The Valley continues to be under an ozone health watch Monday, with the Arizona Department of Environmental Quality extending that warning into Tuesday.
On Sunday, five area ozone monitors registered unhealthy concentrations. It was the sixth day of the season so far with at least one exceedance of the federal ozone standard.
The Valley has been under an ozone health watch since Tuesday, with a high pollution advisory issued over the weekend.
A health watch is issued when ozone levels are expected to approach the federal health standard.
A high pollution advisory is issued when ozone levels are expected to exceed federal health standards.
Ozone is an invisible gas created when other pollutants in the air are heated by the sun. Above average daytime high temperatures and minimal cloud cover have made for very efficient ozone production recently.
Residents with existing health conditions such as asthma should limit time outdoors, especially in the early evening when ozone production is at its peak.
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