Generation and classification of airborne molecular clusters

Seit geraumer Zeit ist das Verhalten von Partikel im Nanometerbereich bis zu molekularen Clustern von besonderem Interesse für viele Wissenschaftsbereiche (Materialforschung, Sensortechnologie, Partikelbildung in der Atmosphäre, Biophysik, physikalische Chemie, Messtechnik für kleine Partikel, etc.). Für Grundlagenforschung unter Laborbedingungen ist die Charakterisierung wie auch Generierung von wohldefiniertem "Nano-Aerosol", mit Größen die bis in den Bereich von molekularen Clustern reichen, von entscheidender Bedeutung. Da verschiedene experimentelle Untersuchungen unterschiedliche Partikeleigenschaften erfordern, müssen sowohl physikalische wie chemische Eigenschaften der generierten Partikel bestimmt und kontrolliert werden. Daher soll diese Arbeit einen Überblick über verschiedene Techniken zur Clustergenerierung mit einer detaillierten Evaluierung der Electrospray Methode geben. Der in dieser Arbeit benutzte Electrospray Generator bewies Langzeitstabilität sowohl bezüglich generierter Clusterkonzentration wie auch Partikelgrößenverteilung. Da die Korngrößenverteilung von Tetraalkylammoniumhalidsalzen, gelöst in qualitiativ hochwertigen Alkoholen, erzeugt mit der Electrospray Methode, mehrere voneinander getrennt identifizierbare monomobile Clusterspezies aufweist, sind diese Substanzen hervorragend geeignet für verschiedene Anwendungen aerosolbezogener Forschung. In Kombination mit einem geeigneten hoch auflösenden Klassifiikator ist ein Electrospray Generator ein ausgezeichnetes Werkzeug für Studien, die wohldefinierte monodisperse bzw. monomobile Partikel erfordern.Recently, the behavior of nanometer sized particles down to molecular clusters has become of special interest for numerous scientific fields (material sciences, sensor technology, atmospheric particle formation, biophysics, physical chemistry, measurement techniques of small particles, etc.). For basic studies performed under laboratory conditions, the characterization as well as the generation of well-defined nano-aerosols with sizes down to single molecules is of crucial importance. Further, the physical properties and chemical nature of the generated aerosols have to be known and/or controlled as different experimental studies require different particle properties. Therefore this work gives an overview of different cluster generation techniques with an in depth evaluation of the electrospray method. The electrospray generator used throughout this work proved long time stability regarding generated cluster concentration as well as generated particle size distribution. As the number size distributions (NSD) of electrosprayed solutions of Tetraalkyl ammonium halide salts dissolved in high grade alcohols show several uniquely identifiable monomobile cluster species, they are well qualified for numerous applications in aerosol science. In combination with an appropriate high resolution classifier an electrospray is an excellent tool for studies where high quality monodispersed/monomobile particles are of crucial importance

Performance of diethylene glycol based particle counters in the sub 3 nm size range [Discussion paper]

When studying new particle formation, the uncertainty in determining the "true" nucleation rate is considerably reduced when using Condensation Particle Counters (CPCs) capable of measuring concentrations of aerosol particles at sizes close to or even at the critical cluster size (1–2 nm). Recently CPCs, able to reliably detect particles below 2 nm in size and even close to 1 nm became available. The corrections needed to calculate nucleation rates are substantially reduced compared to scaling the observed formation rate to the nucleation rate at the critical cluster size. However, this improved instrumentation requires a careful characterization of their cut-off size and the shape of the detection efficiency curve because relatively small shifts in the cut-off size can translate into larger relative errors when measuring particles close to the cut-off size. Here we describe the development of two continuous flow CPCs using diethylene glycol (DEG) as the working fluid. The design is based on two TSI 3776 counters. Several sets of measurements to characterize their performance at different temperature settings were carried out. Furthermore two mixing-type Particle Size Magnifiers (PSM) A09 from Airmodus were characterized in parallel. One PSM was operated at the highest mixing ratio (1 L min−1 saturator flow), and the other was operated in a scanning mode, where the mixing ratios are changed periodically, resulting in a range of cut-off sizes. Different test aerosols were generated using a nano-Differential Mobility Analyzer (nano-DMA) or a high resolution DMA, to obtain detection efficiency curves for all four CPCs. One calibration setup included a high resolution mass spectrometer (APi-TOF) for the determination of the chemical composition of the generated clusters. The lowest cut-off sizes were achieved with negatively charged ammonium sulphate clusters, resulting in cut-offs of 1.4 nm for the laminar flow CPCs and 1.2 and 1.1 nm for the PSMs. A comparison of one of the laminar-flow CPCs and one of the PSMs measuring ambient and laboratory air showed good agreement between the instruments

