This review focuses on the observed characteristics of atmospheric newparticle formation (NPF) in different environments of the global troposphere. After a short introduction, wewill present a theoretical background that discusses themethods used to analyzemeasurement data on atmospheric NPF and the associated terminology.Wewill update on our current understanding of regionalNPF, i.e. NPF taking simultaneously place over large spatial scales, and complement that with a full review on reportedNPF and growth rates during regionalNPF events.Wewill shortly review atmospheric NPF taking place at sub-regional scales. Since the growth of newly-formed particles into larger sizes is of great current interest, wewill briefly discuss our observation-based understanding onwhich gaseous compounds contribute to the growth of newly-formed particles, andwhat implications this will have on atmospheric cloud condensation nuclei formation.Wewillfinish the reviewwith a summary of ourmain findings and future outlook that outlines the remaining research questions and needs for additionalmeasurements.

https://iopscience.iop.org/article/10.1088/1748-9326/aadf3c/pdf

Atmospheric new particle formation and growth : review of field observations

. 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.

/pdf/formation-and-growth-of-atmospheric-nanoparticles-in-the-1wy6beoj9e.pdf

Formation and growth of atmospheric nanoparticles in the eastern Mediterranean: results from long-term measurements and process simulations

. To quantify the contribution of new particle formation (NPF) to ultrafine
particle number and cloud condensation nuclei (CCN) budgets, one has to understand the mechanisms that
govern NPF in different environments and its temporal extent. Here, we study
NPF in Cyprus, an Eastern Mediterranean country located at the crossroads of
three continents and affected by diverse air masses originating from
continental, maritime, and desert-dust source areas. We performed 1-year
continuous measurements of aerosol particles down to ∼  1 nm in
diameter for the first time in the Eastern Mediterranean and Middle East
(EMME) region. These measurements were complemented with trace gas data,
meteorological variables, and retroplume analysis. We show that NPF is a
very frequent phenomenon at this site and has higher frequencies of
occurrence during spring and autumn. NPF events were both of local and
regional origin, and the local events occurred frequently during the month
with the lowest NPF frequency. Some NPF events exhibited multiple onsets,
while others exhibited apparent particle shrinkage in size. Additionally,
NPF events were observed during the nighttime and during episodes of high
desert-dust loadings. Particle formation rates and growth rates were
comparable to those in urban environments, although our site is a rural one.
Meteorological variables and trace gases played a role in explaining the
intra-monthly variability of NPF events, but they did not explain why summer
months had the least NPF frequency. Similarly, pre-existing aerosol loading
did not explain the observed seasonality. The months with the least NPF
frequency were associated with higher H 2 SO 4 concentrations but
lower NO 2 concentrations, which is an indicator of anthropogenic
influence. Air masses arriving from the Middle East were not observed during
these months, which could suggest that precursor vapors important for
nucleation and growth are transported to our site from the Middle East.
Further comprehensive measurements of precursor vapors are required to prove
this hypothesis.

/pdf/towards-understanding-the-characteristics-of-new-particle-406nwfws90.pdf

Towards understanding the characteristics of new particle formation in the Eastern Mediterranean

Aerosol particle shrinkage event phenomenology in a South European suburban area during 2009-2015

. Although new particle formation (NPF) events have been studied extensively
for some decades, the mechanisms that drive their occurrence and development
are yet to be fully elucidated. Laboratory studies have done much to
elucidate the molecular processes involved in nucleation, but this knowledge
has yet to be conclusively linked to NPF events in the atmosphere. There is
great difficulty in successful application of the results from laboratory
studies to real atmospheric conditions due to the diversity of atmospheric
conditions and observations found, as NPF events occur almost everywhere in
the world without always following a clearly defined trend of frequency,
seasonality, atmospheric conditions, or event development. The present study seeks common features in nucleation events by applying a
binned linear regression over an extensive dataset from 16 sites of various
types (combined dataset of 85 years from rural and urban backgrounds as well
as roadside sites) in Europe. At most sites, a clear positive relation with the frequency of NPF events is
found between the solar radiation intensity (up to R2=0.98 ),
temperature (up to R2=0.98 ), and atmospheric pressure (up to R2=0.97 ), while relative humidity (RH)
presents a negative relation (up to R2=0.95 ) with NPF event
frequency, though exceptions were found among the sites for all the
variables studied. Wind speed presents a less consistent relationship, which
appears to be heavily affected by local conditions. While some
meteorological variables (such as the solar radiation intensity and RH)
appear to have a crucial effect on the occurrence and characteristics of NPF
events, especially at rural sites, it appears that their role becomes less
marked at higher average values. The analysis of chemical composition data presents interesting results.
Concentrations of almost all chemical compounds studied (apart from O 3 )
and the condensation sink (CS) have a negative relationship with NPF event
frequency, though areas with higher average concentrations of SO 2 had
higher NPF event frequency. Particulate organic carbon (OC), volatile
organic compounds (VOCs), and particulate-phase sulfate consistently had a
positive relation with the growth rate of the newly formed particles. As
with some meteorological variables, it appears that at increased
concentrations of pollutants or the CS, their influence upon NPF frequency
is reduced.

/pdf/the-effect-of-meteorological-conditions-and-atmospheric-40a5nfbr0p.pdf

M. Petrakakis

Papers

Nucleation events at a coastal city during the warm period: Kerbside versus urban background measurements