10 Worst Smog Cities in America

2020 is the 50th anniversary of the Clean Air Act, a law passed to improve air quality. But many U.S. cities, mostly in California, still have unhealthy levels of smog, according to the American Lung Association’s annual State of the Air rankings. Warming trends from climate change increase ozone and worsen air quality.

The Denver-Aurora metro area’s 3.5 million residents include more than 300,000 people with asthma. High levels of ozone, also called smog, irritate your lungs and trigger asthma. While ranking 10th among cities for smog, Denver’s air has improved over the years. There were three fewer annual high ozone days there in 2020 compared to 1996.

While the Las Vegas-Henderson metro area had 17 fewer smoggy days in 2020 than in 1996, the city still ranked ninth for high ozone. It’s also home to 342,326 seniors out of a total population of 2.2 million. Older adults are more at risk for smog-related breathing problems. The state of Nevada has set lofty goals to cut ozone to zero or near-zero by 2050.

The Bay Area’s geography may make it more likely for air pollution to travel from one valley to another. On any given day, the 9.6 million residents of San Francisco, San Jose, and Oakland can check for alerts that unhealthy air may drift their way over the next 5 days. High teleworking rates in spring 2020 led to a 26% drop in CO2 emissions during what is a typically smoggy season for the region.

Dry, hot Phoenix is home to more than 250,000 people with COPD, a lung disease worsened by air pollution. One thing driving high smog may be that as many as 89% of residents commute to work daily alone by car or motorcycle. A local program to encourage cleaner commutes shows that 6% now bicycle one day a week instead.

While the San Diego-Chula Vista-Carlsbad metro area has 52 fewer high smog days each year now than in the 1990s, its ozone levels are still sixth highest in the U.S. The community is also home to 866,445 residents who are current or former smokers. They’re at higher risk for lung cancer due to the toxic blend of high smog levels in the city and exposure to tobacco.

The Sacramento-Roseville metro area’s yearly number of high ozone days held steady over the past year, but its air particle pollution rose. That netted California’s capital low marks for air quality. While smog levels are highest in summer, Sacramento asks residents to not burn wood in fireplaces, stoves, or firepits in winter to improve air quality.

The Fresno-Madera-Hanford metro area only has 1.3 million residents. Ozone levels have dipped slightly in the past few years, but the area still fails to meet national air quality standards. One reason is its location in the bowl-shaped San Joaquin Valley, which traps emissions from millions of motor vehicles driving in the region.  

Bakersfield sits in California’s smog-trapping San Joaquin Valley. But one of its sources of air pollution may be oil and gas production. Some Bakersfield plants have violated the Clean Air Act for greenhouse gas emissions. And the city has almost 40,000 residents with heart disease. Smoggy air can increase their risk of a deadly heart attack.

Visalia ranks second among U.S. cities for ozone and third for year-round air particle pollution. Visalia and Tulare County, located in California’s San Joaquin Valley, are home to more than 1 million cattle, over twice the human population. Industrial dairies in Visalia play a big part in its air pollution, which includes high levels of methane emissions.

2020’s smog capital is the Los Angeles-Long Beach metro area, home to 18.7 million people. High ozone levels in the busy city may result from the many cars and trucks that clog highways and byways, but its famous sunny weather doesn’t help. Sunshine ramps up smog levels, aggravating symptoms for the 1.5 million residents who have some form of asthma.

This California city reclaims the No. 1 spot when it comes to year-round particle pollution. Bakersfield led this category from 2016 to 2018. Oil and gas production facilities may also play a role, along with its location in the San Joaquin Valley, which captures pollution and holds it in.

Four cities ranked highest in the U.S. for three measures of clean air: ozone, year-round particle pollution, and short-term particle pollution in 2020. They also repeated this honor two years in a row. That’s good news for residents: People who live in cities with good air quality may live longer, healthier lives.

Bangor’s ranking among America’s top clean air cities may be due in part to its many greenspaces and public parks. It’s home to the Rolland F. Perry City Forest, which boasts more than 100 miles of nature trails.

Burlington, a city of 279,000 residents near the Canadian border, has received A grades for its clean air. One reason may be that Burlington has fewer automobiles and less heavy industry, two big sources of air pollution.

Out of 204 metropolitan areas in the State of the Air report, Honolulu ranked 204th for annual particle pollution levels. That means tropical Honolulu, home to nearly 1 million people, has very clean air. Lots of year-round wind and rain, and a lack of heavy industry, play a role.

The only Southern city on the clean air list is Wilmington, home to 294,000 residents. This beach community on the Atlantic Ocean ranks near the bottom for annual particle pollution levels. North Carolina is also a hotspot for clean power research, with billions being invested to develop solar and wind energy projects.