The American Lung Association "State of the Air" report shows California is home to seven of the top 10 most ozone-polluted cities in the nation, with Los Angles topping the list.
Bakersfield and Merced are tied for having the most soot pollution.
But this year's report also shows improvement in air quality.
California had fewer unhealthy ozone days since the Lung Association began their report 14 years ago.
"If you look at the snapshot, it reminds us that we have very profound air pollution problems and the public's health is very seriously affected," says Bonnie Holms-Gen, with the American Lung Association in California.
"If we look at the trends over time, we see we've made a lot of progress."