Preprints
https://doi.org/10.5194/acp-2021-643
https://doi.org/10.5194/acp-2021-643

  03 Aug 2021

03 Aug 2021

Review status: this preprint is currently under review for the journal ACP.

The contribution of Saharan dust to the ice nucleating particle concentrations at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland

Cyril Brunner1, Benjamin Tobias Brem2, Martine Collaud Coen3, Franz Conen4, Maxime Hervo3, Stephan Henne5, Martin Steinbacher5, Martin Gysel-Beer2, and Zamin Abdulali Kanji1 Cyril Brunner et al.
  • 1Institute for Atmospheric and Climate Science, ETH, Zurich, CH-8092, Switzerland
  • 2Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
  • 3Federal Office of Meteorology and Climatology, MeteoSwiss, CH-1530 Payerne, Switzerland
  • 4Department of Environmental Sciences, University of Basel, CH-4056 Basel, Switzerland
  • 5Laboratory for Air Pollution/Environmental Technology, Empa, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland

Abstract. The ice phase in mixed-phase clouds has a pivotal role in global precipitation formation as well as for Earth's radiative budget. Above 235 K, sparse particles with the special ability to initiate ice formation, ice nucleating particles (INPs), are responsible for primary ice formation within these clouds. However, the abundance and distribution of INPs remain largely unknown. Mineral dust is known to be the most abundant INP in the atmosphere at temperatures colder than 258 K. To better constrain and quantify the impact of mineral dust on ice nucleation, we investigate the frequency of Saharan dust events (SDEs) and their contribution to the INP number concentration at 243 K and at a saturation ratio with respect to liquid water (Sw) of 1.04 at the High Altitude Research Station Jungfraujoch (JFJ; 3580 m a.s.l.) from February to December 2020. Using the single scattering albedo Angström exponent, satellite retrieved dust mass concentrations, simulated tropospheric residence times, and the attenuated backscatter signal from a ceilometer as proxies, we detected 26 SDEs, which in total contributed to 17 % of the time span analyzed. We found every SDE to show an increase in median INP concentrations compared to that of all non-SDE periods, however, not always statistically significant. Median INP concentrations of individual SDEs spread between 1.7 and 161 INP std L−1, thus, two orders of magnitude. In the entire period analyzed, 74.7 ± 0.2 % of all INPs were measured during SDEs. Based on satellite retrieved dust mass concentrations, we argue that mineral dust is also present at the JFJ outside of SDEs, but at much lower concentrations, thus still contributing to the INP population. We estimate 97.0 ± 0.3 % of all INPs active in the immersion mode at 243 K Sw = 1.04 at the JFJ to be mineral dust particles. Overall, we found INP number concentrations to follow a leptokurtic log-normal frequency distribution. We found the INP number concentrations during SDEs to correlate with the ceilometer backscatter signals from a ceilometer located 4.5 km north of the JFJ and 1510 m lower in altitude, thus scanning the air masses at the same altitude as the JFJ. Using the European ceilometer network allows studying the atmospheric pathway of mineral dust plumes over a large domain, which we demonstrate in two case studies. These studies showed that mineral dust plumes form ice crystals at cirrus altitudes, which then sediment to lower altitudes. Upon sublimation in dryer air layers, the residual particles are left potentially pre-activated. Future improvements to the sampling lines of INP counters are required to study if these particles are indeed pre-activated, leading to larger INP number concentrations than reported here.

Cyril Brunner et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-643', Paul DeMott, 25 Aug 2021
  • RC2: 'Comment on acp-2021-643', Anonymous Referee #2, 16 Sep 2021
  • RC3: 'Comment on acp-2021-643', Anonymous Referee #3, 17 Sep 2021

Cyril Brunner et al.

Cyril Brunner et al.

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Short summary
Special microscopic particles called ice-nucleating particles (INPs) are essential for ice crystals to form in the atmosphere. INPs are sparse and their atmospheric concentration and properties are not well understood. Mineral dust particles make up a significant fraction of INPs, but how much remains unknown. Here, we address this knowledge gap by studying periods when mineral particles are present in large quantities at a mountain top station in central Europe.
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