New Hampshire environmental officials expect air pollution concentrations on Saturday to reach unhealthy levels for those with asthma and other lung ailments.
Officials say Rockingham County and areas above 3,000 feet will have unhealthy concentrations of ground-level ozone - the main component of smog.
Environmental officials say "sensitive individuals" - including children, older adults and anyone with lung diseases such as asthma, emphysema and bronchitis, and people who are active outdoors - should take precautions and limit prolonged outdoor exertion.
The latest news from around the state
Symptoms of ozone exposure include coughing, wheezing, chest tightness or pain when inhaling deeply, and shortness of breath.
The unhealthy air quality is due to the persistence of high temperatures under sunny skies and light winds transporting pollution into New Hampshire from surrounding areas.