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State smog numbers show N.C. air quality is getting better

2009 could yield record-low number of high-ozone days

Contact: Dr. Roy Cordato
919-828-3876
rcordato@johnlocke.org

September 02, 2009

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RALEIGH -- North Carolina could tally in 2009 the lowest number of high-ozone days of any year on record if current trends continue. That's a key finding in a new John Locke Foundation Spotlight report.

Click here to view and here to listen to Dr. Roy Cordato discussing this Spotlight report.

"What can be seen easily from the state's own data is that over the last six years there has been a dramatic improvement in ozone levels across North Carolina," said report author Dr. Roy Cordato, JLF Vice President for Research and Resident Scholar. "That improvement has occurred even as the federal government tightened its standards for defining a high-ozone day. Air quality, at least with respect to ozone, has been getting better, not worse."

Cordato analyzed state numbers from the past 10 years for ground-level ozone, often called smog. The state's 2009 data showed signs of continued improvement, Cordato said.

"As of September 1, the entire state of North Carolina had reported only nine high-ozone days," he said. "And we should be clear about what that means. It does not mean the entire state suffered through nine days of high ozone."

The data actually present an even better picture, Cordato said. "Those nine 'high-ozone days' were recorded on only four distinct days," he said. "In addition, they were recorded on just five of the 41 ozone monitors the government maintains across North Carolina. In other words, this means that 36 of the 41 monitors across the state have not registered a single instance of high ozone so far in 2009."

Ozone season runs from April through October. The chance of additional high-ozone days drops as temperatures start to cool in the fall, Cordato said. "If we've faced no high-ozone problems by September 1, we're not likely to see any problems this year."

Cordato's report does more than offer good news about 2009 ozone levels. It places a decade of smog data in perspective, he said. "North Carolinians have gotten used to hearing about 'ozone alert days' on their radio and television newscasts during the hot summer months of June, July, and August," he said. "The purpose of these alerts is to warn people that ground-level ozone levels may exceed a certain threshold."

"The standards relate to atmospheric concentrations of ozone considered more or less safe for certain groups to breathe," Cordato added. "The state determines whether to issue an ozone alert based on guidelines set by the U.S. Environmental Protection Agency."

The EPA made year-to-year comparisons more difficult in 2008, when it changed the rules for determining when to trigger a high-ozone day, Cordato said.

"Under the old rules, which were already quite restrictive, a high-ozone day resulted if one monitor registered an ozone concentration level of 0.085 parts per million in the atmosphere, sustained over an eight-hour period," Cordato said. "Last year, the EPA put in place the new, more restrictive standard of 0.076 parts per million. With a lower threshold, it should be easier for any monitor to trigger an ozone alert."

North Carolina has 41 monitors across the state. "Clearly, the more monitors a state has, the more likely it is that any one monitor will cross that threshold on any given day," Cordato said. "Different states have different numbers of monitors. The number of monitors within a state also changes. For that reason, comparisons among states that do not adjust for differing numbers of monitors are illegitimate and will always be biased against states with higher-than-average numbers of monitoring sites, such as North Carolina."

While state-to-state comparisons are difficult, Cordato's report focuses on year-to-year comparisons for North Carolina and its regions. "This report makes available some consistent data that avoids apples-and-oranges comparisons between time periods that could occur because of the two different EPA standards," he said. "It shows the number of high-ozone days on an average per-monitor basis over a 10-year time period from 1999 to 2008. All data are based on the new, more restrictive standard."

Cordato offers one caveat. "People should note that ozone levels are very localized, even within metropolitan areas or regions," he said. "A monitor on one end of a county or region might cross the EPA threshold while, at the same time, a monitor a few miles away might not. It's not possible to use this data as a good gauge of how air quality has varied in a particular neighborhood or local community."

One fact is clear, Cordato said. "Even under the new federal standard, the number of ozone alerts across the state has declined," he said. "The state has experienced a significant reduction in the number of high-ozone days."

Dr. Roy Cordato's Spotlight report, "A Decade of Data on Smog: Just the facts," is available at the JLF Web site. For more information, please contact Cordato at (919) 828-3876 or rcordato@johnlocke.org. To arrange an interview, contact Mitch Kokai at (919) 306-8736 or mkokai@johnlocke.org.

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