[Show abstract][Hide abstract] ABSTRACT: Archaea are widespread and abundant in many terrestrial and aquatic environments, and are thus outside extreme environments, accounting for up to ~10% of the prokaryotes. Compared to bacteria and other microorganisms, however, very little is known about the abundance, diversity, and dispersal of archaea in the atmosphere. By means of DNA analysis and Sanger sequencing targeting the 16S rRNA (435 sequences) and amoA genes in samples of air particulate matter collected over 1 year at a continental sampling site in Germany, we obtained first insights into the seasonal dynamics of airborne archaea. The detected archaea were identified as Thaumarchaeota or Euryarchaeota, with soil Thaumarchaeota (group I.1b) being present in all samples. The normalized species richness of Thaumarchaeota correlated positively with relative humidity and negatively with temperature. This together with an increase in bare agricultural soil surfaces may explain the diversity peaks observed in fall and winter. The detected Euryarchaeota were mainly predicted methanogens with a low relative frequency of occurrence. A slight increase in their frequency during spring may be linked to fertilization processes in the surrounding agricultural fields. Comparison with samples from the Cape Verde islands (72 sequences) and from other coastal and continental sites indicates that the proportions of Euryarchaeota are enhanced in coastal air, which is consistent with their suggested abundance in marine surface waters. We conclude that air transport may play an important role in the dispersal of archaea, including assumed ammonia-oxidizing Thaumarchaeota and methanogens.
[Show abstract][Hide abstract] ABSTRACT: We report first measurements of ultrafine particles from a semi-rural location, Gadanki, from tropical Southern India. Measurements of particle number size distributions in the diameter range of 5 nm–32 μm were performed during 2 May–31 July 2012. The mean number concentrations of nucleation (NNUC), Aitken (NAIT), accumulation (NACCU), and total particles (NTOT) at this site were (1.1 ± 0.9) × 103 cm−3, (2.2 ± 1.3) × 103 cm−3, (1.5 ± 1.2) × 103 cm−3 and (4.8 ± 2.4) × 103 cm−3, respectively, comparable to other rural to semi-rural locations globally and declined as the season progressed, perhaps due to wet removal of aerosols with onset of monsoon in early June. Particle bursts in the nucleation mode size range (5–25 nm), followed by a sustained growth in size were observed very rarely (only 5 out of 79 observation days) at this site, less frequently than at most other locations around the world during May–July. Most factors affecting new particle formation (NPF) were similar on NPF and nonNPF event days, such as condensation sink, relative humidity, temperature, wind speed and direction, and mixing layer height. Thus, the infrequent occurrence of NPF at our site appeared to be linked to lower precursor gas concentrations and weak gas-phase oxidation chemistry due to diminished solar radiation on persistently cloudy days with the onset of the monsoon in early June over this region. The derived particle growth rates (GR > 5 nm) and formation rates of 5 nm particles (J5) ranged from 2.2 to 4.7 nm h−1 and 0.4–2.4 cm−3 s−1, with a mean and standard deviation of 3.4 ± 0.9 nm h−1 and 1.2 ± 2.3 cm−3 s−1, respectively, comparable to previous investigations at rural to semi-rural locations. The observed behavior in aerosol and meteorological parameters on NPF and nonNPF event days appeared to be distinctive compared to other rural to urban locations across the globe. However, this distinct behavior is limited and restricted to this site and season of the year, and should therefore not be generalized over a larger spatio-temporal scale. This emphasizes the need for long-term aerosol and precursor measurements over this and other regions of India.
[Show abstract][Hide abstract] ABSTRACT: Dynamical and microphysical processes in pyro-convective clouds in mid-latitude conditions are investigated using idealized three-dimensional simulations with the Ac-tive Tracer High resolution Atmospheric Model (ATHAM). A state-of-the-art two-moment microphysical scheme build-ing upon a realistic parameterization of cloud condensation nuclei (CCN) activation has been implemented in order to study the influence of aerosol concentration on cloud devel-opment. The results show that aerosol concentration influ-ences the formation of precipitation. For low aerosol concen-trations (N CN = 200 cm −3), rain droplets are rapidly formed by autoconversion of cloud droplets. This also triggers the formation of large graupel and hail particles, resulting in an early onset of precipitation. With increasing aerosol concen-tration (N CN = 1000 cm −3 and N CN = 20 000 cm −3) the for-mation of rain droplets is delayed due to more but smaller cloud droplets. Therefore, the formation of ice crystals and snowflakes becomes more important for the eventual forma-tion of graupel and hail, which is delayed at higher aerosol concentrations. This results in a delay of the onset of precipi-tation and a reduction of its intensity with increasing aerosol concentration. This study is the first detailed investigation of the interaction between cloud microphysics and the dy-namics of a pyroconvective cloud using the combination of a high-resolution atmospheric model and a detailed micro-physical scheme.
