ALA State of the Air: 4 in 10 Americans Suffer from Unhealthy Air Pollution Levels


The 2021 annual report finds that Los Angeles remains the most polluted US city, while negative impacts of climate change and COVID-19 are both linked to increased pollution rates.

The 2021 State of the Air Report from the American Lung Association (ALA) found that more than 40% of people in the United States live in an area with an unhealthy level of air pollution, while people of color are 3 times more likely to breathe polluted air compared to White people.

The annual State of the Air reports on the most widespread air pollutants, including ozone and fine particulate matter. Data is collected from monitoring sites across the United States and then calculated by the ALA, to rank cities and counties with the most pollution.

The ALA stated that while the data show some progress in cleaning up air pollution, the 3 assessed years (2017, 2018, and 2019) in their 2021 report rank among the 6 hottest years on record.

Polluted air can trigger serious effects, with new data showing it may even worsen outcomes of COVID-19 among infected persons.

Particle pollution is linked to triggers of asthma and cardiovascular (CV) events including heart attacks, as well as dementia. Ozone pollution effects have been linked to asthma attacks, shortened life and an increased risk of metabolic disorders.

Analysis of Study


The data on air quality in the study was obtained from the US Environmental Protection Agency (EPA) Air Quality System (AQS).

Investigators used AQS data from 2017 – 2019 to calculate daily eight-hour maximum concentration for each ozone monitoring area and the highest maximum in each county was identified. The national ambient air quality standard for ozone was reflected by a 70 parts per billion (ppb) measure over an eight-hour period.

The daily maximum data of an eight-hour average is obtained from 17 consecutive eight-hour averages, beginning with a 7:00 A.M. to 3:00 P.M. period and ending with the 8-hour period from 11:00 P.M. to 7:00 A.M.

The ALA investigators then identified the air quality of each day in the observed counties, as orange (Unhealthy for Sensitive Groups), red (Unhealthy), or purple ( Very Unhealthy).

Short-Term Particle Pollution

The team identified the maximum daily 24-hour AQS coarse particle (PM) concentration for the years 2017 – 2019 and data was compiled into 24-hour average PM values.

The standard concentration for moderate air quality index levels is 12.1 µg/m3 to 35.4 µg/m3 n.

Investigators identified the number of days when the maximum of daily PM in each county occurred.

The ALA identified the number of days each county, with at ≥1 PM monitor, experienced air quality designated as orange (Unhealthy for Sensitive Groups), red (Unhealthy), purple (Very Unhealthy) or maroon (Hazardous).

For year-round particle pollution calculations, the EPA listed counties at 12 µg/m3 and were given grades of “pass.” Counties listed at or above 12.1 µg/m3 were given grades of “fail.” If data was insufficient, counties were given a grade of “incomplete.”

2021 Report

The report found more than 135 million Americans live in the 217 counties with monitors that capture unhealthy pollution levels.

The rate is nearly 15 million fewer people compared to last year’s report, but there was an increase of over 1 million people in areas with unhealthy levels of short-term particle pollution compared to last year.

Over 20 million people live in the 13 counties that fail all 3 measures, and 14 million (~70%) people in this group were people of color. People of color were also 61% more likely to live in a county with a failing grade for 1 pollutant and more than 3 times as likely to live in a county with a failing grade for 3 pollutants.

Los Angeles is the city with the worst pollution in the nation, remaining in this spot for all but 1 of the 22 years observed in the annual report.

Health Impacts

The data shows 3 out of every 8 Americans, or 123.2 million people, live in the 163 counties that received an “F” for ozone.

Investigators said the 135 million Americans who live in places with unhealthy levels of pollution are at risk of harm to their health, but some groups are more vulnerable to death and illness from exposure.

These groups included people experiencing poverty, with more 15.8 million people meeting the federal poverty definition living in a county with an “F” in at least 1 pollutant metric. Nearly 3 million people in poverty live in counties that failed all 3 measures.

Investigators additionally reported that 4.9 million children and 2.9 million seniors live in counties that failed all 3 pollutant measures.

Groups with underlying health conditions, including asthma, chronic obstructive pulmonary disease (COPD), lung cancer and CV disease, also experience high rates of exposure to pollutants.

Rates included 2.3 million children and 9.2 million adults with asthma, nearly 5.9 million people with COPD, more than 67,000 people with lung cancer, and nearly 10 million people with CV disease who live in a county that received a “F” for at least 1 measured pollutant.

More than 14.6 million Americans with a history of smoking live in counties that received an “F,” a group with a greater risk of premature death and lung cancer when subjected to long-term pollution exposure.

