State environmental regulators have issued an ozone health watch for Thursday in the Phoenix area, the second such watch in 10 days.
Arizona Department of Environmental Quality officials said pollution levels could approach the federal health standard for air quality.
People who are unusually sensitive to air quality should consider limiting their time outdoors, because ozone can irritate the lungs and aggravate existing health conditions such as asthma, according to state health officials.
Officials recommend that people avoid waiting in their cars at drive-thru restaurants, unplug electronic devices that aren't being used, unplug unused appliances, connect outdoor lighting to a timer or use solar lighting and fuel their cars after dark or during cooler evening hours.
The ozone season in Maricopa County runs from April through September.
Copyright 2013 CBS 5 (KPHO Broadcasting Corporation). All rights reserved. The Associated Press contributed to this report.