Preprints
https://doi.org/10.5194/acpd-13-32575-2013
https://doi.org/10.5194/acpd-13-32575-2013
10 Dec 2013
 | 10 Dec 2013
Status: this preprint was under review for the journal ACP. A revision for further review has not been submitted.

Size-resolved and integral measurements of cloud condensation nuclei (CCN) at the high-alpine site Jungfraujoch

D. Rose, S. S. Gunthe, Z. Jurányi, M. Gysel, G. P. Frank, J. Schneider, J. Curtius, and U. Pöschl

Abstract. As part of the CLACE-6 campaign we performed size-resolved CCN measurements for a~supersaturation range of S = 0.079 % to 0.66% at the high-alpine research station Jungfraujoch, Switzerland, in March~2007. The derived effective hygroscopicity parameter κ describing the influence of particle composition on CCN activity was on average 0.23–0.30 for Aitken (50–100 nm) and 0.32–0.43 for accumulation mode particles (100–200 nm). The campaign average value of κ = 0.3 is similar to the average value of κ for other continental locations. When air masses came from southeasterly directions crossing the Po Valley in Italy, particles were much more hygroscopic (κ ≈ 0.42) due to large sulfate mass fractions. The κ values obtained at S = 0.079 % exhibited a good negative correlation with the organic mass fractions derived from PM1 aerosol mass spectrometer (AMS) measurements. Applying a simple mixing rule the organic and inorganic mass fractions observed by the AMS could be used to reproduce the temporal fluctuations of the hygroscopicity of accumulation mode particles quite well.

We show how during a cloud event the aerosol particles were activated as cloud droplets and then removed from the air by precipitation leaving behind only a small amount of accumulation mode particles consisting mainly of weakly CCN-active particles, most likely externally mixed unprocessed soot particles.

During the campaign we had the opportunity to directly compare two DMT CCN counters for a certain time. The total CCN concentration (NCCN,tot) obtained by the two instruments at equal supersaturations agreed well for both possible operating modes: detecting NCCN,tot directly by sampling the polydisperse aerosol with the CCNC, or indirectly by combining size-resolved measurements of the activated fraction with parallel measurements of the particle size distribution (e.g., by SMPS). However, some supersaturation setpoints differed between the two CCNCs by as much as 20% after applying the instrument calibrations, which resulted in differences of the corresponding NCCN,tot of up to 50%. This emphasizes that it is extremely important to carefully calibrate the supersaturation of the instrument, especially at low S.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
D. Rose, S. S. Gunthe, Z. Jurányi, M. Gysel, G. P. Frank, J. Schneider, J. Curtius, and U. Pöschl
 
Status: closed (peer review stopped)
Status: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed (peer review stopped)
Status: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
D. Rose, S. S. Gunthe, Z. Jurányi, M. Gysel, G. P. Frank, J. Schneider, J. Curtius, and U. Pöschl
D. Rose, S. S. Gunthe, Z. Jurányi, M. Gysel, G. P. Frank, J. Schneider, J. Curtius, and U. Pöschl

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