Verursachen Funken ein Feuer? Eine qualitative Fallstudie an der Grenze von Bildung und Wissenschaft

"Der Übertritt von der Schule an die Universität ist ein zentraler Angelpunkt der modernen Gesellschaft. Das Forschungsprogramm 'Sparkling- Science' des österreichischen Bundesministeriums für Wissenschaft und Forschung, das Schülerinnen in reale Forschungsprojekte einbindet, will die betroffenen Akteurinnen bei dieser Entscheidung unterstützen. Der vorliegende Beitrag untersucht im Rahmen einer qualitativen Fallstudie ein Projekt dieses Programms hinsichtlich der Modi zur Entfachung von Leidenschaft für die Wissenschaft. Aufgrund der Emergenz einer hierarchischen Struktur, die jener des Organisationstyps Unternehmens ähnelt, und der Umkehrung der intendierten Zweck-Mittel-Konfiguration lässt sich jedoch nur bedingt ein loderndes Feuer der Leidenschaft für die Wissenschaft konstatieren. Vielmehr zeigt sich, wie nicht-intendierte Effekte von zweckgerichtetem Handeln formale Absichten unterwandern und zur Bildung von hierarchischen quasi-organisationalen Strukturen beitragen." (Autorenreferat

Counting on chemistry : laboratory evaluation of seed-material-dependent detection efficiencies of ultrafine condensation particle counters

Condensation particle counters (CPCs) are crucial instruments for detecting sub-10 nm aerosol particles. Understanding the detection performance of a CPC requires thorough characterization under well-controlled laboratory conditions. Besides the size of the seed particles, chemical interactions between the working fluid and the seed particles also influence the activation efficiencies. However, common seed particle materials used for CPC characterizations are not chosen with respect to chemical interactions with vapor molecules of the working fluid by default. Here, we present experiments on the influence of the seed particle material on the detection efficiencies and the 50% cutoff diameters of commonly used CPCs for the detection of sub-10 nm particles. A remarkable set consisting of six different and commercially available particle detectors, including the newly developed TSI V-WCPC 3789 and a tuned TSI 3776, was tested. The corresponding working fluids of the instruments are n-butanol, diethylene glycol and water. Among other materials we were able to measure detection efficiencies with nanometer-sized organic seed particles reproducibly generated by the oxidation of beta-caryophyllene vapor in a flow tube. Theoretical simulations of supersaturation profiles in the condensers were successfully related to measured detection efficiencies. Our results demonstrate the importance of chemical similarities between seed particles and the working fluids used when CPCs are characterized. We anticipate our study to contribute to a deeper understanding of chemical interactions during heterogeneous nucleation processes.Peer reviewe

LTβR expression on hematopoietic cells regulates acute inflammation and influences maturation of myeloid subpopulations

Lymphotoxin beta-receptor (LTβR) is involved in the formation and maintenance of secondary lymphoid structures, as well as in the regulation of inflammatory responses. Because LTβR lymphoid structure formation continues to develop in infants, we compared two different chimera models: one using adult mice and the other using a transplantation model of neonatal mice. To elucidate the function of LTβR on lymphoid and non-lymphoid cells, we generated bone marrow chimeras on the wild type C57Bl/6 and the LTβR-deficient (LTβR−/−) background, and reconstituted the mice with bone marrow cells reciprocally. These chimeric mice were analyzed in the experimental model of acute dextran sulfate sodium-induced colitis. Interestingly, both models revealed not only equal reconstitution levels but also similar immunological responses: LTβR expression on stromal cells is essential for lymph node formation, whereas LTBR on hematopoietic cells is crucial for a decrease in inflammation. In addition, mice lacking LTβR on hematopoietic cells revealed (a) an increase of immature granulocytic cells in the spleen and (b) a reduced proportion of myeloid cells in peripheral blood and spleen expressing CD11b+Ly6C+Ly6G− (myeloid-derived suppressor cells expression profile). In conclusion, LTβR expression on hematopoietic cells seems to be involved in the down-regulation of acute inflammatory reactions paralleled by the appearance of immature myeloid cells

