An air quality health watch has bee issued for Thursday afternoon and evening because of high ozone production.
The Arizona Department of Environmental Quality reports a plume of ozone will move over parts of the Valley that already have elevated ozone levels.
Ozone is a pollutant created when other pollutants in the air – such as combustion from vehicles - are heated by the sun.
It can aggravate existing respiratory conditions. The elderly, young and those with asthma or other conditions should limit time outdoors.