Weingartner, Ernest

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Ernest
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Weingartner, Ernest

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2003 - 200912010 - 201816
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  • Vorschaubild
    Publikation
    A European aerosol phenomenology - 6. Scattering properties of atmospheric aerosol particles from 28 ACTRIS sites
    (Copernicus, 2018) Pandolfi, Marco; Alados-Arboledas, Lucas; Alastuey, Andrés; Andrade, Marcos; Angelov, Christo; Artiñano, Begoña; Backman, John; Baltensperger, Urs; Bonasoni, Paolo; Bukowiecki, Nicolas; Collaud Coen, Martine; Conil, Sébastien; Coz, Esther; Crenn, Vincent; Dudoitis, Vadimas; Ealo, Marina; Eleftheriadis, Kostas; Favez, Olivier; Fetfatzis, Prodromos; Fiebig, Markus; Flentje, Harald; Ginot, Patrick; Gysel, Martin; Henzing, Bas; Hoffer, Andras; Holubova Smejkalova, Adela; Kalapov, Ivo; Kalivitis, Nikos; Kouvarakis, Giorgos; Kristensson, Adam; Kulmala, Markku; Lihavainen, Heikki; Lunder, Chris; Luoma, Krista; Lyamani, Hassan; Marinoni, Angela; Mihalopoulos, Nikolaos; Moerman, Marcel; Nicolas, José; O'Dowd, Colin D.; Petäjä, Tuukka; Petit, Jean-Eudes; Pichon, Jean Marc; Prokopciuk, Nina; Putaud, Jean-Philippe; Rodríguez, Sergio; Sciare, Jean; Sellegri, Karine; Swietlicki, Erik; Titos, Gloria; Tuch, Thomas; Tunved, Peter; Ulevicius, Vidmantas; Vaishya, Aditya; Vana, Milan; Virkkula, Aki; Vratolis, Stergios; Weingartner, Ernest; Wiedensohler, Alfred; Laj, Paolo [in: Atmospheric Chemistry and Physics]
    This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (σsp) and hemispheric backscattering (σbsp) coefficients, scattering Ångström exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of σsp is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, σsp also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intra-annual variability. At mountain sites, higher σsp and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher σsp values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low σsp values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high σsp values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of σsp are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of σsp are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    A European aerosol phenomenology-5. Climatology of black carbon optical properties at 9 regional background sites across Europe
    (Elsevier, 2016) Zanatta, Marco; Gysel, Martin; Bukowiecki, Nicolas; Müller, Thomas; Weingartner, Ernest; Areskoug, Hans; Fiebig, Markus; Yttri, Karl Espen; Mihalopoulos, Nikolaos; Kouvarakis, Giorgos; Beddows, David; Harrison, Roy; Cavalli, Fabrizia; Putaud, Jean; Spindler, Gerald; Wiedensohler, Alfred; Alastuey, Andrés; Pandolfi, Marco; Sellegri, Karine; Swietlicki, Erik; Jaffrezo, Jean-Luc; Baltensperger, Urs; Laj, Paolo [in: Atmospheric Environment]
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Contribution of new particle formation to the total aerosol concentration at the high‐altitude site Jungfraujoch (3580 m asl, Switzerland)
    (Wiley, 2016) Tröstl, Jasmin; Herrmann, Erik; Frege, Carla; Bianchi, Federico; Molteni, Ugo; Bukowiecki, Nicolas; Hoyle, Christopher R.; Steinbacher, Martin; Weingartner, Ernest; Dommen, Josef; Gysel, Martin; Baltensperger, Urs [in: Journal of Geophysical Research: Atmospheres]
    Previous modeling studies hypothesized that a large fraction of cloud condensation nuclei (CCN) is attributed to new particle formation (NPF) in the free troposphere. Despite the potential importance of this process, only few long‐term observations have been performed to date. Here we present the results of a 12 month campaign of NPF observations at the high‐altitude site Jungfraujoch (JFJ, 3580 m above sea level (asl)). Our results show that NPF significantly adds to the total aerosol concentration at the JFJ and only occurs via previous precursor entrainment from the planetary boundary layer (PBL). Freshly nucleated particles do not directly grow to CCN size (90 nm) within observable time scales (maximum 48 h). The contribution of NPF to the CCN concentration is low within this time frame compared to other sources, such as PBL entrainment of larger particles. A multistep growth mechanism is proposed which allows previously formed Aitken mode particles to add to the CCN concentration. A parametrization is derived to explain formation rates at the JFJ, showing that precursor concentration, PBL influence, and global radiation are the key factors controlling new particle formation at the site.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    A review of more than 20 years of aerosol observation at the high altitude research station Jungfraujoch, Switzerland (3580 m asl)
    (Taiwan Association for Aerosol Research, 2016) Bukowiecki, Nicolas; Weingartner, Ernest; Gysel, Martin; Coen, Martine Collaud; Zieger, Paul; Herrmann, Erik; Steinbacher, Martin; Gäggeler, Heinz W.; Baltensperger, Urs [in: Aerosol and Air Quality Research]
