Speciation and role of iron in cloud droplets at the puy de Dôme station |
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| Authors: | Marius Parazols Angela Marinoni Pierre Amato Otman Abida Paolo Laj Gilles Mailhot |
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| Institution: | (1) Laboratoire de Photochimie Moléculaire et Macromoléculaire, UMR CNRS 6505, Clermont-Ferrand, France;(2) Laboratoire de Météorologie Physique, UMR CNRS 6016, Clermont-Ferrand, France;(3) Laboratoire Synthèse et Etudes de Systèmes à Intérêt Biologique, UMR CNRS 6504, Université Blaise Pascal, Clermont-Ferrand, France;(4) Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Bologna, Italy |
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| Abstract: | Iron is the most abundant transition metal in the atmosphere and can play a significant role in cloudwater chemistry where its reactivity is closely related to the partitioning between Fe(II) and Fe(III). The objective of this work is to determine the total iron content and the iron speciation in a free tropospheric site, and to understand which factors influence these parameters. We collected 147 samples of cloudwater during 34 cloud events over a period of four years at the puy de Dôme summit. Besides iron we measured other chemical compounds, solar radiation, physico-chemical and meteorological parameters potentially connected with iron reactivity. The total iron concentrations ranged from 0.1 to 9.1 μM with the major frequency occurring at low levels. The pH and presence of organic complexants seem to be the most significant factors connected with total dissolved iron; while the iron oxidation state seems to be an independent factor. Light intensity, presence of complexants or oxidants (H2O2) do not influence the Fe(II)/Fe(Total) ratio, that was quite constant at about 0.75. This could be due to the potential redox that forces the Fe(II)-Fe(III) couple to the reduced form or, more probably to the complexation by Natural Organic Matter, that can stabilize iron in its reduced form and prevent further oxidation. Our field measurements did not show the diurnal cycle observed in surface water and predicted by models of atmospheric chemistry. This result prompts a more careful review of the role of iron and, by analogy, all the transition metals in atmospheric liquid phase, often over-estimated in the literature. |
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| Keywords: | Reactivity Cloudwater Field experiment Free troposphere Iron speciation Natural Organic Matter |
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