Environmental regulators have issued an ozone pollution advisory for metro Phoenix.
The advisory was issued because the area is expected to exceed the federal health standard for air quality on Friday.
Regulators recommend that people with respiratory problems limit their outdoor activities on days of elevated ozone levels.
People are encouraged to drive only when necessary, use carpools or public transportation and avoid using gas-powered lawn equipment and drive-thru lines.
Ozone forms when vehicle exhaust and chemical solvents combine with heat and sunlight.