Aerosol properties were studied during an intensive airborne measurement campaign that took place at Rotterdam in Netherlands in May 2008 within the framework of the European Aerosol Cloud Climate ...and Air Quality Interactions project (EUCAARI). The objective of this study is to illustrate seven events of new particle formation (NPF) observed with two Condensation Particle Counters (CPCs) operated on board the ATR-42 research aircraft in airsectors around Rotterdam, and to provide information on the spatial extent of the new particle formation phenomenon based on 1-s resolution measurements of ultra-fine particle (in the size range 3-10 nm diameter, denoted N3-10 hereafter) concentrations. The results show that particle production occurred under the influence of different air mass origins, at different day times and over the North Sea as well as over the continent. The number concentration of freshly nucleated particles (N3-10 ) varied between 5000 and 100 000 cm-3 within the boundary layer (BL). Furthermore the vertical extension for all nucleation events observed on the ATR-42 never exceeded the upper limit of the BL. The horizontal extent of N3-10 could not be delimited due to inflexible flight plans which could not be modified to accommodate real-time results. However, the NPF events were observed over geographically large areas; typically the horizontal extension was about 100 km and larger.
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.
The concentrations of neutral and charged sub-3nm clusters and their connection to new particle formation (NPF) were investigated during the PEGASOS campaign (7 June–9 July 2012) at the San Pietro ...Capofiume measurement station in the Po Valley, Italy. Continuous high concentrations of sub-3nm clusters were detected during the measurement period, although the condensation sink was relatively high (median value 1.1 × 10−2 s−1). The median cluster concentrations were 2140 and 7980 cm−3 in the size bins of 1.5–1.8 and 1.8–3 nm, and the majority of them were electrically neutral. NPF events were observed during the measurement period frequently, on 86 % of the days. The median growth rates of clusters during the events were 4.3, 6.0 and 7.2 nm h−1 in the size ranges of 1.5–3, 3–7 and 7–20 nm. The median formation rate of 1.6 nm clusters was high, 45 cm−3 s−1, and it exceeded the median formation rate of 2 nm clusters by 1 order of magnitude. The ion-induced nucleation fraction was low; the median values were 0.7 % at 1.6 nm and 3.0 % at 2 nm. On NPF event days the neutral cluster concentration had a maximum around 09:00 (local winter time), which was absent on a non-event day. The increase in the cluster concentrations in the morning coincided with the increase in the boundary layer height. At the same time radiation, temperature and SO2 concentration increased, and RH and condensation sink decreased. The concentrations of neutral and charged clusters were observed to have a positive correlation with sulfuric acid proxy, indicating the significance of sulfuric acid for the cluster formation in San Pietro Capofiume. The condensation sink had a negative correlation with the concentration of charged clusters but no clear relation to the neutral cluster concentration. This finding, together with back-trajectory analysis, suggests that the precursor vapors of the clusters and background aerosol particles, acting as their sink, have possibly originated from the same sources, including e.g., power plants and industrial areas in the Po Valley.
This work presents airborne observations of sub-3 nm particles in the lower
troposphere and investigates new particle formation (NPF) within an evolving
boundary layer (BL). We studied particle ...concentrations together with
supporting gas and meteorological data inside the planetary BL over a boreal
forest site in Hyytiälä, southern Finland. The analysed data were
collected during three flight measurement campaigns: May–June 2015,
August 2015 and April–May 2017, including 27 morning and 26 afternoon
vertical profiles. As a platform for the instrumentation, we used a Cessna
172 aircraft. The analysed flight data were collected horizontally within a
30 km distance from SMEAR II in Hyytiälä and vertically from 100 m
above ground level up to 2700 m. The number concentration of 1.5–3 nm
particles was observed to be, on average, the highest near the forest canopy
top and to decrease with increasing altitude during the mornings of NPF event
days. This indicates that the precursor vapours emitted by the forest play a
key role in NPF in Hyytiälä. During daytime, newly formed particles
were observed to grow in size and the particle population became more
homogenous within the well-mixed BL in the afternoon. During undefined days
with respect to NPF, we also detected an increase in concentration of
1.5–3 nm particles in the morning but not their growth in size, which
indicates an interrupted NPF process during these undefined days. Vertical
mixing was typically stronger during the NPF event days than during the
undefined or non-event days. The results shed light on the connection between
boundary layer dynamics and NPF.
Atmospheric ions participate in the formation of new atmospheric aerosol particles, yet their exact role in this process has remained unclear. Here we derive a new simple parameterization for ...ion-induced nucleation or, more precisely, for the formation rate of charged 2-nm particles. The parameterization is semi-empirical in the sense that it is based on comprehensive results of one-year-long atmospheric cluster and particle measurements in the size range ~1–42 nm within the EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions) project. Data from 12 field sites across Europe measured with different types of air ion and cluster mobility spectrometers were used in our analysis, with more in-depth analysis made using data from four stations with concomitant sulphuric acid measurements. The parameterization is given in two slightly different forms: a more accurate one that requires information on sulfuric acid and nucleating organic vapor concentrations, and a simpler one in which this information is replaced with the global radiation intensity. These new parameterizations are applicable to all large-scale atmospheric models containing size-resolved aerosol microphysics, and a scheme to calculate concentrations of sulphuric acid, condensing organic vapours and cluster ions.
