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Juranyi Z.,Paul Scherrer Institute | Juranyi Z.,University of Applied Sciences and Arts Northwestern Switzerland | Tritscher T.,Paul Scherrer Institute | Tritscher T.,TSI GmbH | And 7 more authors.
Atmospheric Chemistry and Physics | Year: 2013

Ambient aerosols are a complex mixture of particles with different physical and chemical properties and consequently distinct hygroscopic behaviour. The hygroscopicity of a particle determines its water uptake at subsaturated relative humidity (RH) and its ability to form a cloud droplet at supersaturated RH. These processes influence Earth's climate and the atmospheric lifetime of the particles. Cloud condensation nuclei (CCN) number size distributions (i.e. CCN number concentrations as a function of dry particle diameter) were measured close to Paris during the MEGAPOLI campaign in January-February 2010, covering 10 different supersaturations (SS =0.1-1.0%). The time-resolved hygroscopic mixing state with respect to CCN activation was also derived from these measurements. Simultaneously, a hygroscopicity tandem differential mobility analyser (HTDMA) was used to measure the hygroscopic growth factor (ratio of wet to dry mobility diameter) distributions at RH =90%. The aerosol was highly externally mixed and its mixing state showed significant temporal variability. The average particle hygroscopicity was relatively low at subsaturation (RH =90%; mean hygroscopicity parameter κ =0.12-0.27) and increased with increasing dry diameter in the range 35-265 nm. The mean κ value, derived from the CCN measurements at supersaturation, ranged from 0.08 to 0.24 at SS =1.0-0.1%. Two types of mixing-state resolved hygroscopicity closure studies were performed, comparing the water uptake ability measured below and above saturation. In the first type the CCN counter was connected in series with the HTDMA and and closure was achieved over the whole range of probed dry diameters, growth factors and supersaturations using the κ-parametrization for the water activity and assuming surface tension of pure water in the Köhler theory. In the second closure type we compared hygroscopicity distributions derived from parallel monodisperse CCN measurements and HTDMA measurements. Very good agreement was found at all supersaturations, which shows that monodisperse CCN measurements are a reliable alternative to determine the hygroscopic mixing state of ambient aerosols. © Author(s) 2013.

The certification and quality control of respirator filters, filtering face pieces etc. as personal protection equipment is regulated and standardized world wide. In the USA, 42 CFR part 841 describes how to test and classify such filters. In Europe, the CEN standard EN 1432 describes how to test filters for respiratory protection.

Keller A.,University of Applied Sciences and Arts Northwestern Switzerland | Tritscher T.,TSI GmbH | Burtscher H.,University of Applied Sciences and Arts Northwestern Switzerland
Journal of Aerosol Science | Year: 2013

The new TSI Inc. Nano Water-based Condensation Particle Counter 3788 (N-WCPC Model 3788) is designed for counting particles down to a mobility diameter of d p = 2.5 nm. Published studies have shown that the use of water as a working fluid does not have a significant effect on the instrument performance. With the exception of a few specific substances, like emery oil or dioctyl sebacate which present a somewhat larger cut-point diameter, data in peer-reviewed literature suggests that the composition of the particles is not an issue as long as the particle diameter falls within the working range of the device. However, we have observed a very reduced counting efficiency from this water condensation particle counter for particles from a propane-rich fuel mixture (i.e. high carbon-to-oxygen ratio) generated by means of a Combustion Aerosol STandard burner (CAST). The percentage of detected particles decreases for an increasingly richer fuel mixture. The reduced efficiency is still present for particles well above the cut-point of the instrument. The 3788 N-WCPC counted only half as many d p = 70 nm particles when compared to two butanol based Condensation Particle Counters (CPC, models 3025A and 3022A, TSI Inc.), and the efficiency was even lower for smaller particles: only 0.14 ± 0.001 and 0.002 ± 0.0001 for monodisperse particles with a mobility diameter of d p = 30 nm and d p = 15 nm, respectively. Preconditioning the polydisperse sample using a thermodenuder at 100 or even 250°C slightly increased the counting efficiency of the N-WCPC, but this still remained below the counts of the butanol CPC. No reduction in counting efficiency was detected for CAST particles from propane-lean fuel-mixtures (otherwise known as black soot) or for organic particles produced by the photo-oxidation of α-pinene. For this reason, we believe that the effect is caused by the combination of the hydrocarbon rich composition of the particles and their low oxidation state. © 2013 Elsevier Ltd.

Laborde M.,Paul Scherrer Institute | Laborde M.,AerosolConsultingML GmbH | Crippa M.,Paul Scherrer Institute | Tritscher T.,Paul Scherrer Institute | And 13 more authors.
Atmospheric Chemistry and Physics | Year: 2013

