California wildfires emitted a year’s worth of car pollution in less than a week

The wildfires in California released as much air pollution in the Bay Area in a matter of days as motorists in the state normally emit in a year, drastically reducing air quality and creating an immediate health threat.

People most vulnerable to breathing problems, such as the elderly or those with asthma or pulmonary disease, are most likely to be affected, experts say, but healthy people are at risk, too.

A half-marathon in San Francisco was canceled because of air issues, and the NFL was considering moving Sunday's game between the Oakland Raiders and the Los Angeles Chargers from Oakland.

Hospitals around the Bay Area have also experienced an increase in visits for breathing difficulties and chest tightness, The San Francisco Chronicle reported.

62 PHOTOS
Devastating wildfires ravage California's wine country
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Devastating wildfires ravage California's wine country
SANTA ROSA, CA - OCTOBER 09: Burned lawn chairs sit next to the swimming pool at the Journey's End Mobile Home Park on October 9, 2017 in Santa Rosa, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Fire consumes a barn as an out of control wildfire moves through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
YOUNTVILLE, CA - OCTOBER 09: A Los Angeles County firefighter monitors approching flames near a building as an out of control wildfire moves through the area on October 9, 2017 in Yountville, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
NAPA, CA - OCTOBER 09: Burned out wine bottles sit on a rack at the fire damaged Signarello Estate winery after an out of control wildfire moved through the area on October 9, 2017 in Napa, California. Tens of thousands of acres and hundreds of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
SONOMA, CA - OCTOBER 09: A burned out home sits next a vineyard after an out of control wildfire moved through the area on October 9, 2017 in Sonoma, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
NAPA, CA - OCTOBER 09: The remains of the fire daaged Signarello Estate winery after an out of control wildfire moved through the area on October 9, 2017 in Napa, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: A resident rushes to save his home as an out of control wildfire moves through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: A resident rushes to save his home as an out of control wildfire moves through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
A burned home smolders in Glen Ellen, California on October 9, 2017. Multiple wind-driven fires continue to ravage the area burning structures and causing widespread evacuations. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: The remains of fire damaged homes after an out of control wildfire moved through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Fire consumes a barn as an out of control wildfire moves through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Fire consumes a home as an out of control wildfire moves through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: The remains of fire damaged homes after an out of control wildfire moved through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: A resident rushes to save his home as an out of control wildfire moves through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Cows stand on a patch of unburned grass after an out of control wildfire moved through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Burned cars sit idle after an out of control wildfire moved through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Fire consumes a home as an out of control wildfire move through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Fire consumes a home as an out of control wildfire move through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: The remains of fire damaged homes after an out of control wildfire moved through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Flames consume a home as an out of control wildfire move through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Flames consume a home as an out of control wildfire move through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: Fire consumes a home as an out of control wildfire move through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: The remains of fire damaged homes after an out of control wildfire moved through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
An aerial photo of the devastation left behind from the North Bay wildfires north of San Francisco, California, October 9, 2017. California Highway Patrol/Golden Gate Division/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY
An aerial photo of the devastation left behind from the North Bay wildfires north of San Francisco, California, October 9, 2017. California Highway Patrol/Golden Gate Division/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY
A burned home smolders in Glen Ellen, California on October 9, 2017. Multiple wind-driven fires continue to ravage the area burning structures and causing widespread evacuations. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
A garage door is left standing in front of a smoldering home in Glen Ellen, California on October 9, 2017. Multiple wind-driven fires continue to ravage the area burning structures and causing widespread evacuations. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
A gas line spews flames at a burned out property in Glen Ellen, California on October 9, 2017. Multiple wind-driven fires continue to ravage the area burning structures and causing widespread evacuations. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
YOUNTVILLE, CA - OCTOBER 09: A Napa Valley public worker sprays water on a building as an out of control wildfire moves through the area on October 9, 2017 in Yountville, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
YOUNTVILLE, CA - OCTOBER 09: A Los Angeles County firefighter monitors approching flames near a building as an out of control wildfire moves through the area on October 9, 2017 in Yountville, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
NAPA, CA - OCTOBER 09: Fire burns a trailer and parking structure as an out of control wildfire moved through the area on October 9, 2017 in Napa, California. Tens of thousands of acres and hundreds of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
NAPA, CA - OCTOBER 09: The remains of the fire damaged Signarello Estate winery after an out of control wildfire moved through the area on October 9, 2017 in Napa, California. Tens of thousands of acres and hundreds of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
NAPA, CA - OCTOBER 09: The remains of the fire damaged Signarello Estate winery after an out of control wildfire moved through the area on October 9, 2017 in Napa, California. Tens of thousands of acres and hundreds of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
