A day in the country may not be as healthy as you think, according to new air pollution standards proposed by the U.S. Environmental Protection Agency (EPA).
Late last year, the EPA proposed a new standard for ground-level ozone, a pollutant associated with photochemical smog. This new standard could cause large portions of the rural eastern United States to be cited as ozone non-attainment areas, according to a study to be published May 9 in the journal Science. This will require a major change in the nation's air pollution control strategies, which until now have largely focused on urban pollution.
Ground-level ozone is produced from chemical reactions in the atmosphere fueled by air pollutants such as hydrocarbons and nitrogen oxides. The federal Clean Air Act empowers the EPA to establish a National Ambient Air Quality Standard (NAAQS) for ozone to protect human health. In response to new medical data indicating adverse health effects at lower ozone concentrations, the EPA has proposed a new NAAQS.
Analysis of ozone levels measured at rural locations in the eastern half of the United States indicates that nearly half the sites would not meet new ozone standard.
"This implies that the harmful effects of air pollution may be a lot more ubiquitous in the United States than previously thought," said Dr. William L. Chameides, Regents Professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, and lead author in the Science paper. "Non-attainment of the current standard is mostly limited to urban areas and thus most people's perception is that air pollution is an urban problem. But if EPA's new standard better reflects the health effects of ozone pollution, it suggests that you could probably go just about anywhere in the eastern United States during the summer and encounter unhealthy air."
The new standard of 0.08 parts-per-million would be measured over an eight-hour period, while the current standard of 0.12 parts-per-million is measured over one hour. Sites would be considered in non-attainment if the third highest 8-hour averaged ozone concentration averaged over three years exceeded 0.08 parts-per-million.
"Because of differences in the way ozone fluctuates in urban and rural areas, the new standard is far more likely to be exceeded in rural areas," Chameides explained.
Summertime ozone levels tend to fluctuate dramatically in urban areas, dropping to near zero at night and then building up during the day to a peak in the afternoon. By contrast, rural ozone levels show smaller fluctuations with a lower but longer-lived daytime maximum and less of a fall-off at night.
"Lowering the permissible ozone concentration and averaging it over eight hours instead of one hour brings more rural sites into non-attainment," he said.
Scientists have known that the new standard would increase the number of non-attainment counties in the United States by a factor of about three.
However, Chameides and his collaborators, Dr. Rick D. Saylor of Georgia Tech and Dr. Ellis B. Cowling at North Carolina State University, believed that the impact on rural areas had not been adequately considered. To address this issue, they analyzed 1995 ozone data from 85 rural monitoring sites that were part of the Southern Oxidant Study's Spatial Ozone Network (SON) and the EPA's Clean Air Status and Trends Network (CASTNET).
Forty-one of those sites -- nearly half -- reported three or more ozone readings above the 8-hour, 0.08 parts-per-million level. Under current standards, only 6 of the 85 rural sites have unallowable ozone levels.
Requiring rural areas to meet the new standards would force a major change in ozone control strategies, since few rural areas can control the pollutant emissions that cause their non-attainment problems.
"The way the EPA guidelines are currently written, local and state agencies must develop a strategy to comply with NAAQS by controlling pollutant emissions within their area," Chameides explained. "In rural areas, however, it is unlikely that emissions within the area are contributing very much to the ozone pollution. These areas are not going to be able to solve the problem by controlling local pollutant emissions."
Communities and states would have to take a more regional approach, requiring cooperation of political entities that have not always worked together in the past.
"Pollution in rural areas is caused by a complicated combination of distant urban emissions and local and distant rural emissions, so you need to come up with a regional strategy to address rural air pollution," Chameides noted. "Not only will this change the politics of how we address air pollution in the United States, but it will also probably affect the economics of air pollution control."
Since acceptance of the Science paper, the researchers have repeated their analysis using data from a full three-year period with essentially the same results.
"While the details change depending upon the specific set of rural monitoring sites used and time period considered, the basic conclusion remains," Chameides explained. "Roughly forty to fifty percent of the rural eastern United States is found to violate the new standard."
In order to understand the full implications of this rural non-attainment, Chameides believes more air quality data will be needed from the rural United States.
"If we go forward with this standard, we will have to invest in a much more significant and well-planned rural ozone monitoring network," he concluded. "The network we have now is largely focused on urban and suburban areas and is simply not adequate for documenting the extent of rural air pollution."
VISUALS: Color map comparing rural ozone non-attainment sites under current standards and under proposed standards.