BATH TWP.: Gone are the lines of school buses belching smoke as they're parked outside Revere High and Revere Middle schools on weekday afternoons.

To reduce the clouds of noxious diesel exhaust, the Revere Board of Education adopted a policy that banned idling buses with the start of the 2006-07 school year.

Now, the school system is going a step further to turn its yellow school buses green.

With the help of a state grant, the diesel-powered vehicles soon will be retrofitted with special catalysts and filters that cut air pollution and reduce the health risk to students.

''It's a program that just made sense to us,'' said Kevin Matowitz, Revere's director of business services. ''I can't say if diesel exhaust is a major threat, but what we're doing will improve the ride to school for our children and reduce their exposure to nasty diesel exhaust.''

That's a sentiment that's growing throughout the state and nation.

Though the Revere buses will be the first in Summit County to be equipped with the anti-pollution equipment, hundreds of buses have been retrofitted in the last five years through pilot projects in Cleveland, Columbus and Cincinnati.

A coalition of Stark County districts is working to retrofit buses, and last month the Canton Local school district won a federal grant of $154,848 for such work.

Over the next two years, the Ohio Department of Development is offering $20 million to school districts and public transportation agencies to voluntarily retrofit diesel engines. Congress has authorized $49 million for a similar federal effort.

''We have all been stuck behind a school bus burping out black smoke,'' said David Celebrezze of the Ohio Environmental Council. ''We try to hold our breath or move to another lane to get away from it. For schoolchildren, there is no escape.''

Significant threat

Dr. Sumita Khatri, of Cleveland's MetroHealth Medical Center and Case Western Reserve University's School of Medicine, says the threat to children from school bus fumes is significant.

Diesel exhaust contains tiny particles of soot and vapors that may have more than 40 toxic contaminants, including cancer-causing substances. The exhaust can damage the lungs and aggravate asthma and bronchitis.

Children are more susceptible to air pollution than adults because their respiratory systems are still developing and they breathe at a faster rate than adults.

Retrofitting school buses is a great program, Khatri said, because ''we're not putting a Band-Aid on the problem, but we're getting to the root of the problem and making our children safer.''

Nationwide, an estimated 505,000 diesel-powered school buses transport 23 million children each school day. They travel 4 billion miles a year, and students typically spend up to 90 minutes a day aboard the buses.

Of the 505,000 total, perhaps 20,000 buses have been retrofitted.

Plenty of soot

According to the Ohio Environmental Council, a statewide eco-group that has been involved in retrofitting projects in Stark and Franklin counties, the average Ohio school bus produces 15 pounds of soot per year.

The older the bus, the bigger the problem.

New buses — starting with 2007 models that cost about $80,000 — come equipped with filters. Retrofitting is aimed at the 2006-and-earlier buses that will be on the road until they are retired.

There are two main methods of retrofitting buses, with the equipment on the vehicle determining the method chosen.

Diesel oxidation catalysts use a chemical process to break down pollutants in the exhaust into less-harmful components. They cost $1,000 to $2,000 and can be installed on new or old buses. They run on regular diesel fuel.

Diesel particulate filters are ceramic devices that collect soot in the exhaust. The high exhaust temperature heats the device and allows particles inside to break down into less-harmful components. They cost $5,000 to $10,000 per bus and work best on engines built after 1995. They must be used with ultra-low-sulfur fuel.

Funds for filters

Matowitz, Revere's director of business services, said the district got a $57,354 grant from the Ohio Environmental Protection Agency in October to improve its buses.

Using that money, 17 of the district's 48 buses will be equipped with diesel oxidation catalyst filters at a total cost of about $22,500. In addition, 16 buses will get pre-heaters, costing nearly $35,000, to eliminate early morning idling.

The district also is spending more than $64,000 of its own funds to install catalyst filters and pre-heaters on eight buses and pre-heaters on 17 buses.

Re-equipping Revere's oldest buses, Matowitz said, isn't economically feasible or allowed under the state program.

The retrofitting will be done by Power City International in Akron, he said, and is expected to begin in the next few weeks after the state money is released.

The work is expected to take one to two days per bus.

Money is issue

In Stark County, 17 public school districts and the mental retardation/developmental disabilities board formed a working group a year ago to investigate retrofitting, said Tammy Hurst, director of business operations at the Stark County Educational Service Center.

That effort was aided by grants from the Herbert W. Hoover Foundation and the Stark Community Foundation.

But money is still a big issue for many of the districts, Hurst said, because some grants require a 20 percent cash match.

The Canton Local district is adding $87,000 in local funds toward its project, which calls for purchasing two new buses and installing diesel particulate filters and closed crankcase filtration systems on 24 vehicles.

Tuslaw, Minerva, Alliance, Marlington and North Canton schools all intend to apply for federal and state funds, said Celebrezze of the Ohio Environmental Council.

The first bus retrofitting in Ohio took place in Cleveland. It started in 2002 and was spearheaded by the Cleveland Clean Air Century Campaign, with support from the U.S. EPA, the American Lung Association, the George Gund Foundation and the Cleveland Foundation.

Clean Air Century Campaign spokeswoman Linda Kimble said so far 229 of Cleveland's 315 school buses have been retrofitted with an infusion of more than $1.7 million in federal, state, local and private funds.

Toxic exhaust

The threat from diesel exhaust from school buses first gained attention in 2001, when the Natural Resources Defense Council released a report that said students riding a school bus may be exposed to up to four times more toxic exhaust than someone traveling in a car in front of the bus.

The exhaust levels in the bus were more than eight times the average levels found in outdoor air and 23 to 46 times higher than levels considered to be a significant cancer risk, according to the U.S. EPA.

Evidence has shown that the exhaust comes into the bus through windows and the door at stops. It accumulates on early-morning warm-ups and grows throughout the day. It can seep into the interior of the bus through the floor boards. It is a bigger problem in the winter when windows are closed.

Initially, Ohio took a low-key, voluntary approach to retrofitting buses that involved environmental and health groups, private foundations and regulatory agencies.

Diesel retrofits were seen as a means to improve air quality in regions like Akron-Canton- Cleveland, which fail to meet federal limits for microscopic soot and face cleanup orders. And school buses were an easy, noncontroversial target; it was difficult to oppose a program that would be kid-friendly.

Programs expand

Now school bus retrofitting programs have snowballed and a lot of money is being pumped into them, said Columbus-based air expert Kurt Waltzer.

Twenty-six Ohio school districts have received $1.4 million in state grants to retrofit 545 school buses since early 2006, said Carolyn Watkins and Bill Spires of the Ohio EPA.

Those grants — most of which went to districts in counties with soot problems — resulted in more than 8 tons of pollution being eliminated, they said.

In the new Ohio Department of Development program, which is making $20 million available to bus fleets over the next two years, the money is coming from federal Congestion Mitigation and Air Quality funds.

These funds usually go to highway projects to reduce traffic congestion and pollution. But retrofitting supporters convinced the Ohio legislature that committing transportation funds to improve diesel engines would aid regions with soot problems, help retain jobs and boost economic development.

U.S. Sen. George Voinovich, R-Ohio, played a key role in the Diesel Emission Reduction Act of 2005.

The loan program designed to help public fleets retrofit diesel vehicles was funded for the first time this year by Congress with $49 million.