Collaborative Research: RAPID: Collecting, archiving, and characterizing residual ash, transported ash, and particulate matter from the Los Angeles fire

The wildfires in Los Angeles in January 2025 were the most destructive disaster in recent California history. While much is known about wildfire smoke, a significant knowledge gap remains about how far toxic chemicals spread from the active burn areas. To find out, Dr.

Spada and his community partners set up an air monitoring network at locations across the Los Angeles area, downwind of the largest fires. These monitors continuously collected smoke, dust, and ash while the fires were still active and throughout cleanup activities. For millions of Los Angeles residents, these measurements will provide answers about how much toxic chemicals were released, how far they traveled, and when is safe to return to burned areas.

Insights gained from this project will help bridge our knowledge gaps and allow us to be better prepared for the future.

This RAPID grant will support field research to collect, archive, and characterize samples during and immediately after the Los Angeles (LA) fires that started on January 7th, 2025. The aim of the project is to quantify the concentration and determine the speciation of toxic elements in airborne particulate matter (PM) collected during and following the fires.

Specific objectives are: 1) To collect and archive PM during and following the fires; 2) To quantify the concentrations of elements in all samples; 3) To disseminate validated findings appropriately in order for public health and government agencies to provide accurate recommendations for residents returning to their homes; and 4) To share collected materials with scientific collaborators to maximize the learning potential from this unique scenario. Ambient PM was collected using cascading impactors with rotating stages at four locations distributed across the LA area.

Samples will be analyzed initially at Crocker Nuclear Lab’s 76-inch isochronous cyclotron using Proton-Induced X-ray Emission (PIXE), Proton Elastic Scattering Analysis (PESA), and Rutherford Backscattering Analysis (RBA). These combined measurements provide quantitative results for non-volatile H, C, and O alongside Na – Br and Pb. To the team's knowledge, this will be the first dataset of its kind.

Subsequent measurements will include Synchrotron-induced X-ray Fluorescence (SXRF) at the Stanford Synchrotron Radiation Lightsource to measure higher atomic weight elements such as cadmium, cesium, and rare earth elements. Supporting measurements will include mass concentrations via soft-beta ray attenuation and broadband optical spectroscopy, which will enable factorization and source apportionment analyses by future collaborators.

The sampling campaign captures PM during the fire, immediately after the fires were put out, while the burn areas were still smoldering, and during cleanup activities that may resuspend toxic substances. These results will provide information on the exposures to first and second responders and to residents downwind of the fire areas.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.