Alpert, P. A., Corral Arroyo, P., Dou, J., Krieger, U. K., Steimer, S. S., These parameters are given for a temperature of 293.5 K. The gas phase diffusivity of each species j, Dgj, was approximated via its molar mass (Mj) compared to that of water (MH2O). Phys., 14, 10761–10772. Particles containing FeIII(Cit) ∕ CA were nebulized from aqueous solution with a mole ratio between FeIII(Cit) : CA of 1 : 1. This work focuses on iron carboxylate-catalyzed photochemistry due to its abundance and reactivity in the atmosphere. carboxylic acids, Inorg. We restricted our tuning of the parameters to reach satisfactory agreement with all experimental data simultaneously. Chem. We found this water activity corresponds to that of a 0.81 M aqueous CA solution. for RH > 30 %. https://doi.org/10.1016/j.cplett.2012.01.051, 2012. a, b, c, Pruppacher, H. and Klett, J.: Microstructure of atmospheric clouds and The fraction of FeIII out of total Fe, β, was then determined using the parameterization from Moffet et al. Iron is the most abundant transition metal in the earth's crust. transitions in individual aerosol particles on a substrate using scanning Soc., 113, 2683–2686, https://doi.org/10.1021/ja00007a049, 10, for example, the initial FeIII fraction of the particle was 0.76, indicating that the particle was partially reduced during sample preparation. Technol., 27, 2517–2522. Panel (c) shows the sensitivity to the reaction constant (Reaction R9, see Table 2) and panel (d) shows the sensitivity to oxygen diffusivity (Table 1). Goryacheva, N. V., Gladki, V., and Duka, G. G.: Photochemistry of Fe(III) Meas. waters, Environ. In addition, we observed the mass loss rate was initially ∼1.3 % h−1 and increased to ∼14 % h−1 when 40 % to 60 % of the initial mass was lost. Springer, Berlin, Heidelberg. Chem. Lett., 10, 4484–4489. transfer in carboxylate ion pairs, J. Org. JD wrote the manuscript. 18, transmission x-ray microspectroscopy, Rev. Brandt, C. and van Eldik, R.: Transition metal-catalyzed oxidation of (1999). Exemplary raw data of an experiment at 46 % RH and 293.5 K are shown in Fig. For quantification a numerical model was developed. Chem. Wu, F., and Deng, N.: Intermediates in photochemistry of Fe(III) complexes 9499–9510, https://doi.org/10.1021/jp0350823, 2003. a, Abida, O., Kolar, M., Jirkovsky, J., and Mailhot, G.: Degradation of decreased with RH, with a production rate at 60 % similar to the rate under dry conditions. Thin lines are PRAD model outputs (with ±2 % RH uncertainty shown as the shaded area). Photophysics of Fe(III)–tartrate and Fe(III)–citrate complexes in Hofmann, H., Hoffmann, P., and Lieser, K. H.: Transition metals in atmospheric 4. The water activity of an aqueous 1 M FeIII(Cit) solution was determined using a water activity meter (AquaLab water, Model 3B, Decagon Devices, USA) at room temperature. However, the size dependence is more complex than the expected simple square law if reactions were purely limited by condensed phase diffusion. Lett., 39, L24801. 3.1. The liquid phase diffusion coefficients, Dlj(x,T,aw), where j is an index for all species, depend on RH, T and the molar ratio, x, between FeIII(Cit) and CA. Shell i extends from ri−1 to ri, while shell i+1 extends from ri to ri+1, with r being the distance from the particle center. and Avery, G. B.: Temporal variability of iron speciation in coastal Therefore, the refractive index and density are mostly governed by those of aqueous CA up until half the particle mass is lost. For particles with a radius larger than 50 nm, the time to repartition 10 % of the mass to the gas phase depends almost linearly on size for these specific conditions. alkanoates, J. B., and Ammann, M.: Visualizing reaction and diffusion in xanthan gum A-Chem., 224, 17–33, https://doi.org/10.1016/j.molcata.2004.08.043, 2004. a, b, Corral Arroyo, P., Bartels-Rausch, T., Alpert, P. A., Dumas, S., Perrier, S., George, C., and Ammann, M.: Particle-phase photosensitized radical Dou, J., Luo, B., Peter, T., Alpert, P. A., Corral Arroyo, P., Ammann, M., and Krieger, U. K.: Carbon dioxide diffusivity in single, levitated organic Initially, we exposed a newly injected FeIII(Cit) ∕ CA aqueous particle to blue laser irradiation (473 nm, 4 W cm−2) in pure N2 for 500 s to ensure all FeIII was reduced through photolysis (Reactions R1 and R2 listed in Table 2). 