11. and Otto, T.: Tropospheric Aqueous-Phase Chemistry: Kinetics, Mechanisms, and The degradation processes were faster at higher RH. Figure 3Iron L-edge NEXAFS spectra of FeIII(Cit) ∕ CA particles before and after irradiation with UV light shown as orange and red, respectively. 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 Heterogeneous chemistry involving particulate iron and SO2 can result in sulfate formation and increase aerosol loading (Grgić et al., 1998, 1999; Grgić, 2009). Thin lines are PRAD model outputs (with ±2 % RH uncertainty shown as the shaded area). Chem. Following this procedure we intended to map out the characteristic time for reoxidation at various RH. These diffusivities of O2 are 2–4 orders of magnitude smaller than those of CO2 determined in Dou et al. Clearly, the FeIII fraction increased more significantly more slowly with time at drier conditions. radicals: Influence of molecular structure, J. Phys. Naming chemical compounds . Our results are equal to a mass loss rate of about 0.4 µgm-3(air)h-1 assuming an aerosol population with an organic mass of ∼ 10 µg m−3 (air) undergoing iron carboxylate photochemistry. Quantifying iron atmospheric processing and solubility is of global importance, especially for nutrient input into the world's oceans (Hamilton et al., 2019; Kanakidou et al., 2018). More importantly, O2 taken up by the particle from the gas phase diffused more slowly into the bulk of the particle at lower RH. Moffet, R. C., Furutani, H., Rödel, T. C., Henn, T. R., Sprau, P. O., Chem. 2021. Peter, T., Huthwelker, T., Borca, C. N., Henzler, K. D., Herrmann, H., Raabe, Phys., 12, 7647–7687. For the experiment included in Fig. Chem., 103, 1255–1279, In addition, we will use the PRAD model to simulate photochemical aging processes under atmospheric conditions. Phys., 7, 5989–6023, https://doi.org/10.5194/acp-7-5989-2007, 2007. a, Pozdnyakov, I. P., Kel, O. V., Plyusnin, V. F., Grivin, V. P., and Bazhin, Technol., 27, 2517–2522, Glebov, E. M., Pozdnyakov, I. P., Grivin, V. P., Plyusnin, V. F., Zhang, X., Okochi, H. and Brimblecombe, P.: Potential trace metal–organic complexation 1281–1288, https://doi.org/10.1063/1.1141227, 1990. a, Deguillaume, L., Leriche, M., Desboeufs, K., Mailhot, G., George, C., and D. O., Percival, C., and Cai, C.: Measurements and predictions of binary Ozone in Liquids, J. Phys. decreased with RH, with a production rate at 60 % similar to the rate under dry conditions. production mediated by humic-like substances in atmospheric aerosols: Since FeIII(Cit) only dissolves slowly in water, CA solutions with suspended FeIII(Cit) crystals were sonicated for at least 24 h. The same dissolving procedure was also applied to the FeII(HCit) powders. (2016). In addition, we found that the direct O2 reaction with iron(II) organic complexes does occur and generates radicals inside the particle. Phys., 15, 4399–4981. Alpert, P. A., Corral Arroyo, P., Dou, J., Krieger, U. K., Steimer, S. S., Sodium dithionite is a reducing agent. 3, forms on an old nail. 20613–20627, https://doi.org/10.1039/c9cp03731d, 2019. a, b, c, d, e, f, g, h, Alpert, P. A., Dou, J., Corral Arroyo, P., Schneider, F., Xto, J., Luo, B., For these reasons, it is a valid and reliable proxy for atmospheric iron carboxylate photochemical processes. 79, 411–425, 1994. The overall rate may be well constrained by our experimental studies, however more targeted observations may be necessary for an accurate representation of O2 chemistry, solubility, and molecular transport independently of each other within aerosol particles. Technol., 48, 4901–4908,https://doi.org/10.1021/es500377d, 2014. a, Kanakidou, M., Myriokefalitakis, S., and Tsigaridis, K.: Aerosols in 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 Lienhard et al. Enhancement effects by pyridine, imidazole, and their derivatives, Environ. Figure 7Loss of FeIII in FeIII(Cit) ∕ CA (molar ratio of 1) particles as a function of light exposure time determined using STXM/NEXAFS at 293.5 K. Each data point is the average FeIII fraction over about 16–36 individual particles. Sander, R.: Compilation of Henry's law constants (version 4.0) for water as solvent, Atmos. https://doi.org/10.1016/j.chemosphere.2019.125025, 2020. a, von Sonntag, C. and Schuchmann, H.