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- ItemAn overview of the Lagrangian experiments undertaken during the North Atlantic regional Aerosol Characterisation Experiment (ACE-2)(Milton Park : Taylor & Francis, 2016) Johnson, Doug W.; Osborne, Simon; Wood, Robert; Suhre, Karsten; Johnson, Randy; Businger, Steven; Quinn, Patricia K.; Wiedensohler, Alfred; Durkee, Philip A.; Russell, Lynn M.; Andreae, Meinrat O.; O’Dowd, Colin; Noone, Kevin J.; Bandy, Brian; Rudolph, J.; Rapsomanikis, SpyrosOne of the primary aims of the North Atlantic regional Aerosol Characterisation Experiment (ACE-2) was to quantify the physical and chemical processes affecting the evolution of the major aerosol types over the North Atlantic. The best, practical way of doing this is in a Lagrangian framework where a parcel of air is sampled over several tens of hours and its physical and chemical properties are intensively measured. During the intensive observational phase of ACE-2, between 15 June 1997 and 24 July 1997, 3 cloudy Lagrangian experiments and 3 cloud-free, Lagrangian experiments were undertaken between the south west tip of the Iberian Peninsula and the Canary Islands. This paper gives an overview of the aims and logistics of all of the Lagrangian experiments and compares and contrasts them to provide a framework for the more focused Lagrangian papers in this issue and future process modelling studies and parametrisation development. The characteristics of the cloudy Lagrangian experiments were remarkably different, enabling a wide range of different physical and chemical processes to be studied. In the 1st Lagrangian, a clean maritime air mass was sampled in which salt particle production, due to increased wind speed, dominated the change in the accumulation mode concentrations. In the 2nd Lagrangian, extensive cloud cover resulted in cloud processing of the aerosol in a polluted air mass, and entrainment of air from the free troposphere influenced the overall decrease in aerosol concentrations in the marine boundary layer (MBL). Very little change in aerosol characteristics was measured in the 3rd Lagrangian, where the pollution in the MBL was continually being topped up by entraining air from a residual continental boundary layer (CBL) above. From the analysis of all the Lagrangian experiments, it has been possible to formulate, and present here, a generalised description of a European continental outbreak of pollution over the sub-tropical North Atlantic.
- ItemCollocated observations of cloud condensation nuclei, particle size distributions, and chemical composition(London : Nature Publ. Group, 2017) Schmale, Julia; Henning, Silvia; Henzing, Bas; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Bougiatioti, Aikaterini; Kalivitis, Nikos; Stavroulas, Iasonas; Jefferson, Anne; Park, Minsu; Schlag, Patrick; Kristensson, Adam; Iwamoto, Yoko; Pringle, Kirsty; Reddington, Carly; Aalto, Pasi; Äijälä, Mikko; Baltensperger, Urs; Bialek, Jakub; Birmili, Wolfram; Bukowiecki, Nicolas; Ehn, Mikael; Fjæraa, Ann Mari; Fiebig, Markus; Frank, Göran; Fröhlich, Roman; Frumau, Arnoud; Furuya, Masaki; Hammer, Emanuel; Heikkinen, Liine; Herrmann, Erik; Holzinger, Rupert; Hyono, Hiroyuki; Kanakidou, Maria; Kiendler-Scharr, Astrid; Kinouchi, Kento; Kos, Gerard; Kulmala, Markku; Mihalopoulos, Nikolaos; Motos, Ghislain; Nenes, Athanasios; O’Dowd, Colin; Paramonov, Mikhail; Petäjä, Tuukka; Picard, David; Poulain, Laurent; Prévôt, André Stephan Henry; Slowik, Jay; Sonntag, Andre; Swietlicki, Erik; Svenningsson, Birgitta; Tsurumaru, Hiroshi; Wiedensohler, Alfred; Wittbom, Cerina; Ogren, John A.; Matsuki, Atsushi; Yum, Seong Soo; Myhre, Cathrine Lund; Carslaw, Ken; Stratmann, Frank; Gysel, MartinCloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.