ATMOSPHERIC CHEMISTRY AND PHYSICS 07/2014; 14:7573-7583. · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gaseous nitrous acid (HONO), the protonated form of nitrite, contributes up to ~ 60% to the primary formation of hydroxyl radical (OH), which is a key oxidant in the degradation of most air pollutants. Field measurements and modeling studies indicate a large unknown source of HONO during daytime. Here, we developed a new tracer method based on gas-phase stripping-derivatization coupled to liquid chromatography-mass spectrometry (LC-MS) to measure the 15N relative exceedance, ψ(15N), of HONO in the gas-phase. Gaseous HONO is quantitatively collected and transferred to an azo dye, purified by solid phase extraction (SPE) and analyzed using high performance liquid chromatography coupled to mass spectrometry (HPLC-MS). In the optimal working range of ψ(15N) = 0.2 - 0.5, the relative standard deviation of ψ(15N) is < 4%. The optimum pH and solvents for extraction by SPE and potential interferences are discussed. The method was applied to measure HO15NO emissions from soil in a dynamic chamber with and without spiking 15N labeled urea. The identification of HO15NO from soil with 15N urea addition confirmed biogenic emissions of HONO from soil. The method enables a new approach of studying the formation pathways of HONO and its role for atmospheric chemistry (e.g. ozone formation), and environmental tracer studies on the formation and conversion of gaseous HONO or aqueous NO2- as part of the biogeochemical nitrogen cycle, e.g., in the investigation of fertilization effects on soil HONO emissions and microbiological conversion of NO2- in the hydrosphere.
Environmental Science and Technology 06/2014; · 5.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fungal spores as a prominent type of primary biological aerosol particles (PBAP) have been incorporated into the COSMO-ART regional atmospheric model, using and comparing three different emission parameterizations. Two literature-based emission rates derived from fungal spore colony counts and chemical tracer measurements were used as a parameterization baseline for this study. A third, new emission parameterization was adapted to field measurements of fluorescent biological aerosol particles (FBAP) from four locations across Northern Europe. FBAP concentrations can be regarded as a lower estimate of total PBAP concentrations. Size distributions of FBAP often show a distinct mode at approx. 3 μm, corresponding to a diameter range characteristic for many fungal spores. Previous studies have suggested the majority of FBAP in several locations are dominated by fungal spores. Thus, we suggest that simulated fungal spore concentrations obtained from the emission parameterizations can be compared to the sum of total FBAP concentrations. A comparison reveals that parameterized estimates of fungal spore concentrations based on literature numbers underestimate measured FBAP concentrations. In agreement with measurement data, the model results show a diurnal cycle in simulated fungal spore concentrations, which may develop partially as a consequence of a varying boundary layer height between day and night. Measured FBAP and simulated fungal spore concentrations also correlate similarly with simulated temperature and humidity. These meteorological variables, together with leaf area index, were chosen to drive the new emission parameterization discussed here. Using the new emission parameterization on a model domain covering Western Europe, fungal spores in the lowest model layer comprise a fraction of 15% of the total aerosol mass over land and reach average number concentrations of 26 L-1. The results confirm that fungal spores and biological particles may account for a major fraction of supermicron aerosol particle number and mass concentration over vegetated continental regions and should thus be explicitly considered in air quality and climate studies.
Atmospheric Chemistry and Physics 03/2014; 14(7). · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The dominant component of atmospheric organic aerosol is that derived from the oxidation of volatile organic compounds (VOCs), so-called secondary organic aerosol (SOA). SOA consists of a multitude of organic compounds, only a small fraction of which has historically been identified. Formation and evolution of SOA is a complex process involving coupled chemical reaction and mass transport in the gas and particle phases. Current SOA models do not embody the full spectrum of reaction and transport processes nor do they identify the dominant rate-limiting steps in SOA formation. The recent advent of soft ionization mass spectrometry methods now facilitates a more complete molecular identification of SOA than heretofore possible. Based on such novel measurements, we show here that the chemical evolution of SOA from a variety of VOC precursors adheres to characteristic "molecular corridors" with a tight inverse correlation between volatility and molar mass. Sequential and parallel reaction oxidation and dimerization pathways progress along these corridors through characteristic regimes of reaction-, diffusion-, or accommodation-limited multiphase chemical kinetics that can be classified according to reaction location, degree of saturation, and extent of heterogeneity of gas and particle phases. These molecular corridors constrain the properties of unidentified products and reaction pathways and rates of SOA evolution, thereby facilitating the further development of aerosol models for air quality and climate.
