Widespread occurrence of Magnéli phases in wildland-urban interface fire ashes

Environmental Science and Technology.
By: , and 

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Abstract

The increasing activity of wildland–urban interface (WUI) fires has raised concerns regarding the potential environmental and human health impacts of residual ash remaining after burning. In this study, we investigated the concentration and speciation of titanium in WUI fire ash. Total titanium concentrations in WUI fire ash ranged from 0.53 to 80 g kg–1. Synchrotron-based macro- and microscale X-ray absorption near-edge structure (XANES and μXANES, respectively) spectroscopy were used to quantify the relative abundance of major Ti phases in the fire ash, and the results were corroborated by high resolution-transmission electron microscopy (HR-TEM) measurements. Rutile (α-TiO2), anatase (β-TiO2), ilmenite (FeTiO3), and titanium(III) oxide (Ti2O3) were detected in all 20 ashes investigated by XANES and accounted for 0.26–0.83, 0.19–0.83, 0.33, and 0.17–0.72 of the spectral weight, respectively. Deeper analysis by μXANES of one sample demonstrated that Ti-bearing particles occurred as a mixture of rutile (α-TiO2), anatase (β-TiO2), ilmenite (FeTiO3), and titanium(III) oxide Ti2O3, with the absence of a pure Ti2O3 phase. The presence of Ti2O3 in the WUI fire ash is ascribed to the reduction of rutile and anatase to Magnéli titania (TinO2n–1n = 4–9), which is estimated to be the dominant phase of titanium in the 20 WUI fire ashes investigated by XANES. The occurrence of Magnéli titania was corroborated by HR-TEM. Our findings demonstrate the impact of WUI fires on titanium speciation; fires convert titanium dioxides (e.g., rutile and anatase) to reduced titanium phases (e.g., Magnéli titania). Based on HR-TEM analyses, most of the titanium-bearing particles were less than 500 nm in size. Magnéli particles have been shown to be more toxic than rutile and anatase and have been linked to reduced lung function. Therefore, this study provides critical insights into the pollution characteristics and potential health risks of WUI fire ashes and associated particles, which are currently poorly understood.

Suggested Citation

Baalousha, M., Desmau, M., Colina-Ruiz, R.A., Lanzirotti, A., Singerling, S., Stern, M.A., and Alpers, C.N., 2026, Widespread occurrence of Magnéli phases in wildland-urban interface fire ashes: Environmental Science and Technology., https://doi.org/10.1021/acs.est.5c09885.

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Publication type Article
Publication Subtype Journal Article
Title Widespread occurrence of Magnéli phases in wildland-urban interface fire ashes
Series title Environmental Science and Technology.
DOI 10.1021/acs.est.5c09885
Edition Online First
Publication Date March 29, 2026
Year Published 2026
Language English
Publisher American Chemical Society
Contributing office(s) California Water Science Center
Country United States
State California
Other Geospatial North Complex Fire, Sonoma-Lake-Napa Unit Lightning Complex Fire
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