LOS ANGELES (AP) — At the height of the Los Angeles fires in 2025, millions of residents were exposed in a 24-hour period to toxic lead levels from smoke that were 80 times higher than the typical background level, according to a new study.

Researchers from the California Institute of Technology compared the chemical composition of smoke from the Eaton Fire with that of a wildfire and found that the urban plume had more lead, arsenic and halogens (which include chlorine and bromine) linked to burning vehicles, building materials and electronics.

“The main, key finding is really that wildfire smoke is very different fundamentally from the urban smoke,” said Nga Lee “Sally” Ng, an author of the study published Wednesday in the journal Science Advances. With the new technology they used to measure what was in the smoke, they were able to “actually see the very detailed component of these particles that we are breathing.”