An air quality health watch has been issued for Wednesday afternoon and evening as ozone levels approach unhealthy measures, according to the Arizona Department of Environmental Quality.
Ozone is a pollutant created when other pollutants in the air - such as combustion from vehicles - are heated. Wednesday's high temperatures are expected to reach the mid 90s.
Ozone can aggravate existing respiratory conditions such as asthma. Children, the elderly and people with chronic respiratory conditions should limit time outdoors.
Winds on Thursday should help move the ozone out from the Valley.