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- ItemNumber size distributions and seasonality of submicron particles in Europe 2008–2009(München : European Geopyhsical Union, 2011) Asmi, A.; Wiedensohler, A.; Laj, P.; Fjaeraa, A.-M.; Sellegri, K.; Birmili, W.; Weingartner, E.; Baltensperger, U.; Zdimal, V.; Zikova, N.; Putaud, J.-P.; Marinoni, A.; Tunved, P.; Hansson, H.-C.; Fiebig, M.; Kivekäs, N.; Lihavainen, H.; Asmi, E.; Ulevicius, V.; Aalto, P.P.; Swietlicki, E.; Kristensson, A.; Mihalopoulos, N.; Kalivitis, N.; Kalapov, I.; Kiss, G.; de Leeuw, G.; Henzing, B.; Harrison, R.M.; Beddows, D.; O'Dowd, C.; Jennings, S.G.; Flentje, H.; Weinhold, K.; Meinhardt, F.; Ries, L.; Kulmala, M.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-\AA lesund 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.
- ItemChanges in the production rate of secondary aerosol particles in Central Europe in view of decreasing SO2 emissions between 1996 and 2006(München : European Geopyhsical Union, 2010) Hamed, A.; Birmili, W.; Joutsensaari, J.; Mikkonen, S.; Asmi, A.; Wehner, B.; Spindler, G.; Jaatinen, A.; Wiedensohler, A.; Korhonen, H.; Lehtinen, K.E.J.; Laaksonen, A.In anthropogenically influenced atmospheres, sulphur dioxide (SO2) is the main precursor of gaseous sulphuric acid (H2SO4), which in turn is a main precursor for atmospheric particle nucleation. As a result of socio-economic changes, East Germany has seen a dramatic decrease in anthropogenic SO2 emissions between 1989 and present, as documented by routine air quality measurements in many locations. We have attempted to evaluate the influence of changing SO2 concentrations on the frequency and intensity of new particle formation (NPF) using two different data sets (1996–1997; 2003–2006) of experimental particle number size distributions (diameter range 3–750 nm) from the atmospheric research station Melpitz near Leipzig, Germany. Between the two periods SO2 concentrations decreased by 65% on average, while the frequency of NPF events dropped by 45%. Meanwhile, the average formation rate of 3 nm particles decreased by 68% on average. The trends were statistically significant and therefore suggest a connection between the availability of anthropogenic SO2 and freshly formed new particles. In contrast to the decrease in new particle formation, we found an increase in the mean growth rate of freshly nucleated particles (+22%), suggesting that particle nucleation and subsequent growth into larger sizes are delineated with respect to their precursor species. Using three basic parameters, the condensation sink for H2SO4, the SO2 concentration, and the global radiation intensity, we were able to define the characteristic range of atmospheric conditions under which particle formation events take place at the Melpitz site. While the decrease in the concentrations and formation rates of the new particles was rather evident, no similar decrease was found with respect to the generation of cloud condensation nuclei (CCN; particle diameter >100 nm) as a result of atmospheric nucleation events. On the contrary, the production of CCN following nucleation events appears to have increased by tens of percents. Our aerosol dynamics model simulations suggest that such an increase can be caused by the increased particle growth rate.
- ItemAnalysis of nucleation events in the European boundary layer using the regional aerosol-climate model REMO-HAM with a solar radiation-driven OH-proxy(München : European Geopyhsical Union, 2014) Pietikäinen, J.-P.; Mikkonen, S.; Hamed, A.; Hienola, A.I.; Birmili, W.; Kulmala, M.; Laaksonen, A.This work describes improvements in the regional aerosol–climate model REMO-HAM in order to simulate more realistically the process of atmospheric new particle formation (NPF). A new scheme was implemented to simulate OH radical concentrations using a proxy approach based on observations and also accounting for the effects of clouds upon OH concentrations. Second, the nucleation rate calculation was modified to directly simulate the formation rates of 3 nm particles, which removes some unnecessary steps in the formation rate calculations used earlier in the model. Using the updated model version, NPF over Europe was simulated for the periods 2003–2004 and 2008–2009. The statistics of the simulated particle formation events were subsequently compared to observations from 13 ground-based measurement sites. The new model shows improved agreement with the observed NPF rates compared to former versions and can simulate the event statistics realistically for most parts of Europe.
