People in San Francisco are wearing face masks because the air quality is so bad, and hardware stores can’t keep them in stock

On Thursday morning, the air quality in the Bay Area was worse than in Beijing, which is notorious for having some of the unhealthiest air in the world. In what is being called one of the worst firestorms in California history, smoke heavy with soot continues to blow across the state.

In San Francisco — more than an hour's drive south from the epicenter of the blazes in Santa Rosa — many people are wearing face masks in an attempt to shield themselves from the pollution that hangs like a curtain in the hazy air. The most concerning pollutant is PM2.5, also known as particulate matter. Particulates have a unique ability to penetrate and lodge deep inside the lungs, where they can worsen respiratory issues and trigger asthma attacks.

See how the fire has devastated the region:

25 PHOTOS
Wildfire devastation in Coffey Park, Santa Rosa
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Wildfire devastation in Coffey Park, Santa Rosa
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 TPX IMAGES OF THE DAY
SANTA ROSA, CA - OCTOBER 10: Chloe Hoskins, 7, tags along with her father, who was checking on a neighbors burned out property in the Coffey Park neighborhood on October 10, 2017 in Santa Rosa, California. (Photo by Brian van der Brug/Los Angeles Times via Getty Images)
SANTA ROSA, CA - OCTOBER 10: Spencer Blackwell, left, and Danielle Tate, right, find her father's gun collection, melted and burned, inside a gun safe at her father's home in the Coffey Park neighborhood on October 10, 2017 in Santa Rosa, California. (Photo by Brian van der Brug/Los Angeles Times via Getty Images)
A US flag hangs on a tree in the widfire ravaged Coffey Park neighborhood of Santa Rosa, California, October 11, 2017. The death toll from some of California's worst ever wildfires rose to 17 as thousands of firefighters battled to bring the infernos under control. The fires which have devastated California's wine country are already among the deadliest ever in the western US state and officials warned they expect the toll to go up. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
SANTA ROSA, CA - OCTOBER 10: Jennifer Yarnal searches for keepsakes in the rubble of her home in the Coffey Park neighborhood on October 10, 2017 in Santa Rosa, California. (Photo by Brian van der Brug/Los Angeles Times via Getty Images)
SANTA ROSA, CA - OCTOBER 10: Benicia police officer Alejandro Maravilla, left, offers resident Gwen Adkins, 84, right, a soda while patrolling in the Coffey Park neighborhood on October 10, 2017 in Santa Rosa, California. (Photo by Brian van der Brug/Los Angeles Times via Getty Images)
A police officers looks at the devastation wrought by wildfires in the Coffey Park neighborhood of Santa Rosa, California, on October 11, 2017. 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)
SANTA ROSA, CA - OCTOBER 11: Some houses burned and some did not. Aerial view of the damage caused by wildfire that destroyed the Coffey Park neighborhood on October 11, 2017 in Santa Rosa, California.(Photo by Marcus Yam / Los Angeles Times via Getty Images)
SANTA ROSA, CA - OCTOBER 11: Aerial view of the damage caused by wildfire that destroyed the Coffey Park neighborhood on October 11, 2017 in Santa Rosa, California.(Photo by Marcus Yam / Los Angeles Times via Getty Images)
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)
Firefighters look for hotspots in the destroyed Coffey Park neighborhood in Santa Rosa, California, 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 / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
The remains of the Coffey Park neighborhood in Santa Rosa, California,October 12, 2017. Massive wildfires sweeping through California have killed at least 26 people and damaged thousands of homes, businesses and other buildings, according to authorities. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
The remains of the Coffey Park neighborhood in Santa Rosa, California,October 12, 2017. Massive wildfires sweeping through California have killed at least 26 people and damaged thousands of homes, businesses and other buildings, according to authorities. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
Melted metal from burnt cars is formed on the ground after wildfires ripped through the Coffey Park neighborhood of Santa Rosa, California, on October 11, 2017. 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)
SANTA ROSA, CA - OCTOBER 11: Surrounding neighborhoods untouched by fire outside the Coffey Park neighborhood on October 11, 2017 in Santa Rosa, California.(Photo by Marcus Yam / Los Angeles Times via Getty Images)
SANTA ROSA, CA - OCTOBER 11: Aerial view of the damage caused by wildfire that destroyed the Coffey Park neighborhood on October 11, 2017 in Santa Rosa, California.(Photo by Marcus Yam / Los Angeles Times via Getty Images)
SANTA ROSA, CA - OCTOBER 10: Andrew Hopkins digs around in the rubble of his step-mother Pam Hopkins' home in the Coffey Park neighborhood on October 10, 2017 in Santa Rosa, California. (Photo by Brian van der Brug/Los Angeles Times via Getty Images)
Tangerines burned black by wildfires still hang on a tree in the Coffey Park neighborhood of Santa Rosa, California, on October 11, 2017. 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)
Extensive residential devastation is seen after wildfires ripped through the Coffey Park neighborhood of Santa Rosa, California, on October 11, 2017. 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)
SANTA ROSA, CA - OCTOBER 10: Andrew Hopkins sifts through his father's fire-singed baseball card collection at his step-mother Pam Hopkins' home in the Coffey Park neighborhood on October 10, 2017 in Santa Rosa, California. (Photo by Brian van der Brug/Los Angeles Times via Getty Images)
SANTA ROSA, CA - OCTOBER 10: Andrew Hopkins sifts through his father's fire-singed baseball card collection at his step-mother Pam Hopkins' home in the Coffey Park neighborhood on October 10, 2017 in Santa Rosa, California. (Photo by Brian van der Brug/Los Angeles Times via Getty Images)
SANTA ROSA, CALIFORNIA - OCTOBER 9: Lights from news crews cast an eerie glow on the devastated Coffey Park neighborhood in Santa Rosa on October 9, 2017 in Santa Rosa, California. (Brian van der Brug / Los Angeles Times via Getty Images)
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)
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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For people who live in places like Delhi and Beijing, where the air quality regularly reaches or even exceeds the Bay Area's current levels, avoiding the harmful particles is a daily struggle. But Californians accustomed to some of the world's cleanest air are suddenly anxious about the potential health effects of breathing in the smoke, and face masks quickly sold out in local hardware stores this week.