- ItemAerosol number-size distributions during clear and fog periods in the summer high Arctic: 1991, 1996 and 2001(Milton Park : Taylor & Francis, 2017) Heintzenberg, Jost; Leck, Caroline; Birmili, Wolfram; Wehner, Birgit; Tjernström, Michael; Wiedensohler, AlfredThe present study covers submicrometer aerosol size distribution data taken during three Arctic icebreaker expeditions in the summers of 1991, 1996 and 2001. The size distributions of all expeditions were compared in log-normally fitted form to the statistics of the marine number size distribution provided by Heintzenberg et al. (2004) yielding rather similar log-normal parameters of the modes. Statistics of the modal concentrations revealed strong concentration decreases of large accumulation mode particles with increasing length of time spent over the pack ice. The travel-time dependencies of both Aitken and ultrafine modes strongly indicate, as other studies did before, the occurrence of fine-particle sources in the inner Arctic. With two approaches evidence of fog-related aerosol source processeswas sought for in the data sets of 1996 and 2001 because they included fog drop size distributions. With increasing fog intensity modes in interstitial particle number concentrations appeared in particular in the size range around 80 nm that was nearly mode free in clear air. A second, dynamic approach revealed that Aitken mode concentrations increased strongly above their respective fog-period medians in both years before maximum drop numbers were reached in both years. We interpret the results of both approaches as strong indications of fog-related aerosol source processes as discussed in Leck and Bigg (1999) that need to be elucidated with further data from dedicated fog experiments in future Arctic expeditions in order to understand the life cycle of the aerosol over the high Arctic pack ice area.
- ItemArctic haze over Central Europe(Milton Park : Taylor & Francis, 2017) Heintzenberg, Jost; Tuch, Thomas; Wehner, Birgit; Wiedensohler, Alfred; Wex, Heike; Ansmann, Albert; Mattis, Ina; Müller, Detlef; Wendisch, Manfred; Eckhardt, Sabine; Stohl, AndreasAn extraordinary aerosol situation over Leipzig, Germany in April 2002 was investigated with a comprehensive set of ground-based volumetric and columnar aerosol data, combined with aerosol profiles from lidar, meteorological data from radiosondes and air mass trajectory calculations. Air masses were identified to stem from the Arctic, partly influenced by the greater Moscow region. An evaluation of ground-based measurements of aerosol size distributions during these periods showed that the number concentrations below about 70 nm in diameter were below respective long-term average data, while number, surface and volume concentrations of the particles larger than about 70 nm in diameter were higher than the long-term averages. The lidar aerosol profiles showed that the imported aerosol particles were present up to about 3 km altitude. The particle optical depth was up to 0.45 at 550 nm wavelength. With a one-dimensional spectral radiative transfer model top of the atmosphere (TOA) radiative forcing of the aerosol layer was estimated for a period with detailed vertical information. Solar aerosol radiative forcing values between −23 and −38 W m−2 were calculated, which are comparable to values that have been reported in heavily polluted continental plumes outside the respective source regions. The present report adds weight to previous findings of aerosol import to Europe, pointing to the need for attributing the three-dimensional aerosol burden to natural and anthropogenic sources as well as to aerosol imports from adjacent or distant source regions. In the present case, the transport situation is further complicated by forward trajectories, indicating that some of the observed Arctic haze may have originated in Central Europe. This aerosolwas transported to the European Arctic before being re-imported in the modified and augmented form to its initial source region.
- ItemHorizontal homogeneity and vertical extent of new particle formation events(Milton Park : Taylor & Francis, 2017) Wehner, Birgit; Siebert, Holger; Stratmann, Frank; Tuch, Thomas; Wiedensohler, Alfred; PetäJä, Tuukka; Dal Maso, Miikka; Kulmala, MarkkuDuring the SATURN campaign 2002, new particle formation, i.e. the occurrence of ultrafine particles was investigated simultaneously at four ground-based measurement sites. The maximum distance between the sites was 50 km. Additionally, vertical profiles of aerosol particles from 5–10 nm have been measured by a tethered-balloonborne system at one of the sites. In general, two different scenarios have been found: (i) new particle formation was measured at all sites nearly in parallel with subsequent particle growth (homogeneous case) and (ii) new particle formation was observed at one to three sites irregularly (inhomogeneous case) where subsequent particle growth was often interrupted. The homogeneous case was connected with stable synoptical conditions, i.e. the region was influenced by a high pressure system. Here, the horizontal extent of the phenomenon has been estimated to be 400 km at maximum. In the vertical dimension, the ultrafine particles are well mixed within the entire boundary layer. In the inhomogeneous case the new particle formation depends mainly on the incoming solar radiation and was often interrupted due the occurrence of clouds. Thus, single point measurements are not representative for a larger region in that case.
