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Atmospheric Environment (v.48, #)

Editorial board (pp. i).

Volcanic ash over Europe during the eruption of Eyjafjallajökull on Iceland, April–May 2010 by Baerbel Langmann; Arnau Folch; Martin Hensch; Volker Matthias (pp. 1-8).

During the eruption of Eyjafjallajökull on Iceland in April/May 2010, air traffic over Europe was repeatedly interrupted because of volcanic ash in the atmosphere. This completely unusual situation in Europe leads to the demand of improved crisis management, e.g. European wide regulations of volcanic ash thresholds and improved ash dispersion forecasts. However, the quality of the forecast of fine volcanic ash concentrations in the atmosphere depends to a great extent on a realistic description of the erupted mass flux of fine ash particles, which is rather uncertain. Numerous aerosol measurements (ground based and satellite remote sensing, and in-situ measurements) all over Europe tracked the volcanic ash clouds during the eruption of Eyjafjallajökull offering the possibility for an interdisciplinary effort between volcanologists and aerosol researchers to analyse the release and dispersion of fine volcanic ash in order to better understand the needs for realistic volcanic ash forecasts. In this introductory paper, we provide a general introduction into magma fragmentation processes during explosive volcanic eruptions, describe the evolution of the eruption of Eyjafjallajökull, present the possibilities of ground based in-situ and remote measurements and numerical model studies of volcanic ash and summarise open questions and future directions.► Introduction into magma fragmentation processes during explosive volcanic eruptions. ► Description of the Eyjafjallajökull eruption from the volcanological point of view. ► Short overview volcanic ash dispersion modelling. ► Short overview ground based in-situ and remote measurements of volcanic ash. ► Implications for the future volcanic eruptions with volcanic ash release.

Keywords: Eyjafjallajökull; Volcanic activity on Iceland; Volcanic ash; Dispersion modelling; Ground based measurements

Airborne in-situ investigations of the Eyjafjallajökull volcanic ash plume on Iceland and over north-western Germany with light aircrafts and optical particle counters by K. Weber; J. Eliasson; A. Vogel; C. Fischer; T. Pohl; G. van Haren; M. Meier; B. Grobéty; D. Dahmann (pp. 9-21).

During the time period of the eruption of the Icelandic volcano Eyjafjallajökull in April/May 2010 the Duesseldorf University of Applied Sciences has performed 14 research flights in situations with and without the volcanic ash plume over Germany. In parallel to the research flights in Germany three measurement flights have been performed by the University of Iceland in May 2010 over the western part of Iceland. During two of these flights the outskirts of the eruption plume were entered directly, delivering most direct measurements within the eruption plume during this eruptive event. For all the measurement flights reported here, light durable piston-motor driven aircrafts were used, which were equipped with optical particle counters for in-situ measurements. Real-time monitoring of the particle concentrations was possible during the flights. As different types of optical particle counters have been used in Iceland and Germany, the optical particle counters have been re-calibrated after the flights to the same standard using gravimetric reference methods and original Eyjafjallajökull volcanic ash samples. In-situ measurement results with high spatial resolution, directly from the eruption plume in Iceland as well as from the dispersed and several days old plume over Germany, are therefore presented here for the first time. They are normalized to the same ash concentration calibration standard. Moreover, airborne particles could be sampled directly out of the eruption plume in Iceland as well as during the flights over Germany.During the research flights over Iceland from 9 May 2011 to 11 May 2011 the ash emitted from the vent of the volcano turned out to be concentrated in a narrow well-defined plume of about 10 km width at a distance of 45–60 km away from the vent. Outside this plume the airborne ash concentrations could be proved to be below 50 μg m⁻³ over western Iceland. However, by entering the outskirts of the plume directly the research aircraft could detect ash concentrations of up to 2000 μg m⁻³.On the other hand, the ash plume, which was analysed by research flights over Germany several thousand km away from the eruption vent, appeared to be significantly structured in horizontal and vertical directions. Different sub-plumes could be found. Peak concentrations of more than 330 μg m⁻³ could be detected.The results of the measurements within the ash plume over Germany were compared with the predictions of the London VAAC model. The range of ash concentrations found by the research aircraft in Germany were not in conflict with the calculations of concentration regimes by the London VAAC model. However, the in-situ measurements performed by the research aircraft were able to deliver information about the structure and composition of the ash plume, which could not be covered by the dispersion model.Therefore, light piston-motor driven aircrafts equipped with optical particle counters proved to be a very versatile tool for the real-time in-situ determination of the spatial extension of volcanic ash plumes, the ash particle size distributions and the particle mass concentrations. Moreover, all these parameters could be measured with a high horizontal and vertical spatial resolution. Therefore, these kinds of measurements can deliver immediate data for the validation and verification of dispersion models and can give direct in-situ information additional to LIDAR measurements and satellite observations. As the piston-motor driven aircrafts are able to operate even at elevated volcanic ash concentrations they can provide valuable ash concentration results for air traffic safety.► Aircraft in-situ measurements of the Eyjafjalla ash plume with optical particle counters. ► Direct measurements up to 2000 μg m⁻³ in the outskirts of the ashplume on Iceland. ► Ash plume mapping over northern Germany with concentrations up to 330 μg m⁻³. ► Comparison with London VAAC model. ► Calibration of the optical Particle counters with original Eyjafjalla ash.

Keywords: Eyjafjallajökull; Volcano; Ash plume; Optical particle counter; Research aircraft; UV-DOAS

Aerosol properties of the Eyjafjallajökull ash derived from sun photometer and satellite observations over the Iberian Peninsula by C. Toledano; Y. Bennouna; V. Cachorro; J.P. Ortiz de Galisteo; A. Stohl; K. Stebel; N.I. Kristiansen; F.J. Olmo; H. Lyamani; M.A. Obregón; V. Estellés; F. Wagner; J.M. Baldasano; Y. González-Castanedo; L. Clarisse; A.M. de Frutos (pp. 22-32).

