We compared observations of aerosol particle formation and growth in
different parts of the planetary boundary layer at two different
environments that have frequent new particle formation (NPF) ...events. In
summer 2012 we had a campaign in Po Valley, Italy (urban background), and in
spring 2013 a similar campaign took place in Hyytiälä, Finland
(rural background). Our study consists of three case studies of airborne and
ground-based measurements of ion and particle size distribution from
∼1 nm. The airborne measurements were performed using a
Zeppelin inside the boundary layer up to 1000 m altitude. Our observations
show the onset of regional NPF and the subsequent growth of the aerosol
particles happening almost uniformly inside the mixed layer (ML) in both
locations. However, in Hyytiälä we noticed local enhancement in the
intensity of NPF caused by mesoscale boundary layer (BL) dynamics. Additionally, our
observations indicate that in Hyytiälä NPF was probably also taking
place above the ML. In Po Valley we observed NPF that was limited to a
specific air mass.
Currently, the complete chemical characterization of nanoparticles
(< 100 nm) represents an analytical challenge, since these particles
are abundant in number but have negligible mass. Several ...methods for
particle-phase characterization have been recently developed to better
detect and infer more accurately the sources and fates of sub-100 nm
particles, but a detailed comparison of different approaches is missing.
Here we report on the chemical composition of secondary organic aerosol
(SOA) nanoparticles from experimental studies of α-pinene ozonolysis
at −50, −30, and −10 ∘C and intercompare the results measured by different
techniques. The experiments were performed at the Cosmics Leaving OUtdoor
Droplets (CLOUD) chamber at the European Organization for Nuclear Research
(CERN). The chemical composition was measured simultaneously by four
different techniques: (1) thermal desorption–differential mobility analyzer
(TD–DMA) coupled to a NO3- chemical ionization–atmospheric-pressure-interface–time-of-flight (CI–APi–TOF) mass
spectrometer, (2) filter inlet for gases and aerosols (FIGAERO) coupled to an
I− high-resolution time-of-flight chemical ionization mass spectrometer
(HRToF-CIMS), (3) extractive electrospray Na+ ionization
time-of-flight mass spectrometer (EESI-TOF), and (4) offline analysis of
filters (FILTER) using ultra-high-performance liquid chromatography (UHPLC)
and heated electrospray ionization (HESI) coupled to an Orbitrap
high-resolution mass spectrometer (HRMS). Intercomparison was performed by
contrasting the observed chemical composition as a function of oxidation
state and carbon number, by estimating the volatility and comparing the
fraction of volatility classes, and by comparing the thermal desorption
behavior (for the thermal desorption techniques: TD–DMA and FIGAERO) and
performing positive matrix factorization (PMF) analysis for the thermograms.
We found that the methods generally agree on the most important compounds
that are found in the nanoparticles. However, they do see different parts of
the organic spectrum. We suggest potential explanations for these
differences: thermal decomposition, aging, sampling artifacts, etc. We
applied PMF analysis and found insights of thermal decomposition in the
TD–DMA and the FIGAERO.
In this study we examined performance characteristics of an ultrafine water condensation particle counter (UWCPC, TSI3786). The detection efficiency was investigated using different temperature ...differences between saturator and growth tube. The cut-sizes D90, D50, D10, and D0 were determined by fitting a two-free-parameter equation to the experimental data. The determined cut-sizes were comparable (± 8%) with other two widely used fitting equations. The cut-sizes were studied changing the growth tube temperature from 65 to 78°C and varying the saturator temperature from 8 to 20°C. For silver particles the smallest detected cut-size D50 was 2.9 nm, and the largest one -4.5 nm, and in default operation conditions it was 3.9 nm. Additionally, the effect of particle chemical composition on the detection efficiency was studied. The cut-sizes D50 were 2 2.9, 2.3, and 1.8 nm for silver, ammonium sulfate, and sodium chloride particles, respectively. A concentration calibration was performed with high particle number concentrations. Within ±10% accuracy the highest reliable measured number concentration was 100000 cm
−3
. The determined detection efficiency of the UWCPC was compared with other commercial CPCs (TSI3785, TSI3776, TSI3772, TSI3025, TSI3010, TSI3007) using default operation regimes of the instruments. The results show that the tested UWCPC has a larger cut-size for silver particles than do butanol-based ultrafine CPCs (TSI3776, TSI3025), but smaller cut-size than other tested TSI CPCs. In default operation regime, the tested TSI3776 had the lowest detection limit (D50% = 3.2 nm) of the silver particles, and the corresponding size of TSI3025 was 3.6 nm.
