Year-Round Particle Pollution Trends

Nearly 18.8 million people live in the 17 counties where year-round particle pollution levels do not meet the national air quality standard, and that receive a failing grade in “State of the Air” 2023. This is 1.5 million fewer people living in counties with unhealthy levels of year-round particle pollution compared to last year’s report, continuing a slight downward trend over the past four years. 

By its nature, the year-round measure of average particle pollution is not as volatile as the daily measure. Changes over time may look smaller, but because they represent recurring exposures over many days and weeks, seemingly minor differences can have a big impact on public health. The 25 most polluted cities for year-round particle pollution continued the worsening trend of recent years, but only slightly, by an average of less than 0.1 micrograms per cubic meter (from 12.2 to 12.3 µg/m3).   

Fourteen cities suffered worse year-round levels during 2019-2021 than in last year’s report, with two reporting their worst ever: Sacramento, California and Yakima, Washington for its second consecutive year. In contrast, nine of the 25 most polluted cities had lower year-round levels this year. Although none of the cities with improved levels achieved their best ever in “State of the Air” 2023, Fresno and San Jose-San Francisco-Oakland, California did post their second-best results. 

New on the worst 25 list this year were Birmingham, Alabama; Louisville, Kentucky; and Laredo, Texas. Philadelphia, Pennsylvania; Redding-Red Bluff, California; Shreveport, Louisiana; and St. Louis, Missouri all improved enough to leave the list. 

When Rev. Jenny Wynn wakes up in the morning, she checks two things – the weather and the air quality. As someone with asthma, high air pollution days force her to limit the time she spends outdoors.

Wynn says she often has to consider whether eating a meal outside or running errands on a day with poor air quality might trigger an asthma attack.

“In Phoenix, it seems there are more days than not with bad air quality,” said Wynn, Senior Minister at First Christian Church in Scottsdale, Arizona.

To help improve air quality in the community over the long term, she would like to see greater investments in public transportation and green-energy vehicles.

“As a preacher,” Wynn says, “I’m always preaching to people that when you’re voting or making decisions, you shouldn’t be doing it for your immediate future but thinking generationally, thinking 50+ years out.”

Rev. Jenny Wynn
First Christian Church Scottsdale

Unlike the worst 25 cities for the daily measure of particle pollution, the worst 25 cities for annual particle pollution were more distributed around the country. Although cities most affected by western drought and wildfires, including eight in California, three in Oregon, and three others in Alaska, Arizona, and Washington, still represented the largest share, cities with high power plant emissions as well as local industrial and mobile sources of year-round particle pollution continued to show up on this list. These included Indianapolis, Detroit, Pittsburgh, Augusta, Houston, Cincinnati, Birmingham, McAllen, Louisville, Chicago and Laredo.  

For the year-round average levels of fine particles, all but nine of the cities on the worst 25 list met the current national air quality standard and got a passing grade in “State of the Air.” However, evidence shows that no threshold exists for harmful effects from particle pollution, even below the official standard. Until the standard is strengthened, a passing grade does not mean that the air is safe to breathe. See Recommendations for Action.

National Air Quality Standards and the Air Quality Index: Sending the Wrong Message

The Air Quality Index, or AQI, is a well-designed, easy-to-understand resource to communicate air quality information to the public. Since its inception in 1999, the AQI has become embedded in weather and air quality forecasting. It is used every day to help people plan their outdoor activities and make decisions about when they need to take measures to protect themselves from air pollution that could put their health at risk. It is also the basis of the methodology for grading used in “State of the Air.”

The AQI’s familiar color categories are set according to the levels of air pollution regulated by the National Ambient Air Quality Standards. The breakpoint between the Moderate (code yellow) and Unhealthy for Sensitive Groups (code orange) levels of concern is tied to the national standard. Air quality at levels above the standard is considered unhealthy and triggers increasingly strong health warnings in the AQI. Anything below the standard is considered moderate or good, and the corresponding AQI messages say that the air quality is acceptable.

The AQI only works as the public health tool it is intended to be if the standards accurately reflect what is known about the health harm of ozone and particle pollution. Regrettably, both of these standards are currently inadequate, and the AQI is therefore presenting a misleading picture of health risks. Research has shown that on code yellow days, when all but “unusually sensitive individuals” are told it’s a good day to be active outside, millions of people, including children and the elderly, are at risk of a range of health harms from air pollution, including death.

Setting more protective national standards for ozone and fine particles will not only drive pollution cleanup, but also result in an updated air quality index that will provide more accurate information so families, teachers, coaches and others can make decisions to reduce or prevent exposures to pollution levels that threaten health.

See Recommendations for Action for more information.


Did You Know?

  1. More than 4 out of 10 people live where the air they breathe earned an F in State of the Air 2020.
  2. 150 million people live in counties that received an F for either ozone or particle pollution in State of the Air 2020.
  3. More than 20.8 million people live in counties that got an F for all three air pollution measures in State of the Air 2020.
  4. Breathing ozone irritates the lungs, resulting in something like a bad sunburn within the lungs.
  5. Breathing in particle pollution can increase the risk of lung cancer, according to the World Health Organization.
  6. Particle pollution can also cause early death and heart attacks, strokes and emergency room visits for people with asthma and cardiovascular disease.
  7. Particles are smaller than 1/30th the diameter of a human hair. When you inhale them, they are small enough to get past the body's natural defenses.
  8. Ozone and particle pollution are both linked to increased risk of lower birth weight in newborns.
  9. Do you live near, or work on or near a busy highway? Pollution from the traffic may put you at greater risk of harm.
  10. People who work or exercise outside face increased risk from the effects of air pollution.
  11. Millions of people are especially vulnerable to the effects of air pollution, including infants, older adults and people with lung diseases like asthma.
  12. People of color and those earning lower incomes are often disproportionately affected by air pollution that put them at higher risk for illnesses.
  13. Air pollution is a serious health threat. It can trigger asthma attacks, harm lung development in children, and can even be deadly.
  14. You can protect your family by checking the air quality forecasts in your community and avoiding exercising or working outdoors when the unhealthy air is expected.
  15. Climate change enhances conditions for ozone to form and makes it harder to keep ozone from forming.
  16. Climate change increases the risk of wildfires that spread particle pollution and ozone in the smoke.
  17. This Administration is trying to roll back or create loopholes in core healthy air protections under the Clean Air Act. The Lung Association opposes these actions that will add pollution to the air we breathe.
  18. Cutting air pollution through the Clean Air Act will prevent at least 230,000 deaths and save $2 trillion annually by 2020.
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