AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Enhanced Ligand-Promoted Photochemical Reduction of Ferric Iron by Carbonaceous Nanoparticles
Ashleen Reddy, ANNE JOHANSEN, Central Washington University
Abstract Number: 517 Working Group: Carbonaceous Aerosol
Abstract Iron (Fe) is a limiting nutrient in many parts of the open ocean where atmospheric deposition of Fe-containing aerosol particles may constitute the main source. Although only a small portion of the total aerosol Fe is available for biological uptake, also referred to as the soluble fraction, the mechanisms that control Fe solubility in the atmosphere and surface ocean remain elusive. Here, we focus on atmospheric processes that may contribute to the larger relative soluble Fe concentrations observed in combustion-derived aerosol particles compared to those seen in their crustal counterparts. Laboratory experiments were conducted on acidic slurries of ferrihydrite in the presence of oxalate and various carbonaceous nanoparticles (CNPs), in dark and under simulated solar radiation. Ferrous (Fe(II)) and reducible-ferric iron (Fe(III)), and oxalate were analyzed throughout the experiment using UV-Vis spectrophotometry and ion chromatography, respectively. Results show that under solar radiation, CNPs contribute to increases in (i) Fe(II) production by a factor of up to 5.5, and (ii) reducible-Fe(III) production by a factor of 27 relative to experiments in the absence of CNPs. Generally, Fe(II) constitutes between 61 and 91% of the combined Fe forms quantified. Thus, the presence of CNPs, including soot, seems to facilitate the ligand-promoted photochemical reduction of Fe(III), thereby providing a potential mechanism that explains the higher fractional Fe solubility seen in combustion-derived aerosol particles.