Climate change threatens to reverse decades of progress in cleaning America’s air, especially in the West.
Unhealthy air alerts triggered by particles of pollution are rising in dozens of cities and counties, chiefly in Western states, the American Lung Association reports. The main reason is rampant wildfires, fed by global warming, causing an annual cycle of smoky devastation.
Eight of the 10 cities with the most days of high particle pollution, including soot from fires, sit in California, the lung-disease nonprofit found in its 2023 State of the Air report. Another is Fairbanks, Alaska, a city without enough cars or people to generate much air pollution on its own.
Smoke from wildfires is befouling the air in remote cities that have never known L.A.-style smog: Logan, Utah; Missoula, Mont.; and Fargo, N.D. Wildfire smoke can blanket cities hundreds of miles away.
“A few weeks ago, I was speaking with someone from Colorado who was staying indoors because of smoke from forest fires in Calgary,” said William Barrett, national senior director for clean air advocacy at the American Lung Association.
Particle pollution is spreading at a time when another category of air pollution, ozone, stands in decline. Most large American cities log many fewer days of unhealthy air due to ozone, or smog, than in decades past.
New York now registers roughly 17 high ozone days per year, compared to more than 50 at the start of the millennium. Chicago reports about 15 smoggy days annually, down from nearly 40 in the early 2000s. The Washington, D.C., region logs about seven high ozone days a year, compared to about 60 per year at the turn of the millennium.
“Over the decades, the air has gotten cleaner, and everybody has benefited from that cleaner air,” said Julian Marshall, a professor of civil and environmental engineering at the University of Washington.
Amendments to the federal Clean Air Act in 1990 set emissions standards that gradually cleared the air across the nation. In New York and Chicago and Houston, longtime residents watched a gray smudge of smog melt away.
“Our air has been getting cleaner for four decades now,” said Daniel Cohan, an associate professor of civil and environmental engineering at Rice University in Houston. “We saw especially strong improvement in the 1990s and the first decade of the 2000s.”
The Lung Association has logged steady progress in smog reduction nationwide. The group gave failing grades to 124 U.S. counties for smog in its 2023 report, the smallest number in 24 years of reports.
“We’ve seen, overall, really positive trends in the cleanup of ozone pollution across the United States,” Barrett said.
Particle pollution, by contrast, has trended in the opposite direction.
The most dangerous episodes of particle pollution, coded maroon and categorized as hazardous to the entire population, were unknown between 2002 and 2014, the Lung Association found.
In the years since, maroon warnings in American counties have become a reality: 74 incidents in 2020 and 73 in 2021, based on three-year averages.
Purple warnings for particle pollution, the next-worst category, signaling “very unhealthy” air, increased from 10 in 2016 to 113 in 2021.
While ozone pollution has been trending downward almost everywhere, particle pollution is surging in some Western communities and zigzagging in others, largely because of wildfires.
The San Francisco metropolitan area reported an average of 23.5 high-particle days in the three-year span ending in 2021. That’s about twice as many bad-air days as in the mid-2000s, a low ebb of particle pollution in the city.
Sacramento had 20.8 days of high particle pollution from 2019-21, the report found, compared to a low of 3.7 days of unhealthy air from 2010-12.
“As climate conditions are becoming more and more frequently ripe for catastrophic and uncontrolled wildfires, the associated smoke exposures are really ramping up,” Barrett said.
When considering ozone and particle pollution, the State of the Air report found 120 million Americans live in communities with failing grades for unhealthy air. More than 60 million people live in counties with failing grades for dangerous spikes in particle pollution, the largest number reported in the past 10 years.
With ozone levels falling, air quality activism increasingly focuses on the unequal socioeconomic impact of pollution. The Lung Association report found, for example, that people of color were nearly four times as likely as white people to live in counties with failing grades across three broad pollution measures.
“On average, Black and brown communities are more likely to breathe polluted air,” said Marshall of the University of Washington.
Marshall and his colleagues found race is a stronger predictor than income of exposure to bad air. A recent report in The Guardian, drawn from their work, found urban neighborhoods suffering the worst pollution were “overwhelmingly the same places where Black and Hispanic populations live.”
The worst pockets of urban air pollution include South Los Angeles, Chicago’s South and West sides and neighboring swaths of northwest Indiana.
“Warehouses are being built in areas that are predominantly Latino, Black, immigrant,” said Eloise Gómez Reyes, a Democrat who serves as majority leader in the California State Assembly. “It’s the trucks coming in and out. It’s the diesel particulate matter being spewed into the air.”
Black and Hispanic people are more likely to live near expressways and other freight corridors, air quality research shows. South of downtown Chicago, Black and Hispanic residents have long lived in the shadow of steel mills and other industrial plants.
“There’s a big issue of environmental justice in Chicago,” said Vishal Verma, an assistant professor of environmental engineering at the University of Illinois Urbana-Champaign. “It’s a highly segregated city, in terms of air pollution.”
The Biden administration has proposed to tighten federal standards for fine particle pollution, citing its inordinate impact on low-income families and communities of color. The proposal would lower the federal standard for fine particles to 9 or 10 micrograms per cubic meter of air, from a current standard of 12 micrograms.
Fine particles emitted by vehicles, factories and fires can travel deep into the lungs and are linked to asthma, heart attacks and early death. Federal officials estimate stricter standards could prevent up to 4,200 premature deaths a year.
In Houston, where the air is much cleaner now than 20 or 30 years ago, all air pollution monitors register fine particle pollution below the federal 12-microgram threshold, Cohan said. If the standard were lowered to 9 or 10 micrograms, he said, parts of the city would fail the test.
“You have dozens and dozens of counties in that middle ground, that meet the current standard but would violate the new standard,” he said, including large swaths of California, Oregon and Washington.
“Health effects research has shown us that there is damage, and even deaths, that can occur if pollution meets the current standard.”
