Elevated ozone levels have prompted the Arizona Department of Environmental Quality to issue a health watch for Saturday. The Valley was already under a high pollution advisory Thursday and Friday for particulate matter, prompted by an early morning dust storm Thursday.
Ozone is created when pollutants in the air are heated by the sun. Valley temperatures crossed the 110 mark several times this week.
Ozone can aggravate existing health conditions such as asthma. People with respiratory conditions, as well as the elderly and very young, should limit time outdoors Saturday.
A health watch is issued when levels of ozone or particulate matter (tiny microns of dust that can enter the respiratory system) are expected to approach federal standards. A high pollution advisory is issued when ozone or particulate matter is expected to exceed federal standards.