When Cynthia Pinto-Cabrera developed asthma at 12, it didn't seem that unusual to her. Lots of her classmates in California's San Joaquin Valley carried inhalers to school. Her little brother needed a nebulizer every morning just to start his day breathing right.

But when she left the valley for college in Santa Barbara, Pinto-Cabrera encountered a world with far less air pollution than she had lived with. She found it shocking that other parts of the country simply lived with cleaner air— and their health benefited.

"A lot of people here in the valley don't really know asthma is not the normal," she says. "We've really normalized chronic illnesses."

Pinto-Cabrera is one of many people nationwide celebrating an announcement Wednesday from the U.S. Environmental Protection Agency, which unveiled new, stricter limits for one of the deadliest types of air pollution: tiny particles about 30 times smaller than a human hair. These particles are called PM2.5 (shorthand for particulate matter smaller than 2.5 micrometers in diameter) and are commonly referred to as soot.

The agency lowered the allowable limit for annual PM2.5 levels from 12 micrograms per cubic meter to 9. That's a "significant reduction," says Regan Patterson, an air pollution expert at the University of California, Los Angeles.

"The science is clear," says EPA Administrator Michal Regan. "Soot pollution is one of the most dangerous forms of air pollution and is linked to a range of serious and potentially deadly illnesses, including asthma and heart attacks."

The new standard represents the first tightening of the rules since 2012, but states will have several years to reach the new limits.

The EPA left the daily limits on PM2.5 pollution unchanged, at 35 micrograms per cubic meter, saying the same efforts that will reduce pollution under the revised annual standard will drive down short-term pollution exposures as well.

Decades of research have demonstrated that tiny particles are dangerous to people's health at nearly any concentration. The sources vary: fossil fuel combustion, agriculture, and industrial processes all add to the load, as does wildfire smoke and dust.

In aggregate, the tiny particles drive millions of premature deaths worldwide each year. The EPA estimates that the new, tighter standards will prevent about 4,500 premature deaths a year by 2032 in the U.S. and prevent about 800,000 asthma-related emergency visits. It estimates the lower pollution exposures could reduce healthcare costs by about $46 billion by that time.

If achieved, the standards would have major impacts on communities currently breathing in the dirtiest air—like Pinto-Cabrera's San Joaquin Valley in California or industrial counties in central Pennsylvania. "What we see in study after study, people of color are consistently breathing in the dirtiest air," says Patterson.

A 2022 study, for example, found that communities of color were consistently exposed to more air pollution than white communities. Another analysis shows they are exposed to more pollution than the national average from every single source, from industrial production to agricultural pollution.

The new standards won't erase those differences. But the EPA's analysis suggests the new rules should make them smaller. "It's important to step back and recognize that, by lowering the standards—when you improve air quality with these standards, you have reductions that improve air quality for everyone," says Patterson. But cleaner air will have the biggest health impacts in communities that are now experiencing the worst pollution. "Those are the communities for whom the standard will contribute to the most," says Patterson.

The new standards are still well above the World Health Organization's recommended limit of 5 micrograms per cubic meter averaged over the year.

The inequality of clean air progress

The air in the U.S. has improved significantly since the 1970 Clean Air Act first began to reduce outdoor air pollution.

"There was a time in major cities in this country when you couldn't see across the street, the air was so thick," says Paul Billings, president of the American Lung Association. "Thanks to the Clean Air Act and more than 50 years of progress, we have as a nation cleaned up our air drastically."

The EPA is supposed to review new science and update the standards every five years to protect public health. The annual PM2.5 limit was first implemented in 1997, and was tightened in 2012 from 15 to 12 micrograms per cubic meter of air.

In 2020 under the Trump administration, the EPA decided to keep current standards rather than tightening them. That decision was controversial: longtime EPA scientists recommended stricter standards, while an advisory panel that included several representatives from industry opposed them. In 2021, under the Biden administration, the EPA decided to re-evaluate that decision. The new standards are the outcome of that review.

Public health experts say the updates are necessary because fine particle pollution and its deadly effects are far from gone. Researchers estimate PM2.5 pollution kills up to 100,000 people across the country each year making it, by some measures, the most profound public health hazard in the U.S. today.

The dangers of soot

Tiny particles are dangerous because they can penetrate deep into people's lungs and can pass into the bloodstream, driving inflammation and other chronic problems. Long-term exposure leads to increased risks including heart attacks, strokes, dementia, hypertension, and chronic kidney disease. The health risks occur at annual exposure levels below even the new standard of 9 micrograms per cubic meter per year.

"These small particles, when they penetrate into lungs and bloodstream, they have a devastating impact on the health of humans" in just about every possible way, says Doris Browne, the former president of the National Medical Association.

Fifteen counties out of the country's more than 3,000 counties fail to meet the EPA's current standards. The current violators are concentrated in California, Ohio, and Pennsylvania—places with lots of industrial activity, fossil fuel burning, and agriculture.

Chris Chavez leads policy efforts for California's Coalition for Clean Air and grew up with asthma in one of the counties with air that doesn't meet the EPA's current standards. "While it's great to have new standards, the challenge is still to meet the old ones," he says.

Many of the places with the dirtiest air are home to communities of color. The divide is not accidental: racist zoning and planning practices which persisted for decades and in some cases continue today, often concentrated sources of pollution near Black, brown, and poor communities. Today, middle class and wealthy Black Americans breathe in more heavily polluted air than white Americans in all income brackets.

"We know this impact is greater on African Americans and other underserved people of color," says Browne. Cleaner air, she says, would also benefit those communities the most.

The EPA estimates PM2.5 levels in 119 counties are currently at levels that would not meet the new standards.

Several major industry groups object to the new standards. The American Forest and Paper Association suggests that tighter limits will restrict business activity, limiting development of new facilities and even efficiency upgrades to current ones. The new standards, they say, are too close to the current average background levels of pollution nationwide.

"This rule threatens modernization projects in manufacturing sectors across our country," says Paul Noe, vice president of the American Forest and Paper Association.

Analyses have consistently found negligible impacts of air pollution restrictions on local economic growth.

The tighter annual standards "will deliver real and true public health benefits," says Julie McNamara, a policy expert at the Union of Concerned Scientists. They also fall short in some ways, she says.

While the annual allowable exposure level was lowered, the daily allowable standard was not—and many sources of pollution emit inconsistently, or for short periods. So "there's also room to keep on growing," McNamara says. The EPA said the tighter annual standards are expected to push down short-term soot pollution as well.

Any progress helps, says Pinto-Cabrera. She's 26 now, living back in the San Joaquin Valley near where she grew up. "So many children, this ends up shaping their life, their relationship with physical activity," she says. "I was born here, raised here. I want to see my health improved, and I want my children to grow up here healthy."