lnstitut für Sensorik und Elektronik
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Ergebnisse nach Hochschule und Institut
Publikation Growth and structural change of combustion aerosols at high relative humidity(American Chemical Society, 01.12.1995) Weingartner, Ernest; Baltensperger, Urs; Burtscher, Heinz01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Hygroscopic properties of carbon and diesel soot particles(Elsevier, 08/1997) Weingartner, Ernest; Burtscher, Heinz; Baltensperger, UrsLaboratory experiments were performed in order to study the hygroscopic properties of freshly produced carbon and diesel soot particles at subsaturations (i.e. at relative humidity < 100%). Wetted carbon aggregates collapsed to a more compact structure. In contrast, the diesel combustion particles exhibited a much smaller restructuring combined with condensational growth. The hygroscopicity of the diesel particles was enhanced when the sulfur content of the fuel was increased or when the particles were subjected to an ozone and UV pre-treatment. By extrapolating the data with a Köhler model critical supersaturations were calculated. Freshly emitted combustion particles are unlikely to act as cloud condensation nuclei whereas an aging of the particles will enhance their nucleation ability.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation 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 Seasonal and diurnal variation of aerosol size distributions (10(Wiley, 01.11.1999) Weingartner, Ernest; Nyeki, Stephan; Baltensperger, UrsDuring an extended field campaign at a high-alpine site (Jungfraujoch; 3580 m asl, Switzerland) from March 1997 to May 1998, the particle number size distribution (diameter D = 18–750 nm) and number concentration N (D>10 nm) were measured on a continuous basis. The number size distribution was dominated by particles with D<100 nm, while most of the surface area was in the accumulation mode size range (0.1–1 μm). Average size distributions exhibited a distinct bimodal shape which is generated and maintained by cloud processes and is less distinct in the free troposphere. Fitted modal diameters and standard deviations σ of the Aitken (20–100 nm) and accumulation modes were surprisingly constant throughout the year (DAit = 43±3 nm; DAcc = 140±6 nm; σAit = 2.13±0.11; σAcc = 1.61±0.03). The relative number concentrations in both modes are responsible for the seasonally observed in the shape of the size distribution. The high seasonality of NAcc with summer and winter values of ∼260 and ∼40 cmˉ³, respectively, is mainly due to transport of planetary boundary layer air to the station. In contrast, new particle formation is responsible for the high concentrations of nucleation mode particles (D<20 nm) which exhibited a maximum during the winter months. The relatively low seasonality found for NAit (summer, winter values: ∼530, ∼310 cmˉ³) is due to gas-to-particle conversion as well as transport processes. An analysis showed that a significant fraction of nucleation mode particles were formed by photochemical reactions.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 Condensation nuclei (CN) and ultrafine CN in the free troposphere to 12 km. A case study over the Jungfraujoch High‐Alpine research station(Wiley, 15.09.1999) Nyeki, Stephan; Kalberer, Markus; Lugauer, Matthias; Weingartner, Ernest; Petzold, Andreas; Schröder, Franz; Colbeck, Ian; Baltensperger, UrsCondensation nuclei (CN) were measured in the free troposphere (FT) above the Jungfraujoch (JFJ) high-alpine research station (3454 m; Switzerland) from 4.5 to 12 km asl in a case study on July 30, 1997. Vertical profiles of CN concentration for d ≥ 5 nm (N≥5), d ≥ 15 nm (N≥15 15) were measured, and indicated that ultrafine CN (UCN; 5 ≤ d ≤ 15 nm; N5-15) exhibited a distinct increase with altitude. Some evidence for near-constant values of d(logCN)/dz within discrete layers was found, which generally coincided with different airmasses as delineated by changes in the lapse rate dθ/dz at ∼ 5.5, 6.4, 9.0 and 10.6 km asl. In addition, CN concentration was mapped over a 40 × 75 km horizontal domain at 8.0 km asl centered above the JFJ. A pronounced variation in N≥5,N≥15 and specific humidity, but not in UCN, exhibited quasi-stationary 2-D features and was attributed to the chance encounter of a mountain wave. The case study provides further evidence that the upper FT may be a source of new particles.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Study on the chemical character of water soluble organic compounds in fine atmospheric aerosol at the Jungfraujoch(Springer, 07/2001) Krivácsy, Zoltán; Gelencsér, András; Kiss, Gyula; Mészáros, Ernő; Molnár, Ágnes; Hoffer, András; Mészáros, Tamás; Sárvári, Zsolt; Temesi, Dóra; Varga, Bálint; Baltensperger, Urs; Nyeki, Stephan; Weingartner, ErnestIn this study the chemical nature of the bulk of water soluble organic compounds in fine atmospheric aerosol collected during summer 1998 at the Jungfraujoch, Switzerland (3580 m asl) is characterised. The mass concentration of water soluble organic substances was similar to those of major inorganic ions, and the water soluble organic matter was found to be composed of two main fractions: (i) highly polyconjugated, acidic compounds with a varying degree of hydrophobicity and (ii) slightly polyconjugated, neutral and very hydrophilic compounds. The contribution of both fractions to the total water soluble organic carbon was about 50%. Separation into individual components was impossible either by HPLC or capillary electrophoresis which indicates the presence of a high number of chemically similar but not identical species. Results obtained by ultrafiltration and HPLC-MS have shown that the molecular weights are of the order of several hundreds. Most of the protonation constants for the acidic compounds determined by capillary electrophoresis were in the range 10⁴-10⁷.01A - 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 Zeitschrift