DOVER, Del. --- An annual report on air quality from the American Lung Association said Delaware's three counties have room to improve on ozone pollution.

The State of the Air report gave Kent County a "C" rating, the highest in the state for the number of high-ozone days. Sussex received a "D" and New Castle County was given an "F" for the 19th straight year.

Ozone is a chemical that can be formed from air pollutants that come from sources like cars, some trucks, or power plants. It can irritate the lungs of people who breathe it.

All three counties fared better when it came to daily particulate counts. Kent and Sussex counties received "A" grades, while New Castle County received a "D."