The Eyjafjallajökull ash that crossed over Spain and Portugal on 6–12 May 2010 has been monitored by a set of operational sun photometer sites within AERONET-RIMA and satellite sensors. The sun photometer observations (aerosol optical depth, coarse mode concentrations) and ash products from IASI and SEVIRI satellite sensors, together with FLEXPART simulations of particle transport, allow identifying the volcanic aerosols. The aerosol columnar properties derived from inversions were investigated, indicating specific properties, especially regarding the absorption. The single scattering albedo was high (0.95 at 440 nm) and nearly wavelength independent, although with slight decrease with wavelength. Other parameters, like the fine mode fraction of the volume size distributions (0.20–0.80) or the portion of spherical particles (15–90%), were very variable among the sites and indicated that the various ash clouds were inhomogeneous with respect to particle size and shape.► Ground-based sun photometer and satellite data confirm ash over the Iberian Peninsula on 6–12 May. ► Volcanic ash optical properties, especially regarding absorption, are different from other aerosol types. ► Mean size and shape were highly variable depending on the site and the dates.

Keywords: Eyjafjallajökull; Sun photometer; AERONET; Optical properties; Remote sensing; FLEXPART

Monitoring of Eyjafjallajökull volcanic aerosol by the new European Skynet Radiometers (ESR) network by M. Campanelli; V. Estelles; T. Smyth; C. Tomasi; M.P. Martìnez-Lozano; B. Claxton; P. Muller; G. Pappalardo; A. Pietruczuk; J. Shanklin; S. Colwell; C. Wrench; A. Lupi; M. Mazzola; C. Lanconelli; V. Vitale; F. Congeduti; D. Dionisi; F. Cardillo; M. Cacciani; G. Casasanta; T. Nakajima (pp. 33-45).

The passage of a volcanic plume produced by the eruption of Eyjafjallajökull volcano in April 2010 was measured by the sun–sky radiometers of the new European SkyRad (ESR) network. This network consists of several European sites located in the U.K., Poland, Spain and Italy, and therefore was particularly suitable for monitoring the transport of volcanic ash generated by this particular volcano. The atmospheric aerosol characteristics at each site affected by the passage of the volcanic cloud, during and after the eruption, have been reconstructed. For the U.K. ESR sites three events were identified by the sun–sky radiometers: the first, from April 15 to April 16 2010, related to the advection of fine particles; whilst the second, from April 17 to April 19 and the third from April 23 to April 24 related to the arrival of coarse particles. During the transport from Northern Europe to Italy, columnar radiative properties clearly changed due to both deposition and mixing with local aerosol.► The volcanic plume by Eyjafjallajökull in April 2010 was measured by ESR network. ► In U.K. 3 monitored events: 1st, fine particles; 2nd and 3rd: coarse particles. ► Toward South-Europe: radiative properties change due to deposition and mixing. ► South-Europe: coarse volume concentration lower than in U.K. sites. ► Refractive index closer to the typical local values of each site.

Keywords: Aerosol; Sun–sky radiometer; Columnar radiative properties

Characterization of the Eyjafjallajökull volcanic plume over the Iberian Peninsula by lidar remote sensing and ground-level data collection by M.A. Revuelta; M. Sastre; A.J. Fernández; L. Martín; R. García; F.J. Gómez-Moreno; B. Artíñano; M. Pujadas; F. Molero (pp. 46-55).

In April and May 2010 the eruption of the Eyjafjallajökull volcano disrupted air traffic across Europe. The vast economic impact of this event has stirred interest on accurate plume dispersion estimation and detailed ash characterization, in order to establish a more precise threshold for safe aircraft operation. In this work we study the physical and chemical properties of volcanogenic aerosol detected at ground level at several locations over the Iberian Peninsula, nearly 3000 km away from the Icelandic volcano. Between 4 and 14 May, the volcanogenic plume was detected at ground level, identified by an increase in sulfur dioxide, particle mass concentrations, and particulate sulfate concentration, at most EMEP stations as well as at the CIEMAT site (for the sulfate concentration in PM). At the CIEMAT site, the synergic use of Raman lidar and on-site instruments provided relevant information on the evolution and properties of the plume over the central part of the Iberian Peninsula. Aerosol extinction coefficient profiles provided by the lidar station show the presence of remarkable aerosol layers between 6 May and 15 May. Provenance studies using FLEXTRA backtrajectories confirmed that most of the aerosol layers originated in the Eyjafjallajökull eruption. The large suite of semi-continuous instruments present in the latter site allowed a better characterization of the aerosol properties. Size distribution and chemical composition were continuously monitored during the event, revealing a large increase in the aerosol fine mode, in coincidence with increases in ambient sulfate concentration, while the coarse mode remained almost unaltered. These results show that the plume carried mainly fine particles, with sizes between 0.1 and 0.7 μm in diameter, in contrast with studies of the plume that affected Central Europe in April, where particles with diameters larger than 20 μm were present in the ash layers. A possible explanation for this can be related to the long distance transport suffered by the plume and by the secondary formation of particulate sulfate from the gaseous sulfur dioxide. The information on volcanic aerosol characteristics after long-range transport provided by this study might contribute to better assess the type of aerosol that reach distant locations.► We study the impact of Eyjafjallajökull eruption in 2010 in the Iberian Peninsula. ► Passage of the plume was registered at several background monitoring stations. ► First estimates of mass loading from lidar data are provided. ► Semi-continuous instruments allowed characterizing ground-level aerosol properties. ► Volcanogenic aerosols contributed to the fine mode, leaving coarse mode unaltered.

