ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-9855-2012 Stable water isotopologue ratios in fog and cloud droplets of liquid clouds are not size-dependent Spiegel J. K. 1 Aemisegger F. 2 Scholl M. 3 Wienhold F. G. 2 J. L. Collett Jr. 4 Lee T. 4 van Pinxteren D. 5 Mertes S. 5 Tilgner A. 5 Herrmann H. 5 Werner R. A. 1 Buchmann N. 1 Eugster W. 1 Institute of Agricultural Sciences, ETH Zurich, Zurich, Switzerland Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland US Geological Survey, Reston, VA, USA Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA Leibniz Institute for Tropospheric Research, Leipzig, Germany 29 10 2012 12 20 9855 9863 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/9855/2012/acp-12-9855-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/9855/2012/acp-12-9855-2012.pdf

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.

 References Arends, B G., Kos, G. P A., Maser, R., Schell, D., Wobrock, W., Winkler, P., Ogren, J A., Noone, K J., Hallberg, A., Svenningsson, I B., Wiedensohler, A., Hansson, H C., Berner, A., Solly, I., and Kruisz, C.: Microphysics of clouds at Kleiner Feldberg, J. Atmos. Chem., 19, 59–85, http://dx.doi.org/10.1007/BF00696583doi:10.1007/BF00696583, 1994. Bolin, B.: On the use of tritium as a tracer for water in nature, in: Proc. Sec. Intern. Conf. Peaceful Uses of Atomic Energy, 18, 336–344, International Meteorological Inst., Stockholm, Geneva, 1958. Booker, D.: Exchange between water droplets and tritiated water vapour, Q. J. Roy. Meteor. Soc., 91, 73–79, 1964. Cappa, C D., Hendricks, M B., DePaolo, D J., and Cohen, R C.: Isotopic fractionation of water during evaporation, J. Geophys. Res., 108, 4525, http://dx.doi.org/10.1029/2003JD003597doi:10.1029/2003JD003597, 2003. Collett, Jr., J., Herckes, P., Youngster, S., and Lee, T.: Processing of atmospheric organic matter by California radiation fogs, Atmos. Res., 87, 232–241, http://dx.doi.org/10.1016/j.atmosres.2007.11.005doi:10.1016/j.atmosres.2007.11.005, 2008. Coplen, T. B.: Normalization of oxygen and hydrogen isotope data, Chem. Geol., 72, 293–297, http://dx.doi.org/10.1016/0168-9622(88)90042-5doi:10.1016/0168-9622(88)90042-5, 1988. Coplen, T. B.: Guidelines and recommended terms for expression of stable-isotope-ratio and gas-ratio measurement results, Rapid Commun. Mass Spectrom., 25, 2538–2560, http://dx.doi.org/10.1002/rcm.5129doi:10.1002/rcm.5129, 2011. Criss, R E.: Principles of Stable Isotope Distribution, Oxford University Press, Oxford, p 254, 1999. Dansgaard, W.: Stable isotopes in precipitation, Tellus, 16, 436–468, 1964. Dansgaard, W., Johnsen, S., Clausen, H., Dahl-Jensen, D., Gundestrup, N., Hammer, C., Hvidberg, C., Steffensen, J., Sveinbjörnsdottir, A., Jouzel, J., and Bond, G.: Evidence for general instability of past climate from a 250-kyr ice-core record, Nature, 364, 218–220, 1993. Demoz, B., Collett Jr., J L., and Daube Jr., B.: On the Caltech active strand cloudwater collectors, Atmos. Res., 41, 47–62, http://dx.doi.org/10.1016/0169-8095(95)00044-5doi:10.1016/0169-8095(95)00044-5, 1996. Farquhar, G D., Cernusak, L A., and Barnes, B.: Heavy water fractionation during transpiration., Plant Physiol., 143, 11–8, http://dx.doi.org/10.1104/pp.106.093278doi:10.1104/pp.106.093278, 2007. Friedman, I., Machta, L., and Soller, R.: Water-vapor exchange between a water droplet and its environment, J. Geophys. Res., 57, 2761–2766, 1962. Gedzelman, S. and Arnold, R.: Modeling the isotopic composition of precipitation, J. Geophys. Res., 99, 10455–10471, 1994. Gehre, M., Geilmann, H., Richter, J., Werner, R., and Brand, W.: Continuous flow <sup>2</sup>H/$^1$H and and $^18$O/$^16$O analysis of water samples with dual inlet precision, Rapid Commun. Mass Spectrom., 18, 2650–2660, 2004. Gerber, H.: Direct measurement of suspended particulate volume concentration and far-infrared extinction coefficient with a laser-diffraction instrument, Appl. Opt., 30, 4824–4831, 1991. Hall, W. and Pruppacher, H.: The survival of ice particles falling from cirrus clouds in subsaturated air, J. Atmos. Sci., 33, 1995–2006, 1976. Holm, S.: A simple sequentially rejective multiple test procedure, Scand. J. Stat., 6, 65–70, 1979. Jouzel, J.: Isotopes in Clouds Physics: Multiphase and Multistage Condensation Processes, in: Handbook of Environmental Isotope Geochemistry, Volume 2, The Terrestrial Environment, B, edited by: Fritz, P. and Fontes, J., chap 2, pp. 61–112, Elsevier Science Publischer B.V., Amsterdam, The Netherlands, 1986. Jouzel, J., Merlivat, L., and Roth, E.: Isotopic study of hail, J. Geophys. Res., 80, 5015–5030, http://dx.doi.org/10.1029/JC080i036p05015doi:10.1029/JC080i036p05015, 1975. Kaul, D S., Gupta, T., Tripathi, S N., Tare, V., and Collett, J L.: Secondary organic aerosol: a comparison between foggy and nonfoggy days., Environ. Sci. Technol., 45, 7307–7313, http://dx.doi.org/10.1021/es201081ddoi:10.1021/es201081d, 2011. Kinzer, G D. and Gunn, R.: The evaporation, temperature and thermal relaxation-time of freely falling waterdrops, J. Meteorol., 8, 71–83, 1951. Lee, J.