Hochschule für Technik und Umwelt FHNW
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Publikation Saharan dust events at the Jungfraujoch. detection by wavelength dependence of the single scattering albedo and first climatology analysis(Copernicus, 08.12.2004) Collaud Coen, Martine; Weingartner, Ernest; Schaub, D.; Hueglin, Christoph; Corrigan, C.; Henning, Silvia; Schwikowski, Margit; Baltensperger, UrsScattering and absorption coefficients have been measured continuously at several wave-lengths since March 2001 at the high altitude site Jungfraujoch (3580ma.s.l.). From these data, the wavelength dependences of the Ångström exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo usually increases with wavelength, it decreases with wavelength during Saharan dust events (SDE) due to the greater size of the mineral aerosol particles and their different chemical composition. This change in the sign of the single scattering exponent turns out to be a sensitive means for detecting Saharan dust events. The occurrence of SDE detected by this new method was confirmed by visual in-spection of filter colors and by studying long-range back-trajectories. An examination of SDE over a 22-month period shows that SDE are more frequent during the March-June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5h, with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48-h total suspended particulate matter (TSP) concentration at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the Jungfraujoch is 16µg/m³, which corresponds to an annual mean of 0.8µg/m³ or 24% of TSP.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Characterization and intercomparison of aerosol absorption photometers. result of two intercomparison workshops(Copernicus, 2011) Müller, Thomas; Henzing, Bas; de Leeuw, Gerrit; Wiedensohler, Alfred; Alastuey, Andrés; Angelov, H.; Bizjak, Milan; Collaud Coen, Martine; Engström, J. E.; Gruening, Carsten; Hillamo, Risto; Hoffer, András; Imre, Kornélia; Ivanow, Petko; Jennings, Stephen G.; Sun, Junying; Kalivitis, Nikos; Karlsson, Hanna; Komppula, Mikka; Laj, Paolo; Li, S.-M.; Lunder, Chris; Marinoni, Angela; Martins dos Santos, Sebastiao; Moerman, Marcel; Nowak, Andreas; Ogren, John A.; Petzold, Andreas; Pichon, Jean Marc; Rodriquez, Sergio; Sharma, Sangeeta; Sheridan, Patrick J.; Teinilä, Kimmo; Tuch, Thomas; Viana, Mar; Virkkula, Aki; Weingartner, Ernest; Wilhelm, R.; Wang, YaqiangAbsorption photometers for real time application have been available since the 1980s, but the use of filter-based instruments to derive information on aerosol properties (absorption coefficient and black carbon, BC) is still a matter of debate. Several workshops have been conducted to investigate the performance of individual instruments over the intervening years. Two workshops with large sets of aerosol absorption photometers were conducted in 2005 and 2007. The data from these instruments were corrected using existing methods before further analysis. The inter-comparison shows a large variation between the responses to absorbing aerosol particles for different types of instruments. The unit to unit variability between instruments can be up to 30% for Particle Soot Absorption Photometers (PSAPs) and Aethalometers. Multi Angle Absorption Photometers (MAAPs) showed a variability of less than 5%. Reasons for the high variability were identified to be variations in sample flow and spot size. It was observed that different flow rates influence system performance with respect to response to absorption and instrumental noise. Measurements with non absorbing particles showed that the current corrections of a cross sensitivity to particle scattering are not sufficient. Remaining cross sensitivities were found to be a function of the total particle load on the filter. The large variation between the response to absorbing aerosol particles for different types of instruments indicates that current correction functions for absorption photometers are not adequate.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Chemical composition of free tropospheric aerosol for PM1 and coarse mode at the high alpine site Jungfraujoch(Copernicus, 31.01.2008) Cozic, Julie; Verheggen, Bart; Weingartner, Ernest; Crosier, Jonathan; Bower, Keith N.; Flynn, Michael; Coe, Hugh; Henning, Silvia; Steinbacher, Martin; Henne, Stephan; Collaud Coen, Martine; Petzold, Andreas; Baltensperger, UrsThe chemical composition of submicron (fine mode) and supermicron (coarse mode) aerosol particles has been investigated at the Jungfraujoch high alpine research station (3580 m a.s.l., Switzerland) as part of the GAW aerosol monitoring program since 1999. A clear seasonality was observed for all major components throughout the period with low concentrations in winter (predominantly free tropospheric aerosol) and higher concentrations in summer (enhanced vertical transport of boundary layer pollutants). In addition, mass closure was attempted during intensive campaigns in March 2004, February–March 2005 and August 2005. Ionic, carbonaceous and non-refractory components of the aerosol were quantified as well as the PM1 and coarse mode