For decades, diesel trucks and buses have spewed large amounts of soot, smog-causing gases and carcinogens into the air.
But new diesel engines are more than 90 percent cleaner than a few years ago, far exceeding the emission reductions required by the U.S. Environmental Protection Agency, according to a new study released Thursday.
The quest to clean up diesels has been mounted for several decades, yet its progress has long lagged behind the success stories of car exhaust. But now tests--conducted by independent researchers funded by a coalition of government and industry--now show the diesel technologies are working even better than expected. Truck and bus engines are much cleaner than they are required to be under new federal standards, and for many pollutants, the latest models are emitting the same levels as gasoline-powered automobiles, the researchers said.
Ultra-fine particulates—the tiny pieces of soot that can lodge in lungs and cause respiratory and heart problems—were 99 percent lower in 2007-model trucks and buses than in 2004 models, and 89 percent lower than the amounts allowable under the EPA’s 2007 standards, according to the study.
Particulates have long been considered one of the most dangerous pollutants spewed by diesel engines. The fine particles from diesel can trigger asthma attacks, heart attacks, bronchitis and other serious ailments, and the EPA says they cause several thousand deaths each year.
Other important air pollutants—hydrocarbons, a major ingredient of smog—were 95 percent lower in the new diesels than the amounts required under EPA’s 2007 standards, according to the study. Carbon monoxide was 98 percent lower than required.
Daniel Greenbaum, president of the Health Effects Institute, a nonprofit research group that directed the study with another research group, said "likely a lot of lives will be saved once we get the older fleet replaced."
He said the new models of diesel trucks and buses emit the same levels of particulates as gasoline-powered vehicles. They are equipped “with essentially the same technology that is required in cars,” Greenbaum said.
The one major pollutant that still lags behind is nitrogen oxides, which react with hydrocarbons to cause ozone, or smog. It is particularly a problem in smoggy regions, such as the Los Angeles basin. For the new trucks and buses, levels of nitrogen oxides were 70 percent lower than in 2004, and 10 percent below current federal requirements. Another 80 percent reduction is required beginning in January.
The study was overseen by the Health Effects Institute, a Boston-based independent research group that has studied air pollution since 1980, and the Coordinating Research Council, a nonprofit research partnership between industry and government agencies. It was funded by the EPA, U.S. Dept. of Energy, the diesel and petroleum industries and the California Air Resources Board, but the tests were designed, administered and reported without their influence and using federal test procedures, according to the research teams.
Diesel engine manufacturers say the new data reinforces that “clean diesel” is a reality. They are nearly as low in emissions as engines powered by alternative fuels such as natural gas. “These findings underscore just how clean this new generation of fuels, engines and emissions control technology really is,” said Allen Schaeffer, executive director of the Diesel Technology Forum, which represents manufacturers of diesel engines, fuel and emissions systems.
It would take 60 of the new truck or bus models to emit the same soot as one of the old 1988 models, Schaeffer said. More than 360,000 of the new trucks and buses were purchased in the past two years, which he said will go a long way toward cleaning many cities’ air.