NAPA, CA - OCTOBER 09: The remains of the fire damaged Signarello Estate winery after an out of control wildfire moved through the area on October 9, 2017 in Napa, California. Tens of thousands of acres and hundreds of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
CALIFORNIA, USA - OCTOBER 10: A view of a warning banner in San Francisco as a wildfire from the Santa Rosa and Napa Valley moves through the area in California, United States on October 10, 2017. (Photo by Tayfun Coskun/Anadolu Agency/Getty Images)
CALIFORNIA, USA - OCTOBER 10: Smoke rises as a wildfire from the Santa Rosa and Napa Valley moves through the area in California, United States on October 10, 2017. (Photo by Tayfun Coskun/Anadolu Agency/Getty Images)
CALIFORNIA, USA - OCTOBER 10: A view of a San Francisco gulf as smoke covers the sun as a wildfire from the Santa Rosa and Napa Valley moves through the area in California, United States on October 10, 2017. (Photo by Tayfun Coskun/Anadolu Agency/Getty Images)
CALIFORNIA, USA - OCTOBER 10: A view of a San Francisco gulf as smoke covers the sun as a wildfire from the Santa Rosa and Napa Valley moves through the area in California, United States on October 10, 2017. (Photo by Tayfun Coskun/Anadolu Agency/Getty Images)
SANTA ROSA, CA - OCTOBER 09: Burned out cars sit next to a building on fire in a fire ravaged neighborhood on October 9, 2017 in Santa Rosa, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
CALIFORNIA, USA - OCTOBER 10: A view of a San Francisco gulf as smoke covers the sun as a wildfire from the Santa Rosa and Napa Valley moves through the area in California, United States on October 10, 2017. (Photo by Tayfun Coskun/Anadolu Agency/Getty Images)
SANTA ROSA, CA - OCTOBER 09: A resident goes through personal belongings in a parking lot next to a fire damaged Arby's restaurant on October 9, 2017 in Santa Rosa, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
SANTA ROSA, CA - OCTOBER 09: Flames consume a section of the Hilton Sonoma Wine Country on October 9, 2017 in Santa Rosa, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
SANTA ROSA, CA - OCTOBER 09: Burned out cars sit next to a building on fire in a fire ravaged neighborhood on October 9, 2017 in Santa Rosa, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
SANTA ROSA, CA - OCTOBER 09: Smoke continues to rise from the Hilton Sonoma Wine Country on October 9, 2017 in Santa Rosa, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
SONOMA, CA - OCTOBER 09: An out of control wildfire approaches Gundlach Bundschu winery on October 9, 2017 in Sonoma, California. Ten people have died in wildfires that have burned tens of thousands of acres and destroyed over 1,500 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase TPX IMAGES OF THE DAY
An American flag hangs from a tree in a neighborhood destroyed by wildfire in Santa Rosa, California, U.S., October 12, 2017. REUTERS/Jim Urquhart TPX IMAGES OF THE DAY
Area residents walk through a neighborhood destroyed by wildfire in Santa Rosa, California, U.S., October 12, 2017. REUTERS/Jim Urquhart TPX IMAGES OF THE DAY
Wine stains are seen on a fermentation tank at Paradise Ridge Winery after being destroyed by the Tubbs Fire in Santa Rosa, California, U.S., October 12, 2017. REUTERS/Stephen Lam TPX IMAGES OF THE DAY
Pacific Gas and Electric (PG&E) trucks are seen parked on a road between homes destroyed by the Tubbs Fire in Santa Rosa, California, U.S., October 11, 2017. Picture taken October 11, 2017. REUTERS/Stephen Lam TPX IMAGES OF THE DAY
A wildfire is shown from the air near Atlas Road during an operation to rescue people trapped by wildfire in Napa, California, U.S., October 9, 2017. Photo taken October 9, 2017. Courtesy California Highway Patrol/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY TPX IMAGES OF THE DAY
A burnt tree stands amidst the destroyed Journey's End Mobile Home Park during the Tubbs Fire in Santa Rosa, California, U.S., October 9, 2017. REUTERS/Stephen Lam TPX IMAGES OF THE DAY
Smoke and flame rise from the Hilton Sonoma Wine Country during the Tubbs Fire in Santa Rosa, California, U.S., October 9, 2017. REUTERS/Stephen Lam TPX IMAGES OF THE DAY
An aerial view of properties destroyed by the Tubbs Fire is seen in Santa Rosa, California, U.S., October 11, 2017. REUTERS/Stephen Lam TPX IMAGES OF THE DAY
NAPA, CA -OCTOBER 12: Flowers mark the spot where his father died as Mike Rippey walks through the ruins of the house of 100-year-old Charles and 98-year-old Sara Rippey, who were killed in the Atlas Fire just after it began, on October 12, 2017 near Napa, California. Thousands homes have burned and two dozen people have been confirmed dead so far as numerous wildfires continue to spread in eight Northern California counties. (Photo by David McNew/Getty Images)
SANTA ROSA, CA - OCTOBER 11: An aerial view of homes that were destroyed by the Tubbs Fire on October 11, 2017 in Santa Rosa, California. Twenty one people have died in wildfires that have burned tens of thousands of acres and destroyed over 3,000 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
SANTA ROSA, CA -OCTOBER 10: A toy car is left scorched in a neighborhood destroyed by fire near Cardinal Newman High School on October 10, 2017 in Santa Rosa, California. In one of the worst wildfires in state history, at least 1,500 homes have burned and 11 people have died as more than 14 wildfires continue to spread in eight Northern California counties. (Photo by David McNew/Getty Images)
GLEN ELLEN, CA - OCTOBER 09: A resident rushes to save his home as an out of control wildfire moves through the area on October 9, 2017 in Glen Ellen, California. Tens of thousands of acres and dozens of homes and businesses have burned in widespread wildfires that are burning in Napa and Sonoma counties. (Photo by Justin Sullivan/Getty Images)
Homeowner Phil Rush looks at the remains of his home destroyed by wildfire in Santa Rosa, California, on October 11, 2017. Rush said he and his wife and dog escaped with only their medication, a bag of dog food when flames overtook their entire neighborhood on October 9. The toll from Northern California's ranging wildfires continued to grow as officials said the fires destroyed up to 2,000 structures and killed at least 17 people. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
NAPA, CA -OCTOBER 11: The body of a cow that died in the Atlas Fire is seen in Soda Canyon on October 11, 2017 near Napa, California. In one of the worst wildfires in state history, more than 2,000 homes have burned and at least 21 people have been killed as more than 14 wildfires continue to spread with little containment in eight Northern California counties. (Photo by David McNew/Getty Images)
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The fires released more than 10,000 tons of PM 2.5 — particles that are 2.5 micrometers in diameter or smaller and are regulated by the Environmental Protection Agency because of their health impact — said Sean Raffuse, an air quality analyst at the Crocker Nuclear Laboratory at University of California in Davis. He based his estimate off of U.S. Forest Service models.

