EPA Administrator Scott Pruitt said Thursday he wants to radically revise how basic, health-based national air quality standards are set, giving more weight to the economic costs of achieving them and taking into account their impacts on energy development.

Under the law, the standards, setting uniform goals for breathable air, are supposed to be reviewed periodically asking only one question: whether they are protective enough to ensure the health of even the most vulnerable people, based on the best available science.

A foundational feature of the landmark Clean Air Act, the setting of these standards based on health, and not cost or feasibility, was defended adamantly on the Senate floor in 1970 by the bill's main author, Sen. Edmund Muskie of Maine, who declared: "That concept and that philosophy are behind every page of the proposed legislation."

It has withstood legal and political tests for a generation.

Pruitt's proposal would jettison it.

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His approach, laid out in an agency memorandum, would fundamentally alter the process for how the government sets what are called the National Ambient Air Quality Standards (NAAQS), which govern six especially widespread and noxious pollutants. The law requires the EPA to review these standards periodically. Pruitt's memo says it will complete two reviews of levels set under President Barack Obama—for smog-forming ozone and sooty particulate matter—before President Donald Trump's first term ends.

With other pollutants, including carbon dioxide that causes global warming and toxins such as mercury, the government may weigh costs and benefits from the outset. For these six, however, public health rises above all other considerations, which are relegated to a secondary role when the states make implementation plans.

Clean air advocates say Pruitt's policy is a brazen attempt to weaken the standards and contains several changes that have long been sought by major polluters—foremost the coal, oil and gas industry—to allow more flexibility in deciding what levels of pollutants are safe to breathe.

"This has been the dream of the polluter since the '90s," said Paul Billings, senior vice president of advocacy for the American Lung Association, "and it's the nightmare particularly of parents of kids who have asthma or other chronic lung disease."

Pruitt's Latest Attempt to Silence Science

Pruitt's memo comes after several other attempts to change the role that scientific evidence plays in the EPA's decision-making. Last year, Pruitt said he would bar any scientist who had received agency funding from serving on any of its advisory committees, like the one that recommends the air quality standards.

In April, he formally proposed a policy that would prohibit the agency from using scientific studies that rely on private data, including personal health records. Those types of studies have provided some of the strongest evidence of the health effects of air pollution and are a key basis for the air quality regulations.

"This is all an attempt to create a process that limits the science that can be considered and include external factors that aren't relevant, with a goal of ripping out the heart and lungs of the Clean Air Act," Billings said.

The memo applies to periodic reviews of goals for carbon monoxide, lead, sulfur dioxide, particulate matter, ozone and nitrogen dioxide. If levels of these rise above the standards in a given area, the EPA can require states to implement plans to reduce them.

Many of these are emitted together with carbon dioxide whenever fossil fuels of any kind are burned.

"It is without a doubt the driving force for cleaner air in this country," said Frank O'Donnell, president of Clean Air Watch, an advocacy group.

'Solely on Protecting Public Health and Welfare'

The EPA website says the standards, which it is supposed to review every five years, are to be based "solely on protecting public health and welfare."

A committee of advisers reviews recent science and makes recommendations to the EPA administrator, who has the ultimate decision for where to set them. A 2001 U.S. Supreme Court opinion, written by conservative Justice Antonin Scalia, affirmed that the agency cannot consider the cost of implementation when setting the standards.

Pruitt's memo says that from now on, the agency will ask its advisers to address several specific issues, including "any adverse public health, welfare, social, economic, or energy effects." The memo notes that doing so, "may elicit information which is not relevant to the standard-setting process, but provides important policy context for the public, co-regulators, and EPA."

Sen. Tom Carper of Delaware, the top Democrat on the Environment and Public Works Committee, issued a statement calling the move a "thinly veiled effort to inject politics" into the process.

"Congress's clear intent was for the NAAQS requirements to use the best science available to protect public health," he said, "and Mr. Pruitt's decision today to undermine that science-based process fails to live up to the letter of the law."

It also directs the advisers to address the role of natural sources of pollution, like forest fires or dust-storms. Currently, the EPA can consider these events when it determines whether an area is complying with the rules—a town downwind of a major forest fire might not be deemed out of compliance even if particulate levels from the fire push it above a limit.

But Billings said such a consideration should play no role in determining what levels are safe. "It doesn't matter the source," he said, "because your lungs don't care."

The memo also says the agency should establish "a clearer distinction between the purely scientific findings" contained in its scientific assessments "and the wider range of policy concerns that the Administrator must consider in making judgments about requisite standards."

In a statement, EPA spokeswoman Molly Block said the directives in the memo are consistent with the Clean Air Act and the Supreme Court ruling. She pointed to the memo itself to explain its reasoning.

Expect Legal Challenges

But it is bound to be tested in new litigation. Any standard set under the Pruitt protocol would be certain to face challenges by environmentalists.

The memo followed a directive issued by Trump in April for the EPA to reduce the burden of air quality regulations on manufacturers.

In 2015, the Obama administration lowered the standard for ozone to 70 parts per billion, which was the upper range of what the science committee had advised. The memo says it will complete a review of that standard by October 2020.

"This is a fundamental challenge to the health premise of the Clean Air Act," Billings said. "The public should be very concerned about what this will mean for air pollution cleanup in their communities across the country."