PORTLAND - Biodiesel is a good first step, but not a complete step toward reducing the adverse impact associated with diesel, according to Kevin Downing of Portland, clean diesel program coordinator for the Oregon Department of Environmental Quality.

Air pollution comes in a variety of forms and diesel exhaust is a rather complex mixture of particles and gases, more so than gasoline exhaust, Downing said. Compared to regular diesel fuel, biodiesel has lower emissions of carbon monoxide, particulate matter (the soot most commonly seen in the exhaust) and hydrocarbons.

Engines powered by biodiesel have higher amounts of nitrogen oxide emissions, however, Downing said.

"For instance at a 20 percent biodiesel concentration, nitrogen oxide may increase by 2 percent, which may not seem big, but for the fact that diesel engines typically account for about 35 percent of the nitrogen oxide in a given airshed even though those engines account for just 6 percent of the motor vehicle fleet."

Downing said the nitrogen oxide increase can be reduced with additives or retuning the engine, "so it is not an insurmountable obstacle."

Using 20 percent biodiesel results in about a 13 percent reduction in particulate emissions, according to Downing, who said all air pollution effects from biodiesel are proportional to the amount of fuel blended.

His agency's biggest concern with diesel exhaust relates to the particulate emissions, which medical and scientific research is indicating to be a potent cause of cancer.

"In fact, our preliminary assessment of risk from breathing the outdoor air in Oregon puts diesel particulate as the No. 1 air toxic, with a risk more than 30 times greater than the next one on the list," Downing said. The risk for cancer from diesel is estimated at 748 cancers per million people exposed, averaged across the state. The risk from the next toxic on the list - benzene - is at 25 cancers per million.

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