Aerosol observations and growth rates in the tropical tropopause layer
1School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, UK
2Forschungszentrum Jülich, Germany
3Flinders University, Adelaide, Australia
4Max-Planck-Institute for Nuclear Physics, Heidelberg, Germany
5Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany
6Centre for Research in Earth and Space Sciences, York University, Toronto, Canada
Abstract. We present a case study of Aitken and accumulation mode aerosol observed downwind of the anvils of deep tropical thunderstorms. 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 in the size range 10–100 nm were 25 000 cm−3 STP. By calculating back-trajectories from the observations, and projecting on to infrared satellite images, the time since the air exited cloud was estimated. In this way a time scale of ~ 3–4 h was derived for the 10–100 nm 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 SO2 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.