|A map of counties EPA projects would be in violation of tougher ozone rules. Click to enlarge.|
The US Environmental Protection Agency (EPA) has proposed that US air quality standards for ground-level ozone be strengthened by tightening the standards for the first time since 1997.
The new proposal recommends an ozone standard within a range of 0.070 to 0.075 parts per million (ppm). EPA also is taking comments on alternative standards within a range from 0.060 ppm up to 0.08 ppm, which is the level of the current 8-hour ozone standard.
In December 2006 in a unanimous decision, a Federal court of appeals struck down a 2004 EPA ruling that had loosened the existing 8-hour ozone standard. The court ruled that the EPA violated the Clean Air Act by relaxing those limits to levels in excess of 0.09 ppm. (Earlier post.)
In February 2007, EPA staff scientists published a final paper submitted as part of the current review of national air quality standards concluding that the current primary ozone standard is not adequate to protect public health. (Earlier post.)
Clinical studies show evidence of adverse respiratory responses in healthy adults from exposure to ozone at a level of 0.080 parts per million (ppm). New studies link ozone exposure to important new health effects, including mortality, increased asthma medication use, school absenteeism, and cardiac-related effects. Studies report effects at ozone levels well below the current standard. Furthermore, studies of people with asthma indicate that they experience larger and more serious responses to ozone that take longer to resolve.
The staff paper recommended a range of levels for the EPA administrator to consider in setting the primary ozone standard, extending from below 0.080 ppm down to 0.060 ppm. The final staff paper also recommends specifying the level of the standard to three decimal places. Ozone air quality measurements have advanced sufficiently to now reflect that level of precision.
EPA also is proposing to revise the secondary standard for ozone to improve protection for plants, trees and crops during the growing season. The secondary standard is based on scientific evidence indicating that exposure to even low levels of ozone can damage vegetation.
EPA is proposing two alternatives for this standard: a standard that would be identical to the primary standard to protect public health; and a cumulative standard aimed at protecting vegetation during the growing season.
EPA is estimating the health benefits of meeting a range of alternative ozone standards based on published scientific studies and the opinion of outside experts. These findings will be detailed in a Regulatory Impact Analysis to be released in the next few weeks, which will include both the estimated costs and benefits. EPA projects that health benefits of the proposed standard could be in the billions of dollars.
The agency will take public comment for 90 days following publication of the proposal in the Federal Register and will hold four public hearings. The hearings will be held in Los Angeles and Philadelphia on 30 Aug, and in Chicago and Houston on 5 Sep. The agency will issue a final rule by 12 March 2008.
Ground-level ozone (O3) is not emitted directly into the air, but is created through a reaction of NOx and volatile organic compound emissions in the presence of sunlight. Emissions from industrial facilities, electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are the major man-made sources of these ozone precursors.