The EPA proposal would require states to reduce their fine-particle count from 15 to between 12 and 13 micrograms per cubic meter by 2020.
EPA, which was responding to a court order to issue the proposal, said that these microscopic particles can penetrate deep into the lungs and have been linked to numerous health problems, including heart attacks, strokes and bronchitis.
Glenn Kedzie, a vice president at American Trucking Associations, said he thinks the impact on trucking will be minimal.
EPA projects that just a half-dozen counties in the U.S. would fall short of the standard in 2020, Kedzie said. On the list: Riverside and San Bernandino, Calif.; Santa Cruz, Ariz.; Wayne County, Mich.; Jefferson County, Ala.; and Lincoln County, Mont.
Allen Schaeffer, executive director of the Diesel Technology Forum, agreed.
"It's speculative at this point to think that new standards would have an immediate effect on the industry," he said.
Retrofits and idling restrictions would certainly be a way to bring older diesels into compliance, but regulators have other options because diesel emissions are a relatively small part of the particulate matter problem, he said.
"You have to look at this from a national perspective. All sources of diesel emission, locomotive, marine and on- and off-road, add up to less than 6% of pm emissions," he said.
It is likely that the majority of the on-road diesel fleet will be compliant with EPA's 2007 emission standards by 2020, Schaeffer said. These trucks would meet the 2020 particulate matter standard.
The story might be different for off-road diesels, Schaeffer said. That equipment tends to be in service longer and may not turn over as quickly as highway equipment.
EPA has not made any official statement about whether or not states could mandate diesel retrofits, he said. Certainly California's retrofit program could be seen as a precedent for other states, but Schaeffer thinks legal decisions will have to be made before it's clear what the policy will be.
The diesel engine manufacturers that Schaeffer's group represents say the work they have done over the past decade puts the industry ahead of the curve should the EPA proposal go into effect.
"For the last decade, diesel technology has undergone a fundamental transformation to near zero emissions, based on ultra low sulfur diesel fuel, advanced clean-burning engines and new emissions control technology," he said.
EPA said it is taking comments on the proposal for two months, and will publish final standards by December 14.