EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Iron(III)-carboxylate photochemistry induces iodate reduction

Lucia Iezzi1,2, Margarita Reza1,3, Henning Finkenzeller3, Antoine Roose1, Thorsten Bartels-Rausch1, Rainer Volkamer1,2,3, and Markus Ammann1
Lucia Iezzi et al.
  • 1Laboratory of Environmental Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
  • 2Institute of Atmospheric and Climate Science, ETH Zürich, 8092 Zürich, Switzerland
  • 3Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA

Aerosols and clouds are complex systems containing organic and inorganic species, which play central roles in atmospheric chemistry and physics, climate, air pollution and public health. Particularly chemical reactions which occur in the aqueous phase can change the composition and oxidizing capacity of the troposphere via the production and release of trace gas species. Iron(III)-carboxylate complexes impact the chemistry of the atmospheric aqueous phase due to their photochemistry which can trigger free radical chemistry generating reactive oxygen species (ROS), such as HO2 and H2O2. Several studies have highlighted the importance of iodine chemistry due to its capability to influence both oxidative capacity and radiative balance of the atmosphere. A previous work of this group demonstrated a direct link between carbonyl compounds, ROS and iodine chemistry [1]. Furthermore, observed ratios of iodide to iodate in aerosol particles and cloud droplets of the troposphere are much higher than expected [2, 3]. This is indicative of active chemical recycling of iodine between the gas and particle phases, which may be driven by not well understood reductive processes involving iodate, which is thermodynamically the most favored iodine form in the aqueous phase under oxidizing conditions.

We performed coated wall flow tube experiments (CWFT) with aqueous films containing iodate and Iron(III)-citrate (fe-cit) using citric acid (CA) as a matrix since it is an established proxy for oxygenated atmospheric organic matter and with well characterized microphysical properties. The CWFT was coupled with a CE-DOAS instrument in order to detect I2 [4] resulting from iodate reduction. The results suggest that  photochemistry promotes efficient iodate reduction, linked to the photochemical turnover of the iron(III)-carboxylate complex and to the depletion of the iodine reservoir. We speculate that reduction of iodate is driven by H2O2 according to the Bray-Liebhafsky mechanism, where H2O2 is provided by fe-cit photochemistry. 

1. P. Corral Arroyo, et al., Atmospheric Chemistry and Physics, (2019)

2. A.R. Baker and C. Yodle, Atmos. Chem. Phys. Discuss., 2021, 1 (2021)

3. T.K. Koenig, et al., Sci Adv, 7, eabj6544 (2021)

4. R. Thalman, et al., Journal of Quantitative Spectroscopy and Radiative Transfer, 147, 171 (2014)

How to cite: Iezzi, L., Reza, M., Finkenzeller, H., Roose, A., Bartels-Rausch, T., Volkamer, R., and Ammann, M.: Iron(III)-carboxylate photochemistry induces iodate reduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1922,, 2022.

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