Environmental regulators extended an air quality health watch and burning ban through Sunday in Maricopa County.
The Maricopa County Air Quality Department said the health watch being issued because of significant levels of particulate matter are expected.
Both open burning and woodburning in fireplaces are restricted, which includes residents and businesses which have burn permits for open burning.
The department said burning wood, in addition to air stagnation, will trap soot and may make breathing difficult.
People with respiratory problems are advised to avoid heavy or prolonged outdoor exertion.
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