ACPD Atmospheric Chemistry and Physics Discussions ACPD Atmos. Chem. Phys. Discuss. 1680-7375 Göttingen, Germany 10.5194/acpd-6-7471-2006 Observations of sulfur dioxide uptake and new particle formation in a midlatitude cumulus cloud Peter J. R. 1 7 Siems S. T. 1 Jensen J. B. 2 Gras J. L. 3 Ishizaka Y. 4 Hacker J. M. 5 6 School of Mathematical Sciences, Monash University, Clayton, VIC 3800, Australia National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000, USA CSIRO Marine and Atmospheric Research, 107-121 Station Street, Aspendale, VIC 3195, Australia Hydrospheric Atmospheric Research Center(HyARC) Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan Airborne Research Australia, P.O. Box 335, Salisbury South, SA 5106, Australia School of Chemistry, Physics and Earth Sciences, Flinders University, GPO Box 2100, Adelaide , SA 5001, Australia now at: Institute for Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK 04 08 2006 6 4 7471 7497 Copyright: © 2006 J. R. Peter et al. 2006 This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Generic License. To view a copy of this licence, visit https://creativecommons.org/licenses/by-nc-sa/2.5/ This article is available from https://acp.copernicus.org/preprints/6/7471/2006/acpd-6-7471-2006.html The full text article is available as a PDF file from https://acp.copernicus.org/preprints/6/7471/2006/acpd-6-7471-2006.pdf

Airborne measurements, obtained during the Asian Aerosol Characterisation Experiment (ACE-Asia), of SO<sub>2</sub> and condensation nuclei (CN) concentrations were made in the local environment of a cumulus cloud band. Conserved quantities, wet equivalent potential temperature <i>&theta;</i><sub>q</sub>, and total water content <i>Q</i>, were used to identify the sources of air detrained on the downwind side of the cumulus band. It was found that ~65% of the detrained air originated from below cloud base and the remainder was air that had been entrained from the free troposphere upwind of the cloud and subsequently been detrained. Calculation of the sources of the detrained air parcels enabled a prediction of the concentration of SO<sub>2</sub> and CN, assuming that SO<sub>2</sub> and CN experienced no processing within cloud. A comparison of the predicted concentration of SO<sub>2</sub> and CN was made with those observed. The concentration of SO<sub>2</sub> observed was less than predicted and the amount of SO<sub>2</sub> scavenged within cloud was calculated. The CN concentration observed was also less than predicted and, moreover, inclusion of the loss of CN to cloud droplets due to Brownian scavenging resulted in an enhanced decrease of the number concentration of CN predicted. Clear air regions around the cloud exhibited no indication of being a major source of new particles. It was concluded that new particles were formed within cloud.