PARADISE (California) • The wildfires that have laid waste to vast parts of California are presenting residents with a new danger - air so thick with smoke it ranks among the dirtiest in the world.
Last Friday, residents of smog-choked Northern California woke up to learn that their pollution levels now exceed those in cities in China and India that regularly rank among the worst worldwide.
In the communities closest to the Paradise fire, an apocalyptic fog cloaked the roads, evacuees wandered about in white masks and officials said respiratory hospitalisations had surged.
Nearly 320km to the south, in San Francisco, the smoke was so thick that health warnings prompted widespread closure of schools. Even the city's cable cars were yanked from the streets.
And researchers warned that as large wildfires become more common - spurred by dryness linked to climate change - health risks will almost surely rise. "If this kind of air quality from wildfires doesn't get people concerned," said Dr John Balmes, a pulmonologist at the University of California at San Francisco, "I don't know what will."
At fault, researchers said, is a confluence of two modern events: More people are moving to communities in and around wooded enclaves, pushed out of cities by factors like the rising costs of housing and the desire to be closer to nature - just as warming temperatures are contributing to longer and more destructive wildfires.
Wood smoke contains some of the same toxic chemicals that city pollution does. While humans have long been around fire, they generally inhale it in small doses over cooking or heat fires. Humans have not, however, evolved to handle prolonged inhalation of caustic air from something like the Paradise blaze, Dr Balmes said.
Research into the long-term health effects of large wildfires is still new. But a growing body of science shows how inhalation of minuscule particles from wood fires can nestle in the folds of lung tissue and do harm to the human immune system.
The body creates zealous responses to what it sees as an alien presence and those effects can last for years by priming the body to overreact when it encounters subsequent lung irritation, said Dr Kari Nadeau, a paediatric allergy and asthma specialist at Stanford University. In short, researchers believe that a person's short-term exposure to wildfire can spur a lifetime of asthma, allergy and constricted breathing.
Officials statewide do not have a grasp yet of how damaging and widespread the health effects of the smoke might be.
As the death toll continues to rise in the deadliest wildfire in California history, the sheriff of the Northern California county where the fire still rages said last Friday that more than 1,000 people were still missing, a startling increase from previous lists.
As of last Friday, 71 people had been confirmed dead in the fire, which has razed the city of Paradise and its surrounding areas since Nov 8. President Donald Trump was slated to travel to California yesterday to survey the damage.
Last week, some people around Paradise said that when they inhaled, they could feel the particles cutting their throats. Others likened breathing to a persistent low-level anxiety attack.
"Let me put it this way. You almost feel like you're choking," said Ms Becky Dearing, 66, who already has chronic obstructive pulmonary disease. "We're like zombies walking around," she added.