SAN FRANCISCO (KRON) — A Spare the Air Alert has been issued through Thursday as a large smoke plume covers the entire Bay Area, the Bay Area Air Quality Management District announced. Portions of the North Bay, including Santa Rosa, are graded as “unhealthy” as of Thursday morning.

The agency said wildfires from Northern California and Oregon have increased levels of particulate matter pollution in the air. During the Spare the Air Alert, it is “illegal for Bay Area residents and businesses to use their fireplaces, wood stoves, pellet stoves, outdoor fire pits or any other wood-burning devices,” BAAQMD said.

The National Weather Service wrote, “Smokey air from Northwest California fires may linger near the surface across the Bay Area for the next few days.”

San Jose and the surrounding South Bay had air quality graded as “unhealthy” on Wednesday.

Air quality in San Francisco and Oakland was graded as “unhealthy” on Tuesday and “unhealthy for sensitive groups” as of Wednesday morning. San Francisco emergency dispatchers received a flurry of 911 calls Tuesday reporting smoky air in the city. Bay Area residents are advised to avoid exposure if the smell of smoke is present by staying indoors with the windows and doors closed. To check the air quality near you, use this interactive map.

Sonoma County officials issued a health advisory due to poor air quality.

Sonoma County officials wrote, “Smoke from wildfires currently burning in Northern California and Southern Oregon is expected to impact the air quality throughout Sonoma County today through Wednesday, Sept. 20. The air quality is expected to be in the moderate range during this event. Some people may experience adverse health effects from the smoke. Members of sensitive groups may experience effects that are more serious.”

Smoke drifted as far south as the Santa Cruz mountains.

Cal Fire CZU officials wrote, “Our Felton emergency command center has gotten calls from San Mateo and Santa Cruz counties (from) people concerned about haze and smell of smoke. Winds from the north are pushing smoke from wildfires in NorCal & Oregon into our region.”

A prescribed fire planned for Wednesday in San Mateo County’s bayside is postponed due to the wildfire smoke already impacting the region, according to a tweet from Cal Fire CZU.

Up north, Marin County public health officials urged community members to take precautions by limiting outdoor activity due to the poor air quality. The Marin County Office of Education cautioned school districts to consider canceling or postponing student athletic events until air quality improves.

When will air quality improve?

The smoke and haze will continue Wednesday for much of the Bay Area, according to KRON4 Meteorologist John Shrable. “Some improvements are expected to begin at the coast late today and overnight as cleaner ocean air begins to push into the Bay Area,” Shrable said Wednesday. Starting as soon as Thursday, coastal areas will see improvements, whereas some inland areas may have to wait until Friday or later this weekend.