Atmospheric Chemistry and Physics 02/2014; 14(5). · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A recent parcel model study (Reutter et al., 2009) showed three deterministic regimes of initial cloud droplet formation, characterized by different ratios of aerosol concentrations (NCN) to updraft velocities. This analysis, however, did not reveal how these regimes evolve during the subsequent cloud development. To address this issue, we employed the Active Tracer High Resolution Atmospheric Model (ATHAM) with full microphysics and extended the model simulation from the cloud base to the entire column of a single pyro-convective mixed-phase cloud. A series of 2-D simulations (over 1000) were performed over a wide range of NCN and dynamic conditions. The integrated concentration of hydrometeors over the full spatial and temporal scales was used to evaluate the aerosol and dynamic effects. The results show that: (1) the three regimes for cloud condensation nuclei (CCN) activation in the parcel model (namely aerosol-limited, updraft-limited, and transitional regimes) still exist within our simulations, but net production of raindrops and frozen particles occurs mostly within the updraft-limited regime. (2) Generally, elevated aerosols enhance the formation of cloud droplets and frozen particles. The response of raindrops and precipitation to aerosols is more complex and can be either positive or negative as a function of aerosol concentrations. The most negative effect was found for values of NCN of ∼1000 to 3000 cm-3. (3) The involvement of nonlinear (dynamic and microphysical) processes leads to a more complicated and unstable response of clouds to aerosol perturbation compared with the parcel model results. Therefore, conclusions drawn from limited case studies might require caveats regarding their representativeness, and high-resolution sensitivity studies over a wide range of aerosol concentrations and updraft velocities are strongly recommended.
Atmospheric Chemistry and Physics 02/2014; 14(6). · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitration of the major birch pollen allergen Bet v 1 alters the immune responses towards this protein, but the underlying chemical mechanisms are not yet understood. Here, we address the efficiency and site-selectivity of the nitration reaction of recombinant protein samples of Bet v 1.0101 with different nitrating agents relevant for laboratory investigations (tetranitromethane, TNM), for physiological processes (peroxynitrite, ONOO-), and for the health effects of environmental pollutants (nitrogen dioxide and ozone, O3/NO2). We determined the total tyrosine nitration degrees (ND) and the nitration degrees of individual tyrosine residues (NDY). High performance liquid chromatography coupled with diode array detection (HPLC-DAD) and HPLC coupled with high resolution mass spectrometry (HPLC-HR-MS) analysis of intact proteins, HPLC coupled with tandem mass spectrometry (HPLC-MS/MS) analysis of tryptic peptides, and amino acid analysis (AAA) of hydrolyzed samples were performed. The preferred reaction sites were tyrosine residues at the following positions in the polypeptide chain: Y83 and Y81 for TNM, Y150 for ONOO-, Y83 and Y158 for O3/NO2. The tyrosine residues Y83 and Y81 are located in a hydrophobic cavity, while Y150 and Y158 are located in solvent-accessible and flexible structures of the C-terminal region. The heterogeneous reaction with O3/NO2 was found to be strongly dependent on the phase state of the protein. Nitration rates were about one order of magnitude higher for aqueous protein solutions (~20% per day) than for protein filter samples (~2% per day). Overall, our findings show that the kinetics and site-selectivity of nitration strongly depend on the nitrating agent and reaction conditions, which may also affect the biological function and adverse health effects of the nitrated protein.
Journal of Proteome Research 02/2014; · 5.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Landscapes influence precipitation via the water vapor and energy fluxes they generate. Biologically active landscapes also generate aerosols containing microorganisms, some being capable of catalyzing ice formation and crystal growth in clouds at temperatures near 0 °C. The resulting precipitation is beneficial for the growth of plants and microorganisms. Mounting evidence from observations and numerical simulations support the plausibility of a bioprecipitation feedback cycle involving vegetated landscapes and the microorganisms they host. Furthermore, the evolutionary history of ice nucleation-active bacteria such as Pseudomonas syringae supports that they have been part of this process on geological time scales since the emergence of land plants. Elucidation of bioprecipitation feedbacks involving landscapes and their microflora could contribute to appraising the impact that modified landscapes have on regional weather and biodiversity, and to avoiding inadvertent, negative consequences of landscape management.
