Auflistung nach Autor:in "Mihalopoulos, Nikolaos"

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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
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
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
01A - Beitrag in wissenschaftlicher Zeitschrift
A synthesis of cloud condensation nuclei counter (CCNC) measurements within the EUCAARI network
(Copernicus, 2015) Paramonov, Mikhail; Kerminen, Veli-Matti; Gysel, Martin; Aalto, Pasi Pekka; Andreae, Meinrat O.; Asmi, Eija; Baltensperger, Urs; Bougiatioti, Aikaterini; Brus, David; Frank, Göran; Good, Nicholas; Gunthe, Sachin S.; Hao, Liqing; Irwin, Martin; Jaatinen, Antti; Jurányi, Zsófia; King, S. M.; Kortelainen, Aki; Kristensson, Adam; Lihavainen, Heikki; Kulmala, Markku; Lohmann, Ulrike; Martin, Scot T.; McFiggans, Gordon; Mihalopoulos, Nikolaos; Nenes, Athanasios; O'Dowd, Colin D.; Ovadnevaite, Jurgita; Petäjä, Tuukka; Pöschl, Ulrich; Roberts, Greg; Rose, Diana; Svenningsson, Birgitta; Swietlicki, Erik; Weingartner, Ernest; Whitehead, James; Wiedensohler, Alfred; Wittbom, Cerina; Sierau, Berko
Cloud condensation nuclei counter (CCNC) measurements performed at 14 locations around the world within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) framework have been analysed and discussed with respect to the cloud condensation nuclei (CCN) activation and hygroscopic properties of the atmospheric aerosol. The annual mean ratio of activated cloud condensation nuclei (NCCN) to the total number concentration of particles (NCN), known as the activated fraction A, shows a similar functional dependence on supersaturation S at many locations – exceptions to this being certain marine locations, a free troposphere site and background sites in south-west Germany and northern Finland. The use of total number concentration of particles above 50 and 100 nm diameter when calculating the activated fractions (A50 and A100, respectively) renders a much more stable dependence of A on S; A50 and A100 also reveal the effect of the size distribution on CCN activation. With respect to chemical composition, it was found that the hygroscopicity of aerosol particles as a function of size differs among locations. The hygroscopicity parameter κ decreased with an increasing size at a continental site in south-west Germany and fluctuated without any particular size dependence across the observed size range in the remote tropical North Atlantic and rural central Hungary. At all other locations κ increased with size. In fact, in Hyytiälä, Vavihill, Jungfraujoch and Pallas the difference in hygroscopicity between Aitken and accumulation mode aerosol was statistically significant at the 5 % significance level. In a boreal environment the assumption of a size-independent κ can lead to a potentially substantial overestimation of NCCN at S levels above 0.6 %. The same is true for other locations where κ was found to increase with size. While detailed information about aerosol hygroscopicity can significantly improve the prediction of NCCN, total aerosol number concentration and aerosol size distribution remain more important parameters. The seasonal and diurnal patterns of CCN activation and hygroscopic properties vary among three long-term locations, highlighting the spatial and temporal variability of potential aerosol–cloud interactions in various environments.
01A - Beitrag in wissenschaftlicher Zeitschrift
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, Paolo
Currently 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 Zeitschrift
EUCAARI ion spectrometer measurements at 12 European sites – analysis of new particle formation events
(Copernicus, 25.08.2010) Manninen, Hanna E.; Nieminen, Tuomo; Asmi, Eija; Gagné, Stéphanie; Häkkinen, Silja; Lehtipalo, Katrianne; Aalto, Pasi Pekka; Vana, Marko; Mirme, Aadu; Mirme, Sander; Hõrrak, Urmas; Plass-Dülmer, Christian; Stange, Gert; Kiss, Gyula; Hoffer, András; Törő, N.; Moerman, Marcel; Henzing, Bas; de Leeuw, Gerrit; Brinkenberg, Marcel; Kouvarakis, Giorgos N.; Bougiatioti, Aikaterini; Mihalopoulos, Nikolaos; O'Dowd, Colin D.; Ceburnis, Darius; Arneth, Almut; Svenningsson, Brigitta; Swietlicki, Erik; Tarozzi, Leone; Decesari, Stefano; Facchini, Maria Cristina; Birmili, Wolfram; Sonntag, André; Wiedensohler, Alfred; Boulon, Julien; Sellegri, Karine; Laj, Paolo; Gysel, Martin; Bukowiecki, Nicolas; Weingartner, Ernest; Wehrle, Günther; Laaksonen, Ari; Hamed, Amar; Joutsensaari, Jorma; Petäjä, Tuukka; Kerminen, Veli-Matti; Kulmala, Markku
We present comprehensive results on continuous atmospheric cluster and particle measurements in the size range ~1–42 nm within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) project. We focused on characterizing the spatial and temporal variation of new particle formation events and relevant particle formation parameters across Europe. Different types of air ion and cluster mobility spectrometers were deployed at 12 field sites across Europe from March 2008 to May 2009. The measurements were conducted in a wide variety of environments, including coastal and continental locations as well as sites at different altitudes (both in the boundary layer and the free troposphere). New particle formation events were detected at all of the 12 field sites during the year-long measurement period. From the data, nucleation and growth rates of newly formed particles were determined for each environment. In a case of parallel ion and neutral cluster measurements, we could also estimate the relative contribution of ion-induced and neutral nucleation to the total particle formation. The formation rates of charged particles at 2 nm accounted for 1–30% of the corresponding total particle formation rates. As a significant new result, we found out that the total particle formation rate varied much more between the different sites than the formation rate of charged particles. This work presents, so far, the most comprehensive effort to experimentally characterize nucleation and growth of atmospheric molecular clusters and nanoparticles at ground-based observation sites on a continental scale.
