Aeolian Research 9 (2013) 191–202

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Aeolian Research

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Volcanic ash particulate matter from the 2010 Eyjafjallajökull eruptionin dust deposition at Prague, central Europe

1875-9637/$ - see front matter � 2012 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.aeolia.2012.12.002

⇑ Corresponding author.E-mail address: navratilt@gli.cas.cz (T. Navrátil).

Tomáš Navrátil a,⇑, Jindrich Hladil a, Ladislav Strnad b, Leona Koptíková a, Roman Skála a

a Institute of Geology AS CR, v.v.i., Rozvojova 269, 165 00 Praha 6, Czech Republicb Laboratories of the Geological Institutes, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic

a r t i c l e i n f o

Article history:Available online 12 February 2013

Keywords:Eyjafjallajökull volcanoIcelandic tephraGrain sizeMineralogyGeochemical analysis

a b s t r a c t

Particles originating from the last major Eyjafjallajökull volcano eruption in April 2010 were subse-quently found in settled dust samples collected in a suburban area of Prague, Czech Republic. These dustsamples contained predominantly non-volcanic particulate matter of super-regional but mainly local ori-gin. The highest proportion of the Eyjafjallajökull material recorded in the Prague daily dust samplesreached 12% of the total lithic component mass. Volcanogenic particles, mostly glasses, were concen-trated in particle size classes from 2.5 to 25 lm, but rare fragments of volcanic glasses up to 50 lm indiameter were also found. The most effective method for detection and identification of the volcanicash particles were morpho-textural observations combined with energy dispersive and wavelength dis-persive analysis of individual grains and X-ray powder diffraction. Because of the low percentage of vol-canic ash particles in the total samples, the geochemical signal was rather weak although detectable interms of selected trace elements and REE distributions. The mineralogy, particle size distributions, andgeochemical compositions of the Prague samples were compared with reference materials sampled nearthe Eyjafjallajökull volcano.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

The atmospheric particulate matter (PM) that passively settleson various surfaces represents a portion of the total dust in theatmosphere at any given place. Similarly, settled dust representsonly part of the total particulate matter that is contained in dustplumes or other types of sources, e.g., diluted dispersion streamsand re-concentration clouds. Both the composition and size dis-tribution parameters of settled dust can significantly differ fromair-sampled dust (e.g., Hladil et al., 2008). Comparisons andstrict differentiation between settled dust and air sampled dust(usually expressed as PM2.5 or PM10) have been well establishedfor city- and indoor-dust (Rosas et al., 1997), but studies in out-door conditions usually prefer air sampled dust (Cao et al.,2011). Because of particle size separation, air filtering methodstend to omit recording the largest mineral grains and lithic par-ticles (Valmari et al., 2002). These mineral grains and lithic par-ticles, which can be up to several tens of micrometers in size(rarely even up to hundreds of micrometers), are the main carri-ers of source material petrological signatures. For this reason, wefocus here on settled dust samples. Another important aspect ofour study is that dust transported over long distances suffers a

loss of characteristic uniformity and can have a complex trans-port history (e.g., Aleon et al., 2002; Liu et al., 2004). Atmo-spheric dust can be contaminated with local dust duringtransport because of overlapping wind trajectories, especiallyover heavily industrialized areas (e.g., Mahowald et al., 2009;Sholkovitz et al., 2009). The most common natural sources ofcontinental dust and atmospheric particulate materials are fromweathering processes such as wind-erosion of protosols-soils,lacustrine and river sediments or re-suspension of previouslydeposited dusts that are uplifted to higher altitudes after ex-treme dust storm events like tornadoes.

Natural disasters such as forest fires and volcanic eruptions aresignificant natural processes that emit particulate materials intothe atmosphere, although their contributions are one order of mag-nitude smaller than that of the loess in the atmosphere in terms ofglobal averages – (e.g., Tegen and Schepanski, 2009; Hladil et al.,2010). City dust originates from various anthropogenic industrialand urban activities such as road traffic, combustion or construc-tion, combined with the weathering and bio-erosion of manyanthropogenic materials. It is general knowledge that the Earth’satmosphere has been effective in mediating the transport of finedust and particulate material over long distances. Determiningthe origin of individual components in settled dust is critical to abetter understanding of atmospheric transport/mixing and sedi-mentation pathways.

