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Published March 5, 2013 | Supplemental Material + Published
Journal Article Open

Worldwide data sets constrain the water vapor uptake coefficient in cloud formation


Cloud droplet formation depends on the condensation of water vapor on ambient aerosols, the rate of which is strongly affected by the kinetics of water uptake as expressed by the condensation (or mass accommodation) coefficient, α_c. Estimates of α_c for droplet growth from activation of ambient particles vary considerably and represent a critical source of uncertainty in estimates of global cloud droplet distributions and the aerosol indirect forcing of climate. We present an analysis of 10 globally relevant data sets of cloud condensation nuclei to constrain the value of αc for ambient aerosol. We find that rapid activation kinetics (α_c > 0.1) is uniformly prevalent. This finding resolves a long-standing issue in cloud physics, as the uncertainty in water vapor accommodation on droplets is considerably less than previously thought.

Additional Information

© 2013 National Academy of Sciences. Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved January 18, 2013 (received for review November 13, 2012). Published online before print February 19, 2013. We thank Dr. Xiaohong Liu for advice on using the CAM 5.1 and for providing computer time for the simulations. We also thank all those who contributed to the measurement campaigns; Charles Brock from the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory; and the National Aeronautics and Space Administration (NASA) Langley Aerosol Research Group Experiment for supporting aerosol measurements during Arctic Research of the Composition of the Troposphere from Aircraft and Satellites. T.R. thanks the Finnish Cultural Foundation; S.L. and J.J.L. acknowledge the support of a Georgia Tech President's fellowship and an National Center for Atmospheric Research Advanced Study Program Graduate Fellowship; and J.J.L. thanks the NASA Graduate Student Researchers Program for funding. R.H.M. acknowledges support from a Department of Energy Global Change Education Fellowship, a NASA Earth and Space Science Fellowship, and a NASA postdoctoral fellowship. L.T.P. received funding from a NASA Earth System Science fellowship. T.L.L. acknowledges support from a National Science Foundation (NSF) fellowship and a Georgia Tech institutional fellowship. Funding from a DOE grant (to A.N.), the Electric Power Research Institute, an NSF Faculty Early Career Development award (to A.N.), NOAA grants (to J.H.S. and A.N.), and NASA grants (to A.N.) is acknowledged. Author contributions: T.R. and A.N. designed research; T.R., A.N., J.H.S., R.M., R.H.M., T.L.L., S.L., L.T.P., J.J.L., K.M.C., A.B., J.C., B.E.A., R.C.F., H.J., N.M., and J.N.S. performed research; T.R., A.N., J.H.S., R.M., C.R.R., P.Y.C., B.E.A., and N.M. contributed new reagents/analytic tools; T.R., A.N., R.H.M., T.L.L., S.L., L.T.P., J.J.L., K.M.C., A.B., J.C., B.E.A., R.C.F., N.M., and J.N.S. analyzed data; and T.R., A.N., and J.H.S. wrote the paper.

Attached Files

Published - PNAS-2013-Raatikainen-3760-4.pdf

Supplemental Material - pnas.201219591SI.pdf


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