The US Environmental Protection Agency announced on Wednesday it is tightening federal air pollution standards by setting more stringent ozone limits for the first time since 1997.
"EPA today met its requirements of the Clean Air Act by signing the most stringent eight-hour standard ever for ozone, revising the standards for the first time in more than a decade," the EPA said in a statement.
The rules on smog-forming ozone, a widespread air pollutant, restrict the amount of nitrogen oxides and other compounds that are allowed to be released by power plants, motor vehicle exhaust, industrial facilities and other man-made sources, the EPA said.
The ozone thresholds are now 75 parts per billion (ppb), compared with the previous standard set in 1997 at 80 ppb.
EPA Administrator Stephen Johnson said the new guidelines will help protect public health and the environment.
"America's air is cleaner today than it was a generation ago," he said. "By meeting the requirement of the Clean Air Act and strengthening the national standard for ozone, EPA is keeping our clean air progress moving forward."
The agency reported that ozone levels throughout the nation have dropped 21 percent since 1980 as the EPA has worked with states and local governments to improve air quality.
EPA's new smog standards announcement drew heated reaction from both sides of the issue, with industry groups complaining that the bar was set too high and clean air advocates blasting the administration for disregarding scientists who advocated tougher standards.
The American Chemistry Council (ACC) said in a statement that there was "no clear and substantial basis" for tightening the standards set more than a decade ago.
"This decision by the EPA to lower the ozone standard unnecessarily will impose significant new burdens on states and others even as they continue to try and comply with the 1997 standard," the ACC said.
The non-profit group Clean Air Watch assailed the announcement, accusing the government of "compromising public health to save industry money."
"Once again, the Bush administration has chosen to disregard the advice of the EPA's own independent science advisers," who had unanimously urged a standard tougher than that selected by the agency, said Frank O'Donnell, president of Clean Air Watch.
"Unfortunately, real science appears to have been tainted by political science."
Clean Air Watch said EPA's science advisers had unanimously recommended that the smog standard be lowered to between 60 and 70 ppb.
EPA administrator Johnson said he was seeking changes to the Clean Air Act that would allow polluters "to consider benefits, costs, risk tradeoffs, and feasibility in making decisions about how to clean the air."
O'Donnell said that would allow more flexibility for polluters and would be illegal.
"This would be a radical attack on the Clean Air Act," O'Donnell said.
"It is taking a page directly from the playbook of polluters and their most ardent supporters in Congress."
EPA said it estimated the value of health benefits of the stricter regulations at between two billion and 19 billion dollars, with the cost of implementing the new standards estimated between 7.6 billion and 8.5 billion dollars.