On these days, ozone levels exceed the standard, which is 0.08 parts per million averaged over an 8-hour period. Ozone levels above the standard are considered unhealthy to breathe, particularly among sensitive groups. Most ozone action days occur during the warmer months, from May through September. People can safely go outside on ozone action days, but they should avoid vigorous outdoor exercise or labor in the afternoons. Even on Code Orange or Red days, ozone levels generally do not reach unhealthy levels until the afternoons when temperatures are the hottest.
Morning is the best time for outdoor activities on high ozone days.
Groups that are more sensitive to ozone include children, people with asthma and other respiratory ailments, adults who work or exercise vigorously outdoors, and some healthy individuals with unusual susceptibility. Children are most at risk because they breathe more air per pound of body weight, their lungs are still developing, and they are more likely to have asthma and other respiratory illnesses. North Carolina is taking actions to reduce ozone-forming emissions from cars and trucks, power plants and other industries. In 1999, the N.C. General Assembly enacted legislation that will require cleaner gasoline statewide by 2004 and expand the motor vehicle emissions testing program to nearly half the state by 2006. In 2000, the N.C. Environmental Management Commission began developing new rules to require substantial reductions in NOx emissions from power plants and other large industrial sources.