The American Lung Association says Phoenix is fifth worst city in the nation for ozone pollution.
The group this week released its annual State of the Air report, which says the city had more unhealthy days in the last year than the one prior.
Maricopa County received an F grade for ozone pollution, but Tucson and Nogales had slightly improved rankings.
By contrast, Flagstaff had no unhealthy days and earned a spot on the Lung Association’s cleanest cities list.
The report also noted that Phoenix improved its short-term particle pollution but is still number seven in the nation for year-round levels.