Two environmental groups are mounting an effort to further reduce diesel emissions in Allegheny County.

The Group Against Smog and Pollution, known as GASP, and Clean Water Action plan to target their early efforts toward reducing emissions from school buses.

"Our initial focus is school buses because children ride in them," said Myron Arnowitt, Clean Water Action's western Pennsylvania director, noting that high levels of air pollution can cause asthma attacks and may cause increased cancer risk.

Eventually, the campaign hopes to take steps to reduce diesel emissions from other sources.

Local officials have worked with environmental groups to implement other measures to cut diesel emissions.

But a report last month by a national advocacy group indicated that the battle is far from over.

The Clean Air Task Force found that nationwide, the lifetime cancer risk posed by diesel exhaust is more than eight times greater than the combined risk of 133 air toxics reported by the U.S. Environmental Protection Agency's National Air Toxics Assessment.

"The single most important step in reducing cancer risk from air toxics is to reduce diesel exhaust," noted Bruce Hill, a senior scientist for the Clean Air group.

The report found that Allegheny County ranked third among the state's counties for risk from diesel soot. Philadelphia County ranked first, followed by Delaware County.

Among more than 3,100 counties nationwide, Philadelphia County ranked 13th, Delaware County 32nd and Allegheny County 50th.

Allegheny County implemented a regulation to limit school bus idling in 2004. A similar regulation to limit idling by other diesel-powered road vehicles, such as trucks and commercial buses, took effect last year. Drivers can face penalties for non-compliance ranging from a warning to $500.

Bob Grove, a spokesman for the Port Authority of Allegheny County, said federal emissions standards have grown stricter over time. Besides those restrictions and limits on bus idling, he said the Port authority uses low-sulfur diesel fuel and has six buses that use electric generators in combination with small diesel engines.

Later this year, emissions will be further reduced by requirements to lower the sulfur content in diesel fuel, said Jayme Graham, the Allegheny County Health Department's air quality planning manager.

Other requirements next year for special catalytic converters and filters on new vehicles will result in further reductions, said Rachel Filippini, GASP's executive director.

But the campaign hopes to find additional ways to reduce emissions, such as equipping older vehicles with the converters and filters.

One barrier is cost, but Ms. Graham noted that local officials are working with those in other states to identify funding.

The campaign also may seek funds from local foundations or corporations, Ms. Filippini said.

The North Allegheny and Penn Hills school districts already have used grant funds to improve emissions on their school buses.

Jim Berent, garage supervisor for the Penn Hills district, said the improvement has been much greater than he expected.

"The difference around here is amazing," Mr. Berent said, noting that he no longer goes home with the smell of diesel fuel in his clothes.