| Abstract |
Aerosol-cloud interactions consist one of the major sources of uncertainty in climate
projections according to the recent IPCC report. Ice-nucleating particles (INP), which originate
from terrestrial and marine environments, enable ice formation, profoundly affecting the
microphysical and radiative properties, lifetimes, and precipitation rates of clouds. The
simulated ice crystal concentrations in mixed-phase clouds are affected by uncertainties in
the concentration of INP, leading to discrepancies in the climate sensitivity of the models.
The present work aimsto investigate the global distribution of ice nucleating particles, identify
their major source and aerosol types acting as INP, depending on location and season, and
proposed laboratory-derived parameterizations for use in climate models after testing them
against ground-based and aircraft observations. The study focuses on the impact of INP in
mixed-phase clouds regime.
For this purpose, the 3-dimensional chemistry transport model TM4-ECPL has been used. The
model has been further developed to account for INP concentrations from K-feldspar and
quartz dust minerals, and organic-rich particles that are ejected into the atmosphere from
oceans during bubble bursting or are emitted as terrestrial bioaerosols such as fungi and
bacteria.
In this contribution, first we investigate the global and regional importance of quartz as a
contributor to INP in the atmosphere relative to K-feldspar, applying state-of-the-art
parameterizations based on ice-active surface-site approach for immersion freezing.
Additionally, we investigate the impact of different soil mineralogy atlases on the simulated
concentrations of INP, by comparing with observations.
The results show that, although K-feldspar remains the most important contributor to INP
concentrations globally, affecting mid-level mixed-phase clouds, the contribution of quartz
can also be significant. Quartz dominates the lowest and the highest altitudes of dust-derived
INP, affecting mainly low-level and high-level mixed-phase clouds. These findings support the
inclusion of quartz in addition to K-feldspar as an INP in climate models and highlight the need
for further constraining their abundance in arid soil surfaces along with their abundance, size
distribution, and mixing state in the emitted dust atmospheric particles.
The present study also evaluated the contribution of terrestrial and marine organic aerosols
to the INP concentrations, identifying the dominant INP aerosol precursor per season and
region. Uncertainties in the calculations are determined and some of them are quantified by
performing sensitivity calculations.
Additionally, it is found that at relatively warm temperatures (above −15 °C) the majority of
INP have typically biological origin, while at lower temperatures and high altitudes INP from
mineral dust prevails globally. Marine-derived INP are primarily found over oceans and coastal
areas and dominate between 40°-70°S (Southern Ocean), with higher concentrations in
regions of high sea spray and oceanic biota activity. Marine INP dominate primary ice
nucleation over 600 hPa over the Northern Hemisphere, while dust INP are more abundant
elsewhere. Mineral dust-derived INP are primarily found over and downwind desert regions,
particularly the Sahara Desert, Gobi Desert and the Arabian Peninsula. INP from dust
contribute more to total INP in the mid-latitudes in the Northern Hemisphere than in the
Southern Hemisphere due to the location of dust sources and long-range atmospheric
transport patterns. INP from terrestrial bioaerosols has the potential to form ice crystals in
the NH subtropics at the outflow of continental air. Our simulated INP concentrations predict
∼ 64 % of the observations gathered from different campaigns within 1 order of magnitude
and ∼ 79 % within 1.5 orders of magnitude.
Finally, in collaboration with Barcelona Supercomputing Center, the validated in TM4-ECPL
dust and marine organic aerosol parameterizations of INP have been introduced in the
atmospheric component of the EC-Earth3 Earth System Model and enabled us to provide the
first preliminary evaluation of the impact of these INP on cloud cover, ice water path, surface
temperature, long and short-wave radiation at the top of the atmosphere.
Overall, this thesis improves our understanding of INP global distribution and INP precursors
as well as of the role of INP in the glaciation indirect effect and the broader impact of mixedphase clouds on climate, with the ultimate goal of providing better parameterizations for use
in climate models to improve climate simulations.
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