11 is to use the analytical solutions for a reacto-diffusive kinetic regime. Redox occurs with formation of sulfite: S 2 O 4 2-+ 2 H 2 O → 2 HSO 3 − + 2 e − + 2 H + For instance, even though absorption spectra of FeIII(Cit) have been measured in aqueous solution (Pozdnyakov et al., 2012), the corresponding quantum yield has not, which leaves the photolysis rate of FeIII(Cit), j, unknown. 6. When predicting PHO2. Acta, 226, 117–127, iron(III) complex with pyruvic acid in aqueous solutions, Russ. A, 107, and H2O2 will be produced, which can oxidize FeII back to FeIII via Fenton reactions (Fenton, 1894) with additional oxidant production. Figure 5Schematic illustration of the PRAD model showing the shells, transport fluxes (green arrows), and chemical processes (red arrows) of each species. 163–178. Acta, 226, 117–127. Chem. urban site in the Po valley, Chemosphere, 241, 125025, of HO2/O2- radicals in aqueous solution, J. Phys. Fink, R. H., and Quitmann, C.: PolLux: A new facility for soft x-ray Chem. This led to satisfactory agreement within model uncertainty for most but not all experiments performed. It is used as a food additive, also known as E224. complex with glyoxalic acid in aqueous solution, High Energ. Catal. 113704, Rush, J. D. and Bielski, B. H. J.: Pulse radiolytic studies of the reaction of. A better estimate would require repeat measurements as a function of RH, e.g., to elucidate any systematic uncertainty on iron reduction reactions due to viscosity changes. aerosol by OH radical: the emergent nature of reactive uptake, Phys. The spherical particles were characterized by two methods based on Mie-resonance spectroscopy: (i) a narrow bandwidth tunable diode laser (TDL, tuning range 765–781 nm) was used to determine the refractive index and radius simultaneously with high-precision (Steimer et al., 2015b); and (ii) simultaneously, a broad-band LED centered around 640 nm was used to illuminate the particle. These are both 1 order of magnitude less than the values from PRAD model prediction, but still consistent with each other when considering all uncertainties. Chem. and Otto, T.: Tropospheric Aqueous-Phase Chemistry: Kinetics, Mechanisms, and HO2/O2- with Fe(II)/Fe(III) ions. https://doi.org/10.1007/s11172-007-0136-7, 2007. a, Fenton, H. J. H.: LXXIII.—Oxidation of tartaric acid in presence of iron, Dilute aqueous solutions of FeIII(Cit) ∕ CA and FeII(HCit) ∕ CA were made in ultrapure water (18 M Ω cm−1, Milli-Q). Peter, T.: Measurements of thermodynamic and optical properties of selected Feng, W., Nansheng, D., Glebov, E. M., Pozdnyakov, I. P., Grivin, V. P., The only difference in experimental procedure, compared to what is described above, is that there is no first irradiation step. Its Coupling to a Changing Gas Phase, Chem. Our experiments showed that long exposure (tens of hours) to O2 yielded larger Mie-resonance shifts than those of the initial photolysis of the freshly prepared particle. Red lines: model outputs obtained by varying a single parameter with factors: 10 and 0.1 (dashed), 5 and 0.2 (dotted), 2 and 0.5 (dash-dotted), 1 (solid). impact of iron-carboxylate photochemistry on radical budget and carboxylate 2259–2265, https://doi.org/10.1021/acsearthspacechem.9b00172, 2019. a, Tapparo, A., Di Marco, V., Badocco, D., D’Aronco, S., Soldà, L., Pastore,