That's the same amount of primary PM 2.5 that the EPA estimates come from California vehicles in a year, according to its most recent National Emissions Inventory, Raffuse said. He pointed out cars pollute in other ways, too, but that the wind has blown this much pollution into a populous area is notable, he said.

"In the case of large wildfires, it is not that uncommon. It is the proximity to large populations and the wind direction that is making this smoke event worse from a public health perspective," Raffuse said.

The air quality levels in the Bay Area this week have been so bad, they have rivaled those in smog-enshrouded Beijing.

PM 2.5, which causes haze and can get into lungs, is measured by the air quality index. On a good day, the index is anywhere from zero to 50. In Napa for the last few days, the air quality index topped 200, which is considered "hazardous."

Related: Wineries at Risk as Wildfires Rage in Northern California

By comparison, the air quality on Friday around 1 p.m. ET in Beijing was 59, a "moderate" reading by the air quality index's scale.

28 PHOTOS
Aerial images of California's wildfire devastation
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Aerial images of California's wildfire devastation
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
TOPSHOT - An aerial view shows a burned property in Santa Rosa, California on October 12, 2017. Hundreds of people are still missing in massive wildfires which have swept through California killing at least 26 people and damaging thousands of homes, businesses and other buildings. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
Residences and vineyards burned by wildfires are seen in this aerial photograph taken above Santa Rosa, California, U.S., on Thursday, Oct. 12, 2017. Wildfires that tore through northern California's iconic wine-growing regions have prompted evacuations of more than 20,000 people, killed 11 and damaged some of the most valuable vineyards and wineries in the U.S. About 1,500 commercial, residential and industrial structures were burned, and damage assessment teams have started accounting for the destruction. Photographer: David Paul Morris/Bloomberg via Getty Images
An aerial view shows a burned school in Santa Rosa, California on October 12, 2017. Hundreds of people are still missing in massive wildfires which have swept through California killing at least 26 people and damaging thousands of homes, businesses and other buildings. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase TPX IMAGES OF THE DAY
TOPSHOT - Fire damage is seen from the air in the Coffey Park neighborhood on October 11, 2017, in Santa Rosa, California More than 200 fire engines and firefighting crews from around the country were being rushed to California on Wednesday to help battle infernos which have left at least 21 people dead and thousands homeless. / AFP PHOTO / Elijah Nouvelage (Photo credit should read ELIJAH NOUVELAGE/AFP/Getty Images)
An aerial view shows firefighters working at a burned property in Santa Rosa, California on October 12, 2017. Hundreds of people are still missing in massive wildfires which have swept through California killing at least 26 people and damaging thousands of homes, businesses and other buildings. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
SANTA ROSA, CA - OCTOBER 11: An aerial view of homes that were destroyed by the Tubbs Fire on October 11, 2017 in Santa Rosa, California. At least 21 people have died in wildfires that have burned tens of thousands of acres and destroyed over 3,000 homes and businesses in several Northen California counties. (Photo by Justin Sullivan/Getty Images)
Pacific Gas and Electric Co. crew repairing a downed power line damaged by wildfires are seen in this aerial photograph taken above Santa Rosa, California, U.S., on Thursday, Oct. 12, 2017. Wildfires that tore through northern California's iconic wine-growing regions have prompted evacuations of more than 20,000 people, killed 11 and damaged some of the most valuable vineyards and wineries in the U.S. About 1,500 commercial, residential and industrial structures were burned, and damage assessment teams have started accounting for the destruction. Photographer: David Paul Morris/Bloomberg via Getty Images
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
Residences burned by wildfires are seen in this aerial photograph taken above Santa Rosa, California, U.S., on Thursday, Oct. 12, 2017. Wildfires that tore through northern California's iconic wine-growing regions have prompted evacuations of more than 20,000 people, killed 11 and damaged some of the most valuable vineyards and wineries in the U.S. About 1,500 commercial, residential and industrial structures were burned, and damage assessment teams have started accounting for the destruction. Photographer: Chip Chipman/Bloomberg via Getty Images
