Weingartner, Ernest
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Weingartner, Ernest
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- PublikationNew particle formation in the free troposphere. A question of chemistry and timing(American Association for the Advancement of Science, 2016) Bianchi, Federico; Tröstl, Jasmin; Junninen, Heikki; Frege, Carla; Henne, Stephan; Hoyle, Christopher R.; Molteni, Ugo; Herrmann, Erik; Adamov, Alexey; Bukowiecki, Nicolas; Chen, Xuemeng; Duplissy, Jonathan; Gysel, Martin; Hutterli, Manuel; Kangasluoma, Juha; Kontkanen, Jenni; Kürten, Andreas; Manninen, Hanna E.; Münch, Steffen; Peräkylä, Otso; Petäjä, Tuukka; Rondo, Linda; Williamson, Christina; Weingartner, Ernest; Curtius, Joachim; Worsnop, Douglas R.; Kulmala, Markku; Dommen, Josef; Baltensperger, Urs [in: Science]From neutral to new Many of the particles in the troposphere are formed in situ, but what fraction of all tropospheric particles do they constitute and how exactly are they made? Bianchi et al report results from a high-altitude research station. Roughly half of the particles were newly formed by the condensation of highly oxygenated multifunctional compounds. A combination of laboratory results, field measurements, and model calculations revealed that neutral nucleation is more than 10 times faster than ion-induced nucleation, that particle growth rates are size-dependent, and that new particle formation occurs during a limited time window.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationContribution 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
- PublikationA 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
- PublikationChemical 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
- PublikationStudying the vertical aerosol extinction coefficient by comparing in situ airborne data and elastic backscatter lidar(Copernicus, 2016) Rosati, Bernadette; Herrmann, Erik; Bucci, Silvia; Fierli, Federico; Cairo, Francesco; Gysel, Martin; Tillmann, Ralf; Größ, Johannes; Gobbi, Gian Paolo; Di Liberto, Luca; Di Donfrancesco, Guido; Wiedensohler, Alfred; Weingartner, Ernest; Virtanen, Annele; Mentel, Thomas F.; Baltensperger, Urs [in: Atmospheric Chemistry and Physics]Vertical profiles of aerosol particle optical properties were explored in a case study near the San Pietro Capofiume (SPC) ground station during the PEGASOS Po Valley campaign in the summer of 2012. A Zeppelin NT airship was employed to investigate the effect of the dynamics of the planetary boundary layer at altitudes between ∼ 50 and 800 m above ground. Determined properties included the aerosol particle size distribution, the hygroscopic growth factor, the effective index of refraction and the light absorption coefficient. The first three parameters were used to retrieve the light scattering coefficient. Simultaneously, direct measurements of both the scattering and absorption coefficient were carried out at the SPC ground station. Additionally, a single wavelength polarization diversity elastic lidar system provided estimates of aerosol extinction coefficients using the Klett method to accomplish the inversion of the signal, for a vertically resolved comparison between in situ and remote-sensing results. Note, however, that the comparison was for the most part done in the altitude range where the overlap function is incomplete and accordingly uncertainties are larger. First, the airborne results at low altitudes were validated with the ground measurements. Agreement within approximately ±25 and ±20 % was found for the dry scattering and absorption coefficient, respectively. The single scattering albedo, ranged between 0.83 and 0.95, indicating the importance of the absorbing particles in the Po Valley region. A clear layering of the atmosphere was observed during the beginning of the flight (until ∼ 10:00 LT – local time) before the mixing layer (ML) was fully developed. Highest extinction coefficients were found at low altitudes, in the new ML, while values in the residual layer, which could be probed at the beginning of the flight at elevated altitudes, were lower. At the end of the flight (after ∼ 12:00 LT) the ML was fully developed, resulting in constant extinction coefficients at all altitudes measured on the Zeppelin NT. Lidar estimates captured these dynamic features well and good agreement was found for the extinction coefficients compared to the in situ results, using fixed lidar ratios (LR) between 30 and 70 sr for the altitudes probed with the Zeppelin. These LR are consistent with values for continental aerosol particles that can be expected in this region.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationAnalysis of long‐term aerosol size distribution data from Jungfraujoch with emphasis on free tropospheric conditions, cloud influence, and air mass transport(Wiley, 2015) Herrmann, Erik; Weingartner, Ernest; Henne, Stephan; Vuilleumier, Laurent; Bukowiecki, Nicolas; Steinbacher, Martin; Conen, Franz; Collaud Coen, Martine; Hammer, Emanuel; Jurányi, Zsófia; Baltensperger, Urs; Gysel, Martin [in: Journal of Geophysical Research: Atmospheres]Six years of aerosol size distribution measurements between 20 and 600 nm diameters and total aerosol concentration above 10 nm from March 2008 to February 2014 at the high‐alpine site Jungfraujoch are presented. The size distribution was found to be typically bimodal with mode diameters and widths relatively stable throughout the year and the observation period. New particle formation was observed on 14.5% of all days without a seasonal preference. Particles typically grew only into the Aitken mode and did not reach cloud condensation nucleus (CCN) sizes on the time scale of several days. Growth of preexisting particles in the Aitken mode, on average, contributed very few CCN. We concluded that the dominant fraction of CCN at Jungfraujoch originated in the boundary layer. A number of approaches were used to distinguish free tropospheric (FT) conditions and episodes with planetary boundary layer (PBL) influence. In the absence of PBL injections, the concentration of particles larger than 90 nm (N90, roughly corresponding to the CCN concentration) reached a value ~40 cm−3 while PBL influence caused N90 concentrations of several hundred or even 1000 cm−3. Comparing three criteria for free tropospheric conditions, we found FT prevalence for 39% of the time with over 60% during winter and below 20% during summer. It is noteworthy that a simple criterion based on standard trace gas measurements appeared to outperform alternative approaches.01A - Beitrag in wissenschaftlicher Zeitschrift