ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-6157-2012 Aerosol observations and growth rates downwind of the anvil of a deep tropical thunderstorm Waddicor D. A. 1 Vaughan G. 1 Choularton T. W. 1 Bower K. N. 1 Coe H. 1 Gallagher M. 1 Williams P. I. 1 Flynn M. 1 Volz-Thomas A. 2 Pätz H. -W. 2 Isaac P. 3 Hacker J. 3 Arnold F. 4 Schlager H. 5 Whiteway J. A. 6 School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, UK Forschungszentrum Jülich, Germany Flinders University, Adelaide, Australia Max-Planck-Institute for Nuclear Physics, Heidelberg, Germany Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany Centre for Research in Earth and Space Sciences, York University, Toronto, Canada 17 07 2012 12 14 6157 6172 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/12/6157/2012/acp-12-6157-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/6157/2012/acp-12-6157-2012.pdf

We present a case study of Aitken and accumulation mode aerosol observed downwind of the anvil of a deep tropical thunderstorm. The measurements were made by condensation nuclei counters flown on the Egrett high-altitude aircraft from Darwin during the ACTIVE campaign, in monsoon conditions producing widespread convection over land and ocean. Maximum measured concentrations of aerosol with diameter greater than 10 nm were 25 000 cm<sup>−3</sup> (STP). By calculating back-trajectories from the observations, and projecting onto infrared satellite images, the time since the air exited cloud was estimated. In this way a time scale of about 3 hours was derived for the Aitken aerosol concentration to reach its peak. We examine the hypothesis that the growth in aerosol concentrations can be explained by production of sulphuric acid from SO<sub>2</sub> followed by particle nucleation and coagulation. Estimates of the sulphuric acid production rate show that the observations are only consistent with this hypothesis if the particles coagulate to sizes >10 nm much more quickly than is suggested by current theory. Alternatively, other condensible gases (possibly organic) drive the growth of aerosol particles in the TTL.

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