Why the air in the SF Bay Area is so gross on Friday

Air-quality levels in some parts of the Bay Area were rated as “unhealthy for some” on Friday, and the conditions are expected to persist into Saturday and Sunday as people are burning wood in fireplaces, officials said.

The Bay Area Air Quality Management District issued a Spare the Air Alert for Friday, Saturday and Sunday that makes wood burning both indoors and outdoors illegal. 

“Wood smoke is the number-one source of wintertime pollution in the Bay Area,” said Juan Romero, a spokesperson for the district. “It accounts for about one-third or more of fine particulate emissions.”

There are 1.4 million fireplaces in the Bay Area, he said.

A high-pressure system over the region is exacerbating the pollution. High pressure acts as a lid, pushing the pollution toward the Earth’s surface and trapping it at ground level, Romero said. What’s more, onshore winds are blowing fine-particulate matter from the Central Valley into the Bay Area.

Air quality levels are dependent on the amount of pollutant concentrations in the air and measured on a scale, from good to hazardous. When air-quality levels are considered “unhealthy for sensitive groups,” officials recommend that people with certain health conditions such as asthma or heart disease, reduce prolonged or heavy exercise outdoors.  

Air-quality levels could improve as early as Sunday evening when a low-pressure system is expected to bring rain to the region. More rain is expected next week.