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One recent example of a disastrous volcanic event accompaniedby the emission of large amounts of particulate material into theatmosphere was the 2010 Eyjafjallajökull eruption in Iceland. Thisevent provided a good opportunity to trace explosively emittedvolcanic ash particles and their relatively gradual delivery to dis-tant areas (Schleicher et al., 2011; Rossini et al., 2011). Therefore,the main goal of our study was to use data from daily sampled set-tled dust at the Prague-Suchdol site (suburban district of Prague,Czech Republic) in central Europe to provide insight into the quan-titative and compositional evolution of relevant volcanic ash-com-mon dust mixtures and their signatures in the samples.

The Eyjafjallajökull eruption of 14 April 2010 and subsequentdays emitted large amounts of particulate matter that were trans-ported towards European airspace as a result of atmospheric con-ditions over Iceland (Davies et al., 2010). Because of the possibleadverse effects of atmospheric particulate material on aircraft en-gines, the situation resulted in an extreme disruption of air trafficin Europe and above the northern Atlantic Ocean (15–20 April). De-spite extensive mapping of airborne ash particle dispersal by mod-eling, ground based instruments and satellite techniques, little isknown about ash particle deposition, especially in distal regions(Rossini et al., 2011; Schleicher et al., 2011). The particulate matterof volcanic ash has a characteristic mineralogy (fresh unalteredcrystals, often glass coated), glass-shard morphology, and geo-chemical composition. The major and minor element chemicalcomposition of dust containing volcanic ash is often used as a fin-gerprint of its source (e.g., Tanner et al., 2008; Hladil et al., 2008;Sell and Samson, 2011).

Prague is the capital and largest city of the Czech Republic, withover 1.2 million citizens (Fig. 1). The passive deposition of dust hasbeen monitored in the city for the period 1986–2006 using a net-work of manually operated ground-based stations. Annual valueshave decreased significantly since 1986 (0.716 g m�2 day�1), andthe latest reported annual mean passive dust deposition for Praguewas reported as 0.142 g m�2 day�1 in 2006 when the Prague mea-surements were discontinued (Dusek and Pospisilova, 2007). Thereduced dustiness in the city area is most likely because formerlarge scale industrial sources within Prague were significantlydiminished or abolished during the past 20 years. In contrast, roadtraffic has rapidly increased accompanied by an expansion in roadand building construction activities.

In this paper we present the ‘fingerprint’ of the background dustdeposited in Prague during the 5-month period prior to the Eyjaf-jallajökull eruption on 14 April 2010. Using mineralogical and geo-chemical methods we show that volcanic ash from theEyjafjallajökull eruption is present in dust deposited in Prague onApril 19 and April 21. We used proximal ash fall samples collectedclose to the Eyjafjallajökull volcano on Iceland as referencematerial.

2. Materials and methods

The settled dust samples were collected on sets of 20 plastictrays (each 0.15 m2 in area, for a total area of 3 m2). Trays wereplaced �5 m above ground on a terrace at the Institute of Geologylocated within the Prague-Suchdol Academic Campus (50.12632N,14.38255E, 280 m a.s.l.). A ground monitoring station (50.12652N,14.38463E, 277 m a.s.l.; acronym/code ASUC) belonging to the net-work of the Czech Hydrometeorological Institute is located withinthe campus 155 m away from the settled dust collection site. Thissub-urban background station has been continuously monitoringaerosol concentrations (PM10) and other atmospheric parameters(temperature, relative humidity, concentrations of NOx, SO2 andO3, etc.) since the year 2004.

One tray set was set out for 5 months, prior to the Eyjafjallajökulleruption and serves as a reference for settled dust background (BG)at this collection site. Trays for monitoring of possible contributionof eruption-associated dust were set out from 15 April to 20 May2010 and collected every 24-h at 07:00 UTC. Two 24-h samples fromthis site were selected for detailed analysis: April 19–20 and 21–22(hereafter referred to as samples 19 and 21). We selected these sam-ples based on (1) sufficient sample quantity, (2) a high proportion ofvolcanic material estimated by visible inspection, and (3) substan-tial difference in color compared with the BG sample.