- ItemAerosol number to volume ratios in Southwest Portugal during ACE-2(Milton Park : Taylor & Francis, 2017) Dusek, Ulrike; Covert, David S.; Wiedensohler, Alfred; Neusúss, Christian; Weise, DianaPast studies have indicated that long-term averages of the aerosol number to volume ratios (defined as the number of particles larger than a certain diameter divided by the particle volume over some range less than 1 μm) show little variability over the Atlantic. This work presents number to volume ratios (R) measured during the ACE-2 experiment on the land-based Sagres field site located in Southwest Portugal. The values of R measured in Sagres compare reasonably well with previous measurements over the Atlantic. The main emphasis of this work is therefore to investigate more closely possible reasons for the observed stability of the number to volume ratio. Aerosol number size distributions measured in Sagres are parametrized by the sum of two log-normal distributions fitted to the accumulation and to the Aitken mode. The main factor that limits the variability of R is that the parameters of these log-normal distributions are not always independent but show some covariance. In polluted air mass types correlations between parameters of the Aitken and accumulation mode are mostly responsible for stabilizing R. In marine air mass types the variability of R is reduced by an inverse relationship between the accumulation-mode mean diameter and standard deviation, consistent with condensational processes and cloud processing working on the aerosol. However, despite this reduction, the variability of R in marine air mass types is still considerable and R is linearly dependent on the number concentration of particles larger than 90 nm. This partly due to a mil of Aitken-mode particles extending to sizes larger than 90 nm.
- ItemIn situ aerosol characterization at Cape Verde, Part 1: Particle number size distributions, hygroscopic growth and state of mixing of the marine and Saharan dust aerosol(Milton Park : Taylor & Francis, 2017) Schladitz, Alexander; Müller, Thomas; Nowak, Andreas; Kandler, Konrad; Lieke, Kirsten; Massling, Andreas; Wiedensohler, AlfredParticle number size distributions and hygroscopic properties of marine and Saharan dust aerosol were investigated during the SAMUM-2 field study at Cape Verde in winter 2008. Aitken and accumulation mode particles were mainly assigned to the marine aerosol, whereas coarse mode particles were composed of sea-salt and a variable fraction of Saharan mineral dust. A new methodical approach was used to derive hygroscopic growth and state of mixing for a particle size range (volume equivalent) from dpve = 26 nm to 10 μm. For hygroscopic particles with dpve < 100 nm, the median hygroscopicity parameter κ is 0.35. From 100 nm < dpve < 350 nm, κ increases to 0.65. For larger particles, κ at dpve = 350 nm was used. For nearly hydrophobic particles, κ is between 0 and 0.1 for dpve < 250 nm and decreases to 0 for dpve > 250 nm. The mixing state of Saharan dust in terms of the number fraction of nearly hydrophobic particles showed the highest variation and ranges from 0.3 to almost 1. This study was used to perform a successful mass closure at ambient conditions and demonstrates the important role of hygroscopic growth of large sea-salt particles.
- ItemIn situ aerosol characterization at Cape Verde, Part 2: Parametrization of relative humidity- and wavelength-dependent aerosol optical properties(Milton Park : Taylor & Francis, 2017) Schladitz, Alexander; Müller, Thomas; Nordmann, Stephan; Tesche, Matthias; Silke Groß, Silke Groß; Freudenthaler, Volker; Gasteiger, Josef; Wiedensohler, AlfredAn observation-based numerical study of humidity-dependent aerosol optical properties of mixed marine and Saharan mineral dust aerosol is presented. An aerosol model was developed based on measured optical and microphysical properties to describe the marine and Saharan dust aerosol at Cape Verde. A wavelength-dependent optical equivalent imaginary part of the refractive index and a scattering non-sphericity factor for Saharan dustwere derived. Simulations of humidity effects on optical properties by the aerosol model were validated with relative measurements of the extinction coefficient at ambient conditions. Parametrizations were derived to describe the humidity dependence of the extinction, scattering, and absorption coefficients as well as the asymmetry parameter and single scattering albedo. For wavelengths (300–950 nm) and dry dust volume fractions (0–1), aerosol optical properties as a function of relative humidity (RH = 0–90%) can be calculated from tabulated parameters. For instance, at a wavelength of 550 nm, a volume fraction of 0.5 of dust on the total particle volume (dry conditions) and a RH of 90%, the enhancements for the scattering, extinction and absorption coefficients are 2.55, 2.46 and 1.04, respectively, while the enhancements for the asymmetry parameter and single scattering albedo are 1.11 and 1.04.
