Composition of ice particle residuals in mixed-phase clouds at Jungfraujoch (Switzerland): enrichment and depletion of particle groups relative to total aerosol

Abstract

Ice particle residuals (IRs) and the total aerosol particle population were sampled in parallel during mixedphase cloud events at the high-altitude research station Jungfraujoch in January-February 2017. Particles were sampled behind an ice-selective counterflow impactor (Ice-CVI) for IRs and a heated total inlet for the total aerosol particles. A dilution set-up was used to collect total particles with the same sampling duration as for IRs to prevent overloading of the substrates. About 4000 particles from 10 Ice-CVI samples (from 7 days of cloud events at temperatures at the site between −10 and −18 • C) were analysed and classified with operator-controlled scanning electron microscopy. Contamination particles (identified by their chemical composition), most likely originating from abrasion in the Ice-CVI and collection of secondary ice, were excluded from further analysis. Approximately 3000 total aerosol particles (IRs and interstitial particles) from 5 days in clouds were also analysed. Enrichment and depletion of the different particle groups (within the IR fraction relative to the total aerosol reservoir) are presented as an odds ratio relative to alumosilicate (particles only consisting of Al, Si, and O), which was chosen as reference due to the large enrichment of this group relative to total aerosol and the relatively high number concentration of this group in both total aerosol and the IR samples. Complex secondary particles and soot are the major particle groups in the total aerosol samples but are not found in the IR fraction and are hence strongly depleted. C-rich particles (most likely organic particles) showed a smaller enrichment compared to aluminosilicates by a factor of ∼ 20. The particle groups with enrichment similar to aluminosilicate are silica, Fe aluminosilicates, Ca-rich particles, Ca sulfates, sea-saltcontaining particles, and metal/metal oxide. Other aluminosilicates -consisting of variable amounts of Na, K, Ca, Si, Al, O, Ti, and Fe -are somewhat more enriched (factor ∼ 2) and Pb-rich particles are more (factor ∼ 8) enriched than aluminosilicates. None of the sampled IR groups showed a temperature or size dependence in respect to ice activity, which might be due to the limited sampling temperature interval and the similar size of the particles. Footprint plots and wind roses could explain the different total aerosol composition in one sample (carbonaceous particle emission from the urban/industrial area of Po Valley), but this did not affect the IR composition. Taking into account the relative abundance of the particle groups in total aerosol and the ice nucleation ability, we found that silica, aluminosilicates, and other aluminosilicates were the most important ice particle residuals at Jungfraujoch during the mixed-phase cloud events in winter 2017.

Using freezing spectra characteristics to identify ice-nucleating particle populations during the winter in the Alps

“…Air mass transport analyses were conducted using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYS-PLIT) model with the SplitR package for RStudio (https: //github.com/rich-iannone/SplitR, last access: August 2018) (Draxler, 1999;Draxler and Rolph, 2011;Stein et al, 2015). Reanalysis data from the National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR) (2.5 • latitude-longitude; 6hourly; https://www.ready.noaa.gov/gbl_reanalysis.php, last access: August 2018) were used as the meteorological fields in HYSPLIT simulations.…”

The ice-nucleating ability of quartz immersed in water and its atmospheric importance compared to K-feldspar

“…Homogeneous freezing of cloud droplets becomes increasingly important below −33 • C (Herbert et al, 2015), but clouds commonly glaciate at much warmer temperatures (Kanitz et al, 2011;Ansmann et al, 2009). Freezing at these warmer temperatures can occur through secondary ice production (Field et al, 2017) or heterogeneous freezing on ice-nucleating particles (INPs) (Murray et al, 2012;Hoose and Möhler, 2012). The presence of INPs, which tend to comprise only a small fraction of cloud condensation nuclei and can dramatically reduce the lifetime of shallow clouds (Vergara-Temprado et al, 2018), alter the development of deep convective clouds through, for example, the release of latent heat, which invigorates the updraught thus altering cloud structure (Lohmann, 2017;Rosenfeld et al, 2011).…”

Spatial and temporal variability in the ice-nucleating ability of alpine snowmelt and extension to frozen cloud fraction

“…Mixed-phase clouds are responsible for the majority of precipitation over land (Hande and Hoose, 2017;Henneberg et al, 2017;Mülmenstädt et al, 2015;Murray et al, 2012) through immersion freezing, defined by the freezing of cloud droplets due to the presence of an immersed INP (de Boer et al, 2011). As the majority of ice precipitation in mixed-phase clouds is initiated via immersion freezing, the composition (de Boer et al, 2011), abundance and sources of INPs responsible for the precipitation can be obtained through the analysis of precipitation samples (Fan et al, 2018;Morris et al, 2014;Petters and Wright, 2015;Stopelli et al, 2015;Wright et al, 2014).…”