The plastic trays containing the dust were rinsed with distilledwater, cleaned with a plastic window cleaner and rinsed again to min-imize the contamination between the sample periods. The resultingsuspension was first collected in mixing buckets and then settled inglass cylinders. Settled particulate matter was re-suspended in dis-tilled water and poured into large-size Petri dish for drying under lab-oratory temperature in a flow box. The analyzed particulate materialwas depleted from water-soluble colloid complexes or easily solubleinorganic compounds. For whole-particle analysis, the dried particu-late matter was mixed and powdered using a pestle and mortar to400 mesh (0.037 mm) size for ICP-MS analysis.

Four proximal ash fall samples from the Eyjafjallajökull area onIceland were also analyzed. The first sample was collected on 15April 2010, �06:00 UTC (58 km ESE of the vent, in the Pykkvabaej-arklaustur–Fjardragljufur area, �63.515N, 18.485W). Fine ash fromthe margins of the earliest deposited proximal material was col-lected on 28 April 2010 (sample code in the text = Ey; the originalsample code = 15.04.10-2b). Three more proximal coarse-grainedsamples were collected more than 1 month after the eruption (Ey-jafjallajökull peripheries, �6 km N and �8 km S of the volcanoeruption center, respectively; sample 55 was collected at63.68258N, 19.63627W, 184 m a.s.l., and samples 56 and 57 at63.56150N, 19.61874W, 67 m a.s.l.; on 24 June 2010). Proximalsamples were mixed and powdered for whole-rock analysis byICP-MS. The major and trace element analyses were performed atthe Faculty of Science, Charles University, Prague. Whole rock ma-jor element analyses were determined by the wet chemistry tech-nique and followed the methods described in Johnson and Maxwell(1981) and Potts (1995).

Trace elements were determined using a modified total diges-tion in mineral acids (HF + HClO4) and borate fusion (Na2CO3 + Na2-

B4O6) followed by conventional solution nebulisation of ICP-MSThermo Scientific X Series 2 (Faculty of Science, Charles University,Prague) (Strnad et al., 2005). The analytical precision, calculated asone relative standard deviation (RSD), ranged from 0.5% to 8%. TheQA/QC was controlled using the granite (G-2, USGS) and basalt(BCR-2, USGS) reference materials.

In addition to standard optical methods using a binocular lensand a polarizing microscope, we used scanning electron micros-copy (SEM) and analyses applying energy dispersive (EDS) andwavelength-dispersive (WDS) spectrometers. Particle size was as-sessed using SEM and analyzing six slides each of a single-particlethick layer and tracing 225 imaged particles using a square grid(i.e., the total number of analyzed particles for one sample was ap-prox. n = 1350). Equivalent particle diameters were calculatedusing image analysis and assigning to size classes of the most com-monly used mean size classes (1; 2.5; 5; 10; 25; 50 lm). Grain sizeand shape plus textural relations of the mineral grains and lithicparticulates were studied on an SEM TESCAN VEGA3. The compo-sition of individual phases was determined using EDS on a JEOLJSM 6460 (Institute of Physics AS CR, v.v.i.), and precise determina-tions of compositions in polished sections were made by the elec-tron probe microanalyzer (EPMA) CAMECA SX-100 (Institute ofGeology AS CR, v.v.i.) operated at an accelerating voltage of15 kV, sample current of 10 nA and beam diameter �2 lm. Thestandards used were: leucite (K), apatite (Ca, P), rutile (Ti),

Fig. 1. Location and trajectories. Selected ensemble backward air mass trajectories provide proxies for the possible transport of volcanic ash and mixing with other dustcomponents in the atmosphere (calculated using the online HYSPLIT-model tool, isentropic mode). Left column: 19 April 2010, 19:00 UTC (mid-time of the 24-h 19–20 settleddust sampling interval); right column: 21 April. Rows: altitudes 500, 2000 and 5000 m a.s.l. at Prague-Suchdol (50.13, 14.38 position point).

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synthetic Mn,Cr-spinel (Mn, Cr), magnetite (Fe), jadeite (Na, Al),quartz (Si), olivine (Mg), marcasite (S), pentlandite (Ni) and barite(Ba). All elements were analyzed on Ka spectral lines except Bawhich was analyzed on La line. Chemical data were further pro-cessed using SYSTAT software.

