DOVER, Del. -- Kent and Sussex counties improved in ozone pollution ratings last year, according to an annual study on air quality from the American Lung Association.

The State of the Air study looks at qualities like the number of days with ozone smog as well as daily and annual particle pollution numbers, associating letter grades with counties to demonstrate air quality. The association says ozone and particle pollution can cause illnesses or death and aggravate conditions like asthma.

Kent and Sussex counties both received "F" ratings in the 2015 report, though both improved to "B" and "D" ratings, respectively. Both counties received "A" ratings for daily and annual particle pollution. New Castle County received an "F" for ozone pollution.

Harold Sechrest of Wyoming said he thinks the air quality in Kent County is fine, but said the number of vehicles on area roadways can sometimes make breathing unpleasant.

"It's alright until you get them big machines out here. That diesel smell...It's nasty," he said.

DNREC Secretary Shawn Garvin said Delaware sees a lot of cars and trucks on its roadways, putting a lot of vehicle exhaust into the air. The ALA attributes things like diesel exhaust and coal-fired generators as causes of ozone and particle pollution.

"Delaware as a whole doesn't have a very detailed mass-transit system so people need to get in their cars to go from point A to point B," he said.

