The Maine Department of Environmental Protection has issued an air quality alert for Friday because of a forecast for “unhealthy” levels of ground-level ozone along the Maine coast from Kittery to Acadia National Park.

In addition to unhealthy levels of polluted air along the coast, the DEP also expects moderate levels of pollution farther Down East and in inland areas.

The Maine Department of Environmental Protection's air quality forecast for Friday, July 22, 2016.

Ground-level ozone is a byproduct of emissions from factories, power plants and motor vehicle exhaust.

The Maine DEP warns that ground-level ozone can cause “reduced lung function and irritation” for children, healthy adults working or exercising outdoors, and individuals who are suffering respiratory diseases such as asthma.