The X-ray powder diffraction patterns (XRD) were acquiredwith a Philips X’Pert diffractometer employing CoKa radiation.Phase identification was carried out with the program Bede ZDSSearch/Match with Powder Diffraction File database of The Inter-national Centre for Diffraction Data (ICDD PDF-2). The detectionlimit of individual phases may be estimated to be �1–5 wt%depending on the scattering powers of matrix and analyte,respectively.

Fig. 2. Atmospheric conditions and deposition parameters. Relative humidity (h)and daily mean temperatures (Tm) compared with PM10 concentrations – see thetext; near-ground data from Prague-Suchdol. Daily mean values of precipitation arecompared with amounts of settled dust (24-h data); the lines show the trends, notdata in between. The proportional evolution of the volcanic component is on thelogarithmic scale.

3. Results and discussion

3.1. Volcanic ash dispersal conditions related to the geographiclocation of Prague

In the early morning of 14 April 2010 (after �06:00 UTC), thesubglacial Eyjafjallajökull eruption (63.629�N, 19.630�W) entereda strong explosive phase and emitted tephra with volcanic gasses�8 km up into the atmosphere. During the first week, eruptionclouds of various heights occurred (on average 4 km) (e.g., Gislasonet al., 2011; and reports cited therein). The dispersion of particu-late materials was mostly determined by the presence of a typicalhighly stable jet stream at the time of eruption. This jet stream wasaccompanied by extremely high velocity winds in middle to uppertropospheric altitudes, which headed directly toward central Eur-ope during the first 2 days (with trajectories directly to Prague,Fig. 1). Almost all trajectories calculated for the early eruptionstages (http://ready.arl.noaa.gov/HYSPLIT.php; Draxler and Rolph,2010) indicated that particulate matter from the plume’s mainbody could reach Prague as early as 18 h after the beginning oferuption. Although the masses of the earliest daily settled dustwere small, they contained a relatively high proportion of volcanicparticles (Fig. 2). On 19 and 20 April, when the highest PM10 con-centrations were measured by ground-based automatic stationASUC, all back trajectories originated from Eyjafjallajökull (Fig. 1).

According to concentrations detected in lidar profiles, a highpressure system reported over the southern part of Iceland on14/15 April moved further over Scandinavia and caused north-westerly winds that mediated transport of volcanic ash acrossthe North Atlantic towards Great Britain, Scandinavia, and laterinto central Europe (Flentje et al., 2010; Belosi et al., 2011). Asshown by many online sources, the areas impacted by volcanicash concentrations extended very rapidly, so that the situationon 17 April showed a broad belt from the central mid-latitudeNorth Atlantic Ocean, reaching the Adriatic coast and Crimea,and continuing to the Volga River Basin and Northern Urals (e.g.,Timofte et al., 2011).

Due to the increased probability of higher particulate matterconcentrations in air at altitudes �5–6 km, the Czech airspacewas closed from 11:00 UTC on 16 April to 10:00 UTC on 19 April.Over the area of Prague, visibly increased dust concentrations werefound only episodically (satellite RGB-composite data; 24-h atmo-spheric microphysics tool – Czech Hydrometeorological Institute);such mid-tropospheric re-concentration clouds occurred, e.g., dur-ing the night hours on 16/17 and 19/20 April. On the other hand,the closely adjacent ground station ASUC reported PM10 concentra-tion values that did not exceed 45 lg m�3 in the air 2 m above theground (with an average of 23 lg m�3) for the entire relevant per-iod of settled dust monitoring (14 April to 19 May 2010). Moreover,fluctuations in these values correlate negatively (r = �0.75, n = 31,p < 0.001) with relative air humidity but positively with mean daily

temperatures (r = 0.46, n = 31, p < 0.05) (Fig. 2). This means thatvariation patterns of such type (and also the absolute values ofair-sampled PM10) were almost indistinguishable from most com-mon situations, which occur regularly in the Czech Republic (Sker-il, 2009).