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
TOPSHOT - Fire damage is seen from the air in the Coffey Park neighborhood October 11, 2017, in Santa Rosa, California. More than 200 fire engines and firefighting crews from around the country were being rushed to California on Wednesday to help battle infernos which have left at least 21 people dead and thousands homeless. / AFP PHOTO / Elijah Nouvelage (Photo credit should read ELIJAH NOUVELAGE/AFP/Getty Images)
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
Fire damage is seen from the air in the Coffey Park neighborhood October 11, 2017, in Santa Rosa, California More than 200 fire engines and firefighting crews from around the country were being rushed to California on Wednesday to help battle infernos which have left at least 21 people dead and thousands homeless. / AFP PHOTO / Elijah Nouvelage (Photo credit should read ELIJAH NOUVELAGE/AFP/Getty Images)
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
Traffic travelling along a highway near a Kmart discount store burned by wildfires is seen in this aerial photograph taken above Santa Rosa, California, U.S., on Thursday, Oct. 12, 2017. Wildfires that tore through northern California's iconic wine-growing regions have prompted evacuations of more than 20,000 people, killed 11 and damaged some of the most valuable vineyards and wineries in the U.S. About 1,500 commercial, residential and industrial structures were burned, and damage assessment teams have started accounting for the destruction. Photographer: David Paul Morris/Bloomberg via Getty Images
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
In this aerial view, burned properties are seen in Santa Rosa, California on October 12, 2017. Hundreds of people are still missing in massive wildfires which have swept through California killing at least 26 people and damaging thousands of homes, businesses and other buildings. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
Fire damage is seen from the air in the Coffey Park neighborhood on October 11, 2017, in Santa Rosa, California More than 200 fire engines and firefighting crews from around the country were being rushed to California on Wednesday to help battle infernos which have left at least 21 people dead and thousands homeless. / AFP PHOTO / Elijah Nouvelage (Photo credit should read ELIJAH NOUVELAGE/AFP/Getty Images)
An aerial shows damage caused by wildfires in Santa Rosa, California, U.S October 11, 2017. Picture taken October 11, 2017. REUTERS/DroneBase
Residences burned by wildfires are seen in this aerial photograph taken above Santa Rosa, California, U.S., on Thursday, Oct. 12, 2017. Wildfires that tore through northern California's iconic wine-growing regions have prompted evacuations of more than 20,000 people, killed 11 and damaged some of the most valuable vineyards and wineries in the U.S. About 1,500 commercial, residential and industrial structures were burned, and damage assessment teams have started accounting for the destruction. Photographer: David Paul Morris/Bloomberg via Getty Images
In this aerial view, burned properties are seen in Santa Rosa, California on October 12, 2017. Hundreds of people are still missing in massive wildfires which have swept through California killing at least 26 people and damaging thousands of homes, businesses and other buildings. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
TOPSHOT - An aerial view shows burned properties in Santa Rosa, California on October 12, 2017. Hundreds of people are still missing in massive wildfires which have swept through California killing at least 26 people and damaging thousands of homes, businesses and other buildings. / AFP PHOTO / JOSH EDELSON (Photo credit should read JOSH EDELSON/AFP/Getty Images)
Residences burned by wildfires are seen in this aerial photograph taken above Santa Rosa, California, U.S., on Thursday, Oct. 12, 2017. Wildfires that tore through northern California's iconic wine-growing regions have prompted evacuations of more than 20,000 people, killed 11 and damaged some of the most valuable vineyards and wineries in the U.S. About 1,500 commercial, residential and industrial structures were burned, and damage assessment teams have started accounting for the destruction. Photographer: David Paul Morris/Bloomberg via Getty Images
TOPSHOT - Fire damage is seen from the air in the Coffey Park neighborhood October 11, 2017, in Santa Rosa, California More than 200 fire engines and firefighting crews from around the country were being rushed to California on Wednesday to help battle infernos which have left at least 21 people dead and thousands homeless. / AFP PHOTO / Elijah Nouvelage (Photo credit should read ELIJAH NOUVELAGE/AFP/Getty Images)
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The stifling smoke in Northern California has prompted health advisories, canceled outdoor events, and closed schools for days.

