Preprints
https://doi.org/10.5194/acp-2020-831
https://doi.org/10.5194/acp-2020-831

  26 Aug 2020

26 Aug 2020

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Laboratory study of the collection efficiency of submicron aerosol particles by cloud droplets. Part I – Influence of relative humidity

Alexis Dépée1,2, Pascal Lemaitre1, Thomas Gelain1, Marie Monier2,3, and Andrea Flossmann2,3 Alexis Dépée et al.
  • 1Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSN-RES, SCA, Gif-sur-Yvette, France
  • 2Université Clermont Auvergne, Laboratoire de Météorologie Physique, Clermont-Ferrand, France
  • 3CNRS, INSU, UMR 6016, LaMP, Aubière, France

Abstract. A new In-Cloud Aerosol Scavenging Experiment (In-CASE) has been conceived to measure the collection efficiency (CE) of submicron aerosol particles by cloud droplets. In this setup, droplets fall at their terminal velocity through a one-meter-high chamber in a laminar flow containing aerosol particles. At the bottom of the In-CASE's chamber, the droplet train is separated from the aerosol particle flow – droplets are collected in an impaction cup whereas aerosol particles are deposited on a High Efficiency Particulate Air (HEPA) filter. The collected droplets and the filter are then analysed by fluorescence spectrometry since the aerosol particles are atomised from a sodium fluorescein salt solution (C20H10Na2O5). In-CASE fully controls all the parameters which affect the CE – the droplets and aerosol particles size distributions are monodispersed, the electric charges of droplets and aerosol particles are controlled, while the relative humidity is indirectly set via the chamber's temperature. This novel In-CASE setup is presented here as well as the first measurements obtained to study the impact of relative humidity on CE. For this purpose, droplets and particles are electrically neutralised. A droplet radius of 49.6 ± 1.3 μm has been considered for six particle dry radii between 50 and 250 nm and three relative humidity levels of 71.1 ± 1.3, 82.4 ± 1.4 and 93.5 ± 0.9 %. These new CE measurements have been compared to the Wang et al. (1978) and the extended model of Dépée et al. (2019) where thermophoresis and diffusiophoresis are implemented. Both models adequately describe the relative humidity influence on the measured CE.

Alexis Dépée et al.

 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Alexis Dépée et al.

Alexis Dépée et al.

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Short summary
Present article describe a new In-Cloud Aerosol Scavenging Experiment (In-CASE) that has been conceived to measure the collection efficiency of submicron aerosol particles by cloud droplets. Present article focus on the influence of phoretic effect on the collection efficeincy.
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