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Chemical and physical influences on aerosol activation in liquid clouds. A study based on observations from the Jungfraujoch, Switzerland
    (Copernicus, 2016) Hoyle, Christopher R.; Webster, Clare S.; Rieder, Harald E.; Nenes, Athanasios; Hammer, Emanuel; Herrmann, Erik; Gysel, Martin; Bukowiecki, Nicolas; Weingartner, Ernest; Steinbacher, Martin; Baltensperger, Urs [in: Atmospheric Chemistry and Physics]
    A simple statistical model to predict the number of aerosols which activate to form cloud droplets in warm clouds has been established, based on regression analysis of data from four summertime Cloud and Aerosol Characterisation Experiments (CLACE) at the high-altitude site Jungfraujoch (JFJ). It is shown that 79 % of the observed variance in droplet numbers can be represented by a model accounting only for the number of potential cloud condensation nuclei (defined as number of particles larger than 80 nm in diameter), while the mean errors in the model representation may be reduced by the addition of further explanatory variables, such as the mixing ratios of O3, CO, and the height of the measurements above cloud base. The statistical model has a similar ability to represent the observed droplet numbers in each of the individual years, as well as for the two predominant local wind directions at the JFJ (northwest and southeast). Given the central European location of the JFJ, with air masses in summer being representative of the free troposphere with regular boundary layer in-mixing via convection, we expect that this statistical model is generally applicable to warm clouds under conditions where droplet formation is aerosol limited (i.e. at relatively high updraught velocities and/or relatively low aerosol number concentrations). A comparison between the statistical model and an established microphysical parametrization shows good agreement between the two and supports the conclusion that cloud droplet formation at the JFJ is predominantly controlled by the number concentration of aerosol particles.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Sensitivity estimations for cloud droplet formation in the vicinity of the high-alpine research station Jungfraujoch (3580 m a.s.l.)
    (Copernicus, 2015) Hammer, Emanuel; Bukowiecki, Nicolas; Luo, Beiping; Lohmann, Ulrike; Marcolli, Claudia; Weingartner, Ernest; Baltensperger, Urs; Hoyle, Christopher R. [in: Atmospheric Chemistry and Physics]
    Aerosol radiative forcing estimates suffer from large uncertainties as a result of insufficient understanding of aerosol–cloud interactions. The main source of these uncertainties is dynamical processes such as turbulence and entrainment but also key aerosol parameters such as aerosol number concentration and size distribution, and to a much lesser extent, the composition. From June to August 2011 a Cloud and Aerosol Characterization Experiment (CLACE2011) was performed at the high-alpine research station Jungfraujoch (Switzerland, 3580 m a.s.l.) focusing on the activation of aerosol to form liquid-phase clouds (in the cloud base temperature range of −8 to 5 °C). With a box model the sensitivity of the effective peak supersaturation (SSpeak), an important parameter for cloud activation, to key aerosol and dynamical parameters was investigated. The updraft velocity, which defines the cooling rate of an air parcel, was found to have the greatest influence on SSpeak. Small-scale variations in the cooling rate with large amplitudes can significantly alter CCN activation. Thus, an accurate knowledge of the air parcel history is required to estimate SSpeak. The results show that the cloud base updraft velocities estimated from the horizontal wind measurements made at the Jungfraujoch can be divided by a factor of approximately 4 to get the updraft velocity required for the model to reproduce the observed SSpeak. The aerosol number concentration and hygroscopic properties were found to be less important than the aerosol size in determining SSpeak. Furthermore turbulence is found to have a maximum influence when SSpeak is between approximately 0.2 and 0.4 %. Simulating the small-scale fluctuations with several amplitudes, frequencies and phases, revealed that independently of the amplitude, the effect of the frequency on SSpeak shows a maximum at 0.46 Hz (median over all phases) and at higher frequencies, the maximum SSpeak decreases again.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    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, Ernest [in: Boundary-Layer Meteorology]
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Investigation of the effective peak supersaturation for liquid-phase clouds at the high-alpine site Jungfraujoch, Switzerland (3580 m a.s.l.)
