NEW YORK — As a yellow school bus starts up its roaring engine in front of PS 61 on Manhattan's Lower East Side, Rebecca Kalin runs over and knocks on the door. The engine can't idle here, she explains to the driver, because the pollution hurts kids. Without an argument, he shuts the bus down - another victory for Ms. Kalin's Asthma Free School Zone project.
Kalin is not alone. Around the nation, a concerted effort has sprung up to fight exposure to toxic diesel exhaust from one of childhood's friendliest icons: the old yellow school bus.
Some schools are updating older buses while others are buying new, more efficient models. But despite the effort, the Natural Resources Defense Council (NRDC) estimates that 90 percent of the nation's school buses run on diesel and, in most states, are not required to undergo emissions inspections. For many schools, the pollution issue presents a budget dilemma: They can afford to buy either books or new buses, but not both.
"Some school districts are doing a better job than others and some parts of the country are doing a better job than others. But the bottom line is just about every district needs some support in cleaning up their bus fleets," says Michelle Robinson, senior advocate for the Clean Vehicles Program at the Union of Concerned Scientists (UCS).
The EPA judges diesel fuel to be one of the most harmful air pollutants, and many studies have shown a correlation between the chemicals in diesel exhaust and increased respiratory illness.
Despite the problems they cause, large diesel vehicles have been one of the last categories of engines to be subject to emissions requirements. Federal emissions regulations on new buses went into effect in the mid-'90s, and new ones are now in the works. By 2007, permitted particle levels will be reduced to 80 percent of today's levels, and by 2010 nitrous oxide emissions will be cut by 90 percent.
Although new, better-built buses will help to ease future problems, today's concern remains older buses, many of which still will be in use for years.
Not only do diesel buses emit harmful particle-laden exhaust into the air outside, but older vehicles also leak fumes into their interiors.
In a 2001 NRDC study of California school buses, the air inside running buses carried up to four times the amount of soot in air monitored around the exteriors, and measured up to 46 times the cancer-risk threshold designated by the EPA.
"What we now have is a lot of data that shows that kids on school buses are breathing a lot of soot," says Rich Kassel, director of national vehicles and fuels at the NRDC.
Both the UCS and the NRDC propose that all buses built before 1991 be replaced, and those built afterward be retrofitted. The task is formidable. According to a UCS study released in 2002, 48 percent of buses in California and 54 percent of those in Oklahoma were built before 1991. There are also thousands of school buses in use nationwide that were built before 1977, when the first highway safety regulations were imposed.
Since the study by NRDC in 2001, the issue has caught the attention of the EPA. Under former administrator Christine Todd Whitman, the agency created the Clean School Bus USA Program, the goal of which is to upgrade all school buses by 2010, which will cost about $8,000 per bus.
"I think the real big win is ahead of us, which is the full funding of this program over time and the full use of it by school districts," says Mr. Kassel.