01A - Beitrag in wissenschaftlicher Zeitschrift
Number size distributions and seasonality of submicron particles in Europe 2008–2009
(Copernicus, 15.06.2011) Asmi, Ari; Wiedensohler, Alfred; Laj, Paolo; Fjaeraa, Ann Mari; Sellegri, Karine; Birmili, Wolfram; Weingartner, Ernest; Baltensperger, Urs; Zdimal, Vladimir; Zikova, Nadezda; Putaud, Jean-Philippe; Marinoni, Angela; Tunved, Peter; Hansson, Hans-Christen; Fiebig, Markus; Kivekäs, Niku; Lihavainen, Heikki; Asmi, Eija; Ulevicius, Vidmantas; Aalto, Pasi Pekka; Swietlicki, Erik; Kristensson, Adam; Mihalopoulos, Nikolaos; Kalivitis, Nikos; Kalapov, Ivo; Kiss, Gyula; de Leeuw, Gerrit; Henzing, Bas; Harrison, Roy; Beddows, David; O'Dowd, Colin; Jennings, Stephen G.; Flentje, Harald; Weinhold, Kay; Meinhardt, Frank; Ries, Ludwig; Kulmala, Markku
Two years of harmonized aerosol number size distribution data from 24 European field monitoring sites have been analysed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle diameter. Spatial and temporal distribution of aerosols in the particle sizes most important for climate applications are presented. We also analyse the annual, weekly and diurnal cycles of the aerosol number concentrations, provide log-normal fitting parameters for median number size distributions, and give guidance notes for data users. Emphasis is placed on the usability of results within the aerosol modelling community. We also show that the aerosol number concentrations of Aitken and accumulation mode particles (with 100 nm dry diameter as a cut-off between modes) are related, although there is significant variation in the ratios of the modal number concentrations. Different aerosol and station types are distinguished from this data and this methodology has potential for further categorization of stations aerosol number size distribution types. The European submicron aerosol was divided into characteristic types: Central European aerosol, characterized by single mode median size distributions, unimodal number concentration histograms and low variability in CCN-sized aerosol number concentrations; Nordic aerosol with low number concentrations, although showing pronounced seasonal variation of especially Aitken mode particles; Mountain sites (altitude over 1000 m a.s.l.) with a strong seasonal cycle in aerosol number concentrations, high variability, and very low median number concentrations. Southern and Western European regions had fewer stations, which decreases the regional coverage of these results. Aerosol number concentrations over the Britain and Ireland had very high variance and there are indications of mixed air masses from several source regions; the Mediterranean aerosol exhibit high seasonality, and a strong accumulation mode in the summer. The greatest concentrations were observed at the Ispra station in Northern Italy with high accumulation mode number concentrations in the winter. The aerosol number concentrations at the Arctic station Zeppelin in Ny-Ålesund in Svalbard have also a strong seasonal cycle, with greater concentrations of accumulation mode particles in winter, and dominating summer Aitken mode indicating more recently formed particles. Observed particles did not show any statistically significant regional work-week or weekday related variation in number concentrations studied. Analysis products are made for open-access to the research community, available in a freely accessible internet site. The results give to the modelling community a reliable, easy-to-use and freely available comparison dataset of aerosol size distributions.
01A - Beitrag in wissenschaftlicher Zeitschrift
Primary versus secondary contributions to particle number concentrations in the European boundary layer
(Copernicus, 05.12.2011) Reddington, Carly L.; Carslaw, Ken S.; Spracklen, Dominick V.; Frontoso, Maria Grazia; Collins, Lisa M.; Merikanto, Joonas; Minikin, Andreas; Hamburger, Thomas; Coe, Hugh; Kulmala, Markku; Aalto, Pasi Pekka; Flentje, Harald; Plass-Dülmer, Christian; Birmili, Wolfram; Wiedensohler, Alfred; Wehner, Birgit; Tuch, Thomas; Sonntag, Alfred; O'Dowd, Collin D.; Jennings, Stephen G.; Dupuy, Regis; Baltensperger, Urs; Weingartner, Ernest; Hansson, Hans-Christen; Tunved, Peter; Laj, Paolo; Sellegri, Karine; Boulon, Julien; Putaud, Jean-Philippe; Gruening, Carsten; Swietlicki, Erik; Roldin, Pontus; Henzing, J.S.; Moerman, Marcel; Mihalopoulos, Nikolaos; Kouvarakis, Giorgos; Ždímal, Vladimir; Zíková, Nadezda; Marinoni, Angela; Bonasoni, Paolo; Duchi, Rocco
It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter >50 nm (N50) and >100 nm (N100) were well captured by the model (R2≥0.8) and the normalised mean bias (NMB) was also small (−18% for N50 and −1% for N100). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias (R2≥0.8, NMB = −52% and −29%), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the "effective emission size" and composition of primary particles appropriate for different resolution models.
01A - Beitrag in wissenschaftlicher Zeitschrift
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
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