Production of Dissolved Iron from Atmospheric Processing of Ultrafine and Fine Iron Oxides: Effects of Size and Mineralogy

HEATH D.K. PATTERSON, Sarah C. Garrett, Jenny P.S. Wong, Mount Allison University

     Abstract Number: 344
     Working Group: Aerosol Chemistry

Abstract
Iron-containing particles influence oxidative potential and nutrient cycling, with their solubilization through atmospheric processing regulated by mineralogy, particle size, pH, and particle loading. In particular, dissolved iron is an important contributor to aerosol oxidative potential. Natural mineral dust, predominantly in the fine and coarse size ranges (~1–10 µm) and composed of iron oxides and iron-containing clays, has been extensively studied for its ability to produce dissolved iron. However, most of these studies have focused on mineral dust >250 nm. Anthropogenic sources, such as non-exhaust vehicle emissions, industrial activities, and solid biomass burning, also contribute iron oxide particles, including those in the ultrafine (<100 nm) range. Notably, iron oxides contribute to a large mass fraction of ultrafine particles emitted by emergent sources such as non-exhaust emissions. Despite the prevalence of iron-containing ultrafine particles, direct comparisons of iron solubility across different iron oxide minerals and particle sizes, specifically those in the ultrafine range, remain limited.

Here, we developed a semi-automated system using syringe pumps and a flow-through absorbance spectrophotometer to monitor dissolved iron produced during acid dissolution. This system was applied to systematically study iron dissolution from two iron oxides, in both ultrafine (<100 nm) and fine (~1–2 µm) size ranges, under varying pH and particle loading conditions. Results show that iron dissolution was rapid, with dependence on particle size and mineralogy. Mineralogy effects were less significant under the most acidic conditions. By isolating the effects of particle size, mineralogy, loading, and pH conditions, this study provides new insight into the factors regulating the solubility of iron oxide-containing ultrafine particles.