Global Change Biology 02/2014; 20(2):341-51. · 8.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ice nucleation on fungal spores may affect the frequency and properties of ice and mixed-phase clouds. We studied the ice nucleation properties of 12 different species of fungal spores chosen from three classes: Agaricomycetes, Ustilaginomycetes, and Eurotiomycetes. Agaricomycetes include many types of mushroom species and are cosmopolitan. Ustilaginomycetes are agricultural pathogens and have caused widespread damage to crops. Eurotiomycetes are found on all types of decaying material and include important human allergens. We focused on these classes since they are thought to be abundant in the atmosphere and because there is very little information on the ice nucleation ability of these classes of spores in the literature. All of the fungal spores investigated were found to cause freezing of water droplets at temperatures warmer than homogeneous freezing. The cumulative number of ice nuclei per spore was 0.001 at temperatures between -19 °C and -29 °C, 0.01 between -25.5 °C and -31 °C, and 0.1 between -26 °C and -36 °C. On average, the order of ice nucleating ability for these spores is Ustilaginomycetes > Agaricomycetes ≃ Eurotiomycetes. We show that at temperatures below -20 °C, all of the fungal spores studied here are less efficient ice nuclei compared to Asian mineral dust on a per surface area basis. We used our new freezing results together with data in the literature to compare the freezing temperatures of spores from the phyla Basidiomycota and Ascomycota, which together make up 98% of known fungal species found on Earth. The data show that within both phyla (Ascomycota and Basidiomycota) there is a wide range of freezing properties, and also that the variation within a phylum is greater than the variation between the average freezing properties of the phyla. Using a global chemistry-climate transport model, we investigated whether ice nucleation on the studied spores, followed by precipitation, can influence the atmospheric transport and global distributions of these spores in the atmosphere. Simulations show that inclusion of ice nucleation scavenging of these fungal spores in mixed-phase clouds can decrease the annual mean concentrations of fungal spores in near-surface air over the oceans and polar regions and decrease annual mean mixing ratios in the upper troposphere.
Atmospheric Chemistry and Physics 01/2014; 14(4). · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Primary biological aerosol particles (PBAP) can contribute significantly to the coarse particle burden in many environments, may thus influence climate and precipitation systems as cloud nuclei, and can spread disease to humans, animals, and plants. Measurements of PBAP in natural environments taken at high time- and size- resolution are, however, sparse and so large uncertainties remain in the role that biological particles play in the Earth system. In this study two commercial real-time fluorescence particle sensors and a Sporewatch single-stage particle impactor were operated continuously from 2 August to 2 September 2010 at a rural sampling location in Killarney National Park in south western Ireland. A cascade impactor was operated periodically to collect size-resolved particles during exemplary periods. Here we report the first ambient comparison of the waveband integrated bioaerosol sensor (WIBS-4) with the ultraviolet aerodynamic particle sizer (UV-APS) and also compare these real-time fluorescence techniques with results of fluorescence and optical microscopy of impacted samples. Both real-time instruments showed qualitatively similar behaviour, with increased fluorescent bioparticle concentrations at night when relative humidity was highest and temperature was lowest. The fluorescent particle number from the FL3 channel of the WIBS-4 and from the UV-APS were strongly correlated and dominated by a 3 μm mode in the particle size distribution. The WIBS FL2 channel exhibited particle modes at approx. 1 and 3 μm, and each were correlated with the concentration of fungal spores commonly observed in air samples collected at the site (ascospores, basidiospores, Ganoderma spp.). The WIBS FL1 channel exhibited variable multi-modal distributions turning into a broad featureless single mode after averaging and exhibited poor correlation with fungal spore concentrations, which may be due to the detection of bacterial and non-biological fluorescent particles. Cladosporium spp., which are among the most abundant fungal spores in many terrestrial environments, were not correlated with any of the real-time fluorescence channels, suggesting that the real-time fluorescence instruments are insensitive to PBAP classes with dark, highly absorptive cell walls. Fluorescence microscopy images of cascade impactor plates showed large numbers of coarse mode particles consistent with the morphology and weak fluorescence expected of sea salt. Some of these particles were attached to biological cells, suggesting that a marine source influenced the PBAP observed at the site and that the ocean may be an important contributor to PBAP loadings in coastal environments.
