The Biden administration is proposing to tighten a key air pollution regulation after the Trump administration declined to do so. 

The Environmental Protection Agency (EPA) proposed on Friday to tighten limits on how much soot can be in the air, though some environmentalists are calling on the agency to go even further to protect public health. 

Exposure to soot pollution, also known as fine particle pollution, has been linked to heart attacks, asthma and premature deaths. 

This type of pollution can come from burning fossil fuels in cars or at power plants or from other places like fires or construction sites. It disproportionately impacts communities of color and low-income households. 

The administration estimated that its move could prevent as many as 4,200 premature deaths per year.

“Fine particulate matter is both deadly and extremely costly,” EPA Administrator Michael Regan told reporters on Thursday, adding that strengthening the standard “could result in significant public health benefits.”

The decision came after the Biden administration reviewed a Trump-era decision that left a less stringent standard in place. 

The maximum Trump-era air pollution level was originally set under the Obama administration, which had tightened it from an even looser standard. 

In 2020, the Trump administration said that its decision to leave the Obama standard in place was adequately “protective of public health.”

But, Regan said that the agency found upon review that “the 2012 standards are no longer sufficient to protect public health.”

Environmental activists described the Biden administration’s move as a step in the right direction, but also said it still wasn’t good enough to prevent pollution exposure. 

“It’s progress,” said Vijay Limaye, a climate and health scientist with the Natural Resources Defense Council. “The problem is, that still leaves a lot of dangerous air pollution exposures on the table.”

The Biden administration is proposing to limit how much of the pollutant can be in the air on average to a concentration of somewhere between 9 and 10 micrograms per cubic meter annually — down from 12 micrograms under the previous standard. 

The 4,200 premature deaths could be avoided at the more stringent level of 9 micrograms per cubic meter; it’s unclear where in the 9 to 10 range the agency may ultimately set the level.

The EPA is also considering looser standards of up to 11 micrograms per cubic meter and stricter standards of as low as 8 micrograms per cubic meter. 

Limaye said that the standard of eight micrograms per cubic meter would be more appropriate. 

He cited a recent report prepared for the Environmental Defense Fund, which found that lowering the standard to 8 micrograms per cubic meter would save nearly 15,000 more lives annually than a standard of 10 micrograms per cubic meter — the looser end of what was proposed by the Biden administration. 

Meanwhile, the World Health Organization (WHO) has called for even lower levels, recently updating its guideline to 5 micrograms per cubic meter of annual exposure. 

Asked why the EPA was not more aggressive, Regan said that the agency came to its proposal after consulting with both internal experts and a range of stakeholders. 

“We arrived to this space based on sound science and a rigorous evaluation of the data that we have at hand,” he told reporters. 

The standards themselves don’t directly set limits on any particular pollution source. Instead, they serve as a national guideline that can trigger EPA actions to ensure the air quality requirement is being met across the country. 

“Locking in a strong limit at this point, it’ll play out essentially over the next few years in terms of EPA taking a look at air monitoring data collected across the country and then making decisions,” said Limaye, who is a former EPA scientist. 

Both air pollution broadly and particle pollution specifically have been linked to millions of deaths worldwide.

The WHO has found that broadly, 7 million people are killed each year by air pollution. Some estimates have been even higher, with one study last year finding that particle pollution killed 8 million people in 2018, making it responsible for nearly 20 percent of all deaths worldwide.