A Spare the Air alert has been issued for Saturday, making it illegal to burn wood and firelogs inside and outside of homes that day.

The Bay Area Air Quality Management District issued the alert, which prohibits the use of fireplaces, wood stoves and inserts, pellet stoves and outdoor fire pits.

Wood smoke is the Bay Area’s largest source of pollution during the winter, according to the air management district.

Smoke pollutants become trapped close to the ground if there isn’t wind to disperse them, so air alerts are issued on days with unfavorable weather forecasts.

The smoke pollutants can build up to unhealthy levels and make breathing difficult for people with asthma and other respiratory conditions, according to the air management district.

Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, southern Sonoma and southwestern Solano counties will all be affected by the ban.

Additional details about the alert can be found at www.sparetheair.org.

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