Date of Award
Spring 2026
Document Type
Open Access Dissertation
Department
Public Health
First Advisor
Mohammed Baalousha
Abstract
Wildland–urban interface (WUI) fires are increasing in frequency and severity, generating complex mixtures of contaminants of emerging concerns that pose substantial environmental and human health risks. While bulk particulate matter and dissolved pollutants from fires have been widely studied, the occurrence, composition, and behavior of incidental nanomaterials (INMs) and environmentally persistent free radicals (EPFRs) produced during WUI fires remain poorly understood. This dissertation research contributes to advancing the characterization and mechanistic understanding of fire- derived nanomaterials and persistent radicals in fire-impacted environments, with a focus on WUI fire ash and post-fire environmental systems.
The primary objective of this dissertation is to investigate the formation, composition, transformation, environmental fate, and potential implications of INMs and EPFRs generated during WUI fires. Fire ash and soil samples were collected from two major WUI fires during the 2020 California fire season: the North Complex Fire and the Sonoma–Lake–Napa Unit (LNU) Lightning Complex Fire. These collected ash samples represent a range of fuel sources, including vegetation, structural materials, vehicles, and treated wood, allowing evaluation of source-specific nanomaterial signatures. They also cover a range of combustion completeness, allowing fundamental understanding of INM and EPFR formation and concentration as a function of combustion processes. In addition, samples were further classified based on visual color inspection, reflecting differences in the degree of combustion completeness.
A suite of complementary analytical techniques was employed to achieve total elemental composition and particle-resolved characterization. Electron paramagnetic resonance (EPR) spectroscopy was used to quantify EPFRs and other paramagnetic species. Total elemental concentrations were determined using inductively coupled plasma–time-of-flight mass spectrometry (ICP-TOF-MS) following microwave-assisted acid digestion. Incidental nanomaterials were characterized at the single-particle level using single-particle ICP-TOF-MS (SP-ICP-TOF-MS) and high-resolution transmission electron microscopy (HR-TEM). Magnetic separation combined with time-domain nuclear magnetic resonance (TD-NMR) relaxometry, and SP-ICP-TOF-MS were applied to isolate and quantify magnetic nanoparticles. Controlled laboratory experiments in synthetic rainwater and surface water were conducted to investigate post-fire transformations of INMs.
Results demonstrate that WUI fires act as high-temperature chemical reactors that generate chemically heterogeneous, metal-rich INMs containing iron, titanium, manganese, chromium, copper, arsenic, and other potentially toxic elements, frequently co- occurring within individual nanoparticles. EPFRs were ubiquitous in WUI fire ash and were closely associated with metal-bearing and magnetic nanomaterials, forming highly redox-active particle systems. Particle-resolved analyses revealed distinct source-specific nanomaterial signatures, including nanoparticles derived from chromated copper arsenate (CCA)-treated wood and magnetically active iron oxide phases. Post-fire aqueous experiments further showed that fire-derived INMs undergo significant post-fire transformations in synthetic rainwater and surface waters, including dissolution, aggregation, and compositional redistribution, which strongly influence their mobility and environmental persistence.
Collectively, this dissertation advances a new framework for understanding WUI fires as sources of complex nanoscale contaminants and highlights the importance of combined total elemental composition and particle-resolved approaches for accurate environmental and human health risk assessment. The findings underscore the need to incorporate INMs and persistent radicals into post-fire monitoring, exposure assessment, and wildfire management strategies.
Rights
© 2026, Mahbub Alam
Recommended Citation
Alam, M.(2026). Characterization and Transformation of Incidental Nanomaterials and Environmentally Persistent Free Radicals In Wildland–Urban Interface Fire Ashes. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/8858