Air-quality experts are warning that metropolitan Phoenix could be in be for a particularly dirty winter.
The first health watch of the season was issued for Friday as a brown cloud settles over the area and a bubble of cold air acts like a lid on airborne dust and smoke.
Friday's warning triggered a Maricopa County Air Quality Department ban on wood-burning fires.
State environmental regulators expect a large number of high-pollution advisories during this winter season.
The period between Christmas and New Year's Day is expected to be the worst of it.
Smoke is a key contributor, and with many people home for vacation, more home fires will be burning.