- ItemCharacteristics of regional new particle formation in urban and regional background environments in the North China Plain(München : European Geopyhsical Union, 2013) Wang, Z.B.; Hu, M.; Sun, J.Y.; Wu, Z.J.; Yue, D.L.; Shen, X.J.; Zhang, Y.M.; Pei, X.Y.; Cheng, Y.F.; Wiedensohler, A.Long-term measurements of particle number size distributions were carried out both at an urban background site (Peking University, PKU) and a regional Global Atmospheric Watch station (Shangdianzi, SDZ) from March to November in 2008. In total, 52 new particle formation (NPF) events were observed simultaneously at both sites, indicating that this is a regional phenomenon in the North China Plain. On average, the mean condensation sink value before the nucleation events started was 0.025 s−1 in the urban environment, which was 1.6 times higher than that at regional site. However, higher particle formation and growth rates were observed at PKU (10.8 cm−3 s−1 and 5.2 nm h−1) compared with those at SDZ (4.9 cm−3 s−1 and 4.0 nm h−1). These results implied that precursors were much more abundant in the polluted urban environment. Different from the observations in cleaner environments, the background conditions of the observed particle homogeneous nucleation events in the North China Plain could be characterized as the co-existing of a stronger source of precursor gases and a higher condensational sink of pre-existing aerosol particles. Secondary aerosol formation following nucleation events results in an increase of particle mass concentration, particle light scattering coefficient, and cloud condensation nuclei (CCN) number concentration, with consequences on visibility, radiative effects, and air quality. Typical regional NPF events with significant particle nucleation rates and subsequent particle growth over a sufficiently long time period at both sites were chosen to investigate the influence of NPF on the number concentration of "potential" CCN. As a result, the NPF and the subsequent condensable growth increased the CCN number concentration in the North China Plain by factors in the range from 5.6 to 8.7. Moreover, the potential contribution of anthropogenic emissions to the CCN number concentration was more than 50%, to which more attention should be drawn in regional and global climate modeling, especially in the polluted urban areas.
- ItemAerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain(München : European Geopyhsical Union, 2014) Liu, H.J.; Zhao, C.S.; Nekat, B.; Ma, N.; Wiedensohler, A.; van Pinxteren, D.; Spindler, G.; Müller, K.; Herrmann, H.Hygroscopic growth of aerosol particles is of significant importance in quantifying the aerosol radiative effect in the atmosphere. In this study, hygroscopic properties of ambient particles are investigated based on particle chemical composition at a suburban site in the North China Plain during the HaChi campaign (Haze in China) in summer 2009. The size-segregated aerosol particulate mass concentration as well as the particle components such as inorganic ions, organic carbon and water-soluble organic carbon (WSOC) are identified from aerosol particle samples collected with a ten-stage impactor. An iterative algorithm is developed to evaluate the hygroscopicity parameter κ from the measured chemical composition of particles. During the HaChi summer campaign, almost half of the mass concentration of particles between 150 nm and 1 μm is contributed by inorganic species. Organic matter (OM) is abundant in ultrafine particles, and 77% of the particulate mass with diameter (Dp) of around 30 nm is composed of OM. A large fraction of coarse particle mass is undetermined and is assumed to be insoluble mineral dust and liquid water. The campaign's average size distribution of κ values shows three distinct modes: a less hygroscopic mode (Dp < 150 nm) with κ slightly above 0.2, a highly hygroscopic mode (150 nm < Dp < 1 μm) with κ greater than 0.3 and a nearly hydrophobic mode (Dp > 1 μm) with κ of about 0.1. The peak of the κ curve appears around 450 nm with a maximum value of 0.35. The derived κ values are consistent with results measured with a high humidity tandem differential mobility analyzer within the size range of 50–250 nm. Inorganics are the predominant species contributing to particle hygroscopicity, especially for particles between 150 nm and 1 μm. For example, NH4NO3, H2SO4, NH4HSO4 and (NH4)2SO4 account for nearly 90% of κ for particles of around 900 nm. For ultrafine particles, WSOC plays a critical role in particle hygroscopicity due to the predominant mass fraction of OM in ultrafine particles. WSOC for particles of around 30 nm contribute 52% of κ. Aerosol hygroscopicity is related to synoptic transport patterns. When southerly wind dominates, particles are more hygroscopic; when northerly wind dominates, particles are less hygroscopic. Aerosol hygroscopicity also has a diurnal variation, which can be explained by the diurnal evolution of planetary boundary layer, photochemical aging processes during daytime and enhanced black carbon emission at night. κ is highly correlated with mass fractions of SO42−, NO3− and NH4+ for all sampled particles as well as with the mass fraction of WSOC for particles of less than 100 nm. A parameterization scheme for κ is developed using mass fractions of SO42−, NO3−, NH4+ and WSOC due to their high correlations with κ, and κ calculated from the parameterization agrees well with κ derived from the particle's chemical composition. Further analysis shows that the parameterization scheme is applicable to other aerosol studies in China.