Methods for determining particle size distribution and growth rates between 1 and 3 nm using the Particle Size Magnifier

The most important parameters describing the atmospheric new particle formation process are the particle formation and growth rates. These together determine the amount of cloud condensation nuclei attributed to secondary particle formation. Due to difficulties in detecting small neutral particles, it has previously not been possible to derive these directly from measurements in the size range below about 3 nm. The Airmodus Particle Size Magnifier has been used at the SMEAR II station in Hyytiälä, southern Finland, and during nucleation experiments in the CLOUD chamber at CERN for measuring particles as small as about 1 nm in mobility diameter. We developed several methods to determine the particle size distribution and growth rates in the size range of 1–3 nm from these data sets. Here we introduce the appearance-time method for calculating initial growth rates. The validity of the method was tested by simulations with the Ion-UHMA aerosol dynamic model

Stereochemistry of phase-1 metabolites of mephedrone determines their effectiveness as releasers at the serotonin transporter

Mephedrone (4-methyl-N-methylcathinone) is a psychostimulant that promotes release of monoamines via the high affinity transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT). Metabolic breakdown of mephedrone results in bioactive metabolites that act as substrate-type releasers at monoamine transporters and stereospecific metabolism of mephedrone has been reported. This study compared the effects of the enantiomers of the phase-1 metabolites nor-mephedrone, 4-hydroxytolyl-mephedrone (4-OH-mephedrone) and dihydro-mephedrone on (i) DAT, NET and SERT mediated substrate fluxes, (ii) determined their binding affinities towards a battery of monoamine receptors and (iii) examined the relative abundance of the enantiomers in human urine. Each of the enantiomers tested inhibited uptake mediated by DAT, NET and SERT. No marked differences were detected at DAT and NET. However, at SERT, the S-enantiomers of nor-mephedrone and 4-OH-mephedrone were several times more potent than the corresponding R-enantiomers. Moreover, the R-enantiomers were markedly less effective as releasers at SERT. S-nor-mephedrone displayed moderate affinities towards human alpha; 1A; , human 5-HT; 2A; and rat and mouse trace amine-associated receptor 1. These results demonstrate that stereochemistry dictates the pharmacodynamics of the phase-1 metabolites of mephedrone at SERT, but not at DAT and NET, which manifests in marked differences in their relative potencies, i.e. DAT/SERT ratios. Chiral analysis of urine samples demonstrated that nor-mephedrone predominantly exists as the S-enantiomer. Given the asymmetric abundance of the enantiomers in biological samples, these findings may add to our understanding of the subjective effects of administered mephedrone, which indicate pronounced effects on the serotonergic system

Evolution of alpha-pinene oxidation products in the presence of varying oxidizers: CI-APi-TOF point of view

Alpha-pinene oxidation was studied in the CERN CLOUD chamber under near atmospheric conditions using varying levels of different oxidizers (i.e., O_3 , HO_x and NO_x with differing gas mixture compositions) in the presence and absence of UV-radiation, SO_2 and additional organic traces; ammonia (NH_3) and dimethylamine (DMA). The oxidation products and their evolution due to aging in the chamber were studied using a novel CI-APi-TOF technique, with the nitrate ion (NO^−_3 ) based chemical ionization (CI) scheme. We aimed to the results that would indicate how different oxidizing pathways lead to different product distributions in the product clusters detected

Diurnal evolution of negative atmospheric ions above the boreal forest : from ground level to the free troposphere

