Pima County's air got mixed scores from the American Lung Society in its 15th annual State of the Air report.

The region performed well for particulate matter, which is essentially fine dust, receiving a grade of A.

Beth Gorman of the Pima County Department of Environmental Quality said the reason for the good grade is the lack of heavy industry in the area.

The city scored lower in its ground level ozone pollution, earning a C grade. High levels of car exhaust and penetrating heat contribute to the city’s ozone pollution.

“The majority of...air pollution in our community is caused by motor vehicle use," Gorman said. "So whatever we can do to try to drive our cars less is going to help our air quality.”

She said the Lung Association’s rankings have tangible public health consequences.

“When you have a C grade for one of the pollutants then you know, unfortunately, that you have people on a fairly regular basis that are probably having some trouble breathing," she said.