-P.: Aufklärung von Dou, J., Alpert, P. A., Corral Arroyo, P., Luo, B., Schneider, F., Xto, J., Huthwelker, T., Borca, C. N., Henzler, K. D., Raabe, J., Watts, B., Herrmann, H., Peter, T., Ammann, M., and Krieger, U. K.: Photochemical degradation of iron(III) citrate/citric acid aerosol quantified with the combination of three complementary experimental techniques and a kinetic process model, Atmos. Springer US, Boston, MA, USA, 1982. a, b, c, Moffet, R. C., Furutani, H., Rödel, T. C., Henn, T. R., Sprau, P. O., 4, Since we observed increasing mass loss rates over time, any decrease in Dlj leading to slower chemical cycling due to increasing x was likely a minor effect. Fitting an exponential function, β=β0ejobst, yields β0=0.93±0.09 and a first-order decay rate of jobs=0.08±0.01 s−1. The 2-L flask contains 4.8 g of gas, and the gas pressure is X atm. Z.: Reactive oxygen species In addition, it indicates that both iron(II) and iron(III) can act as a photocatalyst as long as iron(II) can be oxidized to iron(III), which was also confirmed by Grgić et al. spectromicroscopy at the swiss light source, Rev. and H2O2 formed and less FeII could be reoxidized from the surface to the center of the particle. In other words, this experiment alone allows us to constrain Reaction (R9) or oxygen diffusivity as long as the other parameter is known, but does not allow us to constrain the constants for the two equilibria. MA and UKK conceptualized and planned the study. Phys., 7, 5989–6023. Data, 12, After establishing a parameter set for the PRAD model framework that satisfactorily explains the experimental data obtained with three complementary experimental techniques over a wide parameter range, we used the model to predict photochemical degradation of organic aerosol particles containing carboxylate complexes. After irradiation, we switched the gas flow from N2 to O2 in the dark, We investigated kinetic transport limitations due to high particle viscosity under low relative humidity conditions. In short, an electrically charged aqueous particle (radius ∼ 10 µm) is injected into an EDB. 1. Chem. Phys., 15, 4399–4981, https://doi.org/10.5194/acp-15-4399-2015, 2015. a, Shiraiwa, M. and Seinfeld, J. H.: Equilibration timescale of atmospheric 11, the FeIII fraction as a function of time was calculated as. Chem., 18, 723–731, Pruppacher, H. and Klett, J.: Microstructure of atmospheric clouds and USA, 108, Chem. However, it should be noted that the relative mass loss at higher humidities (between 40 % and 60 % RH) is quite similar. The reactivity of Bull., 56, 900–903. Wind erosion is the main source of iron in the atmosphere, but anthropogenic activities such as industrial processes, traffic, and combustion processes can also potentially release iron in particulate form (Deguillaume et al., 2005). 2000. a, Zardini, A. iron(III)-polycarboxylate complexes: roles in the chemistry of atmospheric Mineral., (A8) and the two constants in Eq. In the experiments described in this work, we used a typical total flow of 40 sccm and set the total pressure inside the cell at 8×104 Pa. Phys., 21, 425–430. where D0=1.39×10-8 m2 s−1, Ts=227.0 K, and m=1.7094. Shiraiwa, M., Pfrang, C., Koop, T., and Pöschl, U.: Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water, Atmos. The encoded protein appears to be involved in the maturation of mitochondrial iron-sulfur proteins. 