Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> 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.

Highlights

  • 20 Free troposphere (FT) designates a part of the troposphere that only occasionally is in exchange with Earth's surface, whereas the planetary boundary layer (PBL) continuously exchanges particles with surface sources and sinks

  • We relied on continuous radon measurements to distinguish free troposphere (FT) conditions from those influenced by the planetary boundary layer

  • The Ice nucleating particles (INP) sampled at Jungfraujoch during FT conditions likely originated from the 95 northern part of western Europe and from the North Atlantic (Fig. 2)

Read more

Summary

Introduction

20 Free troposphere (FT) designates a part of the troposphere that only occasionally is in exchange with Earth's surface, whereas the planetary boundary layer (PBL) continuously exchanges particles with surface sources and sinks. A community of airborne microorganisms, for example, is in the PBL mainly composed of organisms from within a distance of several tens of kilometers (TignatPerrier et al, 2019). Particle populations sampled at a high-altitude mountain station under FT conditions. A special kind of aerosol particles, so-called ice-nucleating particles (INP), is relevant for primary ice formation in mid-level clouds (Findeisen, 1938). Ice formation starts in the midlatitudes a few kilometers above ground at around 5 °C (Kanitz et al, 2011). In FT conditions at the high-altitude observatory Jungfraujoch (3580 m a.s.l.) in the Swiss Alps, Lacher et al (2018) found similar

Objectives
Methods
Results

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.