EPA’s New NOx Rules Could Increase Urban Smog Problem

Published March 17, 2006

The U.S. Environmental Protection Agency (EPA) will be allowed to implement potentially counterproductive smog-prevention regulations after the U.S. Supreme Court on November 14 let stand a lower court decision that a legal technicality prevented the National Alternative Fuels Association (NAFA) from challenging the regulations.

Complex Interactions

EPA says regulations it implemented in 2000 will reduce the formation of ground-level ozone, a key smog component. Ozone forms when nitrous oxides (NOx) react with volatile organic compounds (VOC) on hot, sunny days. Accordingly, “smog season” in the U.S. tends to run from approximately April 1 through September 30.

A cursory look at the components of ozone formation would lead one to believe cutting either NOx or VOC concentrations would reduce ozone and, hence, smog. However, computer models and real-world observations indicate the equation is not so simple.

Ozone formation is not dependent only on the mere presence of NOx and VOC. “Ozone formation depends on the ratio of VOC to NOx, and different ratios of VOC/NOx lead to very different outcomes,” explained Joel Schwartz, a visiting fellow at the American Enterprise Institute.

According to computer models, “when the VOC/NOx ratio is high–greater than about 10 to one–ozone formation is limited by the availability of NOx, and VOC reductions have no effect on ozone levels. But when the VOC/NOx ratio falls below 10 to one, VOC reductions begin to reduce ozone,” Schwartz observed. Paradoxically, when the VOC/NOx ration is below 10 to one, “reducing NOx actually increases ozone.”

Urban areas currently tend to have the lowest VOC/NOx ratios and are therefore most prone to this paradox. According to the computer models, NOx reductions in urban areas will actually increase ozone and, thus, smog.

“Smog in many urban areas increases when NOx concentrations are further reduced, while declines generally occur in less heavily populated areas,” noted Dr. Kay Jones of the Competitive Enterprise Institute.

Real-World Observations

The computer models, moreover, have been verified by real-world observations. “A disproportionate number of exceedances of the ozone standard are occurring on weekends, when emissions of ozone-forming chemicals–especially NOx–are down anywhere from 10 to 40 percent,” Schwartz reports.

“At some monitoring locations in the Los Angeles area,” Schwartz noted, “weekend exceedances account for nearly 80 percent of total exceedances. And these ozone increases are occurring in spite of large declines in NOx. Although the ‘weekend effect’ is most pronounced in California, it is becoming increasingly prevalent in other cities across the nation, including Denver, Chicago, Philadelphia, and New York.”

“EPA failed to consider compelling science that its NOx reducing regulation would actually severely worsen the nation’s air quality,” observed a summary of the issue prepared by NAFA.

“Ozone is not very likely to improve much in the future,” explained Doug Lawson, a researcher with the National Renewable Energy Laboratory. “In fact, it’s very likely to get worse, given that all the regulations in place for the next decade or so have larger NOx reductions built in to them than VOC reductions, which is exactly what takes place now on weekends relative to weekdays.”

Negative Consequences

The negative effects of this policy are twofold. The first negative effect is apparent: Increases in urban smog result in greater discomfort and greater alleged health impairments associated with smog.

Second, a short-term rise in ground-level ozone and resulting smog is likely to be paraded by activist groups as “proof” that EPA’s mandated NOx reductions are not stringent enough. More stringent, and more costly, reductions would then be advocated on the false premise that more stringent NOx reductions would further reduce ground-level ozone.

“EPA ignored other viable less costly solutions, which could have easily resolved the stated ozone problem,” observed the NAFA summary.

A solution, agreed Schwartz, lies in targeting more front-loaded VOC reductions rather than front-loaded NOx reductions.

“What makes this strategy appealing is that VOC reductions will reduce ozone in most places, especially places where most people live,” Schwartz noted.

“After substantial near-term VOC reductions, later NOx reductions would achieve the EPA’s ozone standard on the same schedule as currently planned, but with less harm in the interim,” Schwartz said. “In addition, this change would give each non-attainment area flexibility to tailor its ozone reduction strategy based on the specifics of local emissions and air chemistry.”

James M. Taylor ([email protected]) is managing editor of Environment & Climate News.