Aerosol hygroscopicity and refractory black carbon (rBC) properties were characterised during wintertime at a suburban site in Paris, one of the biggest European cities. Hygroscopic growth factor (GF) frequency distributions, characterised by distinct modes of more-hygroscopic background aerosol and non- or slightly hygroscopic aerosol of local (or regional) origin, revealed an increase of the relative contribution of the local sources compared to the background aerosol with decreasing particle size. BC-containing particles in Paris were mainly originating from fresh traffic emissions, whereas biomass burning only gave a minor contribution. The mass size distribution of the rBC cores peaked on average at an rBC core mass equivalent diameter of DMEV ≈ 150 nm. The BC-containing particles were moderately coated (coating thickness Δcoat ≈ 33 nm on average for rBC cores with DMEV = 180-280 nm) and an average mass absorption coefficient (MAC) of ≈ 8.6 m2 g-1 at the wavelength λ = 880 nm was observed. Different time periods were selected to investigate the properties of BC-containing particles as a function of source and air mass type. The traffic emissions were found to be non-hygroscopic (GF ≈ 1.0), and essentially all particles with a dry mobility diameter (D0) larger than D0 = 110 nm contained an rBC core. rBC from traffic emissions was further observed to be uncoated within experimental uncertainty (Δcoat ≈ 2 nm ± 10 nm), to have the smallest BC core sizes (maximum of the rBC core mass size distribution at DMEV ≈ 100 nm) and to have the smallest MAC (≈ 7.3 m2g-1 at λ = 880 nm). The biomass burning aerosol was slightly more hygroscopic than the traffic emissions (with a distinct slightly-hygroscopic mode peaking at GF ≈ 1.1-1.2). Furthermore, only a minor fraction (≤ 10%) of the slightly-hygroscopic particles with 1.1 ≤ GF ≤ 1.2 (and D0 = 265 nm) contained a detectable rBC core. The BC-containing particles from biomass burning were found to have a medium coating thickness as well as slightly larger mean rBC core sizes and MAC values compared to traffic emissions. The aerosol observed under the influence of aged air masses and air masses from Eastern Continental Europe was dominated by a more-hygroscopic mode peaking at GF ≈ 1.6. Most particles (95%), in the more-hygroscopic mode at D0 = 265 nm, did not contain a detectable rBC core. A significant fraction of the BC-containing particles had a substantial coating with non-refractory aerosol components. MAC values of ≈ 8.8 m2g-1 and ≈ 8.3 m2g-1 at λ = 880 nm and mass mean rBC core diameters of 150 nm and 200 nm were observed for the aged and continental air mass types, respectively. The reason for the larger rBC core sizes compared to the fresh emissions - transport effects or a different rBC source - remains unclear. The dominant fraction of the BC-containing particles was found to have no or very little coating with non-refractory matter. The lack of coatings is consistent with the observation that the BC-containing particles are non- or slightly-hygroscopic, which makes them poor cloud condensation nuclei. It can therefore be expected that wet removal through nucleation scavenging is inefficient for fresh BC-containing particles in urban plumes. The mixing-state-specific cloud droplet activation behaviour of BC-containing particles including the effects of atmospheric aging processes should be considered in global simulations of atmospheric BC, as the wet removal efficiency remains a major source of uncertainty in its life-cycle. © Author(s) 2013.

Heringa M.F.,Paul Scherrer Institute | Decarlo P.F.,Paul Scherrer Institute | Decarlo P.F.,Drexel University | Chirico R.,Paul Scherrer Institute | And 13 more authors.
Atmospheric Chemistry and Physics | Year: 2012

Organic aerosol (OA) represents a significant and often major fraction of the non-refractory PM1 (particulate matter with an aerodynamic diameter d < 1 μm) mass. Secondary organic aerosol (SOA) is an important contributor to the OA and can be formed from biogenic and anthropogenic precursors. Here we present results from the characterization of SOA produced from the emissions of three different anthropogenic sources. SOA from a log wood burner, a Euro 2 diesel car and a two-stroke Euro 2 scooter were characterized with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and compared to SOA from α-pinene. The emissions were sampled from the chimney/tailpipe by a heated inlet system and filtered before injection into a smog chamber. The gas phase emissions were irradiated by xenon arc lamps to initiate photo-chemistry which led to nucleation and subsequent particle growth by SOA production. Duplicate experiments were performed for each SOA type, with the averaged organic mass spectra showing Pearson's r values >0.94 for the correlations between the four different SOA types after five hours of aging. High-resolution mass spectra (HR-MS) showed that the dominant peaks in the MS, m/z 43 and 44, are dominated by the oxygenated ions C 2H 3O + and C 2+, respectively, similarly to the relatively fresh semi-volatile oxygenated OA (SV-OOA) observed in the ambient aerosol. The atomic O:C ratios were found to be in the range of 0.25-0.55 with no major increase during the first five hours of aging. On average, the diesel SOA showed the lowest O:C ratio followed by SOA from wood burning, α-pinene and the scooter emissions. Grouping the fragment ions revealed that the SOA source with the highest O:C ratio had the largest fraction of small ions. The HR data of the four sources could be clustered and separated using principal component analysis (PCA). The model showed a significant separation of the four SOA types and clustering of the duplicate experiments on the first two principal components (PCs), which explained 79% of the total variance. Projection of ambient SV-OOA spectra resolved by positive matrix factorization (PMF) showed that this approach could be useful to identify large contributions of the tested SOA sources to SV-OOA. The first results from this study indicate that the SV-OOA in Barcelona is strongly influenced by diesel emissions in winter while in summer at SIRTA at the southwestern edge of Paris SV-OOA is more similar to alpha-pinene SOA. However, contributions to the ambient SV-OOA from SOA sources that are not covered by the model can cause major interference and therefore future expansions of the PCA model with additional SOA sources is recommended. © 2012 Author(s).

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