Chemical composition and mixing-state of ice residuals sampled within mixed phase clouds

Abstract

Abstract. During an intensive campaign at the high alpine research station Jungfraujoch, Switzerland, in February/March 2006 ice particle residuals within mixed-phase clouds were sampled using the Ice-counterflow virtual impactor (Ice-CVI). Size, morphology, chemical composition, mineralogy and mixing state of the ice residual and the interstitial (i.e., non-activated) aerosol particles were analyzed by scanning and transmission electron microscopy. Ice nuclei (IN) were identified from the significant enrichment of particle groups in the ice residual (IR) samples relative to the interstitial aerosol. In terms of number lead-bearing particles are enriched by a factor of approximately 25, complex internal mixtures with silicates or metal oxides as major components by a factor of 11, and mixtures of secondary aerosol and carbonaceous material (C-O-S particles) by a factor of 2. Other particle groups (sulfates, sea salt, Ca-rich particles, external silicates) observed in the ice-residual samples cannot be assigned unambiguously as IN. Between 9 and 24% of all IR are Pb-bearing particles. Pb was found as major component in around 10% of these particles (PbO, PbCl 2 ). In the other particles, Pb was found as some 100 nm sized agglomerates consisting of 3-8 nm sized primary particles (PbS, elemental Pb). C-O-S particles are present in the IR at an abundance of 17-27%. The soot component within these particles is strongly aged. Complex internal mixtures occur in the IR at an abundance of 9-15%. Most IN identified at the Jungfraujoch station are internal mixtures containing anthropogenic components (either as main or minor constituent), and it is concluded that admixture of the anthropogenic component is responsible for the increased IN efficiency within Correspondence to: M. Ebert (mebert@geo.tu-darmstadt.de) mixed phase clouds. The mixing state appears to be a key parameter for the ice nucleation behaviour that cannot be predicted from the sole knowledge of the main component of an individual particle.

Characterization of individual ice residual particles by the single droplet freezing method: a case study in the Asian dust outflow region

“…For example, several laboratory studies showed that mineral dust particles are capable of nucleating ice crystals at relatively high temperatures and may be important ice nuclei, especially at temperatures below approximately −15 • C (Murray et al, 2012). Additionally, several in situ field studies performed within a mixed-phase cloud at Jungfraujoch, a high-elevation site in the Swiss alpine region, reported that mineral dust was the most abundant component, comprising 40-70 % of the ice residue particles by number (Worringen et al, 2015;Ebert et al, 2011;Kamphus et al, 2010).…”

“…However, field studies have reported the presence of sulfate particles in ice residue, although potential bias from sampling artifacts cannot be entirely excluded (Prenni et al, 2009;Worringen et al, 2015;Ebert et al, 2011).…”

“…In order to overcome the issue of ice nuclei extraction from mixed-phase clouds, several techniques such as the Ice-CVI or the Ice Selective Inlet (ISI) have been proposed (Mertes et al, 2007;Kupizewski et al, 2014), and efforts have been made to characterize ice nuclei using these instruments (Kamphus et al, 2010;Ebert et al, 2011). Worringen et al (2015) reported the size distribution and chemical components of ice residues from mixed-phase clouds collected by three different techniques (Ice-CVI, ISI, and ice nuclei counter combined with CVI) and found that silicates, Carich, carbonaceous, and metal oxide particles constitute the major groups of ice nuclei.…”

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

“…In the case of heterogeneous ice nucleation it is found that mineral dust particles are favorable INP at temperatures below about −20 • C Murray et al, 2012;Augustin-Bauditz et al, 2014) that marine particles seem to be comparably inefficient INPs at temperatures > −25 • C, whereas continental aerosols (mixtures of anthropogenic haze, biomass burning smoke, soil and road dust, and organic and biogenic particles from soils and plants) seem to contain always a significant amount of efficient INPs, already leading to ice nucleation at temperatures as high as −5 to −15 • C (Seifert et al, 2010;Zhang et al, 2010;Kamphus et al, 2010;Ebert et al, 2011;Augustin et al, 2013;Hartmann et al, 2013;Bühl et al, 2013;Pummer et al, 2015;Umo et al, 2015).…”

The origins of ice crystals measured in mixed-phase clouds at the high-alpine site Jungfraujoch

“…Measurements of cloud particle (liquid droplet and ice crystal) residuals at JFJ have been found to be enriched in chemical species such as mineral dust (Kampphus et al, 2010;Schmidt et al, 2015), including lead with complex internal mixtures of silicates and metal oxides, secondary aerosol and carbonaceous material (Ebert et al, 2011) compared to the cloud interstitial aerosol (un-activated aerosol particles). This previous work suggested that particles from industrial activity containing lead were especially important as ice nuclei (IN) along with contributions from dust and organic material.…”