LOS ANGELES -- The explosion of smoke and ash that erupted from two wildfires was beyond belief.

In the foothills of the San Gabriel Mountains, as the Eaton fire engulfed homes and businesses, a thick blanket of smoke rolled over the horizon, blocking out the sun.

The wildfires produced the heaviest smoke and soot the region has seen in recent memory.

On Jan. 8, an air monitor in Chinatown — about 10 miles downwind of the Eaton fire — recorded 483.7 micrograms per cubic meter of fine particulate matter, according to preliminary data from the California Air Resources Board. It was the highest hourly reading by an Environmental Protection Agency-sanctioned air monitor in Los Angeles County in more than four years — only outmatched by clouds of smoke from Fourth of July fireworks in 2020.

Near the coast, the Palisades fire chewed through the Santa Monica Mountains and reduced dream houses with Pacific views to their foundations, sending a jetstream of smoke out to the ocean. As the fire encroached on Pacific Palisades Elementary School, one of Los Angeles Unified School District’s low-cost air monitors recorded 1,100 micrograms per cubic meter of fine particulate matter — the highest mark since air monitors were installed in 2021.

At these levels, this microscopic pollution becomes hazardous. Although the magnitude of the effects of this kind of pollution is still not entirely clear, studies show that it is linked to an increased risk of heart attacks, strokes and serious lung damage.

The specific number of deaths and hospitalizations tied to wildfire smoke often are not well-known until months — if not years — after these natural disasters. That said, during the region’s recent wildfires, fire-related hospital visits spiked 16-fold across Los Angeles County, according to the county Department of Public Health. At its height, on Jan. 8, at least 81 people visited hospitals for burns or smoke exposure.

Experts say children are particularly vulnerable, because their still-growing lungs need to take more breaths and are thus more exposed to any given amount of pollution. In 2018, in the two weeks after the Camp Fire in Northern California — the worst deadliest in the state’s recorded history — 76% of children with asthma suffered an asthma attack or flare-up. Asthma-related emergency room visits in the area rose 27% during that time, according to a study from Stanford University and data firm Komodo Health.

Latino children with asthma seemed to suffer the worst; among that particular population, there was a 95% increase in attacks and flare-ups. Asian and Black children also saw significantly higher increases in attacks compared with white children’s rates of asthma attacks.

Marc Carmichael, who is currently a medical student at Stanford University, says similar disparities could arise in the aftermath of the wildfires in L.A. County. Some of the heaviest pollution from the Eaton fire wafted over Chinatown, Boyle Heights, Compton and Long Beach — historically disadvantaged communities that are largely Latino, Asian and Black, who already have endured some of the worst chronic exposure to industrial pollution in the region.

“Air quality standards aren’t going to do anything for these events,” Carmichael said. “Because these are acute events, you need to have preventive strategies for folks you already know are going to be more vulnerable to adverse consequences.”

As of Wednesday afternoon, there have been 25 confirmed deaths connected to the recent L.A. County wildfires. But researchers suspect that the ensuing smoke wave could contribute to many more.

Already, it may have resulted in as many as five deaths in L.A. County, according to an online tool that estimates countywide mortality from wildfire smoke. The experimental model, which analyzes federal air-quality data and satellite imagery, was created by Cornell University researchers, who hope it can help us better understand how smoke affects public health.

“It’s really hard to know, especially with mortality,” said Alistair Hayden, a Cornell assistant professor and former division chief for the California Governor’s Office of Emergency Services. “We know it has [potentially fatal] impacts, but it’s not showing up on people’s death certificates.”

“What people are really interested in when we’re looking at this is, is this just a nuisance smoke wave, or is this something that maybe is considered an actual disaster?”

Other groups also are trying to answer this question. NASA, for example, uses its satellites to assess air pollution, both chronic and during acute events such as what’s happened in L.A. County. In addition to smoke and soot, the space agency detected large plumes of harmful gases emanating from the wildfires, including lung-irritating nitrogen dioxide and cancer-causing formaldehyde.

“My gut feeling from looking at the numbers that I’ve seen is that it’s comparable to other fires,” NASA air-quality expert Laura Judd said about the emissions that have plagued L.A. County over the last several days. “What might be different is just the footprint — the density of people that are there. It is impacting millions of people that are in that region.”

Some potential good news: Although the smoke was intense at its peak, it was short-lived. Experts say the smoke from other longer-lasting wildfires lingered longer and may have led to more premature deaths than they expect from this case. The wildfire smoke thinned to a gray haze across Los Angeles County over the weekend, and since Monday, strong winds have helped clear out much of the remaining smoke.

But that doesn’t mean L.A. County residents are fully in the clear. Now, air-quality concerns are shifting from smoke to ash. The tons of wildfire ash and rubble that blanket many blocks across the county are likely to contain myriad toxic chemicals from fire-ravaged homes and cars, according to experts. The contaminants in the burn scars may pose a threat for years.

Since Sunday, the South Coast Air Quality Management District has issued dust advisories, warning that wildfire ash could have been whipped up by strong winds. It is encouraging people across much of L.A. County and neighboring areas to keep windows shut and continue to wear N95 masks outdoors to protect themselves.

Although recent air-quality index readings would appear to be safe, officials are cautioning that some wildfire ash is too large to be detected by their instruments and will not be captured by air monitors.

Though it’s unclear whether there will be long-term contamination from the wildfire, NASA scientists are using plane-mounted sensors to evaluate the fire damage and potentially detect toxic substances in the burn scar. The same type of instrument was used to assess the World Trade Center disaster site after the 9/11 terrorist attacks.

“I’m hoping to use data like what we acquired from [these sensors] to understand toxicity in these environments and how it changes as the ash gets redistributed through wind and through water flows,” said Michael Falkowski, a terrestrial ecology scientist at NASA.

The NASA findings could inform what is expected to be a years-long cleanup and recovery.

“We’ve known from other fires, like the Marshall fire in Colorado, that these environments are extremely toxic post-fire for a long time,”Falkowski said. “But we still have a lot to learn.”

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