Updating air quality map (ozone and particles): yellow is moderate, orange unsafe for sensitive groups, red unhealthful.

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California wildfires: Firefighter killed battling blaze sparked by gender-reveal party Smoke from the Wine Country wildfires choked much of the greater Bay Area Wednesday as shifting winds steered unhealthy soot as far south and San Jose and Livermore and east into Antioch.

Several school districts — including West Contra Costa, Antioch and Martinez — and Holy Names College in Oakland planned to close Thursday, and other schools are expected to consider following suit.

At San Francisco International Airport, 80 flights were cancelled Wednesday due to the reduced visibility from the smoke.

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“It was fine this morning but by lunchtime … it’s bad. Very hazy. You can smell the smoke in the air,” said Erin Harrison, a spokeswoman for the Oakland Zoo, where some of the employees were wearing face masks. All night houses were opened up for the animals to seek shelter indoors.

From the zoo’s new gondola, Harrison said, the view to San Francisco is clear on most days. “Today we couldn’t see past the zoo.”

At nearby Chabot Space & Science Center, a red orange sun peered through the haze.

“I’m indoors and I can smell the smoke. It’s pretty thick,” said Ben Burress, a staff astronomer. “We’re at 1,500 feet and we are still getting quite a bit of smoke.”

After a third consecutive day of unhealthy smoke in some areas, the region’s air quality district took the unprecedented step of extending a Bay Area wide smoke health advisory through Sunday.

“We have never done this before, but we have never had smoke this concentrated for an extended period of time,” said Tom Flannigan, a spokesman for the nine-county Bay Area Air Quality Management District.

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“We advise people to wear an N-95 rated mask to protect themselves,” said Eric Stevenson, a technical manager at the air district.

Pollution regulators urge the public to stay indoors as much as possible, limit outdoor activities, and close doors and windows if they smell smoke or find out their area as unhealthy smoke levels.

Many Bay Area school districts are keeping students indoors at recess and lunchtime, and beginning to discuss whether they will need to postpone or cancel Friday night sporting events.

“Our belief is the kids are safer in school, but while in school we want to limit their time outdoors to minimize the exposure to smoke,” said Dionicia Ramos, a spokeswoman for the Hayward Unified School District. “The air seemed better in the morning, but in the afternoon, it looked like the smoke was just rolling in from the north.”

On Monday, parts of the Bay Area such as Napa had the high smoke concentrations ever recorded by the air pollution district.

Early Wednesday morning, offshore breezes kicked in, sweeping the smoke out of San Francisco and some East Bay areas like Oakland, but the relief was short lived.

By the afternoon, a wind shift steered the wildfire smoke back to the south again, sweeping tons of soot into Oakland and the Diablo and Santa Clara valleys.

Air quality in San Jose has been moderate or better until Wednesday afternoon when it become unhealthy for the first time this week, according to a pollution map supported by the air district and the California Environmental Protection Agency.

“The smoke is accumulating,” Flannigan said, “and it’s not being swept out.”

Vallejo became a hot spot for the worst pollution according to an Environmental Protection Agency map that tracked the smoke as it moved about. The city east of the Wine Country was encircled in deep purple on the map Wednesday afternoon, a color indicating hazardous conditions.

The air district issued another Spare the Air alert for Thursday, asking the public not to light barbecues, run lawn mowers, or do other activities that would add more fine particles to the air.

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Smoke can trigger asthma and emphysema attacks, and increase the risk of strokes and heart attacks among the elderly or those with circulatory problems.