Controversial EPA Proposal May Increase Ozone Pollution

Published February 7, 2007

The U.S. Environmental Protection Agency (EPA) is considering new rules for diesel truck engine manufacturers that may actually increase ozone levels in many cities.

EPA may require implementation of a specific technology to reduce emissions of oxides of nitrogen (NOx). Some experts say that technology may be too complicated and expensive to use.

Costly Technology

In a “guidance document” on meeting federal rules for 2010 diesel truck emissions, EPA seems prepared to require truck manufacturers to install a separate chamber in truck engines to carry a chemical called urea. When sprayed at proper ratios into a truck’s exhaust gases as they leave the engine, urea converts NOx into nitrogen.

The urea-based technology envisioned by EPA would drive up engine prices, as new designs will be required to provide room for urea chambers and allow for the precise ratio spraying of urea into engine exhaust. The new technology also would drive up operating costs for truckers, who would need to periodically refill the chambers and maintain the system in good working order.

Spokespersons for truck and engine manufacturers say continuing improvements in emissions control technologies will lead to better ways to reduce NOx emissions in the near future. EPA’s guidance document could lock the industry into one technology path that is complex, costly, and unlikely to be sustainable. That would also have the unfortunate effect of delaying better solutions.

Kill Switches

As part of the urea technology, EPA’s guidance favors a mandatory kill switch that would shut off and disable the engine if the urea chamber were to run out of the chemical. The prospect of truck engines suddenly turning off on busy freeways has raised truckers’ concerns over safety as well as manufacturers’ concerns about legal liability.

Urea freezes when temperatures fall below 11 degrees, so truckers may be stranded on remote highways–through no fault of their own–if the kill switch kicks in during cold winter nights. Urea thawing devices are currently on the drawing board, but even if they could be successfully implemented they would further drive up costs.

Another problem is assigning responsibility for providing adequate supplies of urea to truckers on the road. If the onboard urea runs out, can the driver get to–or find open–a service station or dealership to fill up with urea? EPA seems to be suggesting that engine and truck manufacturers should take responsibility for creating a national urea distribution system, something the industry says it cannot and should not have to do. The organization of the service station industry–a combination of independent distributors, chains, and company-owned stores–makes it unlikely that an effort led by truck manufacturers to create a supply chain for urea would be either successful or expedient.

Ozone Already Declining

EPA’s proposal might make sense, despite all of these concerns, if the nation were facing a crisis of rising ozone levels. However, just the opposite is the case. Since the mid-1970s, the number of days during which ozone levels exceeded federal standards has declined by 80 to 95 percent (depending on whether one is measuring based on the new eight-hour standard or the old one-hour standard). NOx emissions from coal-fired power plants have declined roughly 60 percent since 1998. More NOx reductions from coal-fired power plants will be required under future clean air requirements.

There is growing evidence that further NOx reductions could actually slow current progress toward reducing ozone, or even cause ozone levels to increase. Ground-level ozone forms during summer months when NOx and volatile organic compounds (VOCs) react with oxygen on warm, sunny days. Researchers have shown that NOx emissions drop as much as 50 to 60 percent on weekends (due to much lower amounts of diesel vehicle traffic), but ozone levels stay the same in some cities, such as Atlanta and Cincinnati, or even spike upwards in some cities, such as Los Angeles and San Diego.

Joel Schwartz, a clean air expert with the American Enterprise Institute, notes that NOx reductions reduce ozone levels only when there is a preexisting high ratio of VOC relative to NOx in the atmosphere. At low VOC-to-NOx ratios–which is the situation in most of the U.S.–reducing NOx actually increases ozone formation.

“Over the past few decades, American metropolitan areas have been moving further into the VOC-limited regime,” Schwartz observes, explaining the higher ozone levels on weekends.

“It’s ironic, isn’t it?” observes Schwartz. “All this controversy over a requirement–very low-NOx diesel trucks–that will actually slow progress on or even worsen ozone in populated areas.”

James M. Taylor ([email protected]) is senior fellow for environment policy at The Heartland Institute.