Wednesday's predicted cold temperatures and lack of wind prompted Bay Area air quality officials to declare it a "Spare the Air" day, banning wood or solid fuel fires.
It is the fourth Spare the Air day since Jan. 1. The Bay Area Air Quality Management District designates such days as a way to reduce air pollution.
The 24-hour fire ban encompasses the greater Bay Area, including south of Windsor in Sonoma County.
The ban was imposed due to ongoing stagnant weather conditions, which can trap air pollution close to the ground.
The ban prohibits burning of wood, manufactured fire logs or any other solid fuel in fireplaces, woodstoves, outdoor fire pits or other wood-burning devices.
Air quality officials have stopped issuing warnings to offenders and are now issuing tickets. First-time offenders may choose between taking a wood smoke awareness class, online or by mail, or paying a penalty.
A second-time offender will get a $500 ticket.
The Spare the Air season runs from Nov. 1 to Feb. 28.