Atmos. Chem. Phys. Discuss., 8, 14105-14143, 2008
www.atmos-chem-phys-discuss.net/8/14105/2008/
doi:10.5194/acpd-8-14105-2008
© Author(s) 2008. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Measurements of the relation between aerosol properties and microphysics and chemistry of low clouds in northern Finland
H. Lihavainen1, V.-M. Kerminen1, M. Komppula1, A.-P. Hyvärinen1, J. Laakia1, S. Saarikoski1, U. Makkonen1, N. Kivekäs1, R. Hillamo1, M. Kulmala2, and Y. Viisanen1
1Finnish Meteorological Institute, Research and Development, P. O. Box 503, 00 101 Helsinki, Finland
2University of Helsinki, Department of Physics, P. O. Box 64, 00 014, Finland

Abstract. Physical and chemical properties of boundary layer clouds, together with relevant aerosol properties, were investigated during the first Pallas Cloud Experiment (First PaCE) conducted in northern Finland between 20 October and 9 November, 2004. Two stations located 6 km apart from each other at different altitudes were employed in measurements. The low-altitude station was always below the cloud layer, whereas the high-altitude station was inside clouds about 75% of the time during the campaign. Direct measurements of cloud droplet populations showed that our earlier approach of determining cloud droplet residual particle size distributions and corresponding activated fractions using continuous aerosol number size distribution measurements at the two stations is valid, as long as the cloud events are carefully screened to exclude precipitating clouds and to make sure the same air mass has been measured at both stations. We observed that a non-negligible fraction of cloud droplets originated from Aitken mode particles even at moderately-polluted air masses. We found clear evidence on first indirect aerosol effect on clouds but demonstrated also that no simple relation between the cloud droplet number concentration and aerosol particle number concentration exists for this type of clouds. The chemical composition of aerosol particles was dominated by organic matter (POM) and sulphate in continental air masses and POM, sodium and chlorine in marine air masses. The inorganic composition of cloud water behaved similarly to that of the aerosol phase and was not influenced by inorganic trace gases.

Citation: Lihavainen, H., Kerminen, V.-M., Komppula, M., Hyvärinen, A.-P., Laakia, J., Saarikoski, S., Makkonen, U., Kivekäs, N., Hillamo, R., Kulmala, M., and Viisanen, Y.: Measurements of the relation between aerosol properties and microphysics and chemistry of low clouds in northern Finland, Atmos. Chem. Phys. Discuss., 8, 14105-14143, doi:10.5194/acpd-8-14105-2008, 2008.
 
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