- ItemStructure, variability and persistence of the submicrometre marine aerosol(Milton Park : Taylor & Francis, 2017) Heintzenberg, Jost; Birmili, Wolfram; Wiedensohler, Alfred; Nowak, Andreas; Tuch, ThomasSubmicrometre dry number size distributions from four marine and one continental aerosol experiment were evaluatedjointly in the present study. In the marine experiments only data with back trajectories of at least 120 h without landcontact were used to minimize continental contamination. Log-normal functions were fitted to the size distributions.Basic statistics of the marine aerosol indicate a closed character of the size distribution at the lower size limit as opposedto an open character for corresponding continental data. Together with the infrequent occurrences of marine particlesbelow20 nmthis finding supports hypotheses and model results suggesting lowprobabilities of homogeneous nucleationin the marine boundary layer. The variability of submicrometre marine number concentrations was parametrized witha bimodal log-normal function that quantifies the probability of finding different number concentrations about a givenmedian value. Together with a four-modal log-normal approximation of the submicrometre marine size distributionitself, this model allows a statistical representation of the marine aerosol that facilitates comparison of experiments andvalidation of aerosol models. Autocorrelation at the one fixed marine site with a minimum of interruptions in timesseriesrevealed a strong size dependency of persistence in particle number concentration with the shortest persistenceat the smallest sizes. Interestingly, in the marine aerosol (at Cape Grim) persistence exhibits a size dependency thatlargely matches the modes in dg0, i.e. near the most frequent geometric mean diameters number concentrations aremost persistent. Over the continent, persistence of particle numbers is strongly constrained by diurnal meteorologicalprocesses and aerosol dynamics. Thus, no strong modal structure appears in the size-dependent persistence at Melpitz.As with the aerosol variability, marine aerosol processes in models of aerosol dynamics can be tested with these findings.
- ItemNano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) for investigating hygroscopic properties of sub-10nm aerosol nanoparticles(Katlenburg-Lindau : Copernicus, 2020) Lei, Ting; Ma, Nan; Hong, Juan; Tuch, Thomas; Wang, Xin; Wang, Zhibin; Pöhlker, Mira; Ge, Maofa; Wang, Weigang; Mikhailov, Eugene; Hoffmann, Thorsten; Pöschl, Ulrich; Su, Hang; Wiedensohler, Alfred; Cheng, YafangInteractions between water and nanoparticles are relevant for atmospheric multiphase processes, physical chemistry, and materials science. Current knowledge of the hygroscopic and related physicochemical properties of nanoparticles, however, is restricted by the limitations of the available measurement techniques. Here, we present the design and performance of a nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) apparatus that enables high accuracy and precision in hygroscopic growth measurements of aerosol nanoparticles with diameters less than 10 nm. Detailed methods of calibration and validation are provided. Besides maintaining accurate and stable sheath and aerosol flow rates (1 %), high accuracy of the differential mobility analyzer (DMA) voltage (0:1 %) in the range of 0-50V is crucial for achieving accurate sizing and small sizing offsets between the two DMAs (1:4 %). To maintain a stable relative humidity (RH), the humidification system and the second DMA are placed in a well-insulated and air conditioner housing (0:1 K). We also tested and discussed different ways of preventing predeliquescence in the second DMA. Our measurement results for ammonium sulfate nanoparticles are in good agreement with Biskos et al. (2006b), with no significant size effect on the deliquescence and efflorescence relative humidity (DRH and ERH, respectively) at diameters down to 6 nm. For sodium sulfate nanoparticles, however, we find a pronounced size dependence of DRH and ERH between 20 and 6 nm nanoparticles. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.