lnstitut für Sensorik und Elektronik
Dauerhafte URI für die Sammlunghttps://irf.fhnw.ch/handle/11654/28068
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Ergebnisse nach Hochschule und Institut
Publikation Heterogeneous chemical processing of 13NO2 by monodisperse carbon aerosols at very low concentrations(American Chemical Society, 19.09.1996) Kalberer, Markus; Tabor, K.; Ammann, Markus; Parrat, Yves; Weingartner, Ernest; Piguet, D.; Rössler, E.; Jost, Dieter T.; Türler, Andreas; Gäggeler, Heinz W.; Baltensperger, UrsThe heterogeneous reaction of NO2 with different carbon aerosol particles was investigated in situ. The NO2 was labeled with the β+-emitter 13N (half-life 10.0 min) which allowed application of NO2 at very low concentrations. The carbon aerosol was either produced by a spark discharge generator using graphite electrodes or by a brush generator resuspending commercial soot material. Monodisperse size cuts between 50- and 490-nm diameter were selected and mixed with the 13NO2. After a defined reaction time, the different reaction products were separated by means of selective traps and detected on-line by γ-spectrometry. A sticking coefficient for chemisorption of NO2 between 0.3 × 10ˉ⁴ and 4.0 × 10ˉ⁴ and a rate constant for the reduction of adsorbed NO2 to NO(g) between 4.0 × 10 ˉ⁴ and 9.4 × 10 ˉ⁴ /s were determined for both aerosols. The sticking coefficient obtained in this study in situ with aerosol particles is 2 orders of magnitudes smaller than the uptake coefficient recently reported with bulk carbon material.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Convective boundary layer evolution to 4 km asl over High‐alpine terrain. Airborne lidar observations in the Alps(Wiley, 01.03.2000) Nyeki, Stephan; Kalberer, Markus; Colbeck, Ian; De Wekker, Stephan; Furger, Markus; Gäggeler, Heinz W.; Koßmann, Meinolf; Lugauer, Matthias; Steyn, Douw; Weingartner, Ernest; Wirth, Martin; Baltensperger, UrsMountain ranges have important influences on the structure and composition of the convective boundary layer (CBL) and free troposphere (FT). Evolution of the summer CBL, measured over the European Alps using airborne lidar, was clearly observed to attain a near-uniform height up to 4.2 km asl by early afternoon. A climatology of in-situ high-alpine aerosol measurements suggests that such substantial growth, corresponding to ∼ 0.3 of the mid-latitude tropopause height, often occurs during summer months. Subsequent nocturnal collapse of the CBL was estimated to result in the venting of ∼ 0.8 ± 0.3 (SO4 4) Gg/day into a FT residual layer, leeward of the Alps.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Characterization of size-fractionated aerosol from the Jungfraujoch (3580 m asl) using total reflection x-ray fluorescence (TXRF)(Taylor & Francis, 22.09.2000) Streit, Niklaus; Weingartner, Ernest; Zellweger, Christoph; Schwikowski, Margit; Gäggeler, Heinz W.; Baltensperger, UrsDuring three field campaigns at the Jungfraujoch High Alpine Research Station, Switzerland, size-fractionated aerosol was collected using a cascade impactor. The particles were impacted on silicon oil-coated quartz sampling substrates. The actual analysis was then performed directly on these quartz sampling substrates using total reflection X-ray fluorescence. The resulting size distributions of 16 elements (S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, Se, Br, Rb, Sr, Y, Zr, Pb) were investigated to determine the best cut-off diameter to distinguish between geogenic and anthropogenic particles. The obtained cut-off diameter of 1 μm is an important parameter in the current world-wide measurements under the auspices of the World Meteorological Organization's Global Atmosphere Watch aerosol project.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation The background aerosol size distribution in the free troposphere. An analysis of the annual cycle at a high‐alpine site(Wiley, 01.12.1998) Nyeki, Stephan; Li, F.; Weingartner, Ernest; Streit, Niklaus; Colbeck, Ian; Gäggeler, Heinz W.; Baltensperger, UrsMeasurements during free tropospheric (FT) and planetary boundary layer (PBL) conditions were conducted over an annual cycle at the Jungfraujoch high-Alpine research station (3454 m), Switzerland, in order to establish diurnal and seasonal cycles of the background continental aerosol over central Europe. Using a condensation nucleus counter (TSI 3025) and an optical particle counter (PMS Las-X) from June 1996 to May 1997, the following were determined: (1) accumulation mode lognormal parameters and (2) number concentrations for the nucleation (diameter d < 0.1 μm), accumulation (0.1 ≤ d ≤ 1.0 μm), and part of the coarse (1.0 < d ≤ 7.5 μm, designated “coarse”) modes. Lognormal parameters were found to be similar for FT and PBL conditions, and exhibited a weak seasonality in geometric median diameter dGN =0.13 and 0.10 μm, and standard deviation σG = 1.73 and 1.64 for summer and winter, respectively. Aerosol number concentrations in each mode exhibited a more pronounced seasonality, with FT concentrations being lower than those for PBL. Summer and winter FT median concentrations for the nucleation, accumulation, and “coarse” modes were 405 and 195 cmˉ³, 114 and 26 cmˉ³, and 0.052 and 0.014 cmˉ³, respectively. These results provide tentative support of other long-term observations that the FT background aerosol mode appears to vary mainly in concentration rather than accumulation mode shape. Further analysis indicated that only the total concentration in each mode varied with weather type and a classification between that of a remote continental and polar aerosol model was found for the Jungfraujoch.