Aerosol particles have an important role in Earth's
radiation balance and climate, both directly and indirectly through
aerosol–cloud interactions. Most aerosol particles in the atmosphere are
weakly ...charged, affecting both their collision rates with ions and neutral
molecules, as well as the rates by which they are scavenged by other aerosol
particles and cloud droplets. The rate coefficients between ions and aerosol
particles are important since they determine the growth rates and lifetimes
of ions and charged aerosol particles, and so they may influence cloud
microphysics, dynamics, and aerosol processing. However, despite their
importance, very few experimental measurements exist of charged aerosol
collision rates under atmospheric conditions, where galactic cosmic rays in
the lower troposphere give rise to ion pair concentrations of around 1000 cm−3. Here we present measurements in the CERN CLOUD chamber of the
rate coefficients between ions and small (<10 nm) aerosol particles
containing up to 9 elementary charges, e. We find the rate coefficient of a
singly charged ion with an oppositely charged particle increases from 2.0
(0.4–4.4) × 10−6 cm3 s−1 to 30.6 (24.9–45.1) × 10−6 cm3 s−1 for particles with charges of 1 to
9 e, respectively, where the parentheses indicate the ±1σ
uncertainty interval. Our measurements are compatible with theoretical
predictions and show excellent agreement with the model of
Gatti and Kortshagen (2008).
We investigated atmospheric new particle formation (NPF) in the
Amazon rainforest using direct measurement methods. To our knowledge this is
the first direct observation of NPF events in the Amazon ...region. However,
previous observations elsewhere in Brazil showed the occurrence of nucleation-mode particles. Our measurements covered
two field sites and both the wet and dry
season. We measured the variability of air ion concentrations (0.8–12 nm)
with an ion spectrometer between September 2011 and January 2014 at a
rainforest site (T0t). Between February and October 2014, the same
measurements were performed at a grassland pasture site (T3) as part of the
GoAmazon 2014/5 experiment, with two intensive operating periods (IOP1 and
IOP2 during the wet and the dry season, respectively). The GoAmazon 2014/5
experiment was designed to study the influence of anthropogenic emissions on
the changing climate in the Amazon region. The experiment included basic
aerosol and trace gas measurements at the ground, remote sensing
instrumentation, and two aircraft-based measurements. The results presented in this work are from measurements performed at ground
level at both sites. The site inside the rainforest (T0t) is located 60 km
NNW of Manaus and influenced by pollution about once per week. The pasture
(T3) site is located 70 km downwind from Manaus and influenced by the Manaus
pollution plume typically once per day or every second day, especially in
the afternoon. No NPF events were observed inside
the rainforest (site T0t) at ground level during the measurement period.
However, rain-induced ion and particle bursts (hereafter, “rain events”)
occurred frequently (643 of 1031 days) at both sites during the wet and dry
season, being most frequent during the wet season. During the rain events,
the ion concentrations in three size ranges (0.8–2, 2–4, and 4–12 nm)
increased up to about 104–105 cm−3. This effect was most
pronounced in the intermediate and large size ranges, for which the background
ion concentrations were about 10–15 cm−3 compared with 700 cm−3 for the cluster ion background. We observed eight NPF events at the pasture site during the wet season. We
calculated the growth rates and formation rates of neutral particles and
ions for the size ranges 2–3 and 3–7 nm using the ion spectrometer data.
The observed median growth rates were 0.8 and 1.6 nm h−1
for 2–3 nm sized ions and particles, respectively, with larger growth rates
(13.3 and 7.9 nm h−1) in the 3–7 nm size range. The
measured nucleation rates were of the order of 0.2 cm−3 s−1 for
particles and 4–9×10-3 cm−3 s−1 for ions. There was no
clear difference in the sulfuric acid concentrations between the NPF event
days and nonevent days (∼9×105 cm−3).
The two major differences between the NPF days and nonevent days were a
factor of 1.8 lower condensation sink on NPF event days (1.8×10-3 s−1) compared to nonevents (3.2×10-3 s−1) and different air
mass origins. To our knowledge, this is the first time that results from ground-based
sub-3 nm aerosol particle measurements have been obtained from the Amazon
rainforest.
