In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 23, No. 15 ( 2023-08-08), p. 8659-8681
Abstract:
Abstract. Atmospheric ice nucleation impacts the hydrological cycle and climate by
modifying the radiative properties of clouds. To improve our predictive
understanding of ice formation, ambient ice-nucleating particles (INPs) need
to be collected and characterized. Measurements of INPs at lower latitudes
in a remote marine region are scarce. The Aerosol and Cloud Experiments in
the Eastern North Atlantic (ACE-ENA) campaign, in the region of the Azores
islands, provided the opportunity to collect particles in the marine
boundary layer (MBL) and free troposphere (FT) by aircraft during the
campaign's summer and winter intensive operation period. The particle
population in samples collected was examined by scanning transmission X-ray
microscopy with near-edge X-ray absorption fine structure spectroscopy. The
identified INPs were analyzed by scanning electron microscopy with
energy-dispersive X-ray analysis. We observed differences in the particle
population characteristics in terms of particle diversity, mixing state, and
organic volume fraction between seasons, mostly due to dry intrusion events
during winter, as well as between the sampling locations of the MBL and FT. These
differences are also reflected in the temperature and humidity conditions
under which water uptake, immersion freezing (IMF), and deposition ice
nucleation (DIN) proceed. Identified INPs reflect typical particle types
within the particle population on the samples and include sea salt, sea salt
with sulfates, and mineral dust, all associated with organic matter, as well as
carbonaceous particles. IMF and DIN kinetics are analyzed with respect to
heterogeneous ice nucleation rate coefficients, Jhet, and ice
nucleation active site density, ns, as a function of the water
criterion Δaw. DIN is also analyzed in terms of contact angles
following classical nucleation theory. Derived MBL IMF kinetics agree with
previous ACE-ENA ground-site INP measurements. FT particle samples show
greater ice nucleation propensity compared to MBL particle samples. This
study emphasizes that the types of INPs can vary seasonally and with
altitude depending on sampling location, thereby showing different ice
nucleation propensities, which is crucial information when representing mixed-phase
cloud and cirrus cloud microphysics in models.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-23-8659-2023
DOI:
10.5194/acp-23-8659-2023-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
Permalink