2012. a, b, Abrahamson, H. B., Rezvani, A. the diffusion coefficient of O2 can be estimated to be 3.6×10-16 and 4.4×10-15 m2 s−1 at 48 % and 65 % RH, respectively (details are given in Appendix A4). To show the sensitivity of the PRAD model results to a few of its parameters, Fig. We parameterized k5 as a third degree polynomial function of RH (%): Figure A2Adjusted values of the HO2. Acta, 226, 117–127, Fogg, P. G. T. Hence, we accordingly normalized the FeIII fraction to the data at long (>15 h) exposure times. Chem. precipitation, in: Microphysics of Clouds and Precipitation, vol. Here, O2 taken up from the gas phase by a particle remains confined to a very thin layer below its surface compared to its size provided it reacts reasonably fast with the organic components. Therefore, the production rate of HO2., PHO2., was calculated from the loss rate of NO assuming a 2 : 1 ratio to HO2. B., and Brushmiller, J.: Photochemical and A, 120, 8123–8137. Rev., 115, 4259–4334, Technol., 51, Technol., 49, 6457–6465. In an example CWFT experiment at RH = 29.3 %, a clear NO loss was observed when the UV lights were switched on as shown in Fig. Chim. A11) and confidence intervals at 95 % for the HO2. transfer in carboxylate ion pairs, J. Org. Burden, R. L. and Faires, J. D.: Numerical Analysis, 9th edn., Brooks/Cole, Boston, MA, USA, 2011. Henzler, K. D., Raabe, J., Watts, B., Herrmann, H., Peter, T., Ammann, M., and Krieger, U. K.: Photochemical degradation of iron(III) citrate/citric acid aerosol quantified with the combination of three complementary experimental techniques and a kinetic process model, ETH Zurich, https://doi.org/10.3929/ethz-b-000451609, last access: 24 December 2020. a, Faust, B. C. and Hoigné, J.: Photolysis of Fe(III)-hydroxy complexes as sources of OH radicals in clouds, fog and rain, Atmospheric Environment. P., Mahon, B. M., Kalberer, M., and Giorio, C.: Formation of metal-organic ultraviolet-radiation reaching the earths surface, Ambio, 24, 143–152, Chem. Res. The backscatter signal from the LED was recorded using a spectrograph with a slow-scan back-illuminated charge-coupled device (CCD) array detector to follow the resonance wavelength shift of the particle (Zardini et al., 2006). iron(III) complex with pyruvic acid in aqueous solutions, Russ. This led to satisfactory agreement within model uncertainty for most but not all experiments performed. (A14), HO2DlO2kO2 is actually the constraint, thus any uncertainty in HO2 or kO2 can change DlO2. Sci. For other species, ppartial is negligible and assumed to be zero. 4218–4258, https://doi.org/10.1021/cr500648z, 2015. a, b, Glebov, E. M., Pozdnyakov, I. P., Grivin, V. P., Plyusnin, V. F., Zhang, X., sources, and sinks: A review, Atmos. Chem. Heterogeneous photochemistry in the atmosphere, Chem. photosensitivity, and reactions of transition metal ions in atmospheric Environ., 30, 4233–4249, All data were used to constrain equilibrium and kinetic parameters as well as reaction rate coefficients in a new PRAD model with sufficient complexity to allow comparison with data of all experiments simultaneously. 4218–4258. Student lessons. Shell thickness and the number of shells were adjusted to enable the resolution of steep concentration gradients within a reasonable computation time. The PRAD model code is publicly available and accessible here: https://doi.org/10.3929/ethz-b-000451609 (Dou et al., 2020), and from the corresponding author upon request. Shiraiwa, M., and Ammann, M.: Shikimic acid ozonolysis kinetics of the (2014) reported the diffusion coefficient of water in aqueous CA without iron (i.e., x=0), DCA(aq)H2O(T,aw). Sci. The bulk accommodation coefficients of all species were assumed to be 1. The NO concentration during CWFT photochemical experiments was in excess (> 1013 molecules cm−3) to efficiently scavenge 99 % of HO2. where T0=273.15 K, p0=1013.25 mbar, and DgH2O is in cm2 s−1 (Pruppacher and Klett, 2010). In this work we investigated iron(III) citrate ([FeIII(OOCCH2)2C(OH)(COO)], in short FeIII(Cit)), as a model species to better understand iron carboxylate photochemistry in atmospheric aerosol particles. (How particle mass evolves subsequently until 80 % mass loss in both experiments and models is shown in Fig. self-reaction rate as a function of RH. implications for secondary organic aerosols in the atmosphere, Phys. 1 and 2). Phys., 12, 2777–2794. Chem. Figure 12(a) Measured (black dots, experimental uncertainty of 3 % smaller than symbol size) and modeled (red line and shaded area) HO2. In other words, we expect similar mass degradation in atmospheric particles due to the fact that many other relevant iron carboxylate compounds undergo LMCT similarly as to our