Probing Interactions at the Organic–Inorganic Interface of Biomass Burning Aerosol: Reactivity of Organic Tracer Species with Different Iron Oxide Mineral Phases

As wildfire events become more frequent, there is a need to better understand the impact of smoke on the environment and human health. Smoke, or biomass burning aerosol (BBA), can undergo atmospheric processing changing its chemical and optical properties. We examined the interactions between four lignin pyrolysis products (catechol, syringol, syringic acid, and vanillic acid) and three BBA-relevant iron oxide mineral phases (hematite, maghemite, and magnetite) using attenuated total reflectance-Fourier transform infrared spectroscopy and dissolved iron measurements to better understand how atmospheric processing changes concentrations of soluble iron, iron oxidation state, and brown carbon abundance. Reductive dissolution was the primary dissolution mechanism for catechol and syringol, which led to a substantial amount of iron release (<i>p</i> < 0.05), whereas syringic and vanillic acids had little impact on dissolution. Comparisons with other BBA relevant compounds highlight the importance of both steric and electronic structures in the reductive dissolution process. The maghemite and magnetite phases, which are more likely to be present in BBA, released significantly more dissolved iron than hematite (<i>p</i> < 0.05), emphasizing the need to use BBA relevant iron oxide proxies in laboratory studies. This work provides insight into observations of iron dissolution and transformation of organics in BBA.