Composition of ice particle residuals in mixed-phase clouds at Jungfraujoch (Switzerland): enrichment and depletion of particle groups relative to total aerosol
<p>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 I...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/13987/2018/acp-18-13987-2018.pdf |
| Summary: | <p>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 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.</p> |
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| ISSN: | 1680-7316 1680-7324 |