- ItemOn the abundance and source contributions of dicarboxylic acids in size-resolved aerosol particles at continental sites in central Europe(München : European Geopyhsical Union, 2014) van Pinxteren, D.; Neusüß, C.; Herrmann, H.Dicarboxylic acids (DCAs) are among the most abundant organic compounds observed in atmospheric aerosol particles and have been extensively studied at many places around the world. The importance of the various primary sources and secondary formation pathways discussed in the literature is often difficult to assess from field studies, though. In the present study, a large data set of size-resolved DCA concentrations from several inland sites in Germany is combined with results from a recently developed approach of statistical back-trajectory analysis and additional data. Principal component analysis is then used to reveal the most important factors governing the abundance of DCAs in different particle size ranges. The two most important sources revealed are (i) photochemical formation during intense radiation days in polluted air masses, likely occurring in the gas phase on short timescales (gasSOA), and (ii) secondary reactions in anthropogenically influenced air masses, likely occurring in the aqueous phase on longer timescales (aqSOA). While the first source strongly impacts DCA concentrations mainly in small and large particles, the second one enhances accumulation mode DCAs and is responsible for the bulk of the observed concentrations. Primary sources were found to be minor (sea salt, soil resuspension) or non-existent (biomass burning, traffic). The results can be regarded as representative for typical central European continental conditions.
- ItemIon-particle interactions during particle formation and growth at a coniferous forest site in central Europe(München : European Geopyhsical Union, 2014) Gonser, S.G.; Klein, F.; Birmili, W.; Größ, J.; Kulmala, M.; Manninen, H.E.; Wiedensohler, A.; Held, A.In this work, we examined the interaction of ions and neutral particles during atmospheric new particle formation (NPF) events. The analysis is based on simultaneous field measurements of atmospheric ions and total particles using a neutral cluster and air ion spectrometer (NAIS) across the diameter range 2–25 nm. The Waldstein research site is located in a spruce forest in NE Bavaria, Southern Germany, known for enhanced radon concentrations, presumably leading to elevated ionization rates. Our observations show that the occurrence of the ion nucleation mode preceded that of the total particle nucleation mode during all analyzed NPF events. The time difference between the appearance of 2 nm ions and 2 nm total particles was typically about 20 to 30 min. A cross correlation analysis showed a rapid decrease of the time difference between the ion and total modes during the growth process. Eventually, this time delay vanished when both ions and total particles did grow to larger diameters. Considering the growth rates of ions and total particles separately, total particles exhibited enhanced growth rates at diameters below 15 nm. This observation cannot be explained by condensation or coagulation, because these processes would act more efficiently on charged particles compared to neutral particles. To explain our observations, we propose a mechanism including recombination and attachment of continuously present cluster ions with the ion nucleation mode and the neutral nucleation mode, respectively.
- ItemSimulating ultrafine particle formation in Europe using a regional CTM: Contribution of primary emissions versus secondary formation to aerosol number concentrations(München : European Geopyhsical Union, 2012) Fountoukis, C.; Riipinen, I.; Denier van der Gon, H.A.C.; Charalampidis, P.E.; Pilinis, C.; Wiedensohler, A.; O'Dowd, C.; Putaud, J.P.; Moerman, M.; Pandis, S.N.A three-dimensional regional chemical transport model (CTM) with detailed aerosol microphysics, PMCAMx-UF, was applied to the European domain to simulate the contribution of direct emissions and secondary formation to total particle number concentrations during May 2008. PMCAMx-UF uses the Dynamic Model for Aerosol Nucleation and the Two-Moment Aerosol Sectional (TOMAS) algorithm to track both aerosol number and mass concentration using a sectional approach. The model predicts nucleation events that occur over scales of hundreds up to thousands of kilometers especially over the Balkans and Southeast Europe. The model predictions were compared against measurements from 7 sites across Europe. The model reproduces more than 70% of the hourly concentrations of particles larger than 10 nm (N10) within a factor of 2. About half of these particles are predicted to originate from nucleation in the lower troposphere. Regional nucleation is predicted to increase the total particle number concentration by approximately a factor of 3. For particles larger than 100 nm the effect varies from an increase of 20% in the eastern Mediterranean to a decrease of 20% in southern Spain and Portugal resulting in a small average increase of around 1% over the whole domain. Nucleation has a significant effect in the predicted N50 levels (up to a factor of 2 increase) mainly in areas where there are condensable vapors to grow the particles to larger sizes. A semi-empirical ternary sulfuric acid-ammonia-water parameterization performs better than the activation or the kinetic parameterizations in reproducing the observations. Reducing emissions of ammonia and sulfur dioxide affects certain parts of the number size distribution.