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation The Jungfraujoch high‐alpine research station (3454 m) as a background clean continental site for the measurement of aerosol parameters(Wiley, 01.03.1998) Nyeki, Stephan; Baltensperger, Urs; Colbeck, Ian; Jost, Dieter T.; Weingartner, Ernest; Gäggeler, Heinz W.The first annual data set of climatically important aerosol parameters, measured at the Jungfraujoch (JFJ) high-alpine research station (3454 m, Switzerland) from an ongoing field campaign since July 1995, is presented. Analysis of diurnal variations in continuous measurements of the total and backward hemispheric scattering coefficients (σSP, σBSP), the absorption coefficient (σAP, from aethalometer data), condensation nuclei (CN) concentration, and epiphaniometer signal (related to surface area (S) concentration) established the diurnal period 0300 – 0900 as being representative of the free tropospheric background aerosol. The annual data set was then edited to omit (1) the period 0900–0300 (i.e., 18 hours), taken to represent possible planetary boundary layer influenced conditions and (2) in-cloud conditions using a cloud liquid-water monitor. The seasonal aerosol cycle exhibited a July maximum and a December minimum in most aerosol parameters. Typical monthly median values for the free troposphere exhibit the following seasonal maxima and minima, respectively: σSP (550 nm) ∼ 16.1 and 0.43 × 10ˉ⁶/m, σBSP (550 nm) ∼ 2.10 and 0.09 × 10ˉ⁶/m, σAP (550 nm) ∼ 10.4 and 0.76 × 10ˉ⁷/m (≈ 104 and 7.6 ng mˉ³ black carbon), CN concentration ∼ 670 and 280 cmˉ³, and epiphaniometer signal ∼ 9.26 and 0.67 counts/s (S concentration ≈24.1 and 1.7 μm2 cmˉ³). Aerosol parameters were found to be comparable in magnitude to other NOAA baseline and regional stations and suggest that a clean continental designation for the JFJ site is applicable, when removing the planetary boundary layer influenced period.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Aerosol climatology at the high‐alpine site Jungfraujoch, Switzerland(Wiley, 01.08.1997) Baltensperger, Urs; Gäggeler, Heinz W.; Jost, Dieter T.; Lugauer, Matthias; Schwikowski, Margit; Weingartner, Ernest; Seibert, PetraContinuous aerosol measurements have been performed at the high-alpine site Jungfraujoch (3450 m above sea level) since 1988 by means of an epiphaniometer. The instrument, which determines the Fuchs surface area of the aerosol particles, was operated with a time resolution of 30 min. High correlation coefficients (r>0.8) were found between the epiphaniometer signal and other aerosol parameters, which could be attributed to a rather constant size distribution of the Jungfraujoch aerosol in the accumulation range (0.101A - Beitrag in wissenschaftlicher ZeitschriftPublikation Urban and rural aerosol characterization of summer smog events during the PIPAPO field campaign in Milan, Italy(Wiley, 2002) Baltensperger, Urs; Streit, Niklaus; Weingartner, Ernest; Nyeki, Stephan; Prévôt, André S.H.; Van Dingenen, Rita; Virkkula, Aki; Putaud, Jean-Philippe; Even, A.; ten Brink, Harry; Blatter, Andreas; Neftel, Albrecht; Gäggeler, Heinz W.A comprehensive range of aerosol parameters was measured at an urban and a rural site in the Milan, Italy metropolitan region during summer smog events in summer 1998. Measurements were performed as part of the Pianura Padana Produzione di Ozono (PIPAPO) field campaign to determine the sensitivity of O3 production to NOₓ and volatile organic carbon concentrations at several ground stations. Primary aerosol parameters (i.e., direct emissions) such as aerosol black carbon showed a distinct diurnal variation with maxima at about 0000 and 0800 central European summer time (CEST), in contrast to secondary aerosol parameters such as sulfate and nitrate. Aerosol number size distributions were measured under ambient conditions as well as after conditioning with volatility and hygroscopicity systems. A mode at d = 20–30 nm in the number concentration was found at 0800 CEST and exhibited high volatility at 110°C (∼80% volume lost upon heating) but no hygroscopic behavior. Based on these measurements, small particles (d < 40 nm) are thought to consist mainly of hydrophobic particulate organic matter, rather than soot or H2SO4 aerosols. Two distinct hygroscopic modes with average growth factors d/d0 ∼ 1.02 and 1.21–1.28 were found for particles with dry (relative humidity of <30%) diameters d0 = 50–200 nm. Submicrometer aerosols exhibited lower volatility at the rural than at the urban site, which is attributed to additional particulate mass produced by secondary particle formation.