For the study, part of a five-year project, heavy-duty diesel engines from the four major manufacturers--Cummins, Detroit Diesel, Caterpillar and Volvo-- were tested for more than 300 air pollutants at a laboratory in San Antonio, Texas. The researchers only tested new engines, so the trucks and buses might put out more emissions as they age, Greenbaum said. But under the EPA rules, their warranties for emissions equipment must last 450,000 miles, four times longer than cars.
Greenbaum said one surprise was the extent of reductions in cancer-causing and other toxic compounds. Diesel exhaust is considered a potent human carcinogen because of a variety of substances. Polycyclic aromatic hydrocarbons declined 79 percent from 2004 models, while elemental carbon and metals were down 98 to 99 percent.
The challenge in cleaning up diesel has been finding technologies that can trap particles and gases without reducing fuel efficiency. Spurred by new standards adopted by California and the EPA, the engine manufacturers and oil industries had to develop ultra-low sulfur fuel and new catalysts and other gas-control technologies.
Controlling nitrogen oxides, or NOx, has been the biggest challenge. EPA’s rule for 2007 engines, adopted in 2000 by the Clinton Administration, gave manufacturers three extra years for fully meeting that standard. “The original rule basically recognized that while the [particulate] traps were ready, the NOx control was not,” Greenbaum said.
Schaeffer of the diesel industry added, “clearly more work is needed on NOx, and 2010 models will deliver that starting January 1, 2010.”
“Everything you do to drive down NOx tends to reduce fuel economy,” he said.
Most diesel manufacturers said they will meet the tougher nitrogen oxides standard next year by equipping engines with new catalysts—a technology called selective catalytic reduction, already used in Europe--and an advanced gas recirculation system.
However, one company, Navistar, has said it cannot meet the standard next year so it will use credits to offset the difference and filed suit against the EPA to change the rule. The other three companies have filed a brief in court supporting the EPA rules.
Other diesels, such as construction and farm equipment, must meet the same emission standards, but have until 2013, or in some cases, 2015, to do so. The new tests only checked truck and bus engines.
To meet health standards at many U.S. cities with heavy particulate pollution, manufacturers of both gasoline and diesel engines may have to face even tougher emission standards in the future, Greenbaum said.
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.