Combustion particles, such as fly ash (FA) aerosol emitted from coal-fired power plants, have been proposed as an important source of iron in atmospheric water, with the potential to impact global biogeochemical cycles. Iron content and speciation of fly ash depends closely on the coal source region and combustion process, yet there are few comparative studies of the atmospheric fate of FA from multiple sources. Here, we present an investigation of iron dissolution under atmospherically relevant conditions for fully characterized FA samples from three different sources: US Midwestern (USFA), European (EUFA) and Indian fly ash (INFA). To better understand their atmospheric fate, the effect of the acidic media and solar flux was investigated. Solar radiation and the acidic media can trigger chemical and photochemical reactions on the surface of FA particles leading to significant differences in daytime and nighttime chemistry. Under the acidic atmospheric conditions, iron was found to mobilize primarily due to proton-promoted mechanisms. Suspensions of FA in HCl resulted in larger fractions of iron leached compared to suspensions on HNO3. In general, dissolution showed a variability between source regions with a relative iron leach in the order USFA &gt; INFA &gt; EUFA. A similar order was also observed in the initial rate of iron leach, suggesting that source region is an important factor in iron mobilization of fly ash. Poorly combusted samples leached a larger fraction of bioavailable Fe(II) in HCl, in the presence of HNO3 only Fe(III) was observed, as all leached Fe(II) was rapidly oxidized, reducing nitrates (NO3-) into nitrites (NO2-). The surface-mediated formation nitrites of was observed in all particles with a photoreduction process that depends on the minerology of the FA particle.

Simulated atmospheric processing and iron mobilization of combustion particles: Effects of acid media and solar flux

2019 Fall National Meeting

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