Ice residual properties in mixed‐phase clouds at the high‐alpine Jungfraujoch site

Abstract

Ice residual (IR) and total aerosol properties were measured in mixed‐phase clouds (MPCs) at the high‐alpine Jungfraujoch research station. Black carbon (BC) content and coating thickness of BC‐containing particles were determined using single‐particle soot photometers. The ice activated fraction (IAF), derived from a comparison of IR and total aerosol particle size distributions, showed an enrichment of large particles in the IR, with an increase in the IAF from values on the order of 10−4 to 10−3 for 100 nm (diameter) particles to 0.2 to 0.3 for 1 μm (diameter) particles. Nonetheless, due to the high number fraction of submicrometer particles with respect to total particle number, IR size distributions were still dominated by the submicrometer aerosol. A comparison of simultaneously measured number size distributions of BC‐free and BC‐containing IR and total aerosol particles showed depletion of BC by number in the IR, suggesting that BC does not play a significant role in ice nucleation in MPCs at the Jungfraujoch. The potential anthropogenic climate impact of BC via the glaciation effect in MPCs is therefore likely to be negligible at this site and in environments with similar meteorological conditions and a similar aerosol population. The IAF of the BC‐containing particles also increased with total particle size, in a similar manner as for the BC‐free particles, but on a level 1 order of magnitude lower. Furthermore, BC‐containing IR were found to have a thicker coating than the BC‐containing total aerosol, suggesting the importance of atmospheric aging for ice nucleation.

Impact of Air Mass Conditions and Aerosol Properties on Ice Nucleating Particle Concentrations at the High Altitude Research Station Jungfraujoch

“…However, in this study, a strong correlation between INP concentrations and eBC was not found considering the total of performed measurements in any of the discussed conditions. This suggests that eBC does not have a major contribution to the INP population active at 242 K at the JFJ, which is in agreement to the findings of studies on the ice residuals of MPCs at the same site [48,49]. This observation is also not surprising given previous laboratory studies of ice nucleation onto a variety of soot particles and sizes also concluded no heterogeneous freezing observed the mixed-phase temperature regime (T > −38 • C), and that cirrus temperatures were required to observe ice nucleation [50,51].…”

Is Black Carbon an Unimportant Ice‐Nucleating Particle in Mixed‐Phase Clouds?

“…In one study of mixed‐phase clouds at a high‐altitude observatory in the Alps, soot particles only made up 5% of the submicron aerosol particles, but 27% of ice crystal residues (Cozic et al, ). In contrast, several studies found that BC accounted for only a minor fraction of ice crystal residues, but mineral dust was clearly enhanced (Baustian et al, ; Kamphus et al, ; Kupiszewski et al, ; Schmidt et al, ). More recently, analysis of ice‐nucleating particle (INP) chemical composition in air influenced by biomass burning events using electron microscopy showed that between 0% and 64% of INPs were BC particles and suggested that biomass burning particles could be an important regional source of INP, especially during periods when other INPs such as desert dust are absent (Mccluskey et al, ).…”

Online single particle analysis of ice particle residuals from mountain-top mixed-phase clouds using laboratory derived particle type assignment

“…The ALABAMA consists of three parts: inlet system, detection region and ablation/ionization region. An aerodynamic lens (Liu-type;Liu et al, 1995a, b;Kamphus et al, 2008) and a critical orifice form the inlet system of the ALABAMA, which transmits the particles into the vacuum system and focusses the aerosol particles to a narrow beam. At the exit of the aerodynamic lens the particles are accelerated depending on their particle size to a velocity of about 50-100 ms −1 .…”