- ItemResults from the CERN pilot CLOUD experiment(München : European Geopyhsical Union, 2010) Duplissy, J.; Enghoff, M.B.; Aplin, K.L.; Arnold, F.; Aufmhoff, H.; Avngaard, M.; Baltensperger, U.; Bondo, T.; Bingham, R.; Carslaw, K.; Curtius, J.; David, A.; Fastrup, B.; Gagné, S.; Hahn, F.; Harrison, R.G.; Kellett, B.; Kirkby, J.; Kulmala, M.; Laakso, L.; Laaksonen, A.; Lillestol, E.; Lockwood, M.; Mäkelä, J.; Makhmutov, V.; Marsh, N.D.; Nieminen, T.; Onnela, A.; Pedersen, E.; Pedersen, J.O.P.; Polny, J.; Reichl, U.; Seinfeld, J.H.; Sipilä, M.; Stozhkov, Y.; Stratmann, F.; Svensmark, H.; Svensmark, J.; Veenhof, R.; Verheggen, B.; Viisanen, Y.; Wagner, P.E.; Wehrle, G.; Weingartner, E.; Wex, H.; Wilhelmsson, M.; Winkler, P.M.During a 4-week run in October–November 2006, a pilot experiment was performed at the CERN Proton Synchrotron in preparation for the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment, whose aim is to study the possible influence of cosmic rays on clouds. The purpose of the pilot experiment was firstly to carry out exploratory measurements of the effect of ionising particle radiation on aerosol formation from trace H2SO4 vapour and secondly to provide technical input for the CLOUD design. A total of 44 nucleation bursts were produced and recorded, with formation rates of particles above the 3 nm detection threshold of between 0.1 and 100 cm−3s−1, and growth rates between 2 and 37 nm h−1. The corresponding H2O concentrations were typically around 106 cm−3 or less. The experimentally-measured formation rates and \htwosofour concentrations are comparable to those found in the atmosphere, supporting the idea that sulphuric acid is involved in the nucleation of atmospheric aerosols. However, sulphuric acid alone is not able to explain the observed rapid growth rates, which suggests the presence of additional trace vapours in the aerosol chamber, whose identity is unknown. By analysing the charged fraction, a few of the aerosol bursts appear to have a contribution from ion-induced nucleation and ion-ion recombination to form neutral clusters. Some indications were also found for the accelerator beam timing and intensity to influence the aerosol particle formation rate at the highest experimental SO2 concentrations of 6 ppb, although none was found at lower concentrations. Overall, the exploratory measurements provide suggestive evidence for ion-induced nucleation or ion-ion recombination as sources of aerosol particles. However in order to quantify the conditions under which ion processes become significant, improvements are needed in controlling the experimental variables and in the reproducibility of the experiments. Finally, concerning technical aspects, the most important lessons for the CLOUD design include the stringent requirement of internal cleanliness of the aerosol chamber, as well as maintenance of extremely stable temperatures (variations below 0.1 °C
- ItemSeasonal variability of Saharan desert dust and ice nucleating particles over Europe(München : European Geopyhsical Union, 2015) Hande, L.B.; Engler, C.; Hoose, C.; Tegen, I.Dust aerosols are thought to be the main contributor to atmospheric ice nucleation. While there are case studies supporting this, a climatological sense of the importance of dust to atmospheric ice nucleating particle (INP) concentrations and its seasonal variability over Europe is lacking. Here, we use a mesoscale model to estimate Saharan dust concentrations over Europe in 2008. There are large differences in median dust concentrations between seasons, with the highest concentrations and highest variability in the lower to mid-troposphere. Laboratory-based ice nucleation parameterisations are applied to these simulated dust number concentrations to calculate the potential INP resulting from immersion freezing and deposition nucleation on these dust particles. The potential INP concentrations increase exponentially with height due to decreasing temperatures in the lower and mid-troposphere. When the ice-activated fraction increases sufficiently, INP concentrations follow the dust particle concentrations. The potential INP profiles exhibit similarly large differences between seasons, with the highest concentrations in spring (median potential immersion INP concentrations nearly 105 m−3, median potential deposition INP concentrations at 120% relative humidity with respect to ice over 105 m−3), about an order of magnitude larger than those in summer. Using these results, a best-fit function is provided to estimate the potential INPs for use in limited-area models, which is representative of the normal background INP concentrations over Europe. A statistical evaluation of the results against field and laboratory measurements indicates that the INP concentrations are in close agreement with observations.