High pressure is strengthening in the Phoenix area. DEQ officials say there's the potential for ozone to arrive from southern California and mix with what's already in place over the city and its surrounding areas.
Ozone is an invisible gas that is created when other pollutants in the air are heated by the sun. There could be a high pollution advisory later in the week if the current weather pattern continues.
Health officials say Phoenix-area residents with existing respiratory conditions should limit time outdoors Wednesday, especially in the late afternoon when ozone production peaks.