WASHINGTON — The Trump administration opted Tuesday not to set stricter national air quality standards despite a growing body of scientific evidence linking air pollution to lethal outcomes from respiratory diseases such as COVID-19.

Environmental Protection Agency Administrator Andrew Wheeler announced Tuesday that the agency would maintain the current standards for fine particulate matter, otherwise known as soot, the country’s most widespread deadly pollutant.

EPA’s staff scientists recommended lowering the annual particulate matter standard to between 8 and 10 micrograms per cubic meter in a draft report last year, citing estimates that reducing the limit to 9 could save roughly 12,200 lives a year. EPA’s Clean Air Scientific Advisory Committee (CASAC) was split on the question, with some members calling for tighter standards and others saying the current one is sufficient.

“The United States has some of the cleanest air in the world, and we’re going to keep it that way,” Wheeler told reporters in a phone call. “We believe the current standard is protective of public health.”

Soot comes from smokestacks, vehicles, industrial operations, incinerators and burning wood. The current standards limit annual concentrations to 12 micrograms per cubic meter of air and daily concentrations to 35 per cubic meter. These fine particles enter the lungs and bloodstream, causing inflammation that can lead to asthma, heart attacks and other illnesses.

Poor and minority communities in the United States tend to be exposed to greater air pollution, including soot, because they often live closer to highways or industrial facilities. A 2019 study by the Union of Concerned Scientists found that on average, communities of color in the Northeast and Mid-Atlantic breathe 66 percent more air pollution from vehicles than white residents.

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This long-term exposure has increased the risks Americans of color face when it comes to heart and respiratory illness, including the novel coronavirus that is disproportionately killing African Americans.

The decision regarding particulate matter is the administration’s latest effort to ease industrial regulation. In recent weeks, the White House has rolled back automobile emissions standards, despite projections that it would increase premature deaths. Citing the national emergency sparked by the coronavirus pandemic, the EPA has stopped policing pollution from factories and power plants for an indefinite period. And the agency has weakened emissions limits for coal-burning plants as well as cars and light trucks.

Taken together, these moves are “a death sentence to communities at the front lines of pollution,” said Heather McTeer Toney, the former mayor of Greenville, Mississippi, a majority African American city, who is the national field director for the Moms Clean Air Force.

Several public health experts and environmentalists criticized EPA’s proposal on particulate matter, which is subject to a 60-day comment period and will determine national soot levels for the next five years, as well as the process that led to it. Wheeler’s predecessor, Scott Pruitt, disbanded the independent panel that advised CASAC specifically on soot levels — those experts gathered in October at a two-day meeting organized by the Union of Concerned Scientists and concluded that the annual limit should be lowered to between 8 and 10 micrograms, and the daily between 25 and 30 micrograms per cubic meter.

“The process was doomed from the start,” said Gretchen Goldman, research director for the Union of Concerned Scientists. “It’s not surprising they would retain the standards, because they broke the process.”

But several big business groups in Washington, including the U.S. Chamber of Commerce and American Petroleum Institute, cheered the administration for retaining the existing standards, with both noting that annual concentrations of fine particulate matter are down by 39 percent since 2000. Most areas of the country have now met the annual standards, with the exception of spots including Southern California and parts of Pennsylvania, Idaho and Ohio.

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“We think this strikes the right balance,” said API’s Frank Macchiarola.

Wheeler cited “uncertainties” in existing studies about the impact of lower particulate matter on human health, and the fact that EPA’s advisory panel was split, as reasons to retain the current pollution limits.

But some scientists say even a slight shift in pollution levels, either up or down, can impact the health of those most vulnerable to respiratory problems.

One study published this month from researchers at Harvard’s T.H. Chan School of Public Health concluded that even a small increase in long-term exposure to fine particulate air pollution causes a large increase in the risk of dying of COVID-19, the disease caused by the coronavirus.

The study, which examined 3,080 U.S. counties, found that an increase in long-term exposure to fine particulate pollution of just one microgram per cubic meter is associated with a 15 percent greater likelihood of dying of COVID-19. This stark difference may be explained by the lung damage such pollution causes over time.

“The study results underscore the importance of continuing to enforce existing air pollution regulations to protect human health both during and after the COVID-19 crisis,” the study’s authors wrote.

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“If you’re breathing polluted air and your lungs are inflamed by the disease, you’re going to get very, very sick,” a senior author of the study, Harvard biostatistician Francesca Dominici, told The Washington Post last week.

“Now is not the time to be rolling back environmental regulations,” she added.

Wheeler said that while the findings were “interesting,” it was “premature” to draw conclusions. “We look forward to reviewing the Harvard study once it’s completed and peer reviewed,” he said.

API spokesman Scott Lauermann said regulated industries asked the EPA to suspend emissions monitoring during the pandemic because of practical constraints. “The natural gas and oil industry, faced with limited personnel, is seeking short-term flexibility for reporting requirements,” he said.

Wheeler noted that industries still must meet emissions limits during the enforcement hiatus.

But there is some evidence that particulate matter levels are up around Houston, the heart of the U.S. oil and gas industry. A Texas A&M University analysis of state air quality data between March 1 and April 8 found a “large” increase in fine particulate matter levels in the Houston suburb of Deer Park, home to several refining and chemical manufacturing plants, even as Harris County issued a stay-at-home order and Texas Gov. Greg Abbott, R, closed bars and restaurants.