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

• Published in: Atmospheric chemistry and physics 2018-10, Vol.18 (19), p.13987-14003
• Main Authors: Eriksen Hammer, Stine, Mertes, Stephan, Schneider, Johannes, Ebert, Martin, Kandler, Konrad, Weinbruch, Stephan
• Format: Article
• Language: English
• Subjects: Abrasion; Abundance; Aerosol composition; Aerosol particles; Aerosols; Air sampling; Aluminosilicates; Aluminum; Aluminum silicates; Calcium; Chemical composition; Chemical pollution; Chemical properties; Clouds; Clouds (Meteorology); Contamination; Counterflow; Depletion; Dilution; Duration; Electron microscopy; Enrichment; Environmental aspects; Heavy metals; High altitude; Ice; Ice nucleation; Industrial areas; Inlets (waterways); Iron; Lead; Metals; Natural history; Organic chemistry; Particle emission; Pollution control; Relative abundance; Sampling; Scanning electron microscopy; Silica; Silicon dioxide; Soot; Substrates; Temperature; Temperature dependence; Wind roses
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-18-13987-2018

Ice particle residuals (IRs) and the total aerosol particle population were sampled in parallel during mixed-phase 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-salt-containing 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