Eric Risberg / AP

The deadliest fire in California’s history continues to burn, and San Francisco is filled with smoke and ash. On Tuesday, for the fifth day in a row, air throughout Northern California contained high amounts of fine-particulate-matter pollution, and the Bay Area Air Quality Management District warned that the air was unhealthy for everyone. “The public should limit outdoor activity as much as possible,” the agency said Monday, urging residents to stay inside with their windows and doors closed.

But for San Francisco’s thousands of homeless people, this warning is impossible to follow. San Francisco, like many California cities, has seen homelessness rise in recent years, as the cost of housing has gone up and zoning laws have limited the construction of new housing units. Despite an initiative passed on November 6 to tax large businesses to fund homeless services and news that the CEO of Twilio had donated $1 million to fund homeless services until the tax kicks in, thousands of people still have nowhere to go in San Francisco on any given night. As the number and deadliness of fires grows in California, the population of people negatively impacted by the air quality is growing, too.

Trina Smith is one of those people. She has asthma, and says that as early as Thursday, when the fires began, she noticed that she was having more difficulty breathing. She’s more congested than usual, she said, but when she asked a doctor what she could do, she says she was told to get a mask and stay inside. “But there’s nowhere to go,” she said, sitting in the smoky air on Polk Street in San Francisco’s Tenderloin district as night fell on Monday.

Many of San Francisco’s homeless are already battling health issues that are worsened by poor air quality. People who don’t have a place to live often can’t eat well or take medications regularly. They are more likely to develop skin disorders and diseases of the extremities; they often suffer from untreated mental illness; and they are frequently victims of crimes such as assault. Self-reported rates of lung disease such as asthma are double those of the general population. The air from the fires is one more thing to contend with. “The things that are an inconvenience for the rest of us, to say nothing of the devastation for those in the path of the fires, present more danger and uncertainty for our unhoused neighbors,” said Sherilyn Adams, the executive director of Larkin Street Youth Services. “Health issues are already more prevalent for individuals experiencing homelessness, and prolonged exposure to the poor air quality increases health risks, as well as discomfort and, ultimately, a sense of the isolation.”

Some groups in San Francisco have tried to help. The City of San Francisco’s Homeless Outreach Team is performing wellness checks and offering masks to unsheltered people, a spokesman told me. The San Francisco Public Library kept its main branch open until 9 p.m. on Friday because of air-quality issues, instead of closing at 6 p.m. as it usually does, but only about 10 people took advantage of the extended hours, a spokeswoman said. St. Anthony’s, which serves meals in San Francisco’s Tenderloin neighborhood and operates an evening shelter in the winter, opened its dining room for people to sleep in from 5 p.m. to 8 a.m. beginning Friday evening. About 14 percent of the people who have stayed since Friday have respiratory problems, said Marnie Regen, St. Anthony’s director of development and outreach. But there are few solutions for people who want to stay inside all the time, as the authorities recommend.

“They should be declaring this a state of emergency. We’re all having problems breathing,” Brian Leany, 50, said. Leany knows how hard it can be to get housing in San Francisco—he said he was run over by a garbage truck and broke both of his feet, but that his medical condition didn’t move him up any wait lists for permanent supportive housing. Still, Leany was hesitant to go to a temporary shelter, since, he said, he could catch something just as unhealthy there, like tuberculosis or the flu. He said he preferred sleeping on the streets, being protected from thieves and criminals by staying near friends outside.

Lisa Cooper got three of the masks that were being handed out by the city, because she was having trouble breathing. But then she fell asleep on the street after being awake for nearly four days, she said, and all three masks had been stolen. On Monday evening, she was on her way to a shelter, but said her spot was only guaranteed for one night—she has addiction issues and some of the shelters are strict about drug use. She is worried for her health if she stays on the streets. “Right now, it’s hard to exhale and inhale fully,” she said.

Smoke from wildfires is dense with tiny, toxic irritants that scientists call particulate matter. It’s a catchall term that refers to any microscopic bit of material released by a fire: a mote of dust, a flake of ash, an unburned shred of wood, or a droplet of sulfuric acid. A messy, incomplete, uncontrollable wildfire can spew any of these things—each many times thinner than a human hair—into the atmosphere.

And when there’s more particulate matter in the air, more people die. It seeps into the tissue of the lungs and heart, triggering heart attacks and aggravating asthma. The closer scientists look, the more harm particulate matter seems to cause: A study published this summer found that particulate matter so inflames the body that it can cause diabetes. More than 150,000 cases of diabetes in the United States are directly attributable to particulate matter, scientists now argue.

“I think everyone would agree that the particulate matter is by far the largest public-health threat [from wildfires] from an air-quality perspective,” said Greg Huey, a professor of atmospheric chemistry at the Georgia Institute of Technology.

There’s reason to believe there are going to be more wildfires in coming years, and cities like Los Angeles and San Francisco that are experiencing high levels of homelessness also happen to be in regions more vulnerable to wildfires. There are currently more than 50,000 homeless people in Los Angeles County, a 36 percent increase from 2010. There are 7,500 homeless people in San Francisco, a 16 percent increase from 2011.

Fires can contribute to homelessness, too. As thousands of homes are destroyed in their path, more people have to look for somewhere to live, battling one another in the Bay Area’s vicious real-estate market. Real-estate agents last year told renters after the fires in Sonoma and Santa Rosa that they were going to have to pay higher rents because of the additional renters on the market.

It’s possible that the terrible air quality will spur cities in California to more effectively address their homelessness problems. Cities on the East Coast, after all, have had to figure out how to house people during blizzards, snowstorms, and periods of extreme cold. California cities, with their year-round balmy weather, have not had to worry that failing to house all of their residents could lead to people dying on the streets. That was then, but this new normal of uncontrollable wildfires in California is raising the already high risks of living on the streets.

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