The accurate measurement of aerosol particles and clusters smaller than 3 nm in diameter is crucial for the understanding of new particle formation processes. The particle counters used for measuring ...these particles are typically calibrated with metal or salt particles under dry conditions, which does not always represent the field conditions where these instruments are later used. In this study, we calibrated the A11 nano Condensation Nucleus Counter (nCNC), consisting of the PSM (Particle Size Magnifier) and a laminar flow butanol based CPC (Condensational Particle Counter), with well-defined biogenic oxidation products from β-caryophyllene oxidation and compared it to a calibration with tungsten oxide under the same conditions. The organic particles were detected less efficiently than the inorganic ones. This resulted in a higher cut-off size for β-caryophyllene oxidation products than for tungsten oxide. At the same PSM settings, the cut-off size for tungsten oxide was 1.2 nm and for β-caryophyllene oxidation products 1.9 nm. However, repeating the calibration of the biogenic particles at 13% relative humidity at 31°C, increased their detection efficiency in the PSM, increasing the cut-off diameter to 1.6 nm.
Additionally, we present a comparison of the ion concentrations measured with the PSM and the NAIS (Neutral Cluster and Air Ion Spectrometer) during new particle formation experiments in the CLOUD (Cosmics Leaving Outdoors Droplets) chamber. In these experiments, we produced particles from different organic precursors, such as α-pinene, β-caryophyllene and isoprene, as well as iodine. This way, we could determine the shift in cut-off diameter of the PSM for several different atmospherically relevant chemical compounds and compare it to the laboratory calibrations. We saw a diameter shift for the organic precursors of +0.3 nm in the PSM compared to the NAIS. These two approaches agreed well with each other and show that it is important to know the chemical composition of the measured particles to determine the exact size distribution using a supersaturation scanning method.
•Accurate measurements of sub-3 nm particles are vital for the understanding of nucleation.•Organic particles are not as well detected by CPCs than inorganic ones.•Detection Efficiency of particle counters increases with increasing humidity.
Most of the ion production in the atmosphere is attributed to ionising radiation. In the lower atmosphere, ionising radiation consists mainly of the decay emissions of radon and its progeny, gamma ...radiation of the terrestrial origin as well as photons and elementary particles of cosmic radiation. These types of radiation produce ion pairs via the ionisation of nitrogen and oxygen as well as trace species in the atmosphere, the rate of which is defined as the ionising capacity. Larger air ions are produced out of the initial charge carriers by processes such as clustering or attachment to pre-existing aerosol particles. This study aimed (1) to identify the key factors responsible for the variability in ionising radiation and in the observed air ion concentrations, (2) to reveal the linkage between them and (3) to provide an in-depth analysis into the effects of ionising radiation on air ion formation, based on measurement data collected during 2003–2006 from a boreal forest site in southern Finland. In general, gamma radiation dominated the ion production in the lower atmosphere. Variations in the ionising capacity came from mixing layer dynamics, soil type and moisture content, meteorological conditions, long-distance transportation, snow cover attenuation and precipitation. Slightly similar diurnal patterns to variations in the ionising capacity were observed in air ion concentrations of the cluster size (0.8–1.7 nm in mobility diameters). However, features observed in the 0.8–1 nm ion concentration were in good connection to variations of the ionising capacity. Further, by carefully constraining perturbing variables, a strong dependency of the cluster ion concentration on the ionising capacity was identified, proving the functionality of ionising radiation in air ion production in the lower atmosphere. This relationship, however, was only clearly observed on new particle formation (NPF) days, possibly indicating that charges after being born underwent different processes on NPF days and non-event days and also that the transformation of newly formed charges to cluster ions occurred in a shorter timescale on NPF days than on non-event days.
We characterized size and chemical composition of ions generated by a corona-needle charger of a Neutral cluster and Air Ion Spectrometer (NAIS) by using a high resolution differential mobility ...analyzer and a time-of-flight mass spectrometer. Our study is crucial to verify the role of corona-generated ions in the particle size spectra measured with the NAIS, in which a corona charger is used to charge aerosol particles down to the size range overlapping with the size of generated ions. The size and concentration of ions produced by the corona discharging process depend both on corona voltage and on properties and composition of carrier gas. Negative ions were <1.6 nm (0.8 cm2 V−1 s−1 in mobility) in all tested gas mixtures (nitrogen, air with variable mixing ratios of water vapour), whereas positive ions were <1.7 nm (0.7 cm2 V−1 s−1). Electrical filtering of the corona generated ions and not removing all charged particles plays an important role in determining the lowest detection limit. Based on our experiments, the lowest detection limit for the NAIS in the particle mode is between 2 and 3 nm.
PDF