In the present-day atmosphere, sulfuric acid is the most
important vapour for aerosol particle formation and initial growth. However,
the growth rates of nanoparticles (<10 nm) from sulfuric acid
...remain poorly measured. Therefore, the effect of stabilizing bases, the
contribution of ions and the impact of attractive forces on molecular
collisions are under debate. Here, we present precise growth rate
measurements of uncharged sulfuric acid particles from 1.8 to 10 nm, performed
under atmospheric conditions in the CERN (European
Organization for Nuclear Research) CLOUD chamber. Our results show
that the evaporation of sulfuric acid particles above 2 nm is negligible,
and growth proceeds kinetically even at low ammonia concentrations. The
experimental growth rates exceed the hard-sphere kinetic limit for the
condensation of sulfuric acid. We demonstrate that this results from
van der Waals forces between the vapour molecules and particles and
disentangle it from charge–dipole interactions. The magnitude of the
enhancement depends on the assumed particle hydration and collision
kinetics but is increasingly important at smaller sizes, resulting in a
steep rise in the observed growth rates with decreasing size. Including the
experimental results in a global model, we find that the enhanced growth rate of
sulfuric acid particles increases the predicted particle number concentrations
in the upper free troposphere by more than 50 %.
This paper revisits the atmospheric new particle formation (NPF) process in the polluted Central European troposphere,
focusing on the connection with gas-phase precursors and meteorological ...parameters. Observations were made at the
research station Melpitz (former East Germany) between 2008 and 2011 involving a neutral cluster and air ion spectrometer
(NAIS). Particle formation events were classified by a new automated method based on the convolution integral of particle
number concentration in the diameter interval 2–20 nm. To study the relevance of gaseous sulfuric acid as
a precursor for nucleation, a proxy was derived on the basis of direct measurements during a 1-month campaign in
May 2008. As a major result, the number concentration of freshly produced particles correlated significantly with the
concentration of sulfur dioxide as the main precursor of sulfuric acid. The condensation sink, a factor potentially
inhibiting NPF events, played a subordinate role only. The same held for experimentally determined ammonia
concentrations. The analysis of meteorological parameters confirmed the absolute need for solar radiation to induce NPF
events and demonstrated the presence of significant turbulence during those events. Due to its tight correlation with
solar radiation, however, an independent effect of turbulence for NPF could not be established. Based on the diurnal
evolution of aerosol, gas-phase, and meteorological parameters near the ground, we further conclude that the particle
formation process is likely to start in elevated parts of the boundary layer rather than near ground level.
To understand the very first steps of atmospheric particle formation and growth processes, information on the size where the atmospheric nucleation and cluster activation occurs, is crucially needed. ...The current understanding of the concentrations and dynamics of charged and neutral clusters and particles is based on theoretical predictions and experimental observations. This paper gives a standard operation procedure (SOP) for Neutral cluster and Air Ion Spectrometer (NAIS) measurements and data processing. With the NAIS data, we have improved the scientific understanding by (1) direct detection of freshly formed atmospheric clusters and particles, (2) linking experimental observations and theoretical framework to understand the formation and growth mechanisms of aerosol particles, and (3) parameterizing formation and growth mechanisms for atmospheric models. The SOP provides tools to harmonize the world-wide measurements of small clusters and nucleation mode particles and to verify consistent results measured by the NAIS users. The work is based on discussions and interactions between the NAIS users and the NAIS manufacturer.
Biogenic organic precursors play an important role in
atmospheric new particle formation (NPF). One of the major precursor species
is α-pinene, which upon oxidation can form a suite of products
...covering a wide range of volatilities. Highly oxygenated organic molecules
(HOMs) comprise a fraction of the oxidation products formed. While it is
known that HOMs contribute to secondary organic aerosol (SOA) formation,
including NPF, they have not been well studied in newly formed particles due
to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures
(−50 and −30 ∘C) and relative
humidities (20 % and 60 %) relevant in the upper free troposphere. The
measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD)
chamber. The particle chemical composition was analyzed by a thermal
desorption differential mobility analyzer (TD-DMA) coupled to a nitrate
chemical ionization–atmospheric pressure interface–time-of-flight
(CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our
measurements revealed the presence of C8−10 monomers and C18−20
dimers as the major compounds in the particles (diameter up to
∼ 100 nm). Particularly, for the system with isoprene added,
C5 (C5H10O5−7) and C15 compounds
(C15H24O5−10) were detected. This observation is consistent
with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate,
our measurements indicate that they can still contribute to the particle
growth at free tropospheric conditions. For the experiments reported here,
most likely isoprene oxidation products enhance the growth of particles
larger than 15 nm. Additionally, we report on the nucleation rates measured
at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower
J1.7 nm values, very likely due to the higher α-pinene and
ozone mixing ratios used in the present study.
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