model system (Weller et al., 2013, 2014). However, our model still needs major improvements, such as including peroxy radical chemistry and better constraints on individual parameters such as diffusion coefficients and reaction rate constants. In order to determine Dlj(x,T,aw) in the PRAD model for a single experiment with a fixed value of x, DlH2O was scaled with DCA(aq)H2O(T,aw) using another factor, fs, following, The diffusion coefficient of CO2 at T=20 ∘C and x=0.05, D∘CO2, was independently measured by Dou et al. Sci., 11, 794–802, https://doi.org/10.1039/c2pp05358f, We performed experiments with single, levitated particles under continuous UV irradiation (375 nm) in pure O2 at different RH to assess the effects of RH on the photocatalytic cycle shown in Fig. Qualitatively, a continuous decrease of particle mass and size is expected to occur due to evaporation of volatile products, as shown in Fig. Technol., 39, 1576–1583, https://doi.org/10.1021/es040439h, 2005. a, Koop, T., Bookhold, J., Shiraiwa, M., and Pöschl, U.: Glass transition Our FeIII(Cit) system undergoes LMCT reactions in the same way as countless other iron(III) carboxylate compounds (Cieśla et al., 2004; Weller et al., 2013, 2014). The film was composed of FeIII(Cit) ∕ CA, and deposited inside the tubular glass flow tube with a thickness between 0.15 and 0.2 µm and an error of about 20 %. Figure 9Schematic of the experimental procedure to investigate the reoxidation rate of FeII. Another set of experiments was done by starting with freshly injected FeII(HCit) ∕ CA particles instead of FeIII(Cit) ∕ CA. A, 107, N. M.: New insight into photochemistry of ferrioxalate, J. Phys. Brandt, C. and van Eldik, R.: Transition metal-catalyzed oxidation of transitions in individual aerosol particles on a substrate using scanning Chem. Kieber, R. J., Skrabal, S. A., Smith, B. J., and Willey, J. D.: Organic 7676–7685, https://doi.org/10.1021/acs.est.7b01299, 2017. a, b, González Palacios, L., Corral Arroyo, P., Aregahegn, K. Z., Steimer, S. S., Bartels-Rausch, T., Nozière, B., George, C., Ammann, M., and Volkamer, R.: Heterogeneous photochemistry of imidazole-2-carboxaldehyde: HO2 radical formation and aerosol growth, Atmos. in the atmosphere, Sci. aging of semisolid organic aerosol particles, P. Natl. Photochemically produced free radicals in the gas phase (mainly .OH) can be taken up by aerosol particles, inducing multiphase chemistry. Förster, J. D., Ditas, F., Pöhlker, C., Rossignol, S., Additionally, iron photochemical processing in aerosol particles, fog droplets, and cloud water is an important radical source (Bianco et al., 2020; Abida et al., 2012) and sink for organic compounds (Weller et al., 2014, 2013; Herrmann et al., 2015). 3.1. 3.1. Ref. R corresponds to the carboxylate side chain -CH2COO-. Excess permanganate is reduced by slow addition of solid sodium hydrogen sulfite until the purple color disappears. Bartels-Rausch, T., and Ammann, M.: Emerging areas in atmospheric The red line and shading is the new parameterization (Eq. 10–73, Springer Netherlands, Dordrecht, https://doi.org/10.1007/978-0-306-48100-0_2, ultrafast decarboxylation of acyloxy radicals via photoinduced electron atmospheric liquid water: The role of Fe(II) and the effect of oxalate, J. Chem. Proc., 879, 505–508, https://doi.org/10.1063/1.2436109, 2007. a, Fogg, P. G. T. complexation of Fe(II) and its impact on the redox cycling of iron in rain, Chem. For the following compounds, give the formulas and the molar masses: Formula 21) sodium phosphide Na 3 P 22) magnesium nitrate Mg(NO 3) 2 23) lead (II) sulfite PbSO 3 24) calcium phosphate Ca 3 (PO 4) 3 25) ammonium sulfate (NH 4) 2 SO 4 26) silver cyanide AgCN 27) aluminum sulfide Al 2 S 3 28) beryllium chloride … where m0 is the particle mass prior to irradiation. Henry's law coefficients for gasses were tuned, however purposefully set at values higher than expected for pure water or highly dilute aqueous solution. One caveat to using Eqs. Details of the film preparation have been described previously (Corral Arroyo et al., 2018; González Palacios et al., 2016). Chem. Phys., 18, 12662–12674, Sci., 11, 794–802. There is satisfactory agreement for the larger RH, but significant underestimation of reoxidation for the experiments at 24 % RH. The sample holders were transported to the endstation in an evacuated container and shielded against ambient light. In STXM/NEXAFS experiments, the freshly prepared FeIII(Cit) mixed with CA at x=1.0 particles were irradiated to determine the FeIII(Cit) photolysis rate, as shown in Fig. reactions and transformation of low-molecular-weight organic matter, J. (1999). 