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Size-dependent aerosol activation at the high-alpine site Jungfraujoch (3580 m asl)(Stockholm University Press, 01.01.2002) Henning, Silvia; Weingartner, Ernest; Schmidt, Sebastian; Wendisch, Manfred; Gäggeler, Heinz W.; Baltensperger, UrsMicrophysical and chemical aerosol properties and their influence on cloud formation were studied in a field campaign at the high-alpine site Jungfraujoch (JFJ, 3580 m asl). Due to its altitude, this site is suitable for ground-based in-cloud measurements, with a high cloud frequency of 40%. Dry total and interstitial aerosol size distributions [18 nm 0.15 g mˉ³. Below this value, D50 increased with decreasing LWC. A dependence of D50 on the accumulation mode (Dp>100 nm) number concentration (Ntot,Dp>100) was only found for concentrations less than 100 cmˉ³. For higher values of Ntot,Dp>100 the D50 remained constant. Furthermore, a decrease of the effective radius of cloud droplets (Reff) with increasing Ntot,Dp>100 was observed, providing experimental evidence for the microphysical relation predicted by the Twomey effect. A modified Köhler model was used to quantify the critical supersaturation for the aerosol observed at the JFJ. Ambient supersaturations were determined from the derived supersaturation curve and the calculated D50. As an example, a critical supersaturation of 0.2% was found for 100 nm particles.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Seasonal variation of water‐soluble ions of the aerosol at the high‐alpine site Jungfraujoch (3580 m asl)(Wiley, 15.01.2003) Henning, Silvia; Weingartner, Ernest; Schwikowski, Margit; Gäggeler, Heinz W.; Gehrig, Robert; Hinz, Klaus-Peter; Trimborn, Achim; Spengler, Bernhard; Baltensperger, UrsWithin the Global Atmosphere Watch (GAW) Aerosol Program of the World Meteorological Organization (WMO), the aerosol chemical composition has been continuously measured since July 1999 at the Jungfraujoch (JFJ) of which the first 1.5-year data set is presented. Sampling is performed in two size classes (total suspended particles (TSP) and particles with aerodynamic diameters smaller than 1 μm). The filters are analyzed for major ions, which constitute 30% of the total dry aerosol mass collected at this site. As annual mean, a total ion mass concentration of 1.04 μg mˉ³ was observed. Sulfate, ammonium, and nitrate were the major components of the fine aerosol fraction, while calcium and nitrate were two major water-soluble components in the coarse mode. Single particle analysis confirmed the internal mixture of calcium and nitrate in the coarse mode. The total ion mass concentration showed strong seasonal differences, with 1.25, 1.62, 0.70, and 0.25 μg mˉ³ for spring, summer, fall, and winter, respectively. The variability was stronger for sulfate, ammonium, and nitrate than for calcium. The reason for this is believed to be local sources of calcium, which do not require vertical transport, along with Sahara dust episodes, which occur occasionally over the whole year, independent from the season.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Generation of submicron Arizona test dust aerosol. Chemical and hygroscopic properties(Taylor & Francis, 20.10.2005) Vlasenko, Alexander; Sjögren, Staffan; Weingartner, Ernest; Gäggeler, Heinz W.; Ammann, MarkusThis article describes a submicron dust aerosol generation system based on a commercially available dust disperser intended for use in laboratory studies of heterogeneous gas–aerosol interactions. Mineral dust particles are resuspended from Arizona Test Dust (ATD) powder as a case study. The system output in terms of number and surface area is adjustable and stable enough for aerosol flow reactor studies. Particles produced are in the 30–1000 nm size range with a lognormal shape of the number size distribution. The particles are characterized with respect to morphology, electrical properties, hygroscopic properties, and chemical composition. Submicron particle elemental composition is found to be similar for the particle surface and bulk as revealed by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. A significant difference in chemical composition is found between the submicron aerosol and the ATD bulk powder from which it was generated. The anionic composition of the water-soluble fraction of this dust sample is dominated by sulfate. Resuspended dust particles show, as expected, nonhygroscopic behavior in a humid environment. Small hygroscopic growth of about 1% (relative change in mobility diameter) was observed for 100 nm particles when the relative humidity (RH) was changed from 12 to 94%. Particles larger than 100–200 nm shrank about 1% once exposed to RH > 90%. This was interpreted as a restructuring of the larger agglomerates of dust to particles of smaller mobility diameter, under the influence of water vapor.01A - Beitrag in wissenschaftlicher Zeitschrift