The Arizona Department of Environmental Quality has issued a high pollution advisory for Maricopa County.
Department officials say the advisory is being called for Monday because ozone levels in the county including Phoenix are expected to exceed the federal health standard during the day.
People most affected by ozone include children, older people, people who work or exercise outdoors and people with respiratory diseases.
Ozone can irritate the respiratory system, aggravate asthma and reduce the immune system's ability to fight off respiratory infections. Ozone-related health problems include shortness of breath, coughing, wheezing, headaches, nausea, as well as irritation of the throat and lungs.
State environmental and county air quality officials recommend that people drive as little as possible, carpool, use public transit or telecommute.