Measured and modelled cloud condensation nuclei number concentration at the high alpine site Jungfraujoch Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Received: 26 March 2010 – Published in Atmos. Chem. Phys. Discuss.: 07 April 2010 Abstract. Atmospheric aerosol particles are able to act as cloud condensation
nuclei (CCN) and are therefore important for the climate and the
hydrological cycle, but their properties are not fully understood.
Total CCN number concentrations at 10 different supersaturations in the
range of SS=0.12–1.18% were measured in May 2008 at the
remote high alpine research station, Jungfraujoch, Switzerland
(3580 m a.s.l.). In this paper, we present a closure study
between measured and predicted CCN number concentrations. CCN
predictions were done using dry number size distribution (scanning
particle mobility sizer, SMPS) and bulk chemical composition data (aerosol
mass spectrometer, AMS, and multi-angle absorption photometer, MAAP) in a
simplified Köhler theory. The predicted and the measured CCN number concentrations
agree very well and are highly correlated. A sensitivity study showed that the
temporal variability of the chemical composition at the Jungfraujoch can be
neglected for a reliable CCN prediction, whereas it is important to know the
mean chemical composition. The exact bias introduced by using a too low or
too high hygroscopicity parameter for CCN prediction was further quantified
and shown to be substantial for the lowest supersaturation.
Revised: 26 July 2010 – Accepted: 13 August 2010 – Published: 25 August 2010
Despite the high average organic mass fraction (~45%) in the fine mode,
there was no indication that the surface tension was substantially
reduced at the point of CCN activation. A comparison between hygroscopicity
tandem differential mobility analyzer (HTDMA), AMS/MAAP, and CCN derived
κ values showed that HTDMA measurements can be used to determine
particle hygroscopicity required for CCN predictions if no suitable chemical composition
data are available.
Citation: Jurányi, Z., Gysel, M., Weingartner, E., DeCarlo, P. F., Kammermann, L., and Baltensperger, U.: Measured and modelled cloud condensation nuclei number concentration at the high alpine site Jungfraujoch, Atmos. Chem. Phys., 10, 7891-7906, doi:10.5194/acp-10-7891-2010, 2010.