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Title: Stable water isotopologue ratios in fog and cloud droplets of liquid clouds are not size-dependent
Authors: Spiegel, J. K.Aemisegger, F.Scholl, M.Wienhold, F. G.Collett Jr., J. L.Lee, T.van Pinxteren, D.Mertes, S.Tilgner, A.Herrmann, H.Werner, R. A.Buchmann, N.Eugster, W.
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Issue Date: 2012
Published in: Atmospheric Chemistry and Physics, Volume 12, Issue 20, Page 9855-9863
Publisher: München : European Geopyhsical Union
Abstract: In this work, we present the first observations of stable water isotopologue ratios in cloud droplets of different sizes collected simultaneously. We address the question whether the isotope ratio of droplets in a liquid cloud varies as a function of droplet size. Samples were collected from a ground intercepted cloud (= fog) during the Hill Cap Cloud Thuringia 2010 campaign (HCCT-2010) using a three-stage Caltech Active Strand Cloud water Collector (CASCC). An instrument test revealed that no artificial isotopic fractionation occurs during sample collection with the CASCC. Furthermore, we could experimentally confirm the hypothesis that the δ values of cloud droplets of the relevant droplet sizes (μm-range) were not significantly different and thus can be assumed to be in isotopic equilibrium immediately with the surrounding water vapor. However, during the dissolution period of the cloud, when the supersaturation inside the cloud decreased and the cloud began to clear, differences in isotope ratios of the different droplet sizes tended to be larger. This is likely to result from the cloud's heterogeneity, implying that larger and smaller cloud droplets have been collected at different moments in time, delivering isotope ratios from different collection times.
Keywords: cloud; droplet; fog; isotopic fractionation; isotopic ratio; particle size; stable isotope; water; water vapor
DDC: 550
License: CC BY 3.0 Unported
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