total aerosol mass concentrations. A relatively low conversion factor of 1.8 for organic carbon (OC) to particulate organic matter (OM) was found in winter (February–March 2005). Organics, sulfate, ammonium, and nitrate were the major components of the fine aerosol fraction that were identified, while calcium and nitrate were the only two measured components contributing to the coarse mode. The aerosol mass concentrations for fine and coarse mode aerosol measured during the intensive campaigns were not typical of the long-term seasonality due largely to dynamical differences. Average fine and coarse mode concentrations during the intensive field campaigns were 1.7 μg m−3 and 2.4 μg m−3 in winter and 2.5 μg m−3 and 2.0 μg m−3 in summer, respectively. The mass balance of aerosols showed higher contributions of calcium and nitrate in the coarse mode during Saharan dust events (SDE) than without SDE.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Minimizing light absorption measurement artifacts of the Aethalometer. evaluation of five correction algorithms(Copernicus, 13.04.2010) Collaud Coen, Martine; Weingartner, Ernest; Apituley, Arnaud; Ceburnis, Darius; Fierz-Schmidhauser, Rahel; Flentje, Harald; Henzing, J.S.; Jennings, Stephen G.; Moerman, Marcel; Petzold, Andreas; Schmid, Otmar; Baltensperger, UrsThe aerosol light absorption coefficient is an essential parameter involved in atmospheric radiation budget calculations. The Aethalometer (AE) has the great advantage of measuring the aerosol light absorption coefficient at several wavelengths, but the derived absorption coefficients are systematically too high when compared to reference methods. Up to now, four different correction algorithms of the AE absorption coefficients have been proposed by several authors. A new correction scheme based on these previously published methods has been developed, which accounts for the optical properties of the aerosol particles embedded in the filter. All the corrections have been tested on six datasets representing different aerosol types and loadings and include multi-wavelength AE and white-light AE. All the corrections have also been evaluated through comparison with a Multi-Angle Absorption Photometer (MAAP) for four datasets lasting between 6 months and five years. The modification of the wavelength dependence by the different corrections is analyzed in detail. The performances and the limits of all AE corrections are determined and recommendations are given.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation New particle formation and ultrafine charged aerosol climatology at a high altitude site in the Alps (Jungfraujoch, 3580 m a.s.l., Switzerland)(Copernicus, 05.10.2010) Boulon, Julien; Sellegri, Karine; Venzac, Hervé; Picard, David; Weingartner, Ernest; Wehrle, Günther; Collaud Coen, Martine; Bütikofer, Rolf; Flückiger, Erwin; Baltensperger, Urs; Laj, PaoloWe investigate the formation and growth of charged aerosols clusters at Jungfraujoch, in the Swiss Alps (3580 m a.s.l.), the highest altitude site of the European EUCAARI project intensive campaign. Charged particles and clusters (0.5–1.8 nm) were measured from April 2008 to April 2009 and allowed the detection of nucleation events in this very specific environment (presence of free tropospheric air and clouds). We found that the naturally charged aerosol concentrations, which are dominated by the cluster size class, shows a strong diurnal pattern likely linked to valley breezes transporting surface layer ion precursors, presumably radon. Cosmic rays were found not to be the major ion source at the measurement site. However, at night, when air masses are more representative of free tropospheric conditions, we found that the cluster concentrations are still high. The charged aerosol size distribution and concentration are strongly influenced by the presence of clouds at the station. Clouds should be taken into account when deriving high altitude nucleation statistics. New particle formation occurs on average 17.5% of the measurement period and shows a weak seasonality with a minimum of frequency during winter, but this seasonality is enhanced when the data set is screened for periods when the atmospheric station is out of clouds. The role of ions in the nucleation process was investigated and we found that the ion-mediated nucleation explains 22.3% of the particle formation. The NPF events frequency is correlated with UV radiation but not with calculated H2SO4 concentrations, suggesting that other compounds such as organic vapors are involved in the nucleation and subsequently growth process. In fact, NPF events frequency also surprisingly increases with the condensational sink (CS), suggesting that at Jungfraujoch, the presence of condensing vapours probably coupled with high CS are driving the occurrence of NPF events. A strong link to the air mass path was also pointed out and events were observed to be frequently occurring in Eastern European air masses, which present the highest condensational sink. In these air masses, pre-existing cluster concentrations are more than three time larger than in other air masses during event days, and no new clusters formation is observed, contrarily to what is happening in other air mass types.