Wavelength Dependence of Fe(II) Photoformation in the Water-Soluble Fraction of Aerosols Collected in Okinawa, Japan

Okada, Kouichirou; Kuroki, Y.; Nakama, Y.; Arakaki, Takemitsu; Tanahara, Akira

doi:10.1021/es061649s

Cited by 16 publications

(6 citation statements)

References 42 publications

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“…Our study reveals that high level of Fe(II)/Fe(t) (Figure ) can be maintained for a long time in the presence of excess Mal. Many field measurements indicated that Fe(II) accounts for most of the dissolved iron in rainwaters ,, , but the mechanism involved for (photo)stability of Fe(II) is unclear . It is of interest to totally identify the dissolved organic matters in rainwaters, particularly dicarboxylic acids, to understand the speciation of dissolved iron in carbon-rich troposphere, although the correlation of Mal with Fe(II) against (photo)oxidation in rainwater remains obscure so far because rainwater may have high concentrations of other oxidants generated via non metal redox pathways.…”

Section: Resultsmentioning

confidence: 99%

Photochemical Cycling of Iron Mediated by Dicarboxylates: Special Effect of Malonate

Wang

Chen

et al. 2009

Environ. Sci. Technol.

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Photochemical redox cycling of iron coupled with oxidation of malonate (Mal) ligand has been investigated under conditions that are representative of atmospheric waters. Malonate exhibited significantly different characteristics from oxalate and other dicarboxylates (or monocarboxylates). Both strong chelating ability with Fe(III) and strong molar absorptivities, but much low efficiency of Fe(II) formation (Phi(Fe(II)) = 0.0022 +/- 0.0009, 300-366 nm) were observed for Fe(III)-Mal complexes (FMCs). Fe(III) speciation calculation indicated that Mal is capable of mediating the proportion between two photoactive species of Fe(III)-OH complexes and FMCs by changing the Mal concentration. Spin-trapping electron spin resonance (ESR) experiments proved the formation of both the (.)CH(2)COOH and (.)OH radicals at lower total Mal concentration ([Mal](T)), but only (.)CH(2)COOH at higher concentrations of malonate, providing strong evidence for competition between malonate and OH(-) and subsequent different photoreaction pathways. Once FMCs dominate the Fe(III) speciation, both photoproduction and photocatalyzed oxidation of Fe(II) will be greatly decelerated. There exists an induction period for both formation and decay of Fe(II) until Fe(III)(OH)(2+) species become the prevailing Fe(III) forms over FMCs as Mal ligand is depleted. A quenching mechanism of Mal in the Fe(II) photoproduction is proposed. The present study is meaningful to advance our understanding of iron cycling in acidified carbon-rich atmospheric waters.

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Section: Resultsmentioning

confidence: 99%

Photochemical Cycling of Iron Mediated by Dicarboxylates: Special Effect of Malonate

Wang

Chen

et al. 2009

Environ. Sci. Technol.

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“…Although an estimate of aerosol transport time was not given, Zhuang et al (1992) found that significant conversion between Fe(II) and Fe(III) can occur during transport, with reduction of Fe(III) to Fe(II) being more significant than oxidation of Fe(II) to Fe(III) in marine aerosols. A number of studies have sought to measure the rates of photoreduction of Fe(III) in aqueous leaches or suspensions of aerosols (Okada et al, 2006;Zhu et al, 1993). These studies found that, in the leachate, the Fe(II) levels quickly increase upon irradiation of the aerosol solution, with the levels reaching a pseudo steady-state within 45 min.…”

Section: >25 µMmentioning

confidence: 99%

Application of synchrotron radiation for measurement of iron red-ox speciation in atmospherically processed aerosols

