What's Causing Hazy Skies Across the Bay Area? Here's What to Know

Update 9 a.m. Monday:

As of Monday morning, air quality has improved substantially across the entire Bay Area, with AQI mainly in the “Good” category/ Visibility is clear outside of any localized valley fog, with little to no haze, according to the Bay Area Air Quality Management District.

Original story, 1 p.m., Sunday:

Officials issued a Spare the Air Alert through Sunday as large parts of the Bay Area experienced a second day of hazy skies.

The haze, which started Saturday, was caused by a combination of pollution in the Central Valley and smoke from winter wood burning, both brought into the region by Saturday’s easterly winds, according to Aaron Richardson, a spokesperson for the Bay Area Air Quality Management District. The air quality is considered unhealthy for sensitive groups, including seniors, young children, and people with respiratory illnesses.

Both sources, Richardson said, led to high levels of fine particle pollution in the evening and overnight that was expected to clear up Sunday, but “that didn’t happen as expected.”

“I think the easterly and northerly winds had a bit of a stalemate overnight,” he said.

Air quality has been impacted on the Peninsula, Santa Clara Valley, Alameda County, West Contra Costa County and parts of the North Bay.

“This is not a wildfire, this is seasonal,” said Richardson. “Wood burning is sort of the number one source of fine particle pollution in the wintertime. There’s automobile exhaust combustion and various things like that, but we are also getting [the pollution] because of the weather patterns.”

According to the National Weather Service, a combination of low temperatures and weak winds are contributing to the hazy conditions across the Bay Area.

Air quality is anticipated to gradually improve Sunday, with light winds picking up from the north in the afternoon and evening.

While the Spare the Air Alert is in effect, all use of wood-burning devices in the Bay Area are prohibited, including fireplaces, wood stoves, pellet stoves and outdoor fire pits. Electric fireplaces, natural gas, and propane are still allowed as well as exemptions for homes without permanently installed heating.

Alerts from the district may be called up to three days in advance to prevent air pollution from exceeding federal standards.

KQED’s Sara Hossaini and Spencer Whitney contributed reporting to this story.