Federal regulators on Wednesday proposed stricter rules for pollution that causes smog, a move that would likely increase the number of ozone-alert days in southern and coastal Maine, but that supporters contend would better protect the public health.

The Obama administration wants to lower the threshold for ground-level ozone, a component of smog that is linked to asthma, lung damage and heart disease. The ozone rules are the latest in the administration’s strategy to reduce air pollution and greenhouse gas emissions despite strong resistance from some business sectors and congressional Republicans.

Maine has made substantial progress reducing in-state sources of ozone pollution in recent decades but is on the receiving end of air pollution from other states. The proposed rules could push several Maine counties into non-compliance with federal standards, requiring additional steps to reduce pollution originating within Maine.

It’s not clear yet what steps Maine might have to take. In the 1990s, the state was required to begin selling reformulated gasoline in southern counties. It also took steps to implement an emission testing program for cars as part of the annual motor vehicle inspection program. But that program, known as CarTest, was later abandoned under considerable controversy.

Currently, the U.S. Environmental Protection Agency has proposed reducing the ground-level ozone standard from 75 parts per billion to between 65 and 70 parts per billion. But the agency also plans to solicit comments on a 60 parts per billion standard, a level supported by many health groups.

The EPA estimates the new standards would cost industry $3.9 billion to $15 billion to implement by 2015, although industry groups say the actual costs would likely be much higher. At the same time, the EPA predicts that the lower levels might avoid thousands of premature deaths, avert up 960,000 asthma attacks in children and save billions of dollars in health care costs.

“Bringing ozone pollution standards in line with the latest science will clean up our air, improve access to crucial air quality information, and protect those most at-risk,” EPA Administrator Gina McCarthy said in a statement.

Although ozone is an important component of the upper atmosphere, it can cause asthma attacks and breathing problems when concentrations rise too high at ground level, especially for children, the elderly and the infirm. Ground-level ozone is produced when pollution from vehicle or smokestack emissions, such as nitrogen oxide and volatile organic compounds, combines with intense sunlight and oxygen.

OUT-OF-STATE SMOG

Maine has reduced in-state emissions of key smog-causing pollutants by more than half during the past 30 years, according to data from the Maine Department of Environmental Protection. But Maine’s location along the Eastern Seaboard means that many of the pollutants that contribute to smog originate in southern and midwestern states with laxer air pollution standards and more coal-burning power plants.

As a result, officials in Maine and elsewhere in New England states have generally supported Obama administration attempts to crack down on air pollution that drifts across state borders.

Maine Department of Environmental Protection spokesman Karl Wilkins said Wednesday that DEP staff were still evaluating the proposal and won’t have additional information until next week because of the Thanksgiving holiday. State offices closed early Wednesday because of the snowstorm and Wilkins did not reply to subsequent requests for comments on potential impacts on Maine.

Health and environmental groups praised the proposal, which came more than three years after Obama – under pressure from businesses and facing a tough re-election – halted an earlier EPA push to lower the threshold.

STANDARDS CALLED OUTDATED

“The science is clear that harm is occurring at levels far below what is currently considered safe,” Effie Craven, Maine healthy air campaign coordinator at the American Lung Association of the Northeast, said in a statement.

“That means we are being assured that the air in our communities is safe to breathe based on a weak and outdated standard. But Maine people are not looking for a false sense of security – every parent has a right to know the truth about the air their children breathe.”

The most visible impact in Maine, as in other states, could be an increase in the number of air quality alerts on hot days when ozone levels rise above healthy levels.

In 2014, Maine did not have any days when ozone levels exceeded 75 parts per billion. Using state data, the American Lung Association calculated that Maine would have experienced three or 10 “unhealthy” days, respectively, with standards of 70 parts per billion or 65 parts per billion.

The change could also knock several Maine counties out of compliance – or into “non-attainment” – with federal ozone standards, thereby requiring the state and counties to prepare plans to bring the areas back into compliance. In 2006, the EPA removed southern and coastal Maine counties from the non-attainment list in recognition of the state’s efforts to reduce ozone pollution.

Data released by the EPA on Wednesday showed that York County would fall out of compliance at the 70 parts per billion level while York, Cumberland, Hancock and Knox counties would be in non-attainment under the 60 parts per billion standard. Those calculations were based on a complex EPA formula that looks at ground-level ozone levels for 2011 through 2013.

REGIONAL APPROACH ADVOCATED

Ed Miller, the American Lung Association’s senior vice president, pointed out that if Maine counties fall out of compliance, they will be accompanied by many others throughout the Northeast. So any approach to combating ground-level ozone will have to be a regional one. But he said the biggest local benefit from the lower thresholds will come from changes elsewhere.

“When these new standards go into effect, we are going to be the beneficiary because areas to the south and west of us are going to have to clean up their air much more than we would,” Miller said.

But some industry and business groups are questioning the scientific basis of the proposal and predicting the stricter standards will squelch economic development, especially when combined with other Obama administration regulations.

“This stricter standard will lead to more non-attainment designations across the United States, which translates into restrictions on expansion, permitting delays, increased costs to industry, and an impact to transportation planning,” said Bill Kovacs, a senior vice president at the U.S. Chamber of Commerce.

“This more stringent standard will also strike at the heart of those areas that are just beginning to appreciate the economic benefits of planning for and building new facilities, expanding existing ones, and developing their communities.”

Republicans in Congress are already pledging to fight the EPA proposal, citing compliance costs for industry.