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Aerosol climatology and planetary boundary influence at the Jungfraujoch analyzed by synoptic weather types(Copernicus, 23.06.2011) Collaud Coen, Martine; Weingartner, Ernest; Furger, Markus; Nyeki, Stephan; Prévôt, André S. H.; Steinbacher, Matjaz; Baltensperger, UrsFourteen years of meteorological parameters, aerosol variables (absorption and scattering coef-ficients, aerosol number concentration) and trace gases (CO, NOx, SO2) measured at the Jungfraujoch (JFJ, 3580 m a.s.l.) have been analyzed as a function of different synoptic weather types. The Schüepp synoptic weather type of the Alps (SYNALP) classification from the Alpine Weather Statistics (AWS) was used to define the synoptic meteorology over the whole Swiss region. The seasonal contribution of each synoptic weather type to the aerosol concentration was deduced from the aerosol annual cycles while the planetary boundary layer (PBL) influence was estimated by means of the diurnal cycles. Since aerosols are scavenged by precipitation, the diurnal cycle of the CO concentration was also used to identify polluted air masses. SO2 and NOx concentrations were used as precursor tracers for new particle formation and growth, respectively. The aerosol optical parameters and number concentration show elevated loadings during advective weather types during the December–March period and for the convective anti-cyclonic and convective indifferent weather types during the April–September period. This study confirms the consensus view that the JFJ is mainly influenced by the free troposphere during winter and by injection of air parcels from the PBL during summer. A more detailed picture is, however, drawn where the JFJ is completely influenced by free tropospheric air masses in win-ter during advective weather types and largely influenced by the PBL also during the night in summer during the subsidence weather type. Between these two extreme situations, the PBL influence at the JFJ depends on both the time of year and the synoptic weather type. The frac-tion of PBL air transported to the JFJ was estimated by the relative increase of the specific hu-midity and CO.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Spatial variation of aerosol optical properties around the high-alpine site Jungfraujoch (3580 m a.s.l.)(Copernicus, 08.08.2012) Zieger, Paul; Kienast-Sjögren, Erika; Starace, Michela; von Bismarck, Jonas; Bukowiecki, Nicolas; Baltensperger, Urs; Wienhold, Frank Gunther; Peter, Thomas; Ruhtz, Thomas; Collaud Coen, Martine; Vuilleumier, Laurent; Maier, Olaf; Emili, Emanuele; Popp, Christian; Weingartner, ErnestThis paper presents results of the extensive field campaign CLACE 2010 (Cloud and Aerosol Characterization Experiment) performed in summer 2010 at the Jungfraujoch (JFJ) and the Kleine Scheidegg (KLS) in the Swiss Alps. The main goal of this campaign was to investigate the vertical variability of aerosol optical properties around the JFJ and to show the consistency of the different employed measurement techniques considering explicitly the effects of relative humidity (RH) on the aerosol light scattering. Various aerosol optical and microphysical parameters were recorded using in-situ and remote sensing techniques. In-situ measurements of aerosol size distribution, light scattering, light absorption and scattering enhancement due to water uptake were performed at the JFJ at 3580 m a.s.l.. A unique set-up allowed remote sensing measurements of aerosol columnar and vertical properties from the KLS located about 1500 m below and within the line of sight to the JFJ (horizontal distance of approx. 4.5 km). In addition, two satellite retrievals from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) as well as back trajectory analyses were added to the comparison to account for a wider geographical context. All in-situ and remote sensing measurements were in clear correspondence. The ambient extinction coefficient measured in situ at the JFJ agreed well with the KLS-based LIDAR (Light Detection and Ranging) retrieval at the altitude-level of the JFJ under plausible assumptions on the LIDAR ratio. However, we can show that the quality of this comparison is affected by orographic effects due to the exposed location of the JFJ on a saddle between two mountains and next to a large glacier. The local RH around the JFJ was often higher than in the optical path of the LIDAR measurement, especially when the wind originated from the south via the glacier, leading to orographic clouds which remained lower than the LIDAR beam. Furthermore, the dominance of long-range transported Saharan dust was observed in all easurements for several days, however only for a shorter time period in the in-situ measurements due to the vertical structure of the dust plume. The optical properties of the aerosol column retrieved from SEVIRI and MODIS showed the same magnitude and a similar temporal evolution as the measurements at the KLS and the JFJ. Remaining differences are attributed to the complex terrain and simplifications in the aerosol retrieval scheme in general.