Journal of Atmospheric Chemistry 19: 107-127, 1994. 107 @ 1994 Kluwer Academic Publishers. Printed in the Netherlands. Phase Partitioning of Aerosol Particles in Clouds at Kleiner Feldberg A. HALLBERG 1, K. J. NOONE l'a, J. A. OGREN 1,b, I. B. SVENNINGSSON 2, A. FLOSSMANN 3' c, A. WIEDENSOHLER 2' d, H.-C. HANSSON 2, j. HEINTZENBERG L d, T. L. ANDERSON l' e B. G. ARENDS 4 and R. MASER 5 1Department of Meteorology, Stockhobn University, S-106 91 Stockholm, Sweden 2Department of Nuclear Physics, University of Lund, S-223 62 Lund, Sweden 3 Institut fiir Physik der Atmosphgire, UniversitZit Mainz, Saarstrasse 21, D-55020, Mainz, Germany 4Netherland Energy Research Foundation, PO Box 1, 1755 ZG Petten, The Netherlands 5Zentrumfiir Umweltforsehang und Institut far Meteorologic und Geophysik, Johann Wolfgang Goethe Universitdt, Postfach 111932, D-60054 Frankfurt a.M., Germany (Received: 23 July 1993; in final form: 30 May 1994) Abstract. The partitioning of aerosol particles between cloud droplets and interstitial air by number and volume was determined both in terms of an integral value and as a function of size for clouds on Mt. Kleiner Feldberg (825 m asl), in the Taunus Mountains north-west of Frankfurt am Main, Germany. Differences in the integral values and the size dependent partitioning between two periods during the campaign were observed. Higher number and volume concentrations of aerosol particles in the accumulation mode were observed during Period II compared to Period I. In Period I on average 87 :f: 11% (+one standard deviation) and 73 • 7% of the accumulation mode volume and number were incorporated into cloud droplets. For Period II the corresponding fractions were 42 ± 6% and 12 ± 2% in one cloud event and 64 ± 4% and 18 ± 2% in another cloud event. The size dependent partitioning as a function of time was studied in Period II and found to have little variation. The major processes influencing the partitioning were found to be nucleation scavenging and entrainment. Key words: Partitioning, aerosol particles, cloud, scavenging, CVI. 1. Introduction The partitioning of aerosol particles between cloud droplets and interstitial air is dependent on several processes. Droplet nucleation causes some of the aerosol particles to grow into cloud droplets while the rest remain as interstitial particles. Present affiliations: a Center for Atmospheric Chemistry Studies, Graduate School of Oceanography, Narrangansett, RI 02882-1197, U.S.A. b NOAA/CMDL/R/E/CG, 325 Broadway, Boulder, CO 80303-3328, U.S.A. c Laboratoire de M6t6orologie Physique, Universit6 Blaise Pascal, 24 Avenue des Landais, F-63177 Anbiere Cedex, France d Institut ft~r Tropospherenforschung e3L, Permoserstrasse 15, D-04303 Leipzig, Germany. e Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, U.S.A.