Keywords: Eyjafjallajökull; Volcanic ash; Particulate sulfate; Atmospheric aerosols

Optical properties and vertical extension of aged ash layers over the Eastern Mediterranean as observed by Raman lidars during the Eyjafjallajökull eruption in May 2010 by A. Papayannis; R.E. Mamouri; V. Amiridis; E. Giannakaki; I. Veselovskii; P. Kokkalis; G. Tsaknakis; D. Balis; N.I. Kristiansen; A. Stohl; M. Korenskiy; K. Allakhverdiev; M.F. Huseyinoglu; T. Baykara (pp. 56-65).

The vertical extension and the optical properties of aged ash layers advected from the Eyjafjallajökull volcanic eruption over the Eastern Mediterranean (Greece and Turkey) are presented for the period May 10–21, 2010. Raman lidar observations performed at three stations of EARLINET (Athens, Thessaloniki and Istanbul), provided clear ash signatures within certain layers, although ash was sometimes mixed with mineral dust advected from the Saharan region. AERONET columnar measurements did not indicate the presence of ash over the area for that period, although they did for the dust particles. This was further investigated and confirmed by simulations of the ash trajectories by the FLEXPART model and the BSC-DREAM8b dust model. Good agreement was found between simulated and observed geometrical characteristics of the ash and dust layers, respectively. Ash particles were observed over the lidar stations after 6–7-days transport from the volcanic source at height ranges between approximately 1.5 and 6 km. Mean ash particle layer thickness ranged between 1.5 and 2.5 km and the corresponding aerosol optical depth (AOD) was of the order of 0.12–0.06 at 355 nm and of 0.04–0.05 at 532 nm. Inside the ash layers, the lidar ratios (LR) ranged between 55 and 67 sr at 355 nm and 76–89 sr at 532 nm, while the particle linear depolarization ratio ranged between 10 and 25%.► We show coordinated EARLINET aerosol lidar measurements in the Eastern Mediterranean. ► Data were obtained during the Eyjafjallajökull eruption on May 2010. ► We compare model results and lidar/sunphotometer measurements. ► We focus on optical properties/vertical extension of the observed aged ash layers.

Keywords: Eyjafjallajökull; Optical properties of volcanic ash; Raman lidar; EARLINET; FLEXPART; HYSPLIT; BSC-DREAM8b

Remote sensing measurements of the volcanic ash plume over Poland in April 2010 by K.M. Markowicz; T. Zielinski; A. Pietruczuk; M. Posyniak; O. Zawadzka; P. Makuch; I.S. Stachlewska; A.K. Jagodnicka; T. Petelski; W. Kumala; P. Sobolewski; T. Stacewicz (pp. 66-75).

This work provides information on selected optical parameters related to volcanic ash produced during the eruption of the Eyjafjöll volcano in Iceland in 2010. The observations were made between 16 and 18 April 2010 at four stations representative for northern (Sopot), central (Warsaw, Belsk) and south-eastern (Strzyzow) regions of Poland. The largest ash plume (in terms of aerosol optical thickness) over Poland was observed at night of 16/17 April 2010 in the layer between 4 and 5.5 km a.s.l. The highest values of the aerosol extinction coefficient reached 0.06–0.08 km⁻¹ at 532 nm (based on lidar observations in Warsaw) and 0.02–0.04 km⁻¹ at 1064 nm (based on ceilometer observations in Warsaw). The corresponding optical thickness due to volcanic ash reached values of about 0.05 at 532 nm and about 0.03 at 1064 nm. These values are similar to those reported for the Belsk station based on lidar observations. The ash mass concentration estimated based on the maximum aerosol extinction coefficient reached 0.22 ± 0.11 mg m⁻³. This value is significantly lower than the limit (2 mg m⁻³) for the aircraft operation.► We observed background volcanic aerosol at 4 Polish station. ► Volcanic ash optical depth reached 0.05 for 532 and 0.03 for 1064 nm. ► Maximum volcanic aerosol altitude was 5–8 km. ► The ash mass concentration was below the limit for aircraft “no fly zone”.

Keywords: Aerosol optical thickness; Remote sensing; Volcano ash; Retrieval; Ceilometer; Lidar; Sun photometer

Volcanic aerosol optical properties and phase partitioning behavior after long-range advection characterized by UV-Lidar measurements by A. Miffre; G. David; B. Thomas; P. Rairoux; A.M. Fjaeraa; N.I. Kristiansen; A. Stohl (pp. 76-84).

In this paper, an UV-polarization Lidar is used to study the optical properties of volcanic aerosol in the troposphere. The particles were released by the mid-April 2010 eruption of the Eyjafjallajökull volcano (63.63°N, 19.62°W, Iceland) and passed in the troposphere above Lyon (45.76°N, 4.83°E, France) after advection over 2600 km. The FLEXPART particle dispersion model was applied to simulate the volcanic ash transport from Iceland to South West Europe, at the border of the air traffic closure area. Time-altitude plots of FLEXPART ash concentrations as well as of aerosol backscattering are presented, showing the arrival of volcanic particles in the troposphere above Lyon and their mixing into the planetary boundary layer. The particle UV-backscattering coefficient was typically 4 Mm⁻¹ sr⁻¹ and highly sensitive and accurate particle UV-depolarization measurements were performed, with depolarization ranging from a few to 44%. After few days long-range transport, observed ash particles are still non spherical. The observed variations of the backscattering and depolarization coefficients can be attributed to variations in the volcanic particles content. Ash mass concentrations are then retrieved. Moreover, a partitioning into spherical and non spherical particles is evaluated from number concentration ratios between solid ash particles and spherical hydrated sulfate particles. The microphysical properties of volcanic particles can thus be studied by associating an UV-polarization remote sensing instrument with a numerical volcanic ash dispersion model.► Volcanic ash particles concentration is measured by ground-based Lidar in troposphere. ► Coupling with FLEXPART ash transport model allows to identify volcanic ash particles. ► Precise UV-depolarization data allows to discern spherical/non spherical particles. ► Phase partitioning between non spherical ash and spherical sulfates is thus evaluated. ► After long-range advection, PBL ash particles are low concentrated and still aspheric.