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Investigation of the planetary boundary layer in the Swiss Alps using remote sensing and in situ measurements(Springer, 2014) Ketterer, Christine; Zieger, Paul; Bukowiecki, Nicolas; Collaud Coen, Martine; Maier, Olaf; Ruffieux, Dominique; Weingartner, Ernest01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Aerosol decadal trends – Part 1. In-situ optical measurements at GAW and IMPROVE stations(Copernicus, 2013) Collaud Coen, Martine; Andrews, Elisabeth; Asmi, Ari; Baltensperger, Urs; Bukowiecki, Nicolas; Day, Derek; Fiebig, Markus; Fjaeraa, Ann Mari; Flentje, Harald; Hyvärinen, Antti-Pekka; Jefferson, Anne; Jennings, Stephen G.; Kouvarakis, Giorgos; Lihavainen, Heikki; Lund Myhre, Cathrine; Malm, William; Mihalopoulos, Nikolaos; Molenar, John; O'Dowd, Colin; Ogren, John A.; Schichtel, Bret; Sheridan, Patrick; Virkkula, Aki; Weingartner, Ernest; Weller, Rolf; Laj, PaoloCurrently many ground-based atmospheric stations include in-situ measurements of aerosol physical and optical properties, resulting in more than 20 long-term (> 10 yr) aerosol measurement sites in the Northern Hemisphere and Antarctica. Most of these sites are located at remote locations and monitor the aerosol particle number concentration, wavelength-dependent light scattering, backscattering, and absorption coefficients. The existence of these multi-year datasets enables the analysis of long-term trends of these aerosol parameters, and of the derived light scattering Ångström exponent and backscatter fraction. Since the aerosol variables are not normally distributed, three different methods (the seasonal Mann-Kendall test associated with the Sen's slope, the generalized least squares fit associated with an autoregressive bootstrap algorithm for confidence intervals, and the least-mean square fit applied to logarithms of the data) were applied to detect the long-term trends and their magnitudes. To allow a comparison among measurement sites, trends on the most recent 10 and 15 yr periods were calculated. No significant trends were found for the three continental European sites. Statistically significant trends were found for the two European marine sites but the signs of the trends varied with aerosol property and location. Statistically significant decreasing trends for both scattering and absorption coefficients (mean slope of −2.0% yr−1) were found for most North American stations, although positive trends were found for a few desert and high-altitude sites. The difference in the timing of emission reduction policy for the Europe and US continents is a likely explanation for the decreasing trends in aerosol optical parameters found for most American sites compared to the lack of trends observed in Europe. No significant trends in scattering coefficient were found for the Arctic or Antarctic stations, whereas the Arctic station had a negative trend in absorption coefficient. The high altitude Pacific island station of Mauna Loa presents positive trends for both scattering and absorption coefficients.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Aerosol decadal trends – Part 2. In-situ aerosol particle number concentrations at GAW and ACTRIS stations(Copernicus, 2013) Asmi, Ari; Collaud Coen, Martine; Ogren, John A.; Andrews, Elisabeth; Sheridan, Patrick; Jefferson, Anne; Weingartner, Ernest; Baltensperger, Urs; Bukowiecki, Nicolas ; Lihavainen, Heikki; Kivekäs, Niku; Asmi, Eija; Aalto, Pasi Pekka; Kulmala, Markku; Wiedensohler, Alfred; Birmili, Wolfram; Hamed, Amar; O'Dowd, Colin; Jennings, Stephen G.; Weller, Rolf; Flentje, Harald; Fjaeraa, Ann Mari; Fiebig, Markus; Myhre, Cathrine Lund; Hallar, Anna Gannet; Swietlicki, Erik; Kristensson, Adam; Laj, PaoloWe have analysed the trends of total aerosol particle number concentrations (N) measured at long-term measurement stations involved either in the Global Atmosphere Watch (GAW) and/or EU infrastructure project ACTRIS. The sites are located in Europe, North America, Antarctica, and on Pacific Ocean islands. The majority of the sites showed clear decreasing trends both in the full-length time series, and in the intra-site comparison period of 2001–2010, especially during the winter months. Several potential driving processes for the observed trends were studied, and even though there are some similarities between N trends and air temperature changes, the most likely cause of many northern hemisphere trends was found to be decreases in the anthropogenic emissions of primary particles, SO2 or some co-emitted species. We could not find a consistent agreement between the trends of N and particle optical properties in the few stations with long time series of all of these properties. The trends of N and the proxies for cloud condensation nuclei (CCN) were generally consistent in the few European stations where the measurements were available. This work provides a useful comparison analysis for modelling studies of trends in aerosol number concentrations.01A - Beitrag in wissenschaftlicher Zeitschrift