These are the US cities with the worst air pollution

Source: 
The New York Post
Julia Musto

The US cities with the worst air pollution levels were ranked in a recent report, which concluded that more than 58 million Americans experienced more than 100 days of polluted air in 2020. 

The research released by non-profit Environment America Research & Policy Center, Frontier Group and US PIRG Education Fund at the beginning of the month, showed the California San Diego-Chula Vista-Carlsbad area with the most number of days with ozone and PM 2.5 (particulate matter 2.5) AQI (Air Quality Index) over 50.