Ozone Risks

Ground-level ozone is formed in the lower atmosphere when a combination of pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), “cook” in sunlight. The chemical reaction can often spread miles from where it originated.

Data show ozone has a harmful effect on the respiratory system, both in short- and long-term exposure to the pollutant. Symptoms that present because of high ozone levels include chest tightness, coughing and shortness of breath, even in healthy adults.

More exposure to ozone can cause lasting damage to the respiratory system, such as new cases of asthma in children and the development of COPD.

Investigators also noted that inflammation and systemic stress caused by exposure to ozone can cause or worsen other diseases, such as metabolic disorders, brain inflammation, reproductive harm, and possible CV events, although evidence is mixed, according to the EPA.

Fine Particulate Matter

Particle pollution is a mixture of tiny particles of solids and liquids in the air, that originate from sources including factories, motor vehicles and equipment, as well as wildfires, woodburning, and NOx that forms into fine particles in the atmosphere.

In high pollution levels, particles are grouped by size as coarse, fine, and ultrafine, which can penetrate the air sacs of the lungs and the smallest are dispersed to other organs of the body. It is estimated that 48,000 premature deaths in the United States can be attributed to PM.

Short-term exposure to particle pollution that lasts from a few hours to days can result in death, even on the day the particle levels are high. Investigators said in many cases these deaths would not have occurred if the air was cleaner.

Other harmful effects include increased mortality rates in infants, increased hospitalization for CV disease and COPD, and increased severity of asthma attacks.

Year-round exposure to particle pollution can have serious negative effects in both infants and adults. Infants were found to have increased fetal mortality, reduced lung development and a higher likelihood of developing asthma.

Adults were linked to increased risk of CV and respiratory disease, higher likelihood of diabetes and lung cancer, and impaired cognitive functioning.

Investigators found communities that reduce their year-round particle pollution had a direct improvement in respiratory health.

The team also looked at other studies linking particle pollution and COVID-19, finding other data that a small increase in long-term average exposure to fine particle pollution was associated with an 11% increase in COVID-19 mortality.

Areas of Impact


In their list of 25 cities most polluted by ozone, the ALA found that the cities mostly remained the same as last year, with a cluster of cities in the west and southwest continuing to be the most polluted. California has 10, while the southwest takes up 8; the remaining 7 are east of the Mississippi River.

The top 5 cities most polluted by ozone are:

  1. Los Angeles-Long Beach, CA
  2. Bakersfield, CA
  3. Visalia, CA
  4. Fresno-Madera-Hanford, CA
  5. Phoenix-Mesa, AZ

In the list of 25 worst cities for short-term particle pollution, there were minor changes, with 13 cities improving since last year’s report with fewer unhealthy days. However, investigators said all the areas remain seriously polluted. These are the 5 worst cities for short-term particle pollution:

  1. Fairbanks, AK
  2. Fresno-Madera-Hanford, CA
  3. Bakersfield, CA
  4. San Jose – San Francisco – Oakland, CA
  5. Yakima, WA

In the list of the 25 cities with the unhealthiest year-round particle pollution levels, 13 worsened since from last year’s report. The 5 worst were:

  1. Bakersfield, California
  2. Fresno-Madera-Hanford, California
  3. Visalia, California
  4. Los Angeles-Long Beach, California
  5. Medford-Grants Pass, Oregon

Investigators also compiled a list of the nation’s cleanest cities, where the city must experience no high ozone or particle pollution days, as well as rank in the 25 cities with the lowest year-round particle pollution levels. The top 5 were:

  1. Burlington-South Burlington-Barre, Vermont
  2. Charlottesville, Virginia
  3. Elmira-Corning, New York
  4. Honolulu, Hawaii
  5. Wilmington, North Carolina


Investigators concluded that climate change remains one of the worst culprits in worsening air pollution. Western cities are experiencing record-breaking particle pollution due to wildfires caused by changing climate patterns, and as temperatures increase, so does ozone pollution.

As more affected groups are the hardest hit by an exposure to poor air quality, including increasing COVID-19 rates, the ALA looks to reduce air pollution to benefit respiratory health for the nation and years to come.

“This report shines a spotlight on the urgent need to curb climate change, clean up air pollution and advance environmental justice,” said ALA President and chief executive officer Harold Wimmer. “The nation has a real opportunity to address all three at once—and to do that, we must center on health and health equity as we move away from combustion and fossil fuels to clean, renewable energy.”

The 2021 State of the Air Report was published online by the American Lung Association.

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