California Air Quality Sees Improvements, Several Cities Remain in “Worst” Lists for Ozone and Particle Pollution Finds American Lung Association ‘State of the Air’ 2020 Report

Editor’s Note: The full report, as well as trend charts and rankings for metropolitan areas and county grades are available at

The American Lung Association’s 2020 “State of the Air” report found California cities continue to dominate the rankings of the nation’s most widespread air pollutants—ozone and particle pollution—both of which can be deadly. In fact, the report found Los Angeles and other California cities among the ten US cities most impacted by ozone, while five California cities are on the Top 10 list for most impacted by unhealthy particle pollution days, including many that experienced their worst ever periods for particle pollution due to historic wildfires.  

The Lung Association’s annual air quality “report card” tracks Americans’ exposure to unhealthful levels of particle pollution and ozone during a three-year period. Once again, the report found that nearly half of all Americans were exposed to unhealthy air in 2016-2018. In California, over 38 million residents live in counties where ozone or particle pollution placed their health at risk, including those who are more vulnerable to the effects of air pollution such as older adults, children and those with a lung disease. Communities of color and lower-income communities also face disproportionate burdens of unhealthy air.

“This year marks the 50th anniversary of the Clean Air Act, which has been responsible for dramatic improvements in air quality. But climate change is making the job of cleaning our air that much more difficult, and putting millions more lives at risks,” said American Lung Association Clean Air Advocacy Director, Will Barrett. With nearly half of Americans – and almost all Californians - affected by unhealthy air, our ‘State of the Air’ report shows that because of increased heat and wildfires driven by climate change, we have to work harder at protecting public health - especially for our most vulnerable and highly polluted communities.”

Each year the “State of the Air” provides a report card on the two most widespread outdoor air pollutants, ozone pollution, also known as smog, and particle pollution, also called soot. The report analyzes particle pollution in two ways: through average annual particle pollution levels and short-term spikes in particle pollution. Both ozone and particle pollution are dangerous to public health and can increase the risk of premature death and other serious health effects such as asthma attacks, cardiovascular damage, and developmental and reproductive harm. Particle pollution can also cause lung cancer, and new research links air pollution to the development of serious diseases, such as dementia.

This year’s report covers 2016, 2017 and 2018, the years with the most recent quality-assured data available collected by states, cities, counties, tribes and federal agencies. Notably, those three years were among the five hottest recorded in global history and witnessed five of the most destructive wildfires in California history. Rising temperatures lead to increased levels of ozone pollution. Changing climate patterns also fuel wildfires and their dangerous smoke, which increase particle pollution. Ozone and particle pollution threaten everyone, especially children, older adults and people living with a lung disease. Although this report does not cover data from 2020, amid the COVID-19 pandemic, the impact of air pollution on lung health is of heightened concern. Learn more about that at

Ozone Pollution in California
Despite decades of major improvements, California still has many of the most ozone-polluted cities in the United States and, while improvements continue, several cities saw increased unhealthy ozone days in 2016-2018. Compared to the 2019 report, the three most polluted cities in the United States – Los Angeles, Bakersfield and Visalia – each experienced more unhealthy days of high ozone in this year’s report.

“Ozone pollution can harm even healthy people, but is particularly dangerous for children, older adults and people with lung diseases like COPD or asthma,” said Barrett. “Breathing ozone-polluted air can trigger asthma attacks in both adults and children with asthma, which can land them in the doctor’s office or the emergency room. Ozone can even shorten people’s lives.”

This report documents that warmer temperatures brought by climate change are making ozone more likely to form and harder to clean up. Significantly more people suffered unhealthy ozone pollution in the 2020 report than in the last three “State of the Air” reports.

Particle Pollution in California
Californians face significant particle pollution impacts due to diesel engines, wood stoves and, increasingly, wildfires that blanket wide areas in harmful smoke. Wildfires across the state in 2018 drove major increases in particle pollution exposures, with all major metropolitan areas experiencing increases in the number of unhealthy days. The 2018 Camp Fire in Butte County was one of the deadliest in U.S. history, killing 85 people and destroying the town of Paradise.

 “State of the Air” 2020 found that 40 of the 44 counties with particle monitors saw increased short-term particle impacts, including several experiencing their highest number of particle pollution days in this year’s report. Similarly, year-round particle pollution levels increased in 37 of the 42 California counties with monitoring data for annual levels.

 Several cities, including Chico, Redding-Red Bluff, Santa-Maria-Santa Barbara and Salinas saw their worst ever air quality levels for particle pollution days in the history of the report. “Particle pollution can lodge deep in the lungs and can even enter the bloodstream. It can trigger asthma attacks, heart attacks and strokes and cause lung cancer,” said Barrett.  

“Once again, this year’s report includes data from some of the most severe wildfire seasons in California history, along with continued detrimental effects to air quality from diesel trucks and ships,” Barrett said. The American Lung Association strongly encourages lawmakers and citizens alike to join our advocacy efforts for cleaner fuel policies, including zero emission trucks and ensuring clean-up at California’s ports. These policies are critical to cleaning up the air and fighting climate change.

“We all have the right to breathe clean, healthy air. The 50th anniversary of the Clean Air Act serves as a critical reminder that Americans breathe healthier air today because of this landmark law and policies that have followed,” said Barrett “At the same time, this year’s report shows that we must stand up for clean air – and support science-based standards that protect public health. California has clear pathways to healthier air - we know transportation pollution is at the heart of our clean air challenges – we need a widespread transition to zero emission cars, trucks and buses and a shift in our travel choices toward more transit and pedestrian friendly communities that reduce traffic and harmful pollution.

While the report examined data from 2016-2018, this 21st annual report also provides air pollution trends back to the first report. Learn more about individual city rankings, as well as air quality across California and the nation, in the 2020 “State of the Air” report at

State of the Air 2020 Rankings
Most Polluted Cities for Ozone

  1. Los Angeles-Long Beach (incl. Inland Empire)
  2. Visalia
  3. Bakersfield
  4. Fresno-Madera-Hanford
  5. Sacramento-Roseville
  6. San Diego-Chula Vista-Carlsbad
  7. Phoenix-Mesa, AZ
  8. San Jose-San Francisco-Oakland
  9. Las Vegas-Henderson, NV
  10. Denver-Aurora, CO

Most Polluted Cities for Short-Term Particle Pollution

  1. Fresno-Madera-Hanford
  2. Bakersfield
  3. San Jose-San Francisco-Oakland
  4. Fairbanks, AK
  5. Yakima, WA
  6. Los Angeles-Long Beach (incl. Inland Empire)
  7. Missoula, MT

7.   Redding-Red Bluff, CA
7.   Salt Lake City-Provo-Orem, UT
10.   Phoenix-Mesa, AZ

Most Polluted Cities for Year-Round Particle Pollution

  1. Bakersfield
  2. Fresno-Madera-Hanford
  3. Visalia
  4. Los Angeles-Long Beach (incl. Inland Empire)
  5. San Jose-San Francisco-Oakland
  6. Fairbanks, AK
  7. Phoenix-Mesa, AZ
  8. El Centro, Pittsburgh-New Castle-Weirton, PA-OH-WV – tie
  9. Detroit-Warren-Ann Arbor, MI
For more information, contact:

Bo Smith
[email protected]

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