At some point this autumn, the people of the San Francisco Bay Area will very likely wake up to find that the air smells of smoke, even indoors, and their cars are coated in ash. A hundred miles to the northeast, in the state’s ever drier forests, a massive wildfire will be burning, fanned by strong seasonal winds that will carry the smoke into the lungs of millions of people. The asthmatic will suffer the most, but the plummeting air quality will elevate the risks of respiratory diseases like pneumonia and tuberculosis. This year they’ll face an additional menace: Covid-19.
A galaxy of conspiring factors, including climate change and land misuse, have turned the California landscape into a tinderbox that now burns with incredible and reliable ferocity. In 2017 came the Tubbs Fire, which caused $ 1.2 billion in damage and killed 22. In 2018, it was the Camp Fire, which virtually obliterated the 30,000-person town of Paradise, killing 86. Last year it was the Kincade Fire, which burned almost 80,000 acres. Each has flung massive clouds of smoke into the air, infiltrating the lungs of the firefighters and evacuees on the frontlines, and even more people downwind.
Scientists still have much to learn about Covid-19, but, says Jessica McCarty, a geographer and fire scientist at Miami University, “We know that there’s linkages between people who live in highly-polluted areas and their likelihood of getting any type of respiratory illness, as well as viral infections.” Smog from cars, for instance, remains a major threat to human health.
With wildfire smoke, the respiratory risk is due to its particulate matter, a form of charred plant material that’s small enough to penetrate deep into the lungs. This causes inflammation and a reduction in lung function, even in healthy people. Fine particles also seem to muck with the lungs’ ability to expel viruses and bacteria, hence the susceptibility to tuberculosis (caused by a bacteria) and pneumonia (an infection caused by both bacteria and viruses). More specifically, one study done in mice found that wildfire smoke decreases the antimicrobial activity of pulmonary macrophages, cells that clear the lungs of harmful microbes. Since the SARS-CoV-2 virus attacks the lungs, anything that weakens their ability to protect themselves may heighten the risk of infection.
But even during a wildfire, not all of the Bay Area’s smoke comes from the blaze itself. Homes, too, are a source of air pollution. “I just never thought this would be the case, but during the wildfires, we had people burning in their fireplaces,” says Wayne Kino, deputy air pollution control officer at the Bay Area Air Quality Management District. People also burn their yard trimmings throughout the summer and fall, worsening air quality—and potentially even starting wildfires.
This fall, by the time the seasonal high winds and the worst part of wildfire season arrive, Bay Area residents may still be staying at home. People may be driving less and enjoying better air quality. And that would be better than usual for lung health. But it’s equally possible that people will be avoiding public transportation for fear of the virus, actually increasing road traffic. More cars idling in traffic means more air pollution.
The biggest wildfires tend to break out when it’s hot—already-parched vegetation gets even drier when hot winds whip through it—and that heat forms its own extra source of air pollution. “Sunlight hits compounds in the air, and then ozone forms,” says McCarty. “If the weather is seasonably warm and a fire happens, you’re going to get other things forming that aren’t that aren’t just particulate matter. So it is a very complex system.”
Plus, if it’s hot out, and residents are already cranky after six months of sheltering in place, officials may struggle to convince them to hermetically seal themselves inside. “If you’re told: don’t open your windows, turn off your HVAC system, we know it’s going to be hot. But just stay in your house during these smoke events—how many people are going to do that?” McCarty asks.