Atmospheric Chemistry and Physics 01/2014; 14(3). · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT:  Lichens and bryophytes may significantly affect global biogeochemical cycles by fixation of nitrogen and biotic enhancement of surface weathering rates. Most of the studies suggesting these effects, however, are either conceptual or rely on upscaling of regional estimates to obtain global numbers. Here, we use a different method, based on estimates of net carbon uptake, to quantify the impacts of lichens and bryophytes on biogeochemical cycles at the global scale. We focus on three processes, namelynitrogen fixation, phosphorus uptake and chemical weathering. Our estimates have the form of potential rates, which means that we quantify the amount of nitrogen and phosphorus needed by the organisms to build up biomass, also accounting for resorption and leaching of nutrients. Subsequently, we use potential phosphorus uptake on bare ground to estimate chemical weathering by the organisms, assuming that they release weathering agents to obtain phosphorus. The predicted requirement for nitrogen ranges from 3.5 to 34 Tg yr − 1 and for phosphorus it ranges from 0.46 to 4.6 Tg yr − 1. Estimates of chemical weathering are between 0.058 and 1.1 km 3 yr − 1 of rock. These values seem to have a realistic order of magnitude and they support the notion that lichens and bryophytes have the potential to play an important role for biogeochemical cycles.
[Show abstract][Hide abstract] ABSTRACT: Inhalation of nitrogen and reactive oxygen species (ROS) is known to induce lung inflammation, which is prevented by enzymatic and nonenzymatic antioxidant systems. These agents form nitrated allergens that were shown to enhance allergenicity. The aim of this study was to examine the influence of nitrated proteins on inflammation and antioxidant status of the lung. Ovalbumin (OVA) in nitrated form (nOVA) was intraperitoneally (ip) injected in mice for sensitization and in nitrated or unmodified form for challenge to induce allergic bronchial inflammation. To study the allergen potential of unrelated protein and verify cross-reactivity, nitrated and unmodified keyhole limpet hemocyanin (nKLH, KLH) was used for challenge. Challenge with OVA or nOVA reduced lung function and increased eosinophilia and protein content in bronchoalveolar lavage fluid (BALF). Challenge with nitrated or native OVA or KLH elevated glutathione (GSH) ratio in type II pneumocytes. Reduced mRNA expression of glutathione peroxidase (GPX) 3, glutathione reductase (GR), superoxide dismutase (SOD) 2, and catalase (CAT) was most prominent after challenge with nitrated OVA and nitrated KLH, respectively. Challenge with nOVA enhanced SOD1 mRNA reduction. Immunostaining of GPX 3 and SOD2 increased after challenge with OVA or nOVA, while reactivity of GR and reactivity of SOD2 were reduced after challenge with KLH or nKLH. SOD1 immunostaining was diminished after challenge with nonnitrated OVA or KLH. CAT immunoreaction was similar in all groups. Nitrated proteins without allergenic potential triggered mRNA reduction of antioxidants in type II cells after sensitization with a nitrated allergen but did not induce bronchial inflammation.
Journal of Toxicology and Environmental Health Part A 01/2014; 77(12):679-695. · 1.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Primary biological aerosol particles (PBAP) are important factors in
atmospheric cycling, climate, and public health. Pollen is a major
fraction of PBAP and is receiving increasing attention due to its high
allergenic potential and the associated impacts on personal life quality
and economy. Recently, autofluorescence-based techniques have proven to
be valuable tools for real time, in situ quantification and
classification of PBAP. First studies suggest that the autofluorescence
of pollen may be sufficiently selective to be utilized for an automated
and real-time monitoring of pollen in ambient air. However, the degree
of selectivity autofluorescence can provide is still in question and
actively debated. This study addresses the origin,
properties, and selectivity of autofluorescence from natural pollen by
fluorescence microscopy and spectroscopy measurements along with a
systematic synthesis of related literature. We show that dry pollen
reveals characteristic and reproducible autofluorescence signatures
which are shaped by cell wall associated fluorophores, such as phenolic
compounds and carotenoid pigments. In addition, fluorescence signals
from proteins and chlorophyll a were observed in some species. The
abundance and intensity of the individual fluorescence signals show
certain taxonomic trends and allow systematic differentiation from
bacteria and fungal spores due to the lack of proteins on the grain
surface. Principal component analysis was used to explore the
discrimination potential of pollen autofluorescence, in combination with
size and shape, revealing a differentiation of pollen on family level.
Our results help explore the levels of selectivity that
autofluorescence-based techniques can provide to PBAP analysis and will
support the development and application of autofluorescence-based
detectors for monitoring of allergenic pollen in the atmosphere.