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3.2. Prague-Suchdol dust deposition in the period affected by volcanicash

The mass of settled dust was monitored daily from 15 April to19 May 2010. The first significant increase in sedimentation of par-ticulate matter started on 16 April 2010 when 0.075 g m�2 day�1

was noted. Deposition of PM at Prague-Suchdol increased gradu-ally from 0.001 g m�2 day�1 on 14 (14–15) April 2010 to0.150 g m�2 day�1 on 19 (19–20) April, with an excessive maxi-mum of 0.600 g m�2 day�1 on 21 (21–22) April (Fig. 2). Since 24April, both the data for dustiness (measured by PM10 monitors)and amounts of settled dust showed fluctuating yet in generaldecreasing trends (Fig. 2). In comparison to concentrations ofPM10 in air (�dustiness), the masses of daily settled dust samplesand the proportion of Eyjafjallajökull ash particles declined muchmore steeply (Fig. 2, bottom panels). The observed fluctuations ofair PM10 in the beginning of May, as well as the fluctuating massesof settled dust, could not be conclusively identified as differing sig-nificantly from the common site conditions.

Most of the daily April settled dust (since 14 April) depositedunder dry conditions: light showers were reported only on 14–15 April, with daily totals of less than 2 mm, and then very slightprecipitation on 21, 26–27 and 30 April (drizzle/spray, daily totalless than 0.1 mm). On the other hand, the dust deposition in May(until 19 May) was both dry and wet, because there were only 3days without precipitation (totally dry days occurred only on 8and 16–17 May). Daily rainfall totals correlated positively withhumidity (Fig. 2); rain occurred when mean daily relative humiditywas �60% or higher. Although the negative correlation betweenhumidity and PM10 concentrations in air was a dominant feature,there were some exceptions, e.g., between 9 and 11 May 2010(Fig. 2). However, the relations of daily settled dust masses tohumidity, rainfall and PM10 concentrations are more complex.The initial period between 15 and 24 April 2010 characterized bythe highest dust deposition corresponds to a relatively low humid-ity period. There was one exception on 21 April, where maximumdust deposition took place with reduced air PM10 concentrationsand slightly increased humidity (Fig. 2). The moderately elevateddeposition masses on 6 and 14 May correspond to increased pre-cipitation (Fig. 2).

These relationships, and particularly the ratio between the Ey-jafjallajökull components and the whole mass of the settled dust(Fig. 2), allowed us to characterize the deposition period from�15–16 April to �24–28 April as clearly forced (but not completelycontrolled) by the delivery of the Eyjafjallajökull volcanic ashmaterial.

3.3. Settled dust deposited at Prague-Suchdol

Samples 19 and 21 were collected in Prague-Suchdol during andshortly after the period of air traffic restriction. They both con-tained particles sized in a broad range between 1 and 50 lm. Sam-ple 19 had an increased abundance of particles with equivalentdiameters of �10 and 2.5 lm, and sample 21 showed an unusuallystrong dominance of mineral grains and lithic particles sized�10 lm (Fig. 3). Volcanogenic particles reaching �100 lm (recal-culated to an equivalent diameter of isometric imaginary shape)were extremely rare.

Routine identification of Eyjafjallajökull volcanogenic particlesusing optical and scanning-electron microscopy was based mainlyon the documentation of indisputable characteristics of volcanicash markers such as large fragments of vesicular glass, presenceof pyroxenes, plagioclases, potassium feldspars and hydrous alu-minum silicate minerals (Fig. 4). Characteristics of distal samplescompare well with those of proximal sample Ey from Iceland. Like-wise, the well determinable volcanic ash particles in all samples

are commonly 10 lm in equivalent diameter regardless if they ex-ist as single particles or aggregates of particles. This size categorywas markedly enhanced in the Prague dust sediment. The well rec-ognizable marker particles were only a small part of the entire vol-canic ash component. The mass proportion of the marker particlesin ash material was usually 25 (±5) wt%; the remaining amount offine volcanic ash adhered to surfaces of common dust particles orwere embedded in loose aggregates of various origin (cf. the over-all tendency to aggregation in volcanic ash since the early phases ofthe volcanic cloud evolution – Taddeucci et al., 2011). According tothe EPMA data, glass was a predominant component within thevolcanogenic lithic material. The analyzed glasses were either al-most pure silica or they were melts containing in average about60 wt% SiO2 and 17 wt% Al2O3; FeO, CaO, Na2O and MgO are on sin-gle % level only (Table 1 and Fig. 4). The most typical were bulkyshards of glass with scattered equant vesicles (Fig. 5), but thinand bent glassy shards were also common. The feldspatic and fer-roan/ferric-silica glasses were present in amounts reaching 25–35 wt% of the total glass amount.

