State environmental officials are warning that parts of New Hampshire could see poor air quality through Saturday as a result of lower temperatures, calm conditions and pollution.
The New Hampshire Department of Environmental Services is advising that children, older adults and people with respiratory health problems in the southwest parts of the state take precautions.
Part of what's causing the change in air quality is known as thermal inversion: as warm air moves in, it slides over cold air, trapping it near the ground.
"If people provide pollution into that ground level, it has nowhere to go, it can't disperse upwards and it would need wind to blow it away," says Jeff Underhill, chief scientist of the Air Resources Division at DES.
He says a lot of that pollution comes from residential wood-burning stoves and boilers, and it's being made worse by a lack of wind.
Healthy individuals should consider limiting strenuous activities.
Symptoms of particle pollution exposure may include chest pain, palpitations, shortness of breath and difficulty breathing.
NHPR reporter Daniela Allee contributed to this report