Cal Fire Capts. Derek Leong, right, and Tristan Gale monitor a firing operation, where crews set a ground fire to stop a wildfire from spreading, Monday while battling the Dixie Fire in Lassen National Forest, California. Credit: Noah Berger / AP

Mainers may find it harder to breathe again Tuesday as plumes of smoke from western wildfires continue to drift over the state.

Particle pollution will be heaviest over the western mountains, southern, central, eastern and Down East Maine, according to the Maine Department of Environmental Protection.

Those particles are expected to have only a moderate impact on air quality across northern Maine.

Mainers with heart and lung diseases, older adults, teens and children have been advised to avoid heavy exertion outside. While outdoor activities are still safe, Mainers with asthma and heart disease should watch for acute heart and lung symptoms. Others should watch for shortness of breath and coughing.

That comes as wildfires raging across the U.S. and Canadian West have burned nearly 9,000 acres on both sides of the border so far this year. It’s affected air quality across the continent as winds have carried plumes of smoke east.

The increased frequency and severity of wildfires in recent years have alarmed scientists and health officials, with new studies showing smoke from the fires can place people at elevated risk of contracting COVID-19 and numerous other ailments, including respiratory illness and cancer, from the particles and heavy metals, such as iron, lead and zinc, carried in the smoke.

Despite the elevated particle pollution, the air quality forecast shows very low levels of ozone pollution Tuesday and Wednesday.

Wednesday’s air quality forecast shows a marked improvement, with particle pollution levels falling steeply.