An ozone health watch issued for Tuesday has been extended through Wednesday by the Arizona Department of Environmental Quality.
Ozone is an invisible gas created when pollutants in the air are heated by the sun. It can aggravate existing health conditions such as asthma.
With the uncertainty of a weak weather system moving near the Valley, and with ozone coming to Arizona from California, the department decided to extend the ozone health watch, according to a statement.
People with respiratory disease, or those at risk because of a compromised immune system, should limit time outdoors Wednesday, especially in the early evening when ozone production is at its highest.