EDS further indicated the presence of plagioclase crystalloclasts(mostly oligoclase–andesine) and even crystals (e.g., plagioclaselaths). Elongated crystals of augite or diopside were rare, but oc-curred regularly and belonged to prominent and reliable markersthat occurred within samples 19 and 21 (Fig. 4). Additional tracesof Eyjafjallajökull volcanic material include subtle and often sub-rounded sanidine–orthoclase crystals (twins) (Fig. 4). Other impor-tant tracers are fine highly porous, floccular mixtures of complexstructured hydrous aluminum silicates, where micas, chlorites,smectites, kaolinite, montmorillonite, various zeolites and crystal-lites occurred in various proportions within individual aggregates.Accessory amounts of olivine were regularly found as small pheno-crysts and fragments. Amphiboles occurred as elongated, usuallyimperfectly preserved crystals and their chemical compositionsshowed Fe > Ca > Mg; fragments of kaersutite were irregularlyshaped. The amounts of amphiboles were mostly below XRDdetection limits. Quartz and calcium carbonate (aragonite or cal-cite) amounts related to volcanic ash were remarkably low and oc-curred in a variety of forms. Volcanogenic particles transported toPrague were morphologically and mineralogically similar to thosefound in volcanic ash fall samples from Iceland (Figs. 4 and 5). Thedistal volcanogenic material comprised size classes between 2.5and 25 lm equivalent diameters of mineral grains and lithic parti-cles. Specifically, pyroxenes and feldspars crystals and shards oc-curred within the size classes centered at 10 lm.

In spite of this evidence, the basic mineralogy (identified byXRD) of samples 19 and 21 was similar to the background sampleBG (see below). They contained predominantly quartz, calcite,mica, microcline, plagioclase, and kaolinite. On closer examination,the approximate content of calcite in samples 19 and 21 was 2/3greater than in the BG sample. Sample 21 contained admixturesof augite and chlorite-group minerals in amounts detectable byXRD. The estimated proportion of volcanic material contained insample 19 was slightly greater, �12 wt% compared to 8 wt% in set-tled dust sample 21 (cf. Fig. 2). Sample 19 is rich in glass shards butonly small amounts of pyroxenes and hydrous aluminum silicatesare present, approximately half the amount compared to sample21.

Both samples 19 and 21 (containing about 10% Eyjafjallajökullvolcanic ash) show greater loss on ignition (LOI) values of 33.6and 29.0 wt% compared to that of sample BG. The most probableexplanation is a greater proportional contribution of pollen grains,because sample BG was collected mostly throughout the coldperiod of the year when pollen are rare (November–April). The rel-atively high concentrations of pollen grains, spores, and other or-ganic detritus were typical for the northern hemisphere andPrague settled dust samples in spring months (Hladil et al., 2008).

Fig. 3. Particle-size distributions of settled dusts and volcanic ash. The diagrams show counts of particles (left column) and calculated volume proportions (right column); alldiscrete, not continuous data; assigned to given size categories from above and below; the lines are merely trends between neighboring classes. Note the mass (weight)significance of even rare large particles, as well as the higher proportions of settled dust particulate matter for the 10 and 25 lm size-classes (19, 21: dust deposition eventson 19 and 21 April). Samples from Iceland (Ey, and 55–57) and samples from Prague (BG, 19, and 21) – see Section 2 for sample descriptions.

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Fig. 4. The most frequently observed visible types of mineral grains of volcanic ash markers. Comparison of Icelandic (Ey) and Prague (19, 21) material; larger but typicalobjects are selected. Figures of relevant grains in samples Ey, 19 and 21 are in columns; mineral groups in rows. Bar scale in all SEM images is 10 lm. Note that aggregates ofhydrous aluminosilicates are extremely soft and porous.

