Measurements and multiphase modeling of dark Fenton chlorine production from iron-salt aerosols at the European Photoreactor (EUPHORE)

Interactions between iron-containing mineral dust and chloride-rich sea salt aerosols lead to the formation of iron(III) chloride salts, which initiate the photocatalytic release of molecular chlorine (Cl2) [1-5]. Photolysis of the chlorine generates reactive Cl radicals—potent atmospheric oxidants with substantial implications for the degradation of methane and other greenhouse gases. This catalytic chlorine production relies on the reoxidation of Fe(II) to Fe(III) through Fenton chemistry. To understand the photolytic chlorine production, the Fenton chemistry in these aerosols must be understood as well. This study presents experimental investigation and multiphase modeling of the dark chlorine production from the reaction of iron(III) chloride aerosols and H2O2. The experiments were performed in the 200 m3 European Photoreactor (EUPHORE) in Valencia, Spain. Measurements were collected with long-path FTIR, OPS, SMPS, PTR-MS, ACSM, Picarro G2108 and G2201-i as well as monitors for O3, NO, NO2, NOx, CO and HCHO. Furthermore, flask samples were collected for analysis of [CO], d13C-CO, [CH4], d13C-CH4 and VOCs at Utrecht University. Multiphase modeling of the experiment has been done through the integration of Fenton reactions and iron chloride chemistry into the kinetic multilayer model for Aerosol Dynamics, gas- and particle-phase chemistry in CHAMber environments (ADCHAM)[6]. A production was observed of 1.14 Cl2 molecules per Fe atom per hour and 4.33 H2O2 were consumed per Cl2 molecule produced. An inhibition of the chlorine production later in the experiment was observed and is under investigation.This work is part of a project supported by the European Commission under the Horizon 2020 –Research and Innovation Framework Program through the ATMO-ACCESS Integrating Activity ATMO-TNA-7—0000000004 (GA N. 101008004)[1] Chen et al. (2024) Environ. Sci. Technol., 58(28), 12585-12597[2] Mikkelsen et al. (2024) Aerosol Research, 2, 31-47[3] Wittmer et al. (2015) Environmental Chemistry, 12(4), 461-475[4] Wittmer et al (2017) Journal of Atmospheric Chemistry, 74, 187-204[5] van Herpen et al. (2023) PNAS, 120, 31[6] Roldin et al. (2014) ACP, 14, 7953–7993