Measurement report: Ice-nucleating particles active ≥ −15 °C in free tropospheric air over western Europe
<p>Ice-nucleating particles (INPs) initiate ice formation in supercooled clouds, typically starting in western Europe at a few kilometres above the ground. However, little is known about the concentration and composition of INPs in the lower free troposphere (FT). Here, we analysed INPs active...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/3433/2022/acp-22-3433-2022.pdf |
| Summary: | <p>Ice-nucleating particles (INPs) initiate ice formation in
supercooled clouds, typically starting in western Europe at a few kilometres above the
ground. However, little is known about the concentration and composition of
INPs in the lower free troposphere (FT). Here, we analysed INPs active at <span class="inline-formula">−10</span> <span class="inline-formula"><sup>∘</sup></span>C (INP<span class="inline-formula"><sub>−10</sub>)</span> and <span class="inline-formula">−</span>15 <span class="inline-formula"><sup>∘</sup></span>C (INP<span class="inline-formula"><sub>−15</sub>)</span> that were collected
under FT conditions at the high-altitude observatory Jungfraujoch between
January 2019 and March 2021. We relied on continuous radon measurements to
distinguish FT conditions from those influenced by the planetary boundary
layer. Median concentrations in the FT were 2.4 INP<span class="inline-formula"><sub>−10</sub></span> m<span class="inline-formula"><sup>−3</sup></span> and 9.8 INP<span class="inline-formula"><sub>−15</sub></span> m<span class="inline-formula"><sup>−3</sup></span>, with a multiplicative standard deviation of 2.0 and
1.6 respectively. A majority of INPs were deactivated after exposure to 60 <span class="inline-formula"><sup>∘</sup></span>C; thus, they probably originated from certain epiphytic bacteria or
fungi. Subsequent heating to 95 <span class="inline-formula"><sup>∘</sup></span>C deactivated another 15 % to
20 % of the initial INPs, which were likely other types of fungal INPs that might have been
associated with soil organic matter or with decaying leaves. Very few
INP<span class="inline-formula"><sub>−10</sub></span> withstood heating to 95 <span class="inline-formula"><sup>∘</sup></span>C, but on average 20 % of
INP<span class="inline-formula"><sub>−15</sub></span> in FT samples did so. This percentage doubled during Saharan
dust intrusions, which had practically no influence on INP<span class="inline-formula"><sub>−10</sub></span>. Overall,
the results suggest that aerosolised epiphytic microorganisms, or parts
thereof, are responsible for the majority of primary ice formation in
moderately supercooled clouds above western Europe.</p> |
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| ISSN: | 1680-7316 1680-7324 |