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Cloud albedo enhancement by surface-active organic solutes in growing droplets

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Abstract

Understanding the properties of clouds in the Earth's atmosphere is currently limited by difficulties at the fundamental level of adequately describing the processes of cloud droplet nucleation and growth. Small changes in droplet population may significantly influence cloud albedo1 as well as formation of precipitation. Models of cloud formation based on laboratory studies with idealized composition of nuclei suggest that organic solutes significantly lower surface tension2—one of the parameters determining droplet population—but the lack of data on composition and properties of the organic material in the atmosphere precludes realistic laboratory or model studies. Here, we report measurements on vacuum-evaporated samples of cloud water from the Po Valley, Italy, that show a large decrease in surface tension, by up to about one-third relative to pure water, for realistic concentrations of organic solutes expected to exist in growing droplets. Such large surface-tension changes, if they occur in cloud droplets near the critical size for nucleation, lead to an increase in droplet population and hence in cloud albedo. The error produced in ignoring this effect is estimated to be comparable to other calculated direct and indirect influences of aerosols on scattering and absorption of solar radiation3.

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Figure 1: Measured change of surface tension.
Figure 2: Köhler curves given by a modified Köhler equation2.

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Acknowledgements

We thank G. Loglio for the surface tension measurements. M.M. was supported by the ‘Abdus Salam’ International Centre for Theoretical Physics, Trieste, Italy under the TRIL Programme.

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Authors and Affiliations

  1. Istituto di Scienze dell'Atmosfera e dell'Oceano—Consiglio Nazionale delle Ricerche (ISAO-CNR), 40129, Bologna, Italy

    Maria Cristina Facchini, Mihaela Mircea & Sandro Fuzzi

  2. Departments of Atmospheric Sciences and Chemistry, University of Washington, Seattle, 98195, Washington, USA

    Robert J. Charlson

  3. National Institute of Meteorology and Hydrology, Bucharest, Romania

    Mihaela Mircea

Authors
  1. Maria Cristina Facchini
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  2. Mihaela Mircea
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  3. Sandro Fuzzi
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  4. Robert J. Charlson
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Correspondence to Maria Cristina Facchini.

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Facchini, M., Mircea, M., Fuzzi, S. et al. Cloud albedo enhancement by surface-active organic solutes in growing droplets. Nature 401, 257–259 (1999). https://doi.org/10.1038/45758

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  • DOI: https://doi.org/10.1038/45758

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