Poor air quality resulting from elevated ozone levels on Martha’s Vineyard may pose a risk to sensitive groups, according to an air quality advisory released by the Massachusetts Department of Environmental Protection Friday.

The advisory is for Dukes, Barnstable, Nantucket, southern Bristol and southern Plymouth counties, and is the second such advisory released by DEP this month. People with asthma, lung disease or heart disease, as well as children and older adults, are advised to take more frequent breaks and reduce their levels of outdoor exertion.

The advisory starts at 11 a.m. Friday and will remain in effect until 11 p.m.

Ozone formation is more frequently a summer pollutant, according to DEP’s website, and forms as a result of high temperatures and direct sunlight.