People across Oakland and San Francisco could also be seen wearing masks as they walked to and from work or transit.

Yang Guo, an employee at Citi Bank, said his girlfriend bought the mask he wore in downtown San Francisco on Thursday from Ace Hardware. "It was the last one," he said.

Cole Hardware, another large hardware chain in the Bay Area, was sold out of face masks at all of its locations. "We sold out this morning at 9am sharp," a representative for the store told Business Insider.

Ariel Schwartz, a Business Insider editor who lives in San Francisco, went to Cole Hardware's downtown location on Wednesday evening. The masks were already sold out (she later found one in an emergency kit).

28 PHOTOS
Aerial images of California's wildfire devastation
See Gallery
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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How to protect yourself from the air: Make sure you're wearing the right kind of mask

The best bet for your health is to stay indoors and avoid working or exercising outside when possible. On the Environmental Protection Agency's air quality website, its message to residents is clear: "Everyone ... should reduce prolonged or heavy exertion," especially "people with heart or lung disease, older adults, and children." That's especially tough advice for people with outdoor jobs and the region's homeless.

If you must be outside, wear a mask — and make sure it's the right kind.

"If you have masks available, you should use them," Kristine Roselius, a spokeswoman for the Bay Area Air Quality Management District, told SF Gate.

Dust and surgical masks won't help. Instead, make sure your mask has a particulate respirator, a device that's specially designed to keep out soot and other particles that can cause the most harm. The right kind of mask will be marked as such, with labels that say either "NIOSH-approved," "N95," or "N100."

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SEE ALSO: The fires devastating California wine country have made the air more toxic than Beijing's — and it's about to get worse

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