In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 22, No. 7 ( 2022-04-14), p. 4985-5016
Abstract:
Abstract. Soot particles, acting as ice nucleating particles
(INPs), can contribute to cirrus cloud formation, which has an important influence on climate. Aviation activities emitting soot particles into the
upper troposphere can potentially impact ice nucleation (IN) in cirrus
clouds. Pore condensation and freezing (PCF) is an important ice formation
pathway for soot particles in the cirrus regime, which requires the soot INP
to have specific morphological properties, i.e., mesopore structures. In this study, the morphology and pore size distribution of two kinds of soot
samples were modified by a physical agitation method without any chemical
modification by which more compacted soot sample aggregates could be produced compared to the unmodified sample. The IN activities of both fresh
and compacted soot particles with different sizes, 60, 100, 200 and 400 nm,
were systematically tested by the Horizontal Ice Nucleation Chamber (HINC)
under mixed-phase and cirrus-cloud-relevant temperatures (T). Our results show that soot particles are unable to form ice crystals at T〉235 K (homogeneous nucleation temperature, HNT), but IN is observed for compacted and larger-sized soot aggregates (〉200 nm) well below the homogeneous freezing relative humidity (RHhom) for T〈 HNT,
demonstrating PCF as the dominating mechanism for soot IN. We also observed
that mechanically compacted soot particles can reach a higher particle
activation fraction (AF) value for the same T and RH condition compared to the same aggregate size fresh soot particles. The results also reveal a
clear size dependence for the IN activity of soot particles with the same
degree of compaction, showing that compacted soot particles with large sizes
(200 and 400 nm) are more active INPs and can convey the single importance
of soot aggregate morphology for the IN ability. In order to understand the
role of soot aggregate morphology for its IN activity, both fresh and
compacted soot samples were characterized systematically using particle mass
and size measurements, comparisons from TEM (transmission electron
microscopy) images, soot porosity characteristics from argon (Ar) and
nitrogen (N2) physisorption measurements, as well as soot–water interaction results from DVS (dynamic vapor sorption) measurements.
Considering the soot particle physical properties along with its IN
activities, the enhanced IN abilities of compacted soot particles are
attributed to decreasing mesopore width and increasing mesopore occurrence
probability due to the compaction process.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-22-4985-2022
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2022
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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