Keywords: Volcanic ash; Lidar; Depolarization; Dispersion model

Dual-wavelength linear depolarization ratio of volcanic aerosols: Lidar measurements of the Eyjafjallajökull plume over Maisach, Germany by Silke Groß; Volker Freudenthaler; Matthias Wiegner; Josef Gasteiger; Alexander Geiß; Franziska Schnell (pp. 85-96).

The ash plume of the Eyjafjallajökull eruption in April 2010 offered an exceptional opportunity to assess the potential of advanced lidar systems to characterize the volcanic aerosols. Consequently, the plume was continuously observed in the framework of EARLINET. In this paper we focus on the EARLINET-Raman-depolarization-lidar measurements at Maisach near Munich, Germany. From these data sets the lidar ratio S_p and the particle linear depolarization ratio δ_p at two wavelengths (355 nm and 532 nm) were retrieved. These quantities can be used to characterize volcanic aerosols and to establish criteria for the discrimination from other aerosol types. In the pure volcanic ash plume, observed until noon of 17 April, wavelength independent values of δ_p as high as 0.35 < δ_p < 0.38, indicating non-spherical particles, were found, and lidar ratios of 50 < S_p < 60 sr at 355 nm and 45 < S_p < 55 sr at 532 nm. Later, volcanic aerosols were mixed into the boundary layer. This mixture showed in general lower values of δ_p as expected from the contribution of boundary layer aerosols. Especially noteworthy is the increase of δ_p with wavelength, when volcanic ash was mixed with small spherical particles.► Lidar ratio and depolarization ratio of volcanic ash is measured at two wavelengths. ► Changes of both parameters are investigated for volcanic ash mixtures. ► Pure volcanic ash layer show high wavelength independent depolarization ratio. ► Mixtures show wavelength dependent depolarization ratio under certain circumstances. ► The contribution of volcanic ash in aerosol mixtures is determined.

Keywords: Volcanic ash; Lidar measurements; Depolarization; Lidar ratio; Remote sensing

Eyjafjallajökull volcanic ash in southern Italy by Antonio Lettino; Rosa Caggiano; Saverio Fiore; Maria Macchiato; Serena Sabia; Serena Trippetta (pp. 97-103).

PM2.5 in situ measurements were performed at the Istituto di Metodologie per l’Analisi Ambientale of the National Research Council of Italy (CNR-IMAA, Tito Scalo – Southern Italy) beginning 20 April 2010, the date when the Eyjafjallajökull volcanic ash plume first arrived over Southern Italy. The PM2.5 particles collected during the passage of the volcanic ash were analyzed for concentration, chemical composition, and mineralogical and morphological features. PM2.5 and Al, Ca, Fe, K, Mg, Mn, and Ti daily concentrations increased during the first days of sampling and reached their highest value on 22 April. On that day, ground-based remote sensing observations performed at the CNR-IMAA Atmospheric Observatory (CIAO) showed the volcanic ash mixing with the underlying local aerosol layer. A Field Emission Scanning Electron Microscope and Energy-Dispersive X-ray Spectroscopy (FESEM-EDS) analysis performed on the PM2.5 samples collected during the period under study revealed the falling of the volcanic ash particles onto the ground. Ash particles were distinguished from background particles in both the fine and coarse size fractions. In particular, complex secondary aerosols (mainly sulphates and nitrates), likely related to the Eyjafjallajökull volcanic emissions, were found in the fine fraction. The coarser volcanic particles were mainly composed of minerals associated with basaltic-to-andesitic magmas. SEM observations conducted on volcanic particles showed that the surfaces of the smallest particles contained condensate phases of soluble components, mainly derived from the oxidation and hydration of SO₂ released during the eruptions. The volcanic ash particles were mainly concentrated in the samples collected on 21–22 April. This agreed with the increase in the concentration of PM2.5 and the volcanic ash-related chemical elements measured in the PM2.5 samples.► PM2.5 measurements were performed during the Eyjafjallajökull volcanic eruption. ► PM2.5 particles were analyzed for concentration, chemical composition and morphological features. ► FESEM observations revealed the falling of the volcanic ash particles onto the ground. ► Volcanic particles were distinguished in both the fine and coarse size fractions. ► Complex secondary aerosols and condensate phases of soluble components were found in the fine and coarse fraction, respectively.

Keywords: Eyjafjallajökull; Aerosol particles; Volcanic ash; Chemical composition; SEM

In-situ observations of Eyjafjallajökull ash particles by hot-air balloon by T. Petäjä; L. Laakso; T. Grönholm; S. Launiainen; I. Evele-Peltoniemi; A. Virkkula; A. Leskinen; J. Backman; H.E. Manninen; M. Sipilä; S. Haapanala; K. Hämeri; E. Vanhala; T. Tuomi; J. Paatero; M. Aurela; H. Hakola; U. Makkonen; H. Hellén; R. Hillamo; J. Vira; M. Prank; M. Sofiev; M. Siitari-Kauppi; A. Laaksonen; K.E.J. lehtinen; M. Kulmala; Y. Viisanen; V.-M. Kerminen (pp. 104-112).

