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 (IPRs) 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 on boron substrates by use of multi MINI cascade impactors operated behind an ice selective counterflow impactor (Ice-CVI) for IPRs and a heated total inlet for the total aerosol particles. Total aerosol samples were collected with a dilution setup to match the much longer 5 sampling time behind the Ice-CVI. About 4000 particles from ten Ice-CVI samples (from seven days of cloud events at temperatures between -10 °C 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 the further analysis. Approximately 3000 total aerosol particles from five days in clouds were also analysed. Enrichment and depletion of the different particle groups (within the IPR fraction relative to total 10 aerosol reservoir) are presented as 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 IPR samples. Complex secondary particles and soot are the major particle groups in the total aerosol samples, but are not found in the IPR fraction and are hence strongly depleted. C-rich particles (most likely organic particles) showed a smaller enrichment compared to alumosilicates by a factor of ~20. The 15 particle groups with similar enrichment as alumosilicate are silica, Fe-alumosilicates, Ca-rich, Ca-sulphates, sea salt and metal/ metal oxide. Other-alumosilicates -consisting of variable amounts of Na, K, Ca, Si, Al, O, Ti and Fe-are somewhat more (factor ~2) and Pb-rich more (factor ~8) enriched than alumosilicates. None of the sampled IPR 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 20 (carbonaceous particle emission from the urban/industrial area of Po Valley), but this did not affect the IPR composition. Taken into account the relative abundance of the particle groups in total aerosol and the ice nucleation ability, we found that silica, alumosilicates and other-alumosilicates were the most important ice particle residuals at Jungfraujoch during the mixed phase cloud events in winter 2017. 30Atmos. Chem. Phys. Discuss., https://doi

Black Carbon Aerosols in the Lower Free Troposphere are Heavily Coated in Summer but Largely Uncoated in Winter at Jungfraujoch in the Swiss Alps

“…the station is often situated completely in the lower FT. At other times it receives variable injections of air masses originating from the PBL depending on the season and the regional weather conditions (Collaud Coen et al, 2011; Herrmann et al, 2015). Numerous BC‐related studies have already taken place at the JFJ focusing on, for example, optical properties (Lavanchy et al, 1999), nucleation scavenging (Cozic et al, 2007), and ice nucleation properties (Eriksen Hammer et al, 2018; Kupiszewski et al, 2016). Liu et al (2010) reported the first single‐particle characterization of BC at the JFJ with a single particle soot photometer (SP2).…”