The Valley is under an ozone health watch that will continue into Saturday.
Ozone is an invisible gas that is created when other pollutants in the air are heated by the sun. Friday and Saturday temperatures are expected to be in the triple digits.
The Arizona Department of Environmental Quality issues a health watch when ozone levels may approach federal standards.
Ozone can aggravate existing heath conditions such as asthma. The elderly, very young and anyone with a respiratory illness should limit time outdoors.
Residents are encouraged to help decrease pollutants in the air by using a car pool, fueling vehicles in the cooler evenings, and avoiding long waits in drive-thrus.
For information, see cleanairmakemore.com.