    (Copernicus, 2014) Hammer, Emanuel; Bukowiecki, Nicolas; Gysel, Martin; Jurányi, Zsófia; Hoyle, Christopher R.; Vogt, Roland; Baltensperger, Urs; Weingartner, Ernest [in: Atmospheric Chemistry and Physics]
    Aerosols influence the Earth's radiation budget directly through absorption and scattering of solar radiation in the atmosphere but also indirectly by modifying the properties of clouds. However, climate models still suffer from large uncertainties as a result of insufficient understanding of aerosol-cloud interactions. At the high altitude research station Jungfraujoch (JFJ; 3580 m a.s.l., Switzerland) cloud condensation nuclei (CCN) number concentrations at eight different supersaturations (SS) from 0.24% to 1.18% were measured using a CCN counter during Summer 2011. Simultaneously, in-situ aerosol activation properties of the prevailing ambient clouds were investigated by measuring the total and interstitial (non-activated) dry particle number size distributions behind two different inlet systems. Combining all experimental data, a new method was developed to retrieve the so-called effective peak supersaturation SSpeak, as a measure of the SS at which ambient clouds are formed. A 17-month CCN climatology was then used to retrieve the SSpeak values also for four earlier summer campaigns (2000, 2002, 2004 and 2010) where no direct CCN data were available. The SSpeak values varied between 0.01% and 2.0% during all campaigns. An overall median SSpeak of 0.35% and dry activation diameter of 87 nm was observed. It was found that the difference in topography between northwest and southeast plays an important role for the effective peak supersaturation in clouds formed in the vicinity of the JFJ, while differences in the number concentration of potential CCN only play a minor role. Results show that air masses coming from the southeast (with the slowly rising terrain of the Aletsch Glacier) generally experience lower SSpeak values than air masses coming from the northwest (steep slope). The observed overall median values were 0.41% and 0.22% for northwest and southeast wind conditions, respectively, corresponding to literature values for cumulus clouds and shallow-layer clouds. These cloud types are consistent with weather observations routinely performed at the JFJ.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Size-dependent particle activation properties in fog during the ParisFog 2012/13 field campaign
    (Copernicus, 2014) Hammer, Emanuel; Gysel, Martin; Roberts, Greg; Elias, Thierry; Hofer, Julian; Hoyle, Christopher R.; Bukowiecki, Nicolas; Dupont, Jean-Charles; Burnet, Frederic; Baltensperger, Urs; Weingartner, Ernest [in: Atmospheric Chemistry and Physics]
    Fog-induced visibility reduction is responsible for a variety of hazards in the transport sector. Therefore there is a large demand for an improved understanding of fog formation and thus improved forecasts. Improved fog forecasts require a better understanding of the numerous complex mechanisms during the fog life cycle. During winter 2012/13 a field campaign called ParisFog aiming at fog research took place at SIRTA (Instrumented Site for Atmospheric Remote Sensing Research). SIRTA is located about 20 km southwest of the Paris city center, France, in a semi-urban environment. In situ activation properties of the prevailing fog were investigated by measuring (1) total and interstitial (non-activated) dry particle number size distributions behind two different inlet systems; (2) interstitial hydrated aerosol and fog droplet size distributions at ambient conditions; and (3) cloud condensation nuclei (CCN) number concentration at different supersaturations (SS) with a CCN counter. The aerosol particles were characterized regarding their hygroscopic properties, fog droplet activation behavior and contribution to light scattering for 17 