Airborne Metal Toxin Particulate Signatures and Legacy at Wildland–Urban Interface

Alireza Namayandeh , Charlie Lamb, Frida Daniela Garcia Ledezma, Jonathon Howell, Catherine Erol, Dan Kubota, Raphael Kim, Charise Young, Katie Huy, Scott Fendorf

Wildland–urban interface (WUI) fires burn urban materials together with soil and vegetation, generating air pollution as smoke during active burning and as resuspended dust during recovery. Here, we combine size-resolved sampling of the Eaton Fire (Altadena, CA) with controlled resuspension of materials collected from properties affected by the Eaton and Palisades (Pacific Palisades, CA) fires. Lead is a clear urban-fire signature when compared with wildland-fire smoke, with ~60% of total Pb residing in the ultrafine fraction. By contrast, Cr in urban smoke remained within the wildland-fire range and followed the geologic composition of the fire perimeter. During resuspension, however, vehicle-associated debris produced >50-fold ultrafine Pb enrichment and >100-fold ultrafine Cr enrichment. Bulk source-metal concentrations alone did not predict airborne Pb and Cr release; total Cr release instead tracked the resuspendable particulate pool behavior. The metal toxins occurred as nanoparticles smaller than 10 nm and as multi-metal aggregates containing Pb, Cu, Zn, Cr, Fe, Ni, and Ti in both smoke and resuspended particulates. Our results establish WUI fires as combustion–resuspension systems in which metal signatures evolve between active burning and post-fire resuspension, providing a basis for phase-specific monitoring, cleanup controls, and exposure protection.