The volcanic ash cloud from Eyjafjallajökull volcanic eruption seriously distracted aviation in Europe. Due to the flight ban, there were only few in-situ measurements of the properties and dispersion of the ash cloud. In this study we show in-situ observations onboard a hot air balloon conducted in Central Finland together with regional dispersion modelling with SILAM-model during the eruption. The modeled and measured mass concentrations were in a qualitative agreement but the exact elevation of the layer was slightly distorted. Some of this discrepancy can be attributed to the uncertainty in the initial emission height and strength. The observed maximum mass concentration varied between 12 and 18 μg m⁻³ assuming a density of 2 g m⁻³, whereas the gravimetric analysis of the integrated column showed a maximum of 45 μg m⁻³ during the first two descents through the ash plume. Ion chromatography data indicated that a large fraction of the mass was insoluble to water, which is in qualitative agreement with single particle X-ray analysis. A majority of the super-micron particles contained Si, Al, Fe, K, Na, Ca, Ti, S, Zn and Cr, which are indicative for basalt-type rock material. The number concentration profiles indicated that there was secondary production of particles possibly from volcano-emitted sulfur dioxide oxidized to sulfuric acid during the transport.► Both sub-micron and super-micron aerosols observed inside Eyjafjallajökull volcanic ash plume. ► Observations consistent with SILAM modelling. ► Indications of secondary particle formation inside the plume.

Keywords: Volcanic ash; Vertical profiles; Atmospheric aerosols

Geochemical characterization of single atmospheric particles from the Eyjafjallajökull volcano eruption event collected at ground-based sampling sites in Germany by Nina Schleicher; Utz Kramar; Volker Dietze; Uwe Kaminski; Stefan Norra (pp. 113-121).

Volcanic particles can be transported over long distances in the atmosphere and can cause severe problems for air traffic. This was the case over large areas of Europe in spring 2010 after the eruption of the Eyjafjallajökull (E15) volcano on Iceland.The scope of this work was to characterize these volcanic particles more in detail with regard to size and chemical composition in order to provide valuable information needed for a better estimation of the possible impact on airplane jet engines and cockpit windows. Another question of this study was which share of the overall atmospheric particles in Germany originated from the E15 eruption and whether this amount of volcanic particles could cause any adverse health effects to humans. To this end, single particle analysis by means of scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) and synchrotron radiation based micro X-ray fluorescence analysis (μS-XRF) together with multivariate statistical methods were applied for samples collected on ground-level in Southwest Germany and Iceland. Based on the obtained chemical fingerprints combined with multivariate statistical methods it was possible to discrimate between the amount of volcanic particles from Iceland and other atmospheric particles from non-volcanic sources. This aspect distinguishes this single particle approach from most other studies. The results of the study showed that at least 40% of the analyzed particles between 2.5 and 10 μm size at the remote sampling sites in the Black Forest area and about 25% in the city of Freiburg were clearly of volcanic origin from the E15 volcano eruption event.► Volcanic particles, deposited on ground-level in Germany, were characterized. ► The focus of this study was on particles between 2.5 and 10 μm size. ► A geochemical fingerprint was obtained by single particle analyses (SEM-EDX, μS-XRF). ► Results showed that 40% of the analyzed particles originated from the E15 volcano.

Keywords: Volcanic particles; Eyjafjallajökull (E15); Single particle analysis; SEM-EDX; Microsynchrotron radiation based X-ray fluorescence analysis (μS-XRF); Geochemical fingerprint

April–May 2010 Eyjafjallajökull volcanic fallout over Rimini, Italy by Paolo Rossini; Emanuela Molinaroli; Giovanni De Falco; Federica Fiesoletti; Stefano Papa; Elena Pari; Alberto Renzulli; Pierpaolo Tentoni; Alessio Testoni; Laura Valentini; Gabriele Matteucci (pp. 122-128).

Located at a distance of approximately 3200 km from Iceland, where the Eyjafjallajökull volcano erupted, Italy was affected by volcanic ash transported by middle altitude air masses across Europe. Volcanic emissions from the Eyjafjallajökull eruption in April 2010 were detected in Rimini (44° 2′ 28" N, 12° 34′ 3" E) (Italy) by means of in-situ measurements (sampling of bulk depositions). Sampling was carried out during the period April–August 2010, and the following parameters were determined: grain size, TSP, mineralogy, particle morphology and chemical content in terms of Br⁻, Cl⁻, F⁻,SO42−, Al, As, Ba, Be, Ca, Cd, Ce, Co, Cr, Cu, Fe, Hg, K, Li, Lu, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Se, Si, Sn, Sr, Tb, Te, Ti, Tl, U, V, Y, Zn and Zr. Information from the Hysplit-NOAA back trajectory helped to identify the origin of the air mass. The results obtained from the observations are in good agreement with similar studies carried out by other European scientists, confirming that the Eyjafjallajökull ash plume also had a surface impact in Italy. The findings of our study support observations made by researchers of the CNR-IMAA Atmospheric Observatory at the EARLINET station in Southern Italy and enlarge the geographical area known to have been affected by fallout from the April–May 2010 eruption of the Eyjafjallajökull volcano.► Eyjafjallajökull volcanic fallout was detected in Rimini, Italy, in April 2010. ► We carried out atmospheric bulk deposition sampling. ► We combined back trajectory modelling, grain size, SEM and chemical data. ► All results agree with similar studies carried out by other scientists. ► The Eyjafjallajökull ash plume had an impact at surface level in Italy, as elsewhere.

Keywords: Eyjafjallajökull ash cloud; Icelandic tephra; Atmosperic bulk deposition chemistry; Grain size; Mineralogy

The Eyjafjallajökull ash plume – Part I: Physical, chemical and optical characteristics by Colin O’Dowd; Darius Ceburnis; Jurgita Ovadnevaite; Giovanni Martucci; Jakub Bialek; Ciaran Monahan; Harald Berresheim; Aditya Vaishya; Tomas Grigas; S. Gerard Jennings; Philip McVeigh; Saji Varghese; Robert Flanagan; Damien Martin; Eoin Moran; Keith Lambkin; Tido Semmler; Cinzia Perrino; Ray McGrath (pp. 129-142).

