Hochschule für Technik und Umwelt FHNW
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Publikation 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 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 ZeitschriftPublikation Partitioning of reactive nitrogen (NOy) and dependence on meteorological conditions in the lower free troposphere(Copernicus, 19.06.2003) Zellweger, Christoph; Forrer, Jann; Hofer, Peter; Nyeki, Stephan; Schwarzenbach, Beat; Weingartner, Ernest; Ammann, Markus; Baltensperger, UrsResults of continuous nitrogen oxide (NO), nitrogen dioxide (NO2), peroxyacetyl nitrate (PAN) and total reactive nitrogen (NOy) measurements along with seasonal field campaigns of nitric acid (HNO3) and particulate nitrate (NO3-) measurements are presented for a two-year period at the high-alpine research station Jungfraujoch (JFJ), 3580 m asl. The NOy mixing ratio and partitioning is shown to strongly depend on meteorological conditions. Knowledge of these meteorological transport processes allows discrimination between undisturbed (i.e. clean) and disturbed (i.e. influenced by regional pollution sources) free tropospheric (FT) conditions at the JFJ. Median NOy concentrations during undisturbed FT periods ranged from 350 pptv (winter, December to February) to 581 pptv (spring, March to May). PAN was found to be the dominant NOy species during spring and summer, whereas NO2 was most abundant during autumn and winter. Particulate nitrate was found to contribute significantly to total NOy during thermally induced vertical transport. Föhn events, synoptical lifting (e.g. fronts) and thermally induced vertical transport resulted in mixing ratios up to 10 times higher at the JFJ compared to undisturbed FT conditions. Furthermore, this meteorological variability of the NOy concentration and partitioning often dominated the seasonal variability. As a consequence the use of filters at the JFJ (and other mountainous sites) is crucial for the interpretation of data from such measurement sites. This study presents a further development of meteorological filters for the high-alpine site Jungfraujoch, which also could be modified and adapted to other mountainous measurement sites.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Properties of jet engine combustion particles during the PartEmis experiment: Hygroscopicity at subsaturated conditions(Wiley, 06.06.2003) Gysel, Martin; Nyeki, Stephan; Weingartner, Ernest; Baltensperger, Urs; Giebl, Heinrich; Hitzenberger, Regina; Petzold, Andreas; Wilson, C. W.Hygroscopic properties of combustion particles were measured online with a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) during PartEmis jet engine combustor experiments. The combustor was operated at old and modern cruise conditions with fuel sulfur contents (FSC) of 50, 410 and 1270 μg/g, and hygroscopic growth factors (HGF) of particles with different dry diameters were investigated at relative humidities RH ≤ 95%. HGFs increased strongly with increasing FSC (HGF[95% RH, 50 nm, modern cruise] = 1.01 and 1.16 for low and high FSC, respectively), and decreased with increasing particle size at fixed FSC, whereas no significant difference was detected between old and modern cruise. HGFs agreed well with a two-parameter theoretical model which provided an estimate of the sulfuric acid content of dry particles, indicating a nearly linear dependence on FSC.01A - 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 Properties of jet engine combustion particles during the PartEmis experiment. Hygroscopic growth at supersaturated conditions(Wiley, 31.07.2003) Hitzenberger, Regina; Giebl, Heinrich; Petzold, Andreas; Gysel, Martin; Nyeki, Stephan; Weingartner, Ernest; Baltensperger, Urs; Wilson, C. W.During the EU Project PartEmis, the microphysical properties of aircraft combustion aerosol were investigated. This study is focused on the ability of exhaust aerosols to act as cloud condensation nuclei (CCN). The combustor was operated at two different conditions representing old and modern aircraft engine technology. CCN concentrations were measured with the University of Vienna CCN counter [Giebl et al., 2002] at supersaturations around 0.7%. The activation ratio (fraction of CCN in total aerosol) depended on the fuel sulphur content (FSC) and also on the operation conditions. CCN/CN ratios increased from 0.93 through 1.43 to 5.15*10ˉ³ (old cruise conditions) and 0.67 through 3.04 to 7.94*10ˉ³ (modern cruise conditions) when FSC increased from 50 through 410 to1270 μg/g. The activation behaviour was modelled using classical theories and with a semi-empirical model [Gysel et al., 2003] based on measured hygroscopicity of the aerosol under subsaturated conditions, which gave the best agreement.01A - Beitrag in wissenschaftlicher Zeitschrift