(NEXSTAR) – Air quality has been a frequently discussed topic this summer as Canadian wildfire smoke has continued to affect portions of the U.S., and could worsen as wildfires spring up in the West. Other states have suffered poor air quality amid hot and humid weather conditions. 

Smoke and humid conditions aside, some areas of the U.S. frequently find themselves with poor air quality. 

Earlier this year, the University of Wisconsin Population Health Institute released its 2023 County Health Rankings and Roadmaps report, which is meant to raise awareness about factors that can impact health outcomes and disparities nationwide.

Researchers use numerous data points to determine the length and quality of life on a state-by-state basis. Among those factors is the physical environment of communities throughout the U.S., including air quality. 

To determine the air quality of states and counties, researchers reviewed air pollution data from monitors and modeled estimates, they explain. That includes data from the Environmental Protection Agency’s Air Quality System, and, for areas without “sufficient air quality monitoring,” a model is used to estimate air pollution. 

Researchers then calculated the annual average measures of PM2.5 in both states and counties. This is fine particulate matter that is comprised of particles 2.5 microns or smaller in diameter. PM2.5 pollution, found in outdoor air, is often from the emissions caused by the “combustion of gasoline, oil, diesel fuel or wood,” the California Air Resources Board explains. 

The particles can travel deep into our lungs, causing tissue damage and lung inflammation. Short-term exposure to PM2.5 has been linked to premature death, hospital admissions, bronchitis, asthma attacks, and other respiratory and cardiac problems, the CARB explains. It’s often “associated with the greatest proportion of adverse health effects related to air pollution, both in the United States and world-wide.”

Based on the 2019 data researchers reviewed, it was Georgia that, as a whole state, had the worst PM2.5 pollution, reporting an average daily rate of 9.4. Nearby Alabama came in second at an average daily PM2.5 at 9.3, followed by Mississippi at 8.9. Densely populated states many may expect to have the worst air – like California or New York – ranked relatively low on the list: California had an average of 7.1 PM2.5 while New York had a 6.9. 

Alternatively, Hawaii and Wyoming tied for the lowest daily average PM2.5 at 3.6, followed by Nevada at 4.2. Nationwide, the average daily PM2.5 was nearly 7. 

Though its state ranked relatively low, California’s San Bernardino County had the highest daily average PM2.5 at 15.6, followed closely by Alaska’s Fairbanks North Star Borough at 15.5. These were the only two communities with PM2.5 rates above 15. 

The majority of the 10 counties at the top of the list are Californian: San Diego, Los Angeles, Kern, Tulare and Riverside. Rounding it out was Pennsylvania’s Allegheny, Michigan’s Wayne, and Indiana’s Marion. 

Montana’s Gallatin County had the lowest daily average PM2.5 at 0.9, researchers found. It was far better than the second-lowest county, Wyoming’s Converse. Wyoming made up the majority of the counties at the lower end of the list, with Campbell, Sublette, Niobrara, and Park counties also landing within the coveted spots. Also among the least polluted were Arizona’s Apache, South Dakota’s Custer, Hawaii’s Kauai, and New Mexico’s Santa Fe counties. 

None of the lower 10 had a daily average PM2.5 above 3. 

It’s important to note that PM2.5 concentrations are estimates. Air quality can change frequently and isn’t always consistent. It can vary even within a county, and by season. The current air quality in your area can be checked on the EPA’s website. 

Earlier this year, the American Lung Association estimated that more than one-third of Americans are exposed to potentially life-shortening air pollution. As part of its 2023 State of the Air report, the ALA said that roughly 119.6 million Americans live in areas the association assigned a failing grade to for particle or ozone pollution. 

The ALA ranked Bakersfield, California as the city with the worst year-round particle pollution and short-term particle pollution. Los Angeles-Long Beach had the worst ozone pollution — Bakersfield came in third on that list. 

The ALA also gave San Bernardino County a failing grade for ozone and particle pollution. Alaska’s Fairbanks North Star Borough received a failing grade for particle pollution as well, but received an “A” for ozone pollution. Despite its low PM2.5, Montana’s Gallatin County also got an “F” for 24-hour particle pollution, while Wyoming’s Converse County got a “D” for its ozone pollution.

The Hill’s Zack Budryk contributed to this report.