At SMEAR II research station in Hyytiala, located in the Finnish boreal forest, the process of new particle formation and the role of ions has been investigated for almost 20 years near the ground and at canopy level. However, above SMEAR II, the vertical distribution and diurnal variation of these different atmospheric ions are poorly characterized. In this study, we assess the atmospheric ion composition in the stable boundary layer, residual layer, mixing layer, and free troposphere, and the evolution of these atmospheric ions due to photochemistry and turbulent mixing through the day. To measure the vertical profile of atmospheric ions, we developed a tailored set-up for online mass spectrometric measurements, capable of being deployed in a Cessna 172 with minimal modifications. Simultaneously, instruments dedicated to aerosol properties made measurements in a second Cessna. We conducted a total of 16 measurement flights in May 2017, during the spring, which is the most active new particle formation season. A flight day typically consisted of three distinct flights through the day (dawn, morning, and afternoon) to observe the diurnal variation and at different altitudes (from 100 to 3200 m above ground), to capture the boundary layer development from the stable boundary layer, residual layer to mixing layer, and the free troposphere. Our observations showed that the ion composition is distinctly different in each layer and depends on the air mass origin and time of the day. Before sunrise, the layers are separated from each other and have their own ion chemistry. We observed that the ions present within the stable layer are of the same composition as the ions measured at the canopy level. During daytime when the mixing layer evolved and the compounds are vertically mixed, we observed that highly oxidized organic molecules are distributed to the top of the boundary layer. The ion composition in the residual layer varies with each day, showing similarities with either the stable boundary layer or the free troposphere. Finally, within the free troposphere, we detected a variety of carboxylic acids and ions that are likely containing halogens, originating from the Arctic Sea.Peer reviewe

Causes and importance of new particle formation in the present-day and preindustrial atmospheres

New particle formation has been estimated to produce around half of cloud-forming particles in the present-day atmosphere, via gas-to-particle conversion. Here we assess the importance of new particle formation (NPF) for both the present-day and the preindustrial atmospheres. We use a global aerosol model with parametrizations of NPF from previously published CLOUD chamber experiments involving sulfuric acid, ammonia, organic molecules, and ions. We find that NPF produces around 67% of cloud condensation nuclei at 0.2% supersaturation (CCN0.2%) at the level of low clouds in the preindustrial atmosphere (estimated uncertainty range 45-84%) and 54% in the present day (estimated uncertainty range 38-66%). Concerning causes, we find that the importance of biogenic volatile organic compounds (BVOCs) in NPF and CCN formation is greater than previously thought. Removing BVOCs and hence all secondary organic aerosol from our model reduces low-cloud-level CCN concentrations at 0.2% supersaturation by 26% in the present-day atmosphere and 41% in the preindustrial. Around three quarters of this reduction is due to the tiny fraction of the oxidation products of BVOCs that have sufficiently low volatility to be involved in NPF and early growth. Furthermore, we estimate that 40% of preindustrial CCN0.2% are formed via ion-induced NPF, compared with 27% in the present day, although we caution that the ion-induced fraction of NPF involving BVOCs is poorly measured at present. Our model suggests that the effect of changes in cosmic ray intensity on CCN is small and unlikely to be comparable to the effect of large variations in natural primary aerosol emissions. Plain Language Summary New particle formation in the atmosphere is the process by which gas molecules collide and stick together to form atmospheric aerosol particles. Aerosols act as seeds for cloud droplets, so the concentration of aerosols in the atmosphere affects the properties of clouds. It is important to understand how aerosols affect clouds because they reflect a lot of incoming solar radiation away from Earth's surface, so changes in cloud properties can affect the climate. Before the Industrial Revolution, aerosol concentrations were significantly lower than they are today. In this article, we show using global model simulations that new particle formation was a more important mechanism for aerosol production than it is now. We also study the importance of gases emitted by vegetation, and of atmospheric ions made by radon gas or cosmic rays, in preindustrial aerosol formation. We find that the contribution of ions and vegetation to new particle formation was also greater in the preindustrial period than it is today. However, the effect on particle formation of variations in ion concentration due to changes in the intensity of cosmic rays reaching Earth was small.Peer reviewe