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EPA Administrator Andrew Wheeler said Tuesday the agency would retain but not strengthen air standards for soot pollution, which is linked to tens of thousands of early deaths and heart and lung conditions.

The agency will leave in place the 2012 regulation on particulate matter—technically called PM2.5—overriding recommendations from nonpartisan EPA officials and independent health experts. Agency experts found in 2019 that regulation "needs strengthening to prevent a substantial number of premature deaths."

Industry groups like the American Petroleum Institute and the U.S. Chamber of Commerce have widely opposed tightening the soot rules. Wheeler told reporters repeatedly he believes the science on particulates, which are fractions of the width of human hair and can lodge in lungs, is not clear.

"I'm saying that there's still a lot of uncertainties and that we believe that the current level that was set by the Obama administration is protective of ," Wheeler said. "We believe that this threshold is protective based on the scientific data that we have."

The agency made the decision to maintain the soot standards during a global pandemic related to lung health and after a recent study of 3,000 U.S. counties linked small increases in particulate matter with cases of COVID-19, the disease the new coronavirus causes.

Authors of the study, published last week by Harvard University's public health school, found a slight increase in particulate matter could in the long term trigger a 15% spike in the mortality rate of COVID-19.

The EPA has unfurled a slew of air pollution proposals during the public health crisis, which has killed more than 20,000 people in the U.S. The agency also rolled back fuel economy standards for cars and trucks and, in mid-March, significantly loosened its pollution regulatory efforts for industry, allowing companies to report on their own if they are meeting legal requirements for air and water pollution during the pandemic.

The EPA is required under federal law to set air quality standards for six main pollutants—carbon monoxide, lead, ground-level ozone, , nitrogen dioxide and particulate matter—and the agency is required to review them every five years and make changes to improve air quality standards.

In 2018, former EPA Administrator Scott Pruitt directed the agency to expedite the reviews for and ground-level ozone. Environmental advocates have cautioned that a speedy review of the standards could mean the public and scientists are denied the opportunity to provide adequate feedback and the EPA wouldn't effectively review the standards.

Addressing reporters Tuesday, Wheeler said the Harvard study was not complete because it has not been peer-reviewed and accused scientists of being biased against the agency.

"And I'd have to say, at least in the press, the scientists seem to have a bias," the administrator said, criticizing news coverage of the decision to permit companies to monitor their own water and air pollution. As written, that decision does not allow pollution increases, he said.

"They either didn't read the enforcement discretion memo or they didn't understand it," Wheeler said of scientists generally. He repeated that phrase twice more.

Health and swiftly condemned the agency's decision not to make rules more stringent.

In a joint statement, 19 health and medical groups, including the American Lung Association, the American Heart Association and the American Thoracic Society, criticized the proposal, which Wheeler said would be released once the Federal Register clears a backlog.

"Particle pollution is dangerous. It can cause breathing trouble, asthma attacks, COPD exacerbations, heart attacks, strokes, lung cancer, and premature death," the groups said. "We know that particle pollution is deadly, and that the current limits do not sufficiently protect Americans—especially children with asthma and adults with lung and heart disease."