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. Lett., 13, 063004, Kawamura, K., Ng, L. L., and Kaplan, I. R.: Determination of organic acids The DC field compensates the gravitational force of the particle and is used as a measure for the mass of the particle. reactions and transformation of low-molecular-weight organic matter, J. Flow-tube experiments performed on thin FeIII(Cit) films showed continuous production of HO2., revealing a radical source inside the particles driven by photochemistry. 1 and tested the model performance under these conditions. The irradiation wavelength was 375 nm, its intensity was 0.25 W cm−2, and the experimental temperature was 293.5 K. (b) EDB experimental data in (a) with PRAD outputs at corresponding RH (with ±2 % RH uncertainty shown as shaded area) as a function of irradiation time (linear scale). aqueous organic and organic-inorganic mixtures of atmospheric relevance, J. Additionally, if a particular system requires parameter values that significantly differ from ours, the PRAD model framework itself should still be valid. production and aerosol aging, Environ. Ref. (b) The maximum HO2. Under these conditions there are always pairs of reaction rate and diffusion constants representing the experiments equally well (Alpert et al., 2019; Steimer et al., 2014). Chem., 29, 315–337. which gives us confidence that the PRAD model captures the essential chemistry and transport during irradiation. The authors declare that they have no conflict of interest. 406–409, https://doi.org/10.1134/S0018143909050129, 2009. a, Pozdnyakov, I. P., Kolomeets, A. V., Plyusnin, V. F., Melnikov, A. Figure 4NO concentration raw data from a CWFT film containing FeIII(Cit) ∕ CA (molar ratio of 0.07) with lamps on (yellow shaded region) and off at 29.3 % RH and 298.15 K. We developed a PRAD model to interpret our experiments and to understand any feedback between transport limitations and photochemistry, especially under low RH conditions, corresponding to high viscosity of the particle phase. (A4) is. increased with RH when the RH was increased from 13 % to 29 % by a factor of about 2. Commun., accepted, G., Vernooij, M. G., and Ammann, M.: An in situ cell to study phase and phase state of organic compounds: dependency on molecular properties and Grivin, V. P., Plyusnin, V. F., and Bazhinb, N. M.: Photochemistry of the 11. Huthwelker, T., Zelenay, V., Birrer, M., Krepelova, A., Raabe, J., Tzvetkov, Finally, reoxidation rates and production of radicals are also reliable, as the system is largely reacto-diffusion limited (see Appendix A4) and these rates occur on the same scales as observed mass loss rates. A Chem., 268, 24–36. We thank Nir Bluvshtein for helpful discussions. G., Vernooij, M. G., and Ammann, M.: An in situ cell to study phase oxidation and removal of arsenic at circumneutral pH in iron containing The PRAD model prediction and uncertainty are given as red solid line and shading, respectively, and use a calculated decay rate of jcalc=0.20±0.12 s−1. A Chem., 268, 24–36, https://doi.org/10.1016/j.jphotochem.2013.06.022, The irradiation wavelength was 375 nm, its intensity was 0.25 W cm−2, and the experimental temperature was 293.5 K. Thick lines are EDB experimental data. Figure 5Schematic illustration of the PRAD model showing the shells, transport fluxes (green arrows), and chemical processes (red arrows) of each species. of hydroxyl radical formation from Fe(II): kinetics of fulvic acid-Fe(II) Interestingly, we also observed that mass loss always accelerated during irradiation, resulting in an increase of the mass loss