The US Environmental Protection Agency has finalized a key update to the federal air quality standard for fine soot – a step toward reducing deadly air pollution that’s been over a decade in the making.

The standards, announced Wednesday, are one of several important finalized regulations coming from EPA this year focused on both improving air quality and cutting down on planet-warming pollution coming from power plants, other major industrial facilities, and vehicles. It comes as President Joe Biden is working to cement an ambitious environmental and climate record and appeal to young voters during a crucial election year.

The current standard, which has been in place for more than a decade, limits the average annual amount of fine particle pollution to 12 micrograms per cubic meter of air. The EPA would reduce that limit to 9 micrograms.

The agency estimates the limit will prevent up to 4,500 premature deaths and avoid around 800,000 cases of asthma symptoms.

“The stronger air quality standard announced today is grounded in the best available science and will undoubtedly save lives,” Regan told reporters on a press call. “We’re also full steam ahead on a series of rulemakings across the power and transportation sector that are drawing down emissions and protecting communities from dangerous air pollution.”

Still, the new limit is higher than what the World Health Organization recommends. In 2021, the international group put out guidance that environmental agencies slash the allowable limit to 5 micrograms per cubic meter of air. Doing so, the organization said, could reduce deaths associated with fine particle pollution by as much as 80%.

Fine particulate matter – also called PM2.5 – pollutes outdoor air when a variety of fossil fuels are burned – including gasoline, diesel and oil, as well as wood. It is the tiniest pollutant – significantly smaller than fine sand, dust, and pollen – but its miniscule size makes it one of the most dangerous to human health. When inhaled, it can travel deep into lung tissue, where it can enter the bloodstream and can contribute to cardiovascular disease, asthma and other respiratory illnesses.

Exposure to this pollution has also been linked to an increased risk of lung cancer in people who have never smoked. Scientists recently found a possible mechanism for that increased risk – some air pollution particles may promote mutations in cells in the airways.

The EPA is required by law to update the standards for fine particulate pollution every five years and according to the latest available science. The last time they were updated under the Obama administration in 2012, they were lowered from 15 to 12 micrograms per cubic meter.

The new standard was criticized by industry groups, who have described it as burdensome and difficult to meet. Tightening the soot standard “threatens economic growth” around the country, said Marty Durbin, senior vice president for policy at the US Chamber of Commerce. The trade group has argued wildfire smoke – not industry pollution – is responsible for much of the tiny soot particulate in the air.

The standards were not tightened during the Trump administration, which prompted an outcry among environmental and public health groups. Many of those groups commended the Biden administration on Wednesday for strengthening soot standards.

“Today is a really big day,” Earthjustice president Abigail Dillen told reporters. “The body of science around this pollution is so robust. We know it takes people before their time; we know it gives children and adults asthma and other sicknesses. This is a big step forward to addressing one of the most deadly environmental injustices in our country.”

But some major public health groups said the rules didn’t go far enough.

American Lung Association president Harold Wimmer called the EPA rule “a step forward for public health” but added, “the standards do fall short of what the Lung Association called for and what the science shows is necessary.”

The threat posed by microscopic soot particles

Millions of people put their health at risk every time they step outside. The American Lung Association’s State of the Air 2023 report says that, after a steady decline in US pollution levels, the number of people living in counties with failing grades for daily spikes in particle pollution was the highest it had been in a decade. Nearly 64 million Americans live in these counties, and communities of color bear the brunt of the negative health effects, regardless of income levels.

No amount of exposure to particle pollution is healthy.

Exposure can lead to cancer, stroke, heart problems and other vascular issues. It can aggravate asthma and is linked to neurodegenerative diseases like Alzheimer’s, Parkinson’s and other dementias, studies have found. People exposed to higher amounts of this pollution for longer periods also have an increased risk of depression and anxiety. Exposure can even contribute to problems thinking clearly.

Scientists believe that particle pollution can shorten lives. The number of people killed or disabled by certain heart problems caused by exposure to air pollution, for example, has risen since 1990, one study found, with particle pollution specifically to blame.

Generally, a 2019 study found that exposure to air pollution was linked to more than 107,000 premature deaths in the United States in just one year, with PM2.5 accounting for the most damage to people’s health. That’s more than the number of people killed each year in traffic accidents and homicides combined, the researchers said.

Since particle pollution is so tiny – 1/20th of a width of a human hair – it can travel past your body’s usual defenses. The particles cause irritation, inflammation and damage to cells. It may also affect the central nervous system and cause the body to release harmful substances that can hurt the blood-brain barrier, the network of blood vessels and tissues made up of closely spaced cells that protect the brain.

Negative health effects were often seen at pollution levels much lower than current US ambient air quality standards. The American Lung Association calls particle pollution one of the “least well-controlled pollutants in the United States” and one of the most dangerous.

As temperatures rise with climate change, the health problems related to this kind of pollution will get worse. The risk of a deadly heart attack, for instance, may double when people are exposed to extreme heat and high levels of particle pollution, studies show.

And soot is caused from wildfires, which are fueled by hot and dry temperatures due to climate change. Although wildfire smoke causes soot pollution, it can’t be regulated by federal agencies like other sources of soot including industrial and agricultural pollutants.