The Bay Area Air Quality Management District issued the season's eighth winter Spare the Air alert for today.
The order bans burning wood, manufactured fire logs or any other solid fuel, both indoors and outdoors for 24 hours.
A persistent high-pressure system dominated the region and led to a succession of the Spare the Air days last week. Although the system weakened, particulate levels increased Tuesday and threatened to reach unhealthy levels today.
"Due to the winter Spare the Air alert calls, we have not yet exceeded the federal health standard, which is exactly what the alerts are designed to do," said Jack Broadbent, executive officer of the air district.
Homes without permanently installed heating, where woodstoves or fireplaces are the only source of heat, are exempt from the burning ban.