Most ozone-polluted cities in the United States
The most ozone-polluted city in the United States is Los Angeles-Long Beach, with an average of 180 days with high ozone in the years 2019, 2020, and 2021. Many of the most ozone-polluted cities in the U.S. are in California.
Ground-level ozone is formed in the atmosphere when nitrogen oxides (NOx) and volatile organic compounds (VOC) react with each other in sunlight and hot temperatures. Human-made sources of NOx include power plants and motor vehicles. California has some of the largest transportation emissions in the U.S., so it is perhaps unsurprising that many of the most ozone-polluted cities are in this state.
Ground-level ozone is formed in the atmosphere when nitrogen oxides (NOx) and volatile organic compounds (VOC) react with each other in sunlight and hot temperatures. Human-made sources of NOx include power plants and motor vehicles. California has some of the largest transportation emissions in the U.S., so it is perhaps unsurprising that many of the most ozone-polluted cities are in this state.
