Atmos. Chem. Phys. Discuss., 7, 13699-13732, 2007
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Hygroscopicity of the submicrometer aerosol at the high-alpine site Jungfraujoch, 3580 m a.s.l., Switzerland
S. Sjogren1, M. Gysel1, E. Weingartner1, M. R. Alfarra1, J. Duplissy1, J. Cozic1, J. Crosier2, H. Coe2, and U. Baltensperger1
1Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen, Switzerland
2School of Earth, Atmospheric and Environmental Science, University of Manchester, UK

Abstract. Data from measurements of hygroscopic growth of submicrometer aerosol with a hygroscopicity tandem differential mobility analyzer (HTDMA) during four campaigns at the high alpine research station Jungfraujoch, Switzerland, are presented. The campaigns took place during the years 2000, 2002, 2004 and 2005, each lasting approximately one month. In parallel, size resolved chemical composition measurements with an aerosol mass spectrometer were performed. A hygroscopic closure was done with the composition data using the Zdanovskii-Stokes-Robinson relation. In general, a good agreement between measured and modeled data was found, with some discrepancies caused by instrumental noise at low aerosol loadings. Hygroscopic growth factors (GF, i.e. the relative change in particle diameter from dry diameter, D0, to diameter measured at higher relative humidity, RH) are presented for three distinct air mass types, namely for: 1) free tropospheric winter conditions, 2) planetary boundary layer influenced air masses (during a summer period) and 3) Saharan dust events (SDE). The GF values at 85% RH (D0=100 nm) were 1.40±0.11 and 1.29±0.08 for the first two situations while for SDE a bimodal GF distribution was often found. No phase changes were observed when the RH was varied between 10–90%, and the continuous water uptake could be well described with a single-parameter empirical model. The frequency distributions of the average hygroscopic growth factors and the width of the retrieved growth factor distributions (indicating whether the aerosol is internally or externally mixed) are presented, which can be used for modeling purposes.

Citation: Sjogren, S., Gysel, M., Weingartner, E., Alfarra, M. R., Duplissy, J., Cozic, J., Crosier, J., Coe, H., and Baltensperger, U.: Hygroscopicity of the submicrometer aerosol at the high-alpine site Jungfraujoch, 3580 m a.s.l., Switzerland, Atmos. Chem. Phys. Discuss., 7, 13699-13732, doi:10.5194/acpd-7-13699-2007, 2007.
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