fired plants combined are blamed for as many as 70,000 excess deaths each year in the U.S. alone. Some states have created incentives for owners of diesel fleets to switch to cleaner fuels, but some environmentalists say the change is coming too slowly. Children may be at an especially high risk, because many of the oldest and most polluting diesel engines are in school bus fleets. From KQED in San Francisco, Cheryl Colopy reports.

(Children laugh and call to each other)

COLOPY: Children emerge from a San Francisco school on a recent afternoon to board the familiar yellow bus. The driver starts the engine.

(The engine revs)

COLOPY: And the bus belches a cloud of black exhaust. Visual evidence, say diesel opponents, of the carcinogen-soaked soot particles kids are breathing as they board and ride these buses. In California, 17,000 diesel buses like this one carry children to and from school each day. Public health advocates deplore the continued use of diesel because they say it increases the risk of cancer. Dr. John Balmes says breathing diesel exhaust can be as bad as living with a heavy smoker.

BALMES: Diesel exhaust and environmental tobacco smoke are probably sort of similar in terms of cancer risk.

COLOPY: As the chief to the Division of Occupational and Environmental Medicine at San Francisco General Hospital, Balms conducts experiments to measure the effect of air pollution on people's lungs.

BALMES: This is the human exposure laboratory. This is a stainless steel chamber designed to expose people in a controlled way to air pollutants. And in general...

COLOPY: The chamber Dr. Balmes describes is like a little gym with a treadmill, a bicycle, and a pile of clean towels, but the air coming through the overhead vent is spiked with vehicle exhaust.

BALMES: It would be like jogging or bicycling on a very bad smoggy day in LA.

COLOPY: Balmes says subjects exposed to high amounts of diesel exhaust show acute inflammation of their lungs, as well as impaired ability to take in air. And some animal studies have linked lung cancer to the chemicals in diesel exhaust. Dr. Balmes is particularly worried about the alarming increase in asthma rates among children. He says diesel exhaust can bring on asthma attacks and may contribute to the disease in the first place. In response to fears like these, some school districts are trying to protect children from daily doses of diesel.

(Bus interior)

COLOPY: The Napa Valley Unified School District has converted about half its 62-bus fleet to less-polluting engines. Napa Valley Unified's transportation director Ralph Knight says most of the new buses, like the one we're riding in, have compressed natural gas engines. The bus is the same familiar yellow, but ...

KNIGHT: We're now burning a fuel that is so much cleaner, you don't have the residue of the oil from the gasoline or the diesel in here. So that's what keeps our motor oil so much cleaner for so longer. Unless something really goes wrong inside that engine, we're talking about an engine that can probably travel 300,000 miles plus before we ever have to do anything to it.

COLOPY: Ralph Knight says compressed natural gas engines emit only a quarter of the pollutants produced by diesel, but school districts that want to convert to natural gas have two big hurdles to overcome. First, the buses cost more. A natural gas bus costs about $130,000 compared to $90,000 for diesel. Napa Valley solved that problem with money from the Bay Area Air Quality Management District, spending only $5,000 per bus. Then there was the problem of refueling. School buses once took hours to fill from portable tanks at the school.

KNIGHT: This is our fueling system here. There's a fuel gauge here that tells you how many pounds of pressure...

COLOPY: But since this natural gas station was built for about a million dollars adjacent to an Exxon station, drivers can fill up here in just a few minutes. Six tanks that look like big white torpedoes store the gas, which is pumped from a gas line at the street.

KNIGHT: We turn the valve on, so that it will allow the flow to begin, and then all we have to do is go ahead and turn the pump on.

(Clanging, hissing)

KNIGHT: So what's happening right now is you hear the gas beginning to flow. The pump is reading the amount of space in the tanks to find out how much it can actually put in there. So it stops and starts this check a couple times...

COLOPY: Environmentalists like Jason Mark of the Union of Concerned Scientists would like to see more school districts convert their fleets.

MARK: Diesel pollution is really becoming the air quality problem that we're going to have to tackle over the next decade. And although school buses are a relatively small portion of the whole diesel pollution problem, they're actually quite critical to the solution.

COLOPY: Because with their small, centrally refueled fleets they're a good testing ground. Jason Mark predicts new bus technology will set a model for freight trucks, the greatest source of diesel pollution. California's Air Resources Board recently released a proposal for new diesel transit bus regulations, to be voted on later this month. Environmentalists were heartened by the requirement that 15 percent of the transit district's new buses be zero-emission vehicles by 2008. But they're disappointed that the new standards don't go far enough to reduce diesel soot. The Air Board plans to tackle school bus regulations some time next year. Whatever decisions are made now are likely to affect health for decades to come, since buses last about 30 years. For Living on Earth, I'm Cheryl Colopy.