Temperature-Dependent Particle Formation During Biomass Combustion: A Combined spICP-TOFMS and Magnetic Study

Abstract

Wildfires increasingly threaten ecosystems worldwide, yet their impact on nanoparticle formation and environmental mobility remains poorly understood. This study investigates how combustion conditions (temperature and duration) influence the production, composition, and magnetic properties of inorganic nanoparticles through controlled laboratory experiments on heather biomass. By combining inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) analyses of individual nanoparticles from leachate and magnetic measurements, we characterized samples formed across a range of combustion temperatures (400–800 °C) and durations (5–30 min). Fresh, organic-rich samples exhibited predominantly diamagnetic behavior. Progressive heating marked increases in saturation magnetization (Ms), suggesting transformation of iron oxide phases with significant changes emerging at 400 °C and intensifying above 550 °C. Leaching experiments revealed pronounced shifts in particle composition: fresh samples released predominantly iron-rich particles (>50%), whereas high-temperature combustion (800 °C) yielded leachates dominated by manganese nanoparticles (>95%). At intermediate temperatures (550 °C), a distinct population of Fe–Mn bimetallic nanoparticles appeared, indicating redox-driven coalescence or intermetallic interactions. Particle concentrations ranged from 1.2× 10⁷ to 1.6 × 109 particles g⁻¹, with complex release patterns reflecting competing processes of enhanced mobilization, particle coarsening, and aerosolization at extreme temperatures. Together, magnetic and leaching data provide complementary constraints on fire-induced transformations. We identify multiple nanoparticle-based proxies for combustion conditions, including enhanced magnetic signatures, manganese enrichment in leachate and bimetallic MnFe particle formation. These proxies serve two practical purposes. First, they enable the reconstruction of burning conditions after a fire without requiring measurements taken during the fire itself. Second, they improve predictions of how fire-derived nanoparticles, which can carry adsorbed contaminants such as heavy metals, migrate through soils and waterways after wildfires. Ultimately, they advance our understanding of how contaminants disperse in fire-affected landscapes.