‘Most polluted': These Arizona counties have some of the worst air quality in the country
Maricopa and Pinal counties have some of the most-polluted air in the country, according to a report by the American Lung Association, continuing a trend of worsening ozone pollution that has puzzled local officials and regulators in recent years.
The Lung Association's annual 'State of the Air' report, released April 23, shows worsening ozone levels and concerning levels of fine particulate pollution in the Phoenix area. The report measured those two pollutants in every U.S. county between 2021-2023.
Pinal and Maricopa counties were among the 26 counties that received 'failing grades' in all three categories — a group called the "most polluted places to live" in the report.
"We want people to be aware of the air they're breathing and the quality of that air," said JoAnna Strother, ALA's senior director of advocacy.
Metro Phoenix now has the fourth-worst ozone pollution in the country, up from fifth place in 2024. The region is ranked 20th for year-round particulate pollution and received a 'failing grade' on its short-term particulate pollution levels.
The report found that 84% of Arizonans live in communities with unsafe levels of at least one pollutant, nearly twice the national percentage of 46%. Both ozone and fine particulate pollution can harm human health, especially for people who work outdoors or suffer from chronic heart or lung conditions.
Across the nation, the report showed more people living with unhealthy air quality than at any other point in the previous decade. The report saw a continued degradation of national air quality levels over the last 10 years, indicating a 'distressing reversal' of previous successes.
What's happening? Ozone pollution is usually a summer problem in Phoenix. This year, it lingered into fall
Using regulations under the Clean Air Act, the U.S. has slashed its air pollution levels, but the report states that climate change is adding new challenges to those victories. The report suggests that wildfires and high temperatures caused much of the worsening air quality noticed in recent reports.
'Extreme heat, drought, and wildfires are all contributing to air pollution across the country but especially here in Arizona and the West," Strother said. "We've seen our changing climate start to almost undo some progress we've made since the Clean Air Act has been in place."
The report states that efforts to clean up ozone-forming emissions in western states have improved air quality, but wildfires and heat waves may have counteracted that success. Across the country, the 2025 State of the Air report showed a rare rise in ozone levels, with previously 'untroubled' areas now receiving bad ozone grades.
Arizona — and Phoenix in particular — struggles with ozone pollution because of sunny, windless days, proximity to western wildfires, and a high reliance on cars. Other sunny western states also ranked high for ozone levels: California, Colorado and Texas all had multiple metro areas in the top 10 for ozone pollution. Arizona also receives ozone-forming emissions from international sources, such as Mexico and China, and other states, such as California.
While stratospheric ozone protects the Earth from ultraviolet radiation, ozone is a health risk at ground level. Chemicals in car exhaust, natural emissions from vegetation and fumes from gasoline pumps and wet house paint all combine in the atmosphere to create ozone. Emissions from wildfires can be components in ozone, while sunlight and a lack of wind create the right conditions for ozone to form.
Regulations: The EPA just hit pause on upping Phoenix's air pollution status. What happens next?
Metro Phoenix has teetered in and out of compliance with the federal government's changing air quality standards for decades. Until 2017, ozone levels were declining in the region as local officials focused on reducing congestion on regional freeways to push down emissions and improve ozone levels, among other measures.
But in recent years, metro Phoenix has seen a strange trend: Human-caused, regional emissions are decreasing, but data collected by ground-level regional monitors show ozone levels are ticking upward.
The Environmental Protection Agency halted the Phoenix area's expected re-designation to the "serious" ozone nonattainment category on April 10. That category could have meant more restrictions for the Phoenix area, including some that local officials feared would harm the local economy. A research team assembled by the Arizona Department of Environmental Quality is conducting field studies to understand the sources and possible solutions for rising ozone levels.
Beyond ozone, the Phoenix area also struggles with particulate pollution — tiny bits of solids and liquids that fill the air from factories, power plants, gasoline engines, wildfires and wood stoves. The Phoenix metro area ranked 28th-worst in the nation for short-term particle pollution and 20th for year-round particle pollution in the State of the Air report, both slight improvements from their rankings in the 2024 report.
For Strother, the two pollutants form a combined health risk for over 1 million Phoenix-area residents. Ozone inflames and damages airways and lungs, increasing vulnerability to pulmonary infections and exacerbating respiratory diseases like asthma.
Recent research has also shown that high ozone levels send more people to the hospital for heart attacks and strokes. Scientists also say ozone has growing linkages to neurological and fertility issues. Particle pollution can be more serious, with numerous scientific studies linking it to premature death in people with heart or lung disease. It can also cause a range of nonfatal but disabling heart and lung conditions and has been linked to lung cancer.
"Ozone acts as sunburn to the lungs, while fine particulate matter can lodge deep down in the lungs," Strother said.
Dust pollution: After months of dry weather, could strong winds spread valley fever fungus in Phoenix?
A significant chunk of the Phoenix area's population is particularly vulnerable to these health risks. The region is home to almost 1 million senior citizens (age 65 and up) and roughly half a million individuals dealing with asthma. Hundreds of thousands of residents also deal with cardiovascular disease and chronic obstructive pulmonary disease, according to the report.
Strother encouraged Phoenix area residents to check local air quality reports and forecasts before going outside. ADEQ issues daily air quality forecasts with hourly outlooks, available at its website. Maricopa County also posts air quality updates on its website.
"We live in a beautiful state where people like to do a lot of activities outdoors, so paying attention to air quality index and forecast will help people to protect themselves," Strother said.
The American Lung Association is a Chicago-based nonprofit dedicated to improving lung health. It has released its State of the Air report each year since the year 2000.
Austin Corona covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to austin.corona@arizonarepublic.com.
Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust.
Sign up for AZ Climate, our weekly environment newsletter, and follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook and Instagram.
This article originally appeared on Arizona Republic: Metro Phoenix ozone problem worsens, now 4th worst in country
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