The Maine Department of Environmental Protection’s Bureau of Air Quality is warning people to avoid strenuous outdoor activity Monday because ground-level ozone concentrations are expected to reach unhealthy levels along most of the state’s coastline and the eastern interior of the state.

Sunday’s air quality alert says that people with heart or lung disease, the elderly, teenagers and children should reduce prolonged or heavy exertion. It is OK to be outside, but people in those sensitive groups should take more breaks and do less intense activities. Symptoms to be aware of include coughing, shortness of breath, uncomfortable chest sensations, palpitations and unusual fatigue.

According to the DEP alert, elevated levels of ground-level ozone were detected last Wednesday near Lake Michigan and have been slowly migrating eastward. Parts of southern New England recorded extremely high levels of ozone on Saturday. Winds are expected to transport ozone into Maine on Monday with the possibility of the entire coast experiencing unhealthy levels.

Monday’s air quality alert is the first one issued in 2021 by the DEP, according to Deputy Commissioner David Madore. He said in an email Sunday evening that Monday’s air quality alert is unusual for this time of year, but not uncommon. The DEP issued a similar early season warning on May 2, 2018. Ozone and particle pollution typically pose health risks in the summer months.

The National Weather Service office in Gray also issued a hazardous weather statement Sunday afternoon warning people that temperatures could soar into the low 90s on Tuesday, pushing heat indices beyond 95 degrees. The NWS said that heat and humidity will exacerbate the impacts of the higher pollution levels on Monday and Tuesday.

Ozone is a photochemical pollutant, which means it needs strong sunlight in order to form from other pollutants in the air. Ozone levels can pose health risks during the summer months and typically peak during the afternoon and early evening hours. Health officials are urging people to avoid strenuous outdoor activity, especially during the afternoon hours on Monday.

Health officials also advise people to change the time or location of their workouts, such as walking instead of jogging or finding a healthier route to exercise, such as on a less congested road. Ozone sources may include automobiles, trucks, and buses and off-road engines such as aircraft, locomotives, boats, construction equipment and lawn and garden equipment.

For more information on daily air quality alerts, people can call the state’s toll-free Air Quality Hotline at 800-223-1196 or visit the DEP’s air quality website.