rate by about a factor of 10. Iron(III) carboxylate complexes [FeIII(OOC-R)]2+ are well-known photoactive compounds (Wang et al., 2012; Weller et al., 2013, 2014). Photochemical production of Fe(II) in rainwater, Environ. Phys., 13, 19238–19255. organic matter and the role of reactive oxygen intermediates in atmospheric Time before 0 represents the initial 15 min irradiation procedure under He. Tech., 8, 2397–2408, https://doi.org/10.5194/amt-8-2397-2015, 2015b. FeIII(Cit) ∕ CA (molar ratio of 0.05) particles at 293.5 K with 24 % RH (red diamonds), 48 % RH (green triangles), and 65 % RH (blue squares). Chim. Sci. 10). oxidation and removal of arsenic at circumneutral pH in iron containing Herrmann, H., Maenhaut, W., and Claeys, M.: 2-Hydroxyterpenylic acid: An We are fairly confident that diffusion coefficients of CO2 and H2O can be used for atmospheric aerosol particles as these were obtained in a more targeted study (Dou et al., 2019). Faust, B. C. and Zepp, R. G.: Photochemistry of aqueous Chem. Chem. Bibliography: List of 131 compounds in the Solution Calculator database for which the density function is defined are for the Perry's Chemical Engineers' Handbook.. D.W. Green, R.H. Perry, Perry's Chemical Engineers' Handbook, McGraw-Hill, … HO2/O2- with ferric ions and its implication on the Phys. urban site in the Po valley, Chemosphere, 241, 125025. von Sonntag, C. and Schuchmann, H.-P.: Aufklärung von Photochemical degradation under atmospheric conditions predicted by the PRAD model shows that release of CO2 and repartitioning of organic compounds to the gas phase may be very important when attempting to accurately predict organic aerosol aging processes. in the condensed phase when RH increases, which was confirmed by an increasing HO2. Photochemistry of iron(III) complexes plays an important role in aerosol aging, especially in... All site content, except where otherwise noted, is licensed under the. (2012) are shown as the blue and green shading, respectively. George, C., D'Anna, B., Herrmann, H., Weller, C., Vaida, V., Donaldson, D. J., (b) Intensity map of low-resolution Mie-resonance spectra. X-ray energy calibration was consistently performed using FeCl2 and compared with the existing literature for FeCl2 and FeCl3 salts (Moffet et al., 2012) and a mixture of xanthan gum and FeCl2 oxidized by O3 (Alpert et al., 2019). In the presence of O2, oxidants such as HO2. will decarboxylate almost instantaneously (kR3≈109–1012 s−1) (Abel et al., 2003; Bockman et al., 1997; Hilborn and Pincock, 1991): The alkyl radical R. will react rapidly with dissolved O2, The observed gradient in the FeIII fraction, β, and the modeled gradients in O2 and ROS in the particle have been shown with radial profiles in Alpert et al. Sci. This is consistent with strong kinetic transport limitations for highly viscous particles. This calculated value for the photochemical reaction rate was used in the PRAD model for analyzing the STXM/NEXAFS experiments shown in Fig. Steimer, S. S., Krieger, U. K., Te, Y.-F., Lienhard, D. M., Huisman, A. J., Luo, B. P., Ammann, M., and Peter, T.: Electrodynamic balance measurements of thermodynamic, kinetic, and optical aerosol properties inaccessible to bulk methods, Atmos. Meas. Instrum., 79, sink in this system. The time step, Δt, for physical transport processes was determined dynamically to ensure both numerical stability and computational efficiency. (Ed. Following a previous procedure (Alpert et al., 2019), we imaged particles at these two energies to determine the OD ratio between them. persistence due to anoxia in viscous Aerosol particles, Nat. iron(III)-polycarboxylate complexes: roles in the chemistry of atmospheric and phase state of organic compounds: dependency on molecular properties and 3. Wang, Z., Chen, C., Ma, W., and Zhao, J.: Photochemical coupling of iron redox self-reaction rate, k5, which was adjusted to match observations in panel (a) (black dots), or times k5 parameterized as a function of RH for our PRAD model (Eq. Figure 3 shows an example of NEXAFS spectra of FeIII(Cit) ∕ CA particles before (orange) and after (red) irradiation with UV light. Res. Bull., the lifetime of organic radicals needs to be reconsidered. near-edge fine structure in the study of minerals, Am. Seven UV lamps (UV-A range, Philips Cleo Effect) Field studies have confirmed that soluble iron is mostly in complexes with carboxylate functions (Tapparo et al., 2020; Tao and Murphy, 2019). Chem., 18, 723–731, Cieśla, P., Kocot, P., Mytych, P., and Stasicka, Z.: Homoge. 