Environmental officials are warning that air pollution concentrations could reach unhealthy levels in parts of New Hampshire during an upcoming temperature inversion.
The New Hampshire Department of Environmental Service says air pollution concentrations are expected to rise on Tuesday night and into Wednesday and could affect people with asthma and other existing lung diseases.
The advisory is for the valley areas in Cheshire, Hillsborough, Merrimack, and Sullivan counties.
The unhealthy pollution levels are caused when warm air traps cold air below, preventing air pollution from mixing with cleaner air above and diluting.
Officials say sensitive people may not be able to breath as deeply or vigorously as normal and may experience coughing or shortness of breath.
Healthy individuals also are advised to limit strenuous or prolonged activities.