developed fog events. Low particle hygroscopicity with an overall median of the hygroscopicity parameter, κ, of 0.14 was found, likely caused by substantial influence from local traffic and wood burning emissions. Measurements of the aerosol size distribution at ambient RH revealed that the critical wet diameter, above which the hydrated aerosols activate to fog droplets, is rather large (with a median value of 2.6μm) and is highly variable (ranging from 1 to 5μm) between the different fog events. Thus, the number of activated fog droplets was very small and the non-activated hydrated particles were found to contribute significantly to the observed light scattering and thus to the reduction in visibility. Combining all experimental data, the effective peak supersaturation, SSpeak, a measure of the peak supersaturation during the fog formation, was determined. The median SSpeak value was estimated to be in the range from 0.031 to 0.046% (upper and lower limit estimations), which is in good agreement with previous experimental and modeling studies of fog.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Variations in tropospheric submicron particle size distributions across the European continent 2008–2009
    (Copernicus, 2014) Beddows, David; Dall'Osto, Manuel; Harrison, Roy; Kulmala, Markku; Asmi, Ari; Wiedensohler, Alfred; Laj, Paolo; Fjaeraa, Ann Mari; Sellegri, Karine; Birmili, Wolfram; Bukowiecki, Nicolas; Weingartner, Ernest; Baltensperger, Urs; Zdimal, Vladimir; Zikova, Nadezda; Putaud, Jean-Philippe; Marinoni, Angela; Tunved, Peter; Hansson, Hans-Christen; Fiebig, Markus; Kivekäs, Niku; Swietlicki, Erik; Lihavainen, Heikki; Asmi, Eija; Ulevicius, Vidmantas; Aalto, Pasi Pekka; Mihalopoulos, Nikolaos; Kalivitis, Nikos; Kalapov, Ivo; Kiss, Gyula; de Leeuw, Gerrit; Henzing, Bas; O'Dowd, Colin; Jennings, Stephen G.; Flentje, Harald; Meinhardt, Frank; Ries, Ludwig; Denier van der Gon, Hugo; Visschedijk, Antoon [in: Atmospheric Chemistry and Physics]
    Cluster~analysis of particle number size distributions from~background sites across Europe~is presented. This generated a total of nine clusters of particle size distributions which could be further combined into two main groups, namely: a south-to-north category (four clusters) and a west-to-east category (five clusters). The first group was identified as most frequently being detected inside and around northern Germany and neighbouring countries, showing clear evidence of local afternoon nucleation and growth events that could be linked to movement of air masses from south to north arriving ultimately at the Arctic contributing to Arctic haze.~The second group of particle size spectra proved to have narrower size distributions and collectively showed a dependence of modal diameter upon the longitude of the site (west to east) at which they were most frequently detected.~These clusters indicated regional nucleation (at the coastal sites) growing to larger modes further inland. The apparent growth rate of the modal diameter was around 0.6–0.9 nm h−1. Four specific air mass back-trajectories were successively taken as case studies to examine in real time the evolution of aerosol size distributions across Europe. ~While aerosol growth processes can be observed as aerosol traverses Europe, the processes are often obscured by the addition of aerosol by emissions en route. This study revealed that some of the 24 stations exhibit more complex behaviour than others, especially when impacted by local sources or a variety of different air masses. Overall, the aerosol size distribution clustering analysis greatly simplifies the complex data set and allows a description of aerosol aging processes, which reflects the longer-term average development of particle number size distributions as air masses advect across Europe.
    01A - Beitrag in wissenschaftlicher Zeitschrift