Los Angeles has once again emerged as the US city with the worst air pollution, topping a new national ranking that paints a worrying picture of deteriorating air quality across several American urban centres. The latest annual assessment by the American Lung Association, cited in a new report, shows a strong concentration of the country’s most polluted cities in California, while major metropolitan hubs in Arizona, Texas, Colorado and beyond have also featured prominently.
The report, which analysed ozone and particulate pollution trends, ranked Los Angeles-Long Beach as the most polluted metro region in the country, followed by California’s Visalia and Bakersfield-Delano. Phoenix-Mesa in Arizona was placed fourth, making it the highest-ranked city outside California, while Fresno-Hanford-Corcoran rounded out the top five. Houston-Pasadena secured sixth place, underscoring how pollution challenges are not confined to the West Coast.
Other cities on the list include San Diego-Chula Vista-Carlsbad, Denver-Aurora-Greeley, Dallas-Fort Worth, El Centro, Las Vegas-Henderson, New York-Newark, Salt Lake City-Provo-Orem, San Jose-San Francisco-Oakland and Chicago-Naperville. The rankings indicate that both sprawling industrial metros and regions affected by climate-linked pollution events are facing worsening conditions.
Experts cited in the report linked rising ozone levels and particle pollution to a combination of factors, including wildfires, higher temperatures, traffic emissions and industrial activity. In California, recurring wildfire smoke has continued to undermine air quality gains made over previous decades. In Houston, emissions linked to petrochemical industries have contributed to persistent pollution concerns, while rapid urban growth and transportation emissions have added to the burden in cities such as Phoenix and Denver.
The findings have also raised concerns over the health impact on children. According to the report, around 33.5 million children in the United States — nearly 46% of those under 18 — live in areas that received failing grades for at least one key measure of air pollution. More than seven million children are reportedly living in places that failed across all major pollution categories, highlighting the scale of exposure.
Researchers warned that air pollution in the US is no longer a challenge limited to traditionally smog-prone regions. Climate change-driven heat, worsening wildfire seasons and pollution from expanding industrial infrastructure are contributing to a broader national problem. Some analysts have also pointed to policy rollbacks and gaps in emissions control as factors threatening previous progress made under clean air regulations.
California’s dominance in the rankings remained one of the most striking takeaways, with multiple cities in the state accounting for a majority of the worst-affected urban regions. Los Angeles, long synonymous with smog struggles, retained its unenviable distinction despite years of pollution control efforts.
The report has renewed calls for stronger environmental safeguards, tighter emissions regulations and accelerated clean-energy transitions as pollution risks intensify. With millions of Americans, including children, living in unhealthy air conditions, the findings underscore that air quality remains a major public health challenge in the United States.
