The Obama administration on Thursday will tighten national smog controls but not limit the pollution as much as health advocates want, according to two sources familiar with the plan.
The Environmental Protection Agency (EPA) will limit ground-level ozone, the main component of smog, to 70 parts per billion (ppb), tightening from the current level of 75 ppb set under former President George W. Bush in 2008.
Officials are likely to publicly announce the ozone threshold and explain their thinking on Thursday afternoon, according to the sources, who were briefed on the plans.
As they deliberated on the new plan's impact, officials have had to contemplate the billion-dollar costs to industry as well as the effect on overall health.
The EPA had said it was considering a range of 65 to 70 ppb. A 65-ppb cap would have cost industry about $11 billion more to implement than a 70-ppb limit but would have prevented three times as many childhood asthma attacks, according to EPA estimates.
The 65-ppb threshold would prevent 960,000 childhood asthma attacks compared with 320,000 incidents at the 70-ppb level, the EPA has predicted. Industry will face costs of $3.9 billion under the plan to be formalized on Thursday.
Setting the new ozone benchmark at 70 ppb might allow the Obama administration to address pollution concerns without provoking either industry or consumer advocates.
"The EPA has threaded the needle in strengthening the ozone standard," said S. William Becker, executive director of the National Association of Clean Air Agencies, which represents state regulators that will have to implement the new rules.
Under the rules, U.S. states would likely have several years to work with power plants, factories and refineries to limit pollutants like nitrogen oxide and volatile organic compounds - the components of health-damaging smog.
The final rules come after months of intense lobbying from industry groups, which warned that stringent ozone rules would harm the economy even more than a sweeping plan to limit carbon emissions from power plants. The power plant rule is at the center of President Barack Obama's climate change strategy.