PHOENIX -- It's a no-burn day in the Phoenix metropolitan area.
Maricopa County's Air Quality Department has issued "no-burn day restrictions" until midnight Friday, prompted by a health alert from the Arizona Department of Environmental Quality.
Restrictions include a ban on wood burning, including fireplaces, fire pits or open outdoor burning. That ban includes restaurants and hotels.
County residents also are being urged to reduce driving by carpooling, using public transit or telecommuting.
The first no-burn day of the season was Dec. 3.
No-burn days are usually declared when the fine particulate matter pollution is high and weather conditions have created an inversion layer. That happens when a layer of warm air traps cold, dense air in lower lying areas like the Valley. The trapped air can't circulate, resulting in stagnant air masses that are visible as a hazy brown cloud hovering over the city.
Everyday road traffic and industrial processes are tied to particulate matter pollution, but the biggest source is credited to fireplace burning activity. Particles of wood smoke are extremely small and therefore are not easily filtered out by the nose or the upper respiratory system. Instead, these small particles end up deep in the lungs.
In addition to the no-burn restrictions, Maricopa County residents are advised to use rakes or brooms instead of leaf blowers. In addition, if you can't avoid driving on unpaved roads or in vacant lots, you should go slowly to avoid kicking up dust.
Fines for violating no-burn day restrictions run from $50 to $250 depending the number of wood-burning violations an individual racks up.
For the latest wood-burning restrictions, call 602-506-6400. To report a violation, call 602-372-2703 or visit Maricopa.gov.
The Associated Press contributed to this report.