In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 18, No. 18 ( 2018-09-20), p. 13363-13392
Abstract:
Abstract. Ice
nucleation by different types of soot particles is systematically
investigated over the temperature range from 218 to 253 K
relevant for both mixed-phase (MPCs) and cirrus clouds. Soot types were selected to
represent a range of physicochemical properties associated with combustion
particles. Their ice nucleation ability was determined as a function of
particle size using relative humidity (RH) scans in the Horizontal Ice
Nucleation Chamber (HINC). We complement our ice nucleation results by a
suite of particle characterization measurements, including determination of
particle surface area, fractal dimension, temperature-dependent mass loss (ML),
water vapor sorption and inferred porosity measurements. Independent of
particle size, all soot types reveal absence of ice nucleation below and at
water saturation in the MPC regime (T〉235 K). In the cirrus
regime (T≤235 K), soot types show different freezing behavior
depending on particle size and soot type, but the freezing is closely linked
to the soot particle properties. Specifically, our results suggest that if
soot aggregates contain mesopores (pore diameters of 2–50 nm) and
have sufficiently low water–soot contact angles, they show ice nucleation
activity and can contribute to ice formation in the cirrus regime at RH well
below homogeneous freezing of solution droplets. We attribute the observed
ice nucleation to a pore condensation and freezing (PCF) mechanism.
Nevertheless, soot particles without cavities of the right size and/or
too-high contact angles nucleate ice only at or well above the RH required for
homogeneous freezing conditions of solution droplets. Thus, our results imply
that soot particles able to nucleate ice via PCF could impact the
microphysical properties of ice clouds.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-18-13363-2018
DOI:
10.5194/acp-18-13363-2018-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2069847-1
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