ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-3117-2011 Size-resolved aerosol water uptake and cloud condensation nuclei measurements as measured above a Southeast Asian rainforest during OP3 Irwin M. 1 Robinson N. 1 Allan J. D. 1 2 Coe H. 1 McFiggans G. 1 School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK National Centre for Atmospheric Science, University of Manchester, Manchester, UK 28 01 2011 11 1 3117 3159 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-discuss.net/11/3117/2011/acpd-11-3117-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/3117/2011/acpd-11-3117-2011.pdf

The influence of the properties of fine particles on the formation of clouds and precipitation in the tropical atmosphere is of primary importance to their impacts on radiative forcing and the hydrological cycle. Measurements of aerosol number size distribution, hygroscopicity in both sub- and supersaturated regimes and composition were taken between March and July 2008 in the tropical rainforest in Borneo, Malaysia, marking the first study of this type in an Asian tropical rainforest. Hygroscopic growth factors (GF) at 90% relative humidity (RH) for the dry diameter range <i>D</i><sub>0</sub>=32–258 nm, supersaturated water uptake behaviour for the dry diameter range <i>D</i><sub>0</sub>=20–300 nm and aerosol chemical composition were simultaneously measured using a Hygroscopicity Tandem Differential Mobility Analyser (HTDMA), a Droplet Measurement Technologies Cloud Condensation Nuclei counter (CCNc) and an Aerodyne Aerosol Mass Spectrometer (AMS), respectively. <br><br> The derived hygroscopicty parameter κ ranged from between 0.05–0.37 for the supersaturation range 0.11–0.73% compared to those between 0.17–0.37 for measurements performed at a relative humidity of 90%. In contrast, results from a study with similar methodology performed in the Amazon basin report more similar values for <i>κ</i>, indicating that the aerosol as measured from both sites shows similar hygroscopic properties. However, the derived number of cloud condensation nuclei (<i>N</i><sub>CCN</sub>) were much higher than those measured in the Amazon, due to the higher particle number concentrations in the rainforests of Borneo. This first contrast between the two environments may be of substantial importance in describing the impacts of particles in the tropical atmosphere.

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