The Arizona Department of Environmental Quality has issued a PM-10 air quality health watch for Sunday.
A health watch is issued when particulate matter-10 levels are expected to approach federal health standards.
It is the third air quality health warning by the state this week. Monday, the department issued an air quality health advisory because of high winds and blowing dust.
PM-10 stands for particulate matter measuring 10 microns or less. State and county agencies measure PM-10 and PM-2.5 which are extremely small solid particles and liquid droplets found circulating in the air. PM, or particulate matter, comes from either combustion (cars, industry, woodburning) or dust stirred up into the air. High levels of PM are typically created when the air is especially stagnant.