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Publisher: Milton Park : Taylor & Francis × Subject: cloud condensation nucleus ×

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    Cloud condensation nuclei spectra derived from size distributions and hygroscopic properties of the aerosol in coastal south-west Portugal during ACE-2
    (Milton Park : Taylor & Francis, 2016) Dusek, Ulrike; Covert, David S.; Wiedensohler, Alfred; Neusüss, Christian; Weise, Diana; Cantrell, Will
    In this work we propose and test a method to calculate cloud condensation nuclei (CCN) spectra basedon aerosol number size distributions and hygroscopic growth factors. Sensitivity studies show thatthis method can be used in a wide variety of conditions except when the aerosol consist mainly oforganic compounds. One crucial step in the calculations, estimating soluble ions in an aerosol particlebased on hygroscopic growth factors, is tested in an internal hygroscopic consistency study. The resultsshow that during the second Aerosol Characterization Experiment (ACE-2) the number concentrationof inorganic ions analyzed in impactor samples could be reproduced from measured growth factorswithin the measurement uncertainties at the measurement site in Sagres, Portugal. CCN spectra were calculated based on data from the ACE-2 field experiment at the Sagres site.The calculations overestimate measured CCN spectra on average by approximately 30%, which iscomparable to the uncertainties in measurements and calculations at supersaturations below 0.5%. Thecalculated CCN spectra were averaged over time periods when Sagres received clean air masses and airmasses influenced by aged and recent pollution. Pollution outbreaks enhance the CCN concentrationsat supersaturations near 0.2% by a factor of 3 (aged pollution) to 5 (recent pollution) compared to theclean marine background concentrations. In polluted air masses, the shape of the CCN spectra changes.The clean spectra can be approximated by a power function, whereas the polluted spectra are betterapproximated by an error function.
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    Size-dependent aerosol activation at the high-alpine site Jungfraujoch (3580 m asl)
    (Milton Park : Taylor & Francis, 2016) Henning, S.; Weingartner, E.; Schmidt, S.; Wendisch, M.; Gäggeler, H.W.; Baltensperger, U.
    Microphysical and chemical aerosol properties and their influence on cloud formation were studied in a field campaign at the high-alpine site Jungfraujoch (JFJ, 3580 m asl). Due to its altitude, this site is suitable for ground-based in-cloud measurements, with a high cloud frequency of 40%. Dry total and interstitial aerosol size distributions [18 nm 0.15 g m−3. Below this value, D50 increased with decreasing LWC. A dependence of D50 on the accumulation mode (Dp>100 nm) number concentration (Ntot,Dp>100) was only found for concentrations less than 100 cm−3. For higher values of Ntot,Dp>100 the D50 remained constant. Furthermore, a decrease of the effective radius of cloud droplets (Reff) with increasing Ntot,Dp>100 was observed, providing experimental evidence for the microphysical relation predicted by the Twomey effect. A modified Köhler model was used to quantify the critical supersaturation for the aerosol observed at the JFJ. Ambient supersaturations were determined from the derived supersaturation curve and the calculated D50. As an example, a critical supersaturation of 0.2% was found for 100 nm particles.