"Some of the air quality readings are-off-the-chart bad. There are people who didn't even have issues before that are experiencing issues now," said NBC News meteorologist Bill Karins.

On Thursday, the Bay Area Air Quality Management District warned that there were "unprecedented levels of air pollution throughout the Bay Area" and cautioned that air quality could either improve at times or get worse very quickly.

Related: Death Toll in California Wildfires Rises; Some Survivors Escaped Just In Time

Shifting winds have since lowered the levels of pollutants a bit, but Ralph Borrmann, a spokesman for the Bay Area Air Quality Management District, said the numbers were changing "hour by hour."

"The worst air quality would be up in Napa, but other parts of the Bay Area are also getting levels which we don't normally see," he said.

The Bay Area Air Quality Management District distributed about 20,000 N-95 masks, special filtration masks that can prevent fine particles from being inhaled, Borrmann said. He recommended that residents impacted by heavy smoke stay inside if it's safe to do so, and take shelter in places with filtered air, such as libraries or malls.

The blazes started Sunday and have killed at least 31 people and destroyed about 3,500 structures.

Part of what makes the smoke from these particular wildfires so noxious, said Jim Roberts of the National Oceanic and Atmospheric Administration's chemical scientist division of the Earth System's Research Laboratory, is the fact that so many buildings burned down.

10 PHOTOS
Satellite images of California's wildfires
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Satellite images of California's wildfires

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

Photo Credit: Copyright DigitalGlobe

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"Those fuels are completely different in several important respects," Roberts said. "You have a lot of plastics and things like carpeting, foam insulation. Those have their own unique emissions and some of them are a lot more toxic than what we normally find in wildfires."

Related: Wildfires in California's Wine Country Hit Vulnerable Immigrant Farmworkers

How long the pollution sticks around all depends on the wind direction. But experts don't think it will impact the area in the long run.

"Most of the stuff that comes out of these fires is what we call short-lived climate species, things like black carbon particles. They'll have an effect, but it's short-term," Roberts said.

Rain could also clear the smoke out, but the area still has a couple of weeks until its rainy season begins, meteorologist Karins said.

Ryan Kittell, a forecaster at the National Weather Service in Oxnard, California, said the more progress that is made on containing the fires, the less smoke pollution residents will experience.

"Obviously we can't predict how the fires are going to behave in the next 24 or 48 hours," he said. "Certainly we're hopeful that no fires get started and the public heeds the message to be really careful with any fire sources."

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