The Eyjafjallajökull ash plume was detected at the Mace Head Atmospheric Research Station numerous times from April 19th till 18th May 2010 following subsidence into, and dilution in, the boundary layer. The three strongest of these events, lasting 12–18 h, are analysed in detail in terms of physical, chemical and optical properties. The ash size distribution was bimodal with a supermicron mode of 2.5 μm diameter for the one case where it was measured. The submicron mode varied from 185 nm during the high-explosive phase to 395 nm during the low-explosive phase. Non-sea-salt (nss)-sulphate mass was 2.5 times higher during the low-explosive phase. Total particle concentrations ranged from 760 cm⁻³ to 1247 cm⁻³ and were typical of clean air in the region. Between 30% and 39% of submicron chemical mass (i.e. exclusive of water content) was ash primarily composed of silicon dioxide while accounting for the water content, the submicron aerosol was composed of primary ash (15%), nss-sulphate (25%) and water (55%). Hygroscopic growth factors were characteristic of sulphate aerosol but revealed an internally-mixed aerosol pointing to a mix of predominantly primary ash, nss-sulphate and water. For the majority of the ash plumes, all condensation nuclei (CN, diameter > 10 nm) were activated into cloud condensation nuclei (CCN) at a supersaturation of 0.25%. Aerosol absorption increased by about a factor of two in the plume, compared to background levels, while aerosol scattering coefficients increased by an order of magnitude.► The physico-chemical characteristics of the Eyjafjallajökull ash plume are reported. ► The submicron ash particles are composed of sulphuric acid, water and silicon dioxide. ► The ash particles are highly water soluble with a very high CCN efficiency.

Keywords: Volcanic ash plume; Aerosol; Dispersion; Mace Head

The Eyjafjallajökull ash plume – Part 2: Simulating ash cloud dispersion with REMOTE by C. O'Dowd; S. Varghese; D. Martin; R. Flanagan; A. McKinstry; D. Ceburnis; J. Ovadnevaite; G. Martucci; J. Bialek; C. Monahan; H. Berresheim; A. Vaishya; T. Grigas; Z. McGraw; S.G. Jennings; B. Langmann; T. Semmler; R. McGrath (pp. 143-151).

The recent eruption of Iceland's Eyjafjallajökull volcano caused extensive disruption across Europe. In this paper, we describe the volcanic ash parameterisation incorporated in the regional climate model (REMOTE) for forecasting volcanic ash dispersion. We investigate model sensitivity to emission parameters including eruption column height and vertical release distribution. Model results over a number of key ash incursion events are assessed in terms of agreement with both ground based measurements and retrieved LIDAR data at a number of European sites.► The capability of a regional climate model to predict volcanic ash dispersion was assessed. ► Sensitivities to emission heights and line source flux distribution are clearly illustrated. ► Model output validated using available in-situ measurements.

Keywords: Eyjafjallajokull; Volcanic ash; Dispersion; Modelling

A study of the arrival over the United Kingdom in April 2010 of the Eyjafjallajökull ash cloud using ground-based lidar and numerical simulations by B.J. Devenish; D.J. Thomson; F. Marenco; S.J. Leadbetter; H. Ricketts; H.F. Dacre (pp. 152-164).

We make a qualitative and quantitative comparison of numerical simulations of the ash cloud generated by the eruption of Eyjafjallajökull in April 2010 with ground-based lidar measurements at Exeter and Cardington in southern England. The numerical simulations are performed using the Met Office’s dispersion model, NAME (Numerical Atmospheric-dispersion Modelling Environment). The results show that NAME captures many of the features of the observed ash cloud. The comparison enables us to estimate the fraction of material which survives the near-source fallout processes and enters into the distal plume. A number of simulations are performed which show that both the structure of the ash cloud over southern England and the concentration of ash within it are particularly sensitive to the height of the eruption column (and the consequent estimated mass emission rate), to the shape of the vertical source profile and the level of prescribed ‘turbulent diffusion’ (representing the mixing by the unresolved eddies) in the free troposphere with less sensitivity to the timing of the start of the eruption and the sedimentation of particulates in the distal plume.► Numerical simulation of ash cloud generated by Eyjafjallajökull in April 2010. ► Comparison with lidar data. ► Sensitivity studies.

Keywords: Atmospheric dispersion; Lidar; Volcanic ash

Validation of the FALL3D ash dispersion model using observations of the 2010 Eyjafjallajökull volcanic ash clouds by A. Folch; A. Costa; S. Basart (pp. 165-183).