Majestic¹,

Schauer²,

Shafer³

2007

Preprint

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Abstract. In this study, ambient atmospheric particulate matter (PM) samples were collected using a size-resolved impactor sampler from three urban sites. The purpose of this study is to gain a better understanding of transformations of aerosol-bound iron as it is processed in the atmosphere. Thus, the aerosol samples were artificially aged to represent long-term transport (10 to 40 days) or short-term transport (1 to 10 days) and were measured for iron at several time points. At each time point, iron was measured in each size fraction using three different techniques; 1) inductively coupled plasma-mass spectrometry (ICPMS) for total iron, 2) x-ray absorbance near edge structure (XANES) spectroscopy for the measurement of total Fe(II) and Fe(III), and 3) a wet-chemical method to measure soluble Fe(II) and Fe(III). Prior to aging, the XANES spectroscopy results show that a majority (>60% for each size fraction) of the total iron in the PM is in the form of Fe(III). Fe(III) was shown to be a significant fraction of the soluble iron (sometimes > 50%), but the relative significance of Fe(III) was found to vary depending on the site. Overall, the total soluble iron depended on the sampling site, but values ranged from less than 1% up to about 18% of the total iron. Over the course of the 40 day aging period, we found moderate changes in the relative Fe(II)/Fe(III) content. A slight increase was noted in the coarse (>2.5 μm) fraction and a slight decrease in the 0.25 to 0.5 μm fraction. The soluble fraction generally showed (excepting one day) a decrease of soluble Fe(II) prior to 10 days of aging, followed by a relatively constant concentration. In the short-term transport condition, we found that the sub-micron fraction of soluble Fe(II) spikes at 1 to 3 days of aging, then decreases to near the initial value at around 6 to 10 days. Very little change in soluble Fe(II) was observed in the super-micron fraction. These results show that changes in the soluble iron fraction occur within the lifetime of urban aerosols (1–3 days) and, therefore, atmospheric processing can have a large effect on human exposure to soluble iron.

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“…Barbeau et al reported the key features of the iron cycle involving photolysis of Fe(III)–ligand complexes, with reduction of Fe(III) to Fe(II) and oxidation of the ligand. The wavelength dependence and quantum yields of Fe(II) photoformation in aerosol particles have been studied, and the results had implications to daytime Fe(III)/Fe(II) cycles in the atmospheric liquid phase . Zhao et al observed a regular oscillation in the ratio of Fe(II) to total iron when dissolved organic matter (DOM) was periodically added into the solution under irradiation.…”

Section: Introductionmentioning

confidence: 99%

Atrazine Photodegradation in Aqueous Solution Induced by Interaction of Humic Acids and Iron: Photoformation of Iron(II) and Hydrogen Peroxide

Quan

Chen

et al. 2007

J. Agric. Food Chem.

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The photochemical formation of Fe(II) and hydrogen peroxide (H 2O 2) coupled with humic acids (HA) was studied to understand the significance of iron cycling in the photodegradation of atrazine under simulated sunlight. The presence of HA significantly enhanced the formation of Fe(II) and H 2O 2, and their subsequent product, hydroxyl radical ( (*)OH), was the main oxidant responsible for the atrazine photodegradation. During 60 h of irradiation, the fraction of iron presented as Fe(II) (Fe(II)/Fe(t)) decreased from 20-32% in the presence of the Fe(III)-HA complex to 10-22% after adding atrazine. The rate of atrazine photodegradation in solutions containing Fe(III) increased with increasing HA concentration, suggesting that the complexation of Fe(III) with HA accelerated the Fe(III)/Fe(II) cycling. Using fluorescence spectrometry, the quenching constant and the percentage of fluorophores participating in the complexation of HA with Fe(III) were estimated by the modified Stern-Volmer equation. Fourier transform infrared spectroscopy (FTIR) offered the direct evidence that Fe(III)-carboxylate complex could be formed by ligand exchange of HA with Fe(III). Based on all the information, a possible reaction mechanism was proposed.

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Wavelength Dependence of Fe(II) Photoformation in the Water-Soluble Fraction of Aerosols Collected in Okinawa, Japan

Cited by 16 publications

References 42 publications

Photochemical Cycling of Iron Mediated by Dicarboxylates: Special Effect of Malonate

Photochemical Cycling of Iron Mediated by Dicarboxylates: Special Effect of Malonate

Application of synchrotron radiation for measurement of iron red-ox speciation in atmospherically processed aerosols

Atrazine Photodegradation in Aqueous Solution Induced by Interaction of Humic Acids and Iron: Photoformation of Iron(II) and Hydrogen Peroxide

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