[Show abstract][Hide abstract] ABSTRACT: Biological aerosol particles have become increasingly important for
atmospheric study, but continuous measurements at high time and size
resolution have not been available until recently. Here we report
seasonal cycles of fluorescent biological aerosol particles (FBAP) from
the boreal forest in Hyytiälä, Finland (18 months) and the
semi-arid Manitou Experimental Forest, Colorado (10 months). FBAP at
both locations were observed to be highest in summer and lowest in
winter, increasing by factors of 12 and 5 between these seasons,
respectively. In addition to the low temperatures and reduced sunlight
during winter, we suggest that snow cover inhibited FBAP release from
local terrestrial surfaces and that more extensive snow cover at the
Finland site contributed to lower winter FBAP concentrations. Average
size distributions at each site exhibited peaks between 1.5 and 6 μm
in aerodynamic diameter. The Finland site consistently showed a
dominant, narrow FBAP peak at ~ 3 μm in addition to discreet modes at
~ 1.5 and ~ 5 μm, whereas the Colorado site showed broader peaks at
1.5 and 5 μm, suggesting different modes of biological particles at
the two sites. FBAP concentrations in both locations were shown to
correlate with daily patterns of relative humidity (RH) during each
season. Also during summer at each site, average FBAP concentration
scaled with RH, but at the Finland site RH values above ~ 82% led to a
significant decrease in FBAP concentration. We hypothesize that this is
due to dew formation that inhibits bioparticle release. Lastly we show
that rain during summer at each location led to pronounced increases in
both fluorescent and total particle concentrations with FBAP peak
particle size at ~ 2 μm and concentration scaling with rain
intensity. We suggest that these particles are primarily fungal spores
and other bioparticles lofted from splashing of rain droplets hitting
soil and leaf surfaces. During the summer at the Colorado site we
consistently observed a mode of ~ 4 μm particles appearing several
hours after rain events that we suggest are fungal spores actively
emitted when ambient conditions are most advantageous for spread and
germination. The pronounced patterns of fluorescent bioparticles
observed here suggest that parameterizations of both daily and seasonal
cycles will be important to accurately reflect bioparticle emissions in
future studies of atmospheric bioaerosols and their potential effects on
clouds and precipitation.
ATMOSPHERIC CHEMISTRY AND PHYSICS 12/2013; 13(23):11987-12001. · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: As part of the CLACE-6 campaign we performed size-resolved CCN
measurements for a~supersaturation range of S = 0.079 % to 0.66% at the
high-alpine research station Jungfraujoch, Switzerland, in March~2007.
The derived effective hygroscopicity parameter κ describing the
influence of particle composition on CCN activity was on average
0.23-0.30 for Aitken (50-100 nm) and 0.32-0.43 for accumulation mode
particles (100-200 nm). The campaign average value of κ = 0.3 is
similar to the average value of κ for other continental locations.
When air masses came from southeasterly directions crossing the Po
Valley in Italy, particles were much more hygroscopic (κ ≈
0.42) due to large sulfate mass fractions. The κ values obtained
at S = 0.079 % exhibited a good negative correlation with the organic
mass fractions derived from PM1 aerosol mass spectrometer
(AMS) measurements. Applying a simple mixing rule the organic and
inorganic mass fractions observed by the AMS could be used to reproduce
the temporal fluctuations of the hygroscopicity of accumulation mode
particles quite well. We show how during a cloud event the
aerosol particles were activated as cloud droplets and then removed from
the air by precipitation leaving behind only a small amount of
accumulation mode particles consisting mainly of weakly CCN-active
particles, most likely externally mixed unprocessed soot particles. During the campaign we had the opportunity to directly compare
two DMT CCN counters for a certain time. The total CCN concentration
(NCCN,tot) obtained by the two instruments at equal
supersaturations agreed well for both possible operating modes:
detecting NCCN,tot directly by sampling the polydisperse
aerosol with the CCNC, or indirectly by combining size-resolved
measurements of the activated fraction with parallel measurements of the
particle size distribution (e.g., by SMPS). However, some
supersaturation setpoints differed between the two CCNCs by as much as
20% after applying the instrument calibrations, which resulted in
differences of the corresponding NCCN,tot of up to 50%. This
emphasizes that it is extremely important to carefully calibrate the
supersaturation of the instrument, especially at low S.
Atmospheric Chemistry and Physics 12/2013; 13(12):32575-32624. · 4.88 Impact Factor