During April–May 2010 volcanic ash clouds from the Icelandic Eyjafjallajökull volcano reached Europe causing an unprecedented disruption of the EUR/NAT region airspace. Civil aviation authorities banned all flight operations because of the threat posed by volcanic ash to modern turbine aircraft. New quantitative airborne ash mass concentration thresholds, still under discussion, were adopted for discerning regions contaminated by ash. This has implications for ash dispersal models routinely used to forecast the evolution of ash clouds. In this new context, quantitative model validation and assessment of the accuracies of current state-of-the-art models is of paramount importance. The passage of volcanic ash clouds over central Europe, a territory hosting a dense network of meteorological and air quality observatories, generated a quantity of observations unusual for volcanic clouds. From the ground, the cloud was observed by aerosol lidars, lidar ceilometers, sun photometers, other remote-sensing instruments and in-situ collectors. From the air, sondes and multiple aircraft measurements also took extremely valuable in-situ and remote-sensing measurements. These measurements constitute an excellent database for model validation. Here we validate the FALL3D ash dispersal model by comparing model results with ground and airplane-based measurements obtained during the initial 14–23 April 2010 Eyjafjallajökull explosive phase. We run the model at high spatial resolution using as input hourly-averaged observed heights of the eruption column and the total grain size distribution reconstructed from field observations. Model results are then compared against remote ground-based and in-situ aircraft-based measurements, including lidar ceilometers from the German Meteorological Service, aerosol lidars and sun photometers from EARLINET and AERONET networks, and flight missions of the German DLR Falcon aircraft. We find good quantitative agreement, with an error similar to the spread in the observations (however depending on the method used to estimate mass eruption rate) for both airborne and ground mass concentration. Such verification results help us understand and constrain the accuracy and reliability of ash transport models and it is of enormous relevance for designing future operational mitigation strategies at Volcanic Ash Advisory Centers.► We perform high-resolution numerical simulations of the Eyafjallajökull volcanic ash clouds. ► Source term is assessed hourly using different models and plume heights from radar. ► We perform quantitative model validations versus in situ and remote ground-based observations. ► Results are crucial for knowing volcanic ash dispersion model limitations.

Keywords: Volcanic ash dispersion; Numerical model; Model validation; 2010 Eyjafjallajökull eruption

The ash dispersion over Europe during the Eyjafjallajökull eruption – Comparison of CMAQ simulations to remote sensing and air-borne in-situ observations by Volker Matthias; Armin Aulinger; Johannes Bieser; Juan Cuesta; Beate Geyer; Bärbel Langmann; Ilya Serikov; Ina Mattis; Andreas Minikin; Lucia Mona; Markus Quante; Ulrich Schumann; Bernadett Weinzierl (pp. 184-194).

The dispersion of volcanic ash over Europe after the outbreak of the Eyjafjallajökull on Iceland on 14 April 2010 has been simulated with a conventional three-dimensional Eulerian chemistry transport model system, the Community Multiscale Air Quality (CMAQ) model. Four different emission scenarios representing the lower and upper bounds of the emission height and intensity were considered. The atmospheric ash concentrations turned out to be highly variable in time and space. The model results were compared to three different kinds of observations: Aeronet aerosol optical depth (AOD) measurements, Earlinet aerosol extinction profiles and in-situ observations of the ash concentration by means of optical particle counters aboard the DLR Falcon aircraft. The model was able to reproduce observed AOD values and atmospheric ash concentrations. Best agreement was achieved for lower emission heights and a fraction of 2% transportable ash in the total volcanic emissions. The complex vertical structure of the volcanic ash layers in the free troposphere could not be simulated. Compared to the observations, the model tends to show vertically more extended, homogeneous aerosol layers. This is caused by a poor vertical resolution of the model at higher altitudes and a lack of information about the vertical distribution of the volcanic emissions. Only a combination of quickly available observations of the volcanic ash cloud and atmospheric transport models can give a comprehensive picture of ash concentrations in the atmosphere.► The ash dispersion during the Eyjafjallajökull eruption could be reconstructed. ► A conventional three-dimensional Eulerian chemistry transport model was used. ► Comparisons to different types of observations show good agreement for concentrations. ► The vertical ash distribution reveals some model deficiencies. ► The model cannot reproduce rather narrow, distinct ash layers.

Keywords: Volcanic eruption; Ash dispersion; Chemistry transport model; Lidar; Sun photometer; Ash concentration

Simulations of the 2010 Eyjafjallajökull volcanic ash dispersal over Europe using COSMO–MUSCAT by Bernd Heinold; Ina Tegen; Ralf Wolke; Albert Ansmann; Ina Mattis; Andreas Minikin; Ulrich Schumann; Bernadett Weinzierl (pp. 195-204).

The ash plume of the Icelandic volcano Eyjafjallajökull covering Europe in April and May 2010 has notably attracted the interest of atmospheric researchers. Emission, transport, and deposition of the volcanic ash are simulated with the regional chemistry-transport model COSMO–MUSCAT. Key input parameters for transport models are the ash injection height, which controls the ash layer height during long-range transport, and the initial particle size distribution, which influences the sedimentation velocity. For each model layer, relative release rates are parameterised using stereo-derived plume heights from NASA’s space-borne Multi-angle Imaging SpectroRadiometer (MISR) observations near the source. With this model setup the ash is emitted at several levels beneath the maximum plume heights reported by the Volcanic Ash Advisory Centre (VAAC) London. The initial particle size distribution used in COSMO–MUSCAT is derived from airborne in-situ measurements. In addition, the impact of different injection heights on the vertical distribution of the volcanic ash plume over Europe is shown. Ash emissions at specific control levels allow to assess the relative contribution of each layer to the spatial distribution after transport. The model results are compared to aerosol optical depths from European Sun photometer sites, lidar profiles measured over Leipzig/Germany, and ground-based microphysical measurements from several German air quality stations. In particular the good agreement between modelled vertical profiles of volcanic ash and lidar observations indicates that using the MISR stereo-height retrievals to characterize atmospheric ash input provide an alternative to injection height models in case of lacking information on eruption dynamics.► The transport of the Icelandic volcano ash plume is simulated with a regional model. ► For parameterising injection heights MISR satellite retrievals are used. ► The model is evaluated with ground-based in-situ and remote sensing measurements. ► The impact of the injection height on the ash plume distribution is studied. ► MISR stereo-height retrievals can be an alternative to injection height models.

Keywords: Volcanic ash plume; Eyjafjallajökull; Aerosol transport modelling; COSMO–MUSCAT model

Impact of volcanic ash plume aerosol on cloud microphysics by G. Martucci; J. Ovadnevaite; D. Ceburnis; H. Berresheim; S. Varghese; D. Martin; R. Flanagan; C.D. O'Dowd (pp. 205-218).

