The state is warning that southwestern New Hampshire will see unhealthy levels of particulate air pollution this weekend.
The Department of Environmental Services says the poor air quality will especially affect Keene and other valley communities. It could potentially last into early next week.
Officials say it's a result of heavy use of wood-burning stoves and boilers, combined with cold temperatures and calm winds. They say residents should consider using alternate heating sources if possible, "until winds increase and air quality improves."
The state says people should try to limit prolonged exertion this weekend, especially outdoors. Children, the elderly and people with lung or heart problems are at greater risk from the pollution.
The state has issued one other air quality alert this year - for the Seacoast area in July, as a result of wind-borne pollution during hot weather.