Los Angeles Eaton Fire Smoke Exposed 7 Million People to Toxic Metals, With Lead 80 Times Normal Levels in 24 Hours, Study Finds

LOS ANGELES — A new study reported on October 29 found that the January 2025 Eaton Fire did more than burn homes: its smoke exposed about 7 million people to high levels of airborne lead and other toxic metals. The fire destroyed more than 9,400 buildings and killed 19 people; the study, published in the journal Science Advances, is the first to quantify in real time the chemical composition of smoke from an urban firestorm — toxic substances released as homes, electronics, cars and infrastructure burned, carried by wind far from the burn zone.

In 24 hours: lead at 80 times normal levels

Over a 24-hour period, researchers measured lead in the smoke at 80 times the concentration normally found in the atmosphere; sensors also detected highly elevated levels of arsenic and other toxins. Lead is a neurotoxin, particularly harmful to children. The plume covered eastern Los Angeles and the San Gabriel Valley and affected about 70 percent of Los Angeles County's population — meaning the exposure reached far beyond residents near the fire itself, to millions of ordinary city dwellers. Nga Lee (Sally) Ng, a co-author of the study and a professor of environmental science and engineering at Caltech, noted that chronic exposure to metals like lead is well studied, but the health effects of short-term exposure to highly concentrated airborne toxins remain largely unknown.

Why it could be measured this time: a sensor network that came online months before

The measurement was possible because a Los Angeles monitoring site of the Atmospheric Science and Chemistry Measurement Network (ASCENT) happened to sit downwind of the Eaton Fire — and the network had come online only months before the fire. Funded by the National Science Foundation, ASCENT runs stations across the country that measure the chemical components and particle sizes of airborne particles in real time. Lead author Haroula Baliaka, a PhD candidate at Caltech at the time of the study, said the system could also track how the smoke's toxic composition changed as the fire burned, helping health researchers pinpoint the effects of urban firestorms. One gap remains: because of wind direction, the site could not collect data on the Palisades Fire, which ignited about 34 miles away hours earlier the same day.

What comes next: evacuation zones for smoke itself

Baliaka's policy suggestion deserves attention from decision-makers: if toxic smoke can affect people far from the burn zone, evacuation planning may need to look beyond the fire perimeter. She said she could envision evacuation zones for smoke exposure in future, and warned that this is not a one-time event but a new reality that needs adapting to sooner rather than later. For Los Angeles residents, the practical takeaway is not panic — the researchers themselves stress that the long-term health consequences of short, high-concentration exposure are still unknown — but a reminder that an urban fire's harm radius is far larger than its fire line, and that residents along a smoke plume's path need protection guidance too, not only households at the fire's edge.