The New Hampshire Department of Environmental Services is expecting unhealthy air pollution concentration levels in southwestern New Hampshire, especially Keene, through Friday morning.
The department is advising older adults, children and anyone with heart or lung disease such as asthma, emphysema, and bronchitis to take precautions by limiting prolonged exertion.
The department says even healthy people may experience mild health effects and should consider limiting strenuous or prolonged activities.
The expected unhealthy particle pollution levels are a combined result of low temperatures, calm winds that limit air movement and inhibit dispersion, and pollution transported from surrounding areas. Much of this pollution is emitted from heating devices, especially residential wood-burning stoves and boilers.
Communities in valleys or other low-lying areas where temperature inversions are common are more strongly affected.