PHOENIX (AP) -- Environmental regulators have issued a high pollution advisory for ozone for the Phoenix area because searing heat and little wind is causing a buildup of the pollutant.
Ozone levels are already moderately high and the Arizona Department of Environmental Quality says they're expected to increase as it heats up on Tuesday.
The National Weather Service has issued an excessive heat warning for large areas of the state and high temperatures in the Phoenix region could reach 112 degrees.
Ozone is an invisible gas created when other pollutants in the air -- such as those created by combustion-- are heated by the sun.
Experts say ozone can irritate the lungs and aggravate existing health conditions such as asthma.
Maricopa County officials have called Tuesday a mandatory no-burn day.
Read: Ozone season officially under way; invisible danger in the air