1. Regional new particle formation as modulators of cloud condensation nuclei and cloud droplet number in the eastern MediterraneanPanayiotis Kalkavouras, Aikaterini Bougiatioti, Nikos Kalivitis, Iasonas Stavroulas, Maria Tombrou, Athanasios Nenes, Nikolaos Mihalopoulos, 2019, original scientific article Abstract: A significant fraction of atmospheric particles that serve as cloud
condensation nuclei (CCN) are thought to originate from the condensational
growth of new particle formation (NPF) from the gas phase. Here, 7 years of
continuous aerosol and meteorological measurements (June 2008 to May 2015)
at a remote background site of the eastern Mediterranean were recorded and
analyzed to assess the impact of NPF (of 162 episodes identified) on CCN and
cloud droplet number concentration (CDNC) formation in the region. A new
metric is introduced to quantitatively determine the initiation and duration
of the influence of NPF on the CCN spectrum. NPF days were found to increase
CCN concentrations (from 0.10 % to 1.00 % supersaturation) between 29 %
and 77 %. Enhanced CCN concentrations from NPF are mostly observed, as
expected, under low preexisting particle concentrations and occur in the
afternoon, relatively later in the winter and autumn than in the summer.
Potential impacts of NPF on cloud formation were quantified by introducing
the observed aerosol size distributions and chemical composition into an
established cloud droplet parameterization. We find that the
supersaturations that develop are very low (ranging between 0.03 % and
0.27 %) for typical boundary layer dynamics (σw
∼0.3 m s−1) and NPF is found to enhance CDNC by a modest
13 %. This considerable contrast between CCN and CDNC response is in part
from the different supersaturation levels considered, but also because
supersaturation drops from increasing CCN because of water vapor competition
effects during the process of droplet formation. The low cloud
supersaturation further delays the appearance of NPF impacts on CDNC to
clouds formed in the late evening and nighttime – which has important
implications for the extent and types of indirect effects induced by NPF
events. An analysis based on CCN concentrations using prescribed
supersaturation can provide very different, even misleading, conclusions and
should therefore be avoided. The proposed approach here offers a simple, yet
highly effective way for a more realistic impact assessment of NPF events on
cloud formation.
Keywords: regional NPF, CCN, cloud droplets, Eastern Mediterranean, regional background
Published in RUNG: 13.05.2024; Views: 123; Downloads: 2
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2. Formation and growth of atmospheric nanoparticles in the eastern Mediterranean : results from long-term measurements and process simulationsNikos Kalivitis, Veli-Matti Kerminen, Giorgos Kouvarakis, Iasonas Stavroulas, Evaggelia Tzitzikalaki, Panayiotis Kalkavouras, Nikos Daskalakis, Stelios Myriokefalitakis, Aikaterini Bougiatioti, Hanna E. Manninen, 2019, original scientific article Abstract: Atmospheric new particle formation (NPF) is a common phenomenon all over
the world. In this study we present the longest time series of NPF records in
the eastern Mediterranean region by analyzing 10 years of aerosol number size
distribution data obtained with a mobility particle sizer. The measurements
were performed at the Finokalia environmental research station on Crete,
Greece, during the period June 2008–June 2018. We found that NPF took place
on 27 % of the available days, undefined days were 23 % and non-event
days 50 %. NPF is more frequent in April and May probably due to the
terrestrial biogenic activity and is less frequent in August. Throughout the
period under study, nucleation was observed also during the night. Nucleation
mode particles had the highest concentration in winter and early spring,
mainly because of the minimum sinks, and their average contribution to the
total particle number concentration was 8 %. Nucleation mode particle
concentrations were low outside periods of active NPF and growth, so there
are hardly any other local sources of sub-25 nm particles. Additional
atmospheric ion size distribution data simultaneously collected for more than
2 years were also analyzed. Classification of NPF events based on ion
spectrometer measurements differed from the corresponding classification
based on a mobility spectrometer, possibly indicating a different
representation of local and regional NPF events between these two measurement
data sets. We used the MALTE-Box model
for simulating a case study of NPF in the eastern Mediterranean region.
Monoterpenes contributing to NPF can explain a large fraction of the observed
NPF events according to our model simulations. However the adjusted
parameterization resulting from our sensitivity tests was significantly
different from the initial one that had been determined for the boreal
environment.
Keywords: particles, number size distributions, new particle formation, regional background, SMPS, Eastern Mediterannean
Published in RUNG: 10.05.2024; Views: 139; Downloads: 2
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