2015a. (6) leads to, We calculated the partial pressure of H2O from RH, and took the partial pressure of O2 based on the total pressure and the fraction of O2 gas flow used in experiments. A1. Res. 1985. a, Kieber, R. J., Hardison, D. R., Whitehead, R. F., and Willey, J. D.: Lienhard, D. M., Huisman, A. J., Bones, D. L., Te, Y.-F., Luo, B. P., Krieger, FS conducted viscosity experiments and the data analysis and interpretation was supervised by PAA. [Fetot] is 0.3192, 0.2763, and 0.2345 M at 24 %, 48 %, and 65 % RH, respectively. For instance, humic-like substances derived from water-soluble organic compounds have been reported to be strong chelating ligands with iron(III) (Dou et al., 2015; Kieber et al., 2003; Okochi and Brimblecombe, 2002; Willey et al., 2000). Organic compounds are a major component in atmospheric aerosol particles and have received more and more attention as potential ligands for iron(III) complexation. T. E., Jaoui, M., Offenberg, J. H., Lewandowski, M., Böge, O., (13), we calculate the moles of O2 in this shell, Nn,O2, as. If not, which contains the gas of higher molar mass? Rev., 95, 119–190. production as a function of RH using CWFT experiments, the HO2. rainwater, J. Atmos. Phys., 16, 16677–16683, https://doi.org/10.1039/C4CP01939C, 2014. a, b, c, Madronich, S., McKenzie, R. L., Caldwell, M., and Björn, L. O.: Changes in https://doi.org/10.3390/molecules25020423, 2020. a, Bielski, B. H. J., Cabelli, D. E., Arudi, R. L., and Ross, A. Herrmann, H., Schaefer, T., Tilgner, A., Styler, S. A., Weller, C., Teich, M., Finally, we discuss the impact and atmospheric importance of kinetic limitations to photochemical degradation in Sect. Res., 8, 125–131, It was also evident from these data that FeII reoxidized by O2 is as important as FeII reoxidized by radicals and peroxides as there is no significant difference between the experiments starting from FeII(HCit) ∕ CA compared to those with FeIII(Cit) ∕ CA. A., Fortner, E., Gaffney, J. S., Gilles, M. K., Gorkowski, K., Gustafson, W. I., Gyawali, M., Hair, J., Hardesty, R. M., Harworth, J. W., Herndon, S., Hiranuma, N., Hostetler, C., Hubbe, J. M., Jayne, J. T., Jeong, H., Jobson, B. T., Kassianov, E. I., Kleinman, L. I., Kluzek, C., Knighton, B., Kolesar, K. R., Kuang, C., Kubátová, A., Langford, A. O., Laskin, A., Laulainen, N., Marchbanks, R. D., Mazzoleni, C., Mei, F., Moffet, R. C., Nelson, D., Obland, M. D., Oetjen, H., Onasch, T. B., Ortega, I., Ottaviani, M., Pekour, M., Prather, K. A., Radney, J. G., Rogers, R. R., Sandberg, S. P., Sedlacek, A., Senff, C. J., Senum, G., Setyan, A., Shilling, J. E., Shrivastava, M., Song, C., Springston, S. R., Subramanian, R., Suski, K., Tomlinson, J., Volkamer, R., Wallace, H. W., Wang, J., Weickmann, A. M., Worsnop, D. R., Yu, X.-Y., Zelenyuk, A., and Zhang, Q.: Overview of the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES), Atmos. Chem. Generally, Dlj(x,T,aw) always decreases when RH or T is lowered. We assumed that half of the C5 species undergo photochemical reactions to produce CO2 and compounds with 2–4 carbon atoms, C4, C3 and C2 (see Reactions R10–R14 shown in Table 2), all of which are capable of being released to the gas phase depending on their solubility. Res., 117, D07204, https://doi.org/10.1029/2011JD016746, 2012. a, b, c, d, e, Okochi, H. and Brimblecombe, P.: Potential trace metal–organic complexation Lines: red (40 % RH), green (50 % RH), and blue (60 % RH) are the FeIII fractions predicted using the PRAD model, the shaded areas indicate model output assuming ±2 % RH, ±0.07 initial FeIII fraction, and ±1.8 % light intensity uncertainty in the STXM experimental conditions.
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