Counterflow Virtual Impactor Based Collection of Small Ice Particles in Mixed-Phase Clouds for the Physico-Chemical Characterization of Tropospheric Ice Nuclei: Sampler Description and First Case Study

Abstract

A ground-based sampling system named Ice-CVI is introduced that is able to extract small ice particles with sizes between 5 and 20 μm out of mixed-phase clouds. The instrument is based on a counterflow virtual impactor (CVI) removing interstitial particles and is supplemented by additional modules that pre-segregate other constituents of mixed-phase clouds. Ice particles of 20 μm and smaller are expected to grow only by water vapor diffusion and there is a negligible probability that they scavenge aerosol particles by impaction and riming. Thus, their residuals which are released by the Ice-CVI can be interpreted as the original ice nuclei (IN). In a first field test within the Cloud and Aerosol Characterization Experiment (CLACE-3) at the high alpine research station Jungfraujoch, the collection behavior of the single components and the complete system was evaluated under atmospheric sampling conditions. By comparing parameters measured by the Ice-CVI with corresponding results obtained from other inlets or with in-situ instrumentation it is verified that the small ice particles are representatively collected whereas all other mixed phase cloud constituents are effectively suppressed. In a case study it is observed that supermicrometer particles preferentially serve as IN although in absolute terms the IN concentration is dominated by sub-micrometer particles. Mineral dust (Si), non-volatile organic matter and black carbon could be identified as IN components by means of different chemical analyses. The latter suggests an anthropogenic influence on the heterogeneous ice nucleation in supercooled, tropospheric clouds.

Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps

“…This is confirmed by Mertes et al (2007) and Kamphus et al (2010) who found a larger number concentration of larger particles in the ice residuals sampled during CLACE-3 and 6, respectively. As mentioned in Sect 2.3, Schwikowski et al (1995) showed that the concentration of larger particles is higher during a dust event than for a non SDE event.…”

Surface modification of mineral dust particles by sulphuric acid processing: implications for ice nucleation abilities

“…Mineral dust has been recognized as the most relevant IN in the atmosphere (Kamphus et al, 2010;Mertes et al, 2007;Richardson et al, 2007;Cziczo et al, 2004;DeMott et al, 2003). However, it is unlikely that mineral dust is found in its pure, untreated form after a few hours or days of residence time in the atmosphere.…”

“…The exact effect of ice clouds on the Earth's climate is yet not well understood (Forster et al, 2007) and more research is needed to determine the mechanisms of heterogeneous ice nucleation (Cantrell and Heymsfield, 2005). Mineral dust has been found to be one of the major components of snow crystal residuals (Kamphus et al, 2010;Mertes et al, 2007;Richardson et al, 2007;Cziczo et al, 2004;DeMott et al, 2003). In the atmosphere mineral dust is often internally mixed with organic and inorganic material due to particle ageing processes in the atmosphere (Wiacek and Peter, 2009;Hinz et al, 2005;Falkovich et al, 2001).…”

Evaluating the capabilities and uncertainties of droplet measurements for the fog droplet spectrometer (FM-100)

“…Several intensive cloud characterization experiments have been conducted there for many years at different times of the year (e.g. Mertes et al, 2007;Verheggen et al, 2007;Cozic et al, 2008;Targino et al, 2009;Kamphus et al, 2010;Zieger et al, 2012). The aerosol measurements performed at the JFJ are part of the Global Atmosphere Watch (GAW) program of the World Meteorological Organization since 1995 (Collaud Coen et al, 2007).…”