Environmental regulators are extending an ozone high pollution advisory for a sixth consecutive day.
The advisory will remain in effect Thursday because the area's ozone levels are expected to surpass a new, lower federal health standard for air quality.
The Arizona Department of Environmental Quality is advising residents with respiratory problems to limit outdoor activity during this time period, especially children and the elderly.
Also, people are encouraged to drive only when necessary or use public transit or carpool.
Other recommendations include making sure containers with household cleaners and other chemicals are sealed to prevent vapors from evaporating into the air.