GRAND RAPIDS, Mich. (WOOD) — How clean is the air you breathe? It depends on where you live in West Michigan.

In the American Lung Association’s new State of the Air report, seven West Michigan counties earned an “F” grade for the number of unhealthy ozone days they experienced last year. Among them were Allegan, Berrien, Cass, Kalamazoo, Kent, Muskegon and Ottawa counties.

More than 50 Michigan counties did not collect air quality data.

Ozone, also known as smog, is the most prevalent air pollutant. It’s created when sunlight reacts with emissions from vehicles and other sources. Ozone can cause wheezing, coughing, asthma attacks and premature death, according to the American Lung Association.

Allegan had 19 orange days last year, second only to Berrien County, which had 20 orange days. Muskegon County had 3 red days for ozone levels; Allegan County was the only other area that measured air quality that had a red ozone day, at 1.

The good news: All Michigan counties with air quality data earned a passing grade when it came to particle pollution.

As for cities, the Grand Rapids metro area tied for 34th most polluted in the nation. The metro Detroit area ranked 14th for particle pollution and 40th for ozone pollution.

The American Lung Association says this year’s report showed ozone levels increased in most U.S. cities, in large part to unusually warm temperatures.