Atmospheric Processing of Anthropogenic Combustion Particles: Effects of Acid Media and Solar Flux on the Iron Mobility from Fly Ash

Abstract

Atmospheric combustion particles, such as fly ash emitted from coal-fired power plants, are a potential source of atmospheric iron, with significant implications in climate and global biogeochemical cycles. While the iron content and speciation of fly ash depend closely on the source region and combustion process, few studies have been carried out comparing the atmospheric processing of fly ash produced from coal-fired power plants in different regions. In this study, we present an investigation of iron dissolution in acidic aqueous solutions: HNO 3 and HCl at pH 1 and pH 2 under daytime and nighttime conditions for three fly ash samples from three different sources: United States (USFA), Central Europe (EUFA), and India fly ash (INFA). Iron mobility and speciation depend on the source region and the combustion efficiency that generates fly ash. In HCl suspensions, proton-promoted mechanisms lead to larger fractions of aqueous-phase iron leached from fly ash particles, with poorly combusted samples providing significant fractions of Fe 2+ . In HNO 3 suspensions, a surface-mediated redox reaction suppresses the mobility of Fe 2+ , leading to the formation of nitrites. In the presence of solar radiation, previously unrecognized pathways of atmospheric processing enhance the formation Fe 2+ and nitrous acid from combustion particles. The information provided herein could be significant to increase our understanding of the effects of combustion particles in the atmospheric chemical balance regarding iron and nitrites.

Iron from coal combustion particles dissolves much faster than mineral dust under simulated atmospheric acid conditions

“…Moreover, the new 3-step dissolution scheme better captured the initial fast dissolution of CFA (Figs. 2-3) which was also observed in previous research (Borgatta et al, 2016;Chen et al, 2012;Chen and Grassian, 2013;Fu et al, 2012;Kim et al, 2020) (except for the certified CFA 2689 in Chen et al (2012) which showed increasing dissolution rates over the duration of the experiment). Furthermore, the new scheme enabled us to account for the different Fe speciation determined in the CFA samples, which could be a key factor contributing to the different Fe dissolution behaviour observed in the present study and in literature (Borgatta et al, 2016;Chen et al, 2012;Chen and Grassian, 2013;Fu et al, 2012;Kim et al, 2020).…”

“…compared the Fe solubility of CFA from USA Midwest, North-East India, and Europe in acidic solution (pH 1-2) containing 1 M NaCl. The Fe solubility measured after 24 hours varied from 15% to 70% in different CFA (bulk samples) at pH 2 with 1 M NaCl, which was considerably higher than that observed at pH 2 with 1 M NaNO3 (<20%) (Kim et al, 2020). Both studies did not investigate the impact of ionic strength on the dissolution behaviour, i.e., by comparing the dissolution at low and high ionic strength.…”

“…Recent studies have considered the effect of the high ionic strength on the Fe dissolution kinetic of CFA under acidic conditions. For example, the Fe solubility of CFA samples was measured at pH 1-2 with high sodium chloride (NaCl) concentrations (Borgatta et al, 2016), and with high sodium nitrate (NaNO3) concentrations Kim et al (2020). In real atmospheric conditions, NaCl or NaNO3 are unlikely to be the main driver of high ionic strength in aged CFA.…”

Particle formation and surface processes on atmospheric aerosols: A review of applied quantum chemical calculations

“…Compared to the C 2 V structure, the less symmetric D 2 h is more reactive in the presence of solar radiation, which is consistent with the aforementioned heterogeneous photochemical pathway of adsorbed nitrates. Recently, Ostaszewski et al carried out QM calculations to simulate the vibrational spectra of nitric acid chemisorbed on TiO 2 , a semiconductor component of mineral dust and combustion particles with a bandgap of 403 nm, [ 32,158–160 ] which corresponds to an energy value below the atmospheric cutoff of solar radiation. [ 21 ] Similar to the calculations done on Al 2 O 3 , the geometry optimization and the vibrational frequencies were calculated using the B3LYP/6‐31 + G(d) level of theory, adjusted for anharmonicity factors.…”

Comment on acp-2021-748

“…These phases have a range of reactivities. Previous studies showed that CFA dissolves much faster during the first 1-2 hours than subsequently (Borgatta et al, 2016;Chen et al, 2012;Chen and Grassian, 2013;Fu et al, 2012;Kim et al, 2020), confirming the large difference in Fe dissolution from different phases.…”