This study focuses on the dispersion of the Eyjafjallajökull volcanic ash plume over the west of Ireland, at the Mace Head Supersite, and its influence on cloud formation and microphysics during one significant event spanning May 16th and May 17th, 2010. Ground-based remote sensing of cloud microphysics was performed using a K_a-band Doppler cloud RADAR, a LIDAR-ceilometer and a multi-channel microwave-radiometer combined with the synergistic analysis scheme SYRSOC ( Synergistic Remote Sensing Of Cloud). For this case study of volcanic aerosol interaction with clouds, cloud droplet number concentration (CDNC), liquid water content (LWC), and droplet effective radius ( r_eff) and the relative dispersion were retrieved. A unique cloud type formed over Mace Head characterized by layer-averaged maximum, mean and standard deviation values of the CDNC, r_eff and LWC: N_max = 948 cm⁻³,N¯=297cm−3,σN=250cm−3, r eff_max = 35.5 μm,reff¯=4.8μm,σreff=4.4μm,LWCmax=0.23gm−3,LWC¯=0.055gm−3,σLWC=0.054gm−3, respectively. The high CDNC, for marine clean air, were associated with large accumulation mode diameter (395 nm) and a hygroscopic growth factor consistent with sulphuric acid aerosol, despite being almost exclusively internally mixed in submicron sizes. Additionally, the Condensation Nuclei (CN, d > 10 nm) to Cloud Condensation Nuclei (CCN) ratio, CCN:CN ∼1 at the moderately low supersaturation of 0.25%. This case study illustrates the influence of volcanic aerosols on cloud formation and microphysics and shows that volcanic aerosol can be an efficient CCN.► The impact of volcanic aerosol CCN on the cloud microphysics. ► The assessment of the ability and accuracy of the SYRSOC ( SYnergistic Remote Sensing Of Cloud) technique in determining the cloud microphysics. ► The relation of the remote sensing measurements with the physical, chemical and optical in-situ detections of the volcanic plume.

Keywords: Microphysics; Volcanic; SYRSOC; CDNC; Effective radius; Liquid water content

Modelling concentrations of volcanic ash encountered by aircraft in past eruptions by Claire Witham; Helen Webster; Matthew Hort; Andrew Jones; David Thomson (pp. 219-229).

Prolonged disruption to aviation during the April–May 2010 eruption of Eyjafjallajökull, Iceland resulted in pressure to predict volcanic ash plume concentrations for the purpose of allowing aircraft to fly in regions with low ash contamination. Over the past few decades there have been a number of incidents where aircraft have encountered volcanic ash resulting in damage to the aircraft and loss of power to engines. Understanding the volcanic ash concentrations that these aircraft have encountered provides important input to determining a safe concentration limit.Aircraft encounters with six volcanic eruption plumes have been studied and ash concentrations predicted using the atmospheric dispersion model NAME. The eruptions considered are Galunggung 1982, Soputan 1985, Redoubt 1989, Pinatubo 1991, Hekla 2000 and Manam 2006. Uncertainties in the eruption source details (start time, stop time and eruption height) and in the aircraft encounter location and flight path are found to be major limitations in some cases. Errors in the driving meteorological data (which is often coarse in resolution for historic studies) and the lack of eruption plume dynamics (e.g. umbrella cloud representation) results in further uncertainties in the predicted ash concentrations.In most of the case studies, the dispersion modelling shows the presence of ash at the aircraft encounter location. Maximum ash concentrations in the vicinity of the aircraft are predicted to be at least 4000 μg m⁻³ although confidence in the estimated concentrations is low and uncertainties of orders of magnitude are shown to be possible.► Modelled volcanic ash clouds show ash presence at aircraft encounter locations. ► Maximum ash concentrations in the encounter vicinity are 4000 to 200,000 μg m^−3. ► Predictions are complicated by uncertainties in the eruption source parameters and aircraft locations. ► Very large eruptions are not well simulated due to lack of eruption plume dynamics.

Keywords: Volcanic ash; Dispersion modelling; Aircraft encounters; Ash concentration

Attracting structures in volcanic ash transport by Jifeng Peng; Rorik Peterson (pp. 230-239).

Volcanic ash clouds are a natural hazard that poses direct threats to aviation safety. Many volcanic ash transport and dispersion (VATD) models have been developed to forecast trajectories of volcanic ash clouds and to plan safety measures in the events of eruptions. Predictions based on these models are heavily dependent on accuracy of wind fields and initial parameters of ash plumes. However, these data of high accuracy are usually difficult to obtain, leading to possible inaccurate predictions of ash clouds trajectories using VATD models. In this study, a new method is developed to predict volcanic ash transport. In contrast to many existing VATD models that simulate the evolution of volcanic ash clouds, the new method focuses on the overall properties of the wind field in which volcanic particles are transported and correlates particle motion to the attracting structures that dictate the transport. As demonstrated in the study of Eyjafjallajökull eruption in Iceland in April, 2010, these structures act as attractors in the atmosphere towards which volcanic ash particles are transported. These attracting structures are associated with hazard zones with high concentrations of volcanic ash. The advantages of the method are that the attracting structures are independent of particle source parameters and are less prone to inaccuracy in the wind field than particle trajectories. The new approach provides the hazard maps of volcanic ash, and is able to help improve long-term predictions and to plan flight route diversions and ground evacuations.► A new model of volcanic ash transport based on a dynamical systems approach. ► The model identifies attracting structures in the wind flow field. ► The attracting structures are associated with volcanic ash hazard zones.

Keywords: Volcanic ash transport; Aviation; Attracting structures

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