-E. and Fung, I.: Amount effect of water isotopes and quantitative analysis of post-condensation processes, Hydrol. Process., 22, 1–8, http://dx.doi.org/10.1002/hyp.6637doi:10.1002/hyp.6637, 2007. Legendre, P. and Legendre, L.: Numerical Ecology, 20, Elsevier Science, p 853, 1998. Michna, P., Schenk, J., Wanner, H., and Eugster, W.: MiniCASCC – A battery driven fog collector for ecological applications, in: Proceedings of the Fourth International Conference on Fog, Fog Collection and Dew, La Serena, Chile, 22–27 July 2007, 169–172, 2007. Moore, K F., Sherman, D E., Reilly, J E., and Collett Jr., J L.: Drop size-dependent chemical composition in clouds and fogs. Part I. Observations, Atmos. Environ., 38, 1389–1402, http://dx.doi.org/10.1016/j.atmosenv.2003.12.013doi:10.1016/j.atmosenv.2003.12.013, 2004a. Moore, K F., Sherman, D E., Reilly, J E., Hannigan, M P., Lee, T., and Collett Jr., J L.: Drop size-dependent chemical composition of clouds and fogs. Part II: Relevance to interpreting the aerosol/trace gas/fog system, Atmos. Environ., 38, 1403–1415, http://dx.doi.org/10.1016/j.atmosenv.2003.12.014doi:10.1016/j.atmosenv.2003.12.014, 2004b. Petit, J. R., Jouzel, J., Raynaud, D., Barkov, N. I., Barnola, J. M., Basile, I., Bender, M., Chappellaz, J., Davis, M., Delaygue, G., Delmotte, M., Kotlyakov, V. M., Legrand, M., Lipenkov, V. Y., Lorius, C., Pepin, L., Ritz, C., Saltzman, E., and Stievenard, M.: Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica, Nature, 399, 429–436, 1999. Pruppacher, H R. and Klett, J D.: Microphysics of Clouds and Precipitation, Kluwer Academic Publishers, Dordrecht, The Netherlands, p 955, 1997. Raja, S., Raghunathan, R., Yu, X.-Y., Lee, T., Chen, J., Kommalapati, R R., Murugesan, K., Shen, X., Qingzhong, Y., Valsaraj, K T., and Collett, J L.: Fog chemistry in the Texas – Louisiana Gulf Coast corridor, Atmos. Environ., 42, 2048–2061, http://dx.doi.org/10.1016/j.atmosenv.2007.12.004doi:10.1016/j.atmosenv.2007.12.004, 2008. Risi, C., Bony, S., Vimeux, F., Descroix, L., Ibrahim, B., Lebreton, E., Mamadou, I., and Sultan, B.: What controls the isotopic composition of the African monsoon precipitation? Insights from event-based precipitation collected during the 2006 AMMA field campaign, Geophys. Res. Lett., 35, L24808, http://dx.doi.org/10.1029/2008GL035920doi:10.1029/2008GL035920, 2008. Schmid, S., Burkard, R., Frumau, K., Tobon, C., Bruijnzeel, L., Siegwolf, R., and Eugster, W.: Using eddy covariance and stable isotope mass balance techniques to estimate fog water contributions to a Costa Rican cloud forest during the dry season, Hydrol. Process., 25, 429–437, http://dx.doi.org/10.1002/hyp.7739doi:10.1002/hyp.7739, 2010. Scholl, M., Eugster, W., and Burkard, R.: Understanding the role of fog in forest hydrology: stable isotopes as tools for determining input and partitioning of cloud water in montane forests, Hydrol. Process., 25, 353–366, http://dx.doi.org/10.1002/hyp.7762doi:10.1002/hyp.7762, 2011. Seinfeld, J H. and Pandis, S N.: Atmospheric Chemistry and Physics: From Air Polution to Climate Change, John Wiley and Sons, New Jersey, USA, 2006. Spiegel, J. K., Aemisegger, F., Scholl, M., Wienhold, F. G., J. L. Collett Jr., Lee, T., van Pinxteren, D., Mertes, S., Tilgner, A., Herrmann, H., Werner, R. A., Buchmann, N., and Eugster, W.: Temporal evolution of stable water isotopologues in cloud droplets during HCCT-2010, Atmos. Chem. Phys. Discuss., 12, 15139-15175, http://dx.doi.org/10.5194/acpd-12-15139-2012doi:10.5194/acpd-12-15139-2012, 2012. Stewart, M.: Stable isotope fractionation due to evaporation and isotopic exchange of falling water drops: application to atmospheric processes and evaporation of lakes, J. Geophys. Res., 80, 1133–1146, 1975. Yakir, D. and Sternberg, L. d. S L.: The use of stable isotopes to study ecosystem gas exchange, Oecologia, 123, 297–311, http://dx.doi.org/10.1007/s004420051016doi:10.1007/s004420051016, 2000.