Preprints
https://doi.org/10.5194/acp-2021-830
https://doi.org/10.5194/acp-2021-830

  15 Nov 2021

15 Nov 2021

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

Time-dependence of Heterogeneous Ice Nucleation by Ambient Aerosols: Laboratory Observations and a Formulation for Models

Jonas Jakobsson1, Vaughan Phillips2, and Thomas Bjerring-Kristensen1 Jonas Jakobsson et al.
  • 1Division of Nuclear Physics, Department of Physics, Lund University, Lund, Sweden
  • 2Department of Physical Geography and Ecosystem Science (INES), Lund University, Lund, Sweden

Abstract. The time dependence of ice-nucleating particle (INP) activity is known to exist, yet for simplicity it is often omitted in atmospheric models as an approximation. Hitherto only limited experimental work has been done to quantify this time dependency, for which published data are especially scarce regarding ambient aerosol samples and longer time scales.

In this study, the time dependence of INP activity is quantified experimentally for ambient environmental samples. The experimental approach includes a series of hybrid experiments with alternating constant cooling and isothermal experiments using a recently developed cold-stage setup called the Lund University Cold-Stage (LUCS). This approach of observing ambient aerosol samples provides the optimum realism for representing their time dependence in any model. Six ambient aerosol samples were collected representing aerosol conditions likely influenced by these types of INPs: marine, mineral dust, continental pristine, continental polluted, combustion-related and rural continental aerosol.

Active INP concentrations were seen to be augmented by about 40 % to 100 % (or 70 % to 200 %), depending on the sample, over 2 (or 10) hours. This degree of time dependence observed was comparable to that seen in previous published works. Our observations show that the minority of active ice nuclei (IN) with strong time dependency on hourly time scales display only weak time dependence on short time scales of a few minutes. A general tendency was observed for the natural time scale of the freezing to dilate increasingly with time. The fractional freezing rate was observed to steadily declines exponentially with the order of magnitude (logarithm) of the time since the start of isothermal conditions. A representation of time dependence for incorporation into schemes of heterogeneous ice nucleation that currently omit time dependence is proposed.

Jonas Jakobsson et al.

Status: open (until 27 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-830', Anonymous Referee #1, 29 Nov 2021 reply

Jonas Jakobsson et al.

Jonas Jakobsson et al.

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Short summary
Long-lived cold layer-clouds at subzero temperatures are observed to be remarkably persistent in their generation of ice particles and snow precipitation. There is uncertainty about why this is so. This motivates the present lab study to observe the long-term ice nucleating ability of aerosol samples from the real troposphere.
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