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Concentrations of Al2O3 and SiO2 are lower in 19 and 21 than inBG, but with a nearly constant ratio (both in wt%) (�0.16 for 19, 21;�0.18 for BG; cf. Table 2). The concentration of CaO was elevated insamples 19 and 21 compared to BG, in accordance with the in-creased proportion of calcite. In terms of Fe2O3, sample 19 con-tained lower concentrations but sample 21 was enriched overthe background. The case of MgO was similar. Concentrations ofNa2O and K2O were virtually similar in both samples and BG. Theconcentration of Zn and Pb were significantly lower for 19 and21 compared to BG, but significantly higher than Icelandic ashsamples (Table 2). The distribution of minor elements in 19 and21 did not vary significantly from BG, with the exception of ele-vated Cr and Ni concentrations in sample 21, not associated withthe presence of volcanic particles.

The BG sample also exhibited particulate matter polydispersionranging from 1 to 50 lm, but proportional contents of mineralgrains and lithic particles around equivalent diameters of 5 and10 lm are significantly enriched (Fig. 3). This enrichment couldbe due to agglutination of tiny particles caused by exposure tomicrobial activity, wetting-evaporation and cryogenic precipita-tion processes. Particle size groups 5 and 10 lm were also typical,with increased count of detrital particles. Due to a relatively highdetection limit, the XRD data show a main overall mineral compo-sition resembling common settled dusts. The sample BG was dom-inated by quartz, calcite, mica, microcline, plagioclase, andkaolinite.

The anthropogenic or urban dust components identified by EDSwere represented by particles originating from various combustion

Table 1Electron probe microanalyses of individual glass particles in samples of proximal (Ey) and distal (19) ejecta.

Na2O MgO SiO2 Al2O3 K2O CaO TiO2 FeO MnO Total

Ey 3.01 1.39 59.26 14.64 2.90 3.85 1.43 8.99 0.40 95.88Ey 7.34 0.05 59.38 25.09 0.47 6.86 0.12 0.87 0.00 100.19Ey 0.99 0.01 69.01 16.81 0.43 7.15 0.02 0.09 0.00 94.52Ey 1.84 1.31 60.40 14.86 2.09 4.01 1.29 9.27 0.31 95.38Ey 3.13 1.31 60.02 15.03 2.14 4.00 1.25 8.73 0.09 95.71Ey 8.08 0.05 61.96 22.24 0.75 5.11 0.15 0.74 0.03 99.13Ey 3.36 1.42 60.09 15.07 2.44 4.01 1.31 9.69 0.06 97.45Ey 6.10 1.17 60.72 15.69 1.92 4.26 1.22 8.14 0.18 99.39Ey 4.92 0.33 65.09 14.00 3.55 2.16 1.05 5.35 0.28 96.72Ey 2.82 0.14 62.84 18.85 2.87 3.73 0.36 0.50 0.16 92.26Ey 5.34 0.98 61.35 14.83 2.59 3.12 1.46 9.69 0.15 99.51Ey 0.46 11.48 48.45 3.25 0.00 20.08 1.55 15.51 0.55 101.32Ey 4.81 0.13 52.93 28.10 0.25 11.75 0.18 1.12 0.00 99.26Ey 2.03 0.37 64.73 20.90 2.55 3.06 0.56 2.02 0.00 96.21Ey 2.83 0.70 65.81 17.07 2.17 4.57 0.39 3.00 0.15 96.7019 1.61 7.27 51.91 8.53 0.93 9.74 2.19 17.79 0.79 100.7619 11.38 0.01 66.84 19.49 0.36 0.52 0.03 0.16 0.03 98.8219 0.09 0.61 69.79 19.94 1.33 0.47 2.01 0.62 0.00 94.8619 7.31 0.24 59.69 16.82 2.09 3.16 1.29 4.69 0.06 95.3519 8.79 0.05 62.65 22.27 0.84 4.63 0.14 0.69 0.16 100.2219 7.63 0.20 60.73 21.58 0.66 5.22 0.20 1.03 0.13 97.3919 1.36 11.66 51.80 4.67 0.17 10.04 0.95 18.75 1.15 100.5519 2.82 1.44 55.93 21.60 5.29 4.57 0.46 5.20 0.19 97.49

Avg prox (15) 3.80 1.39 60.80 17.10 1.81 5.85 0.82 5.58 0.16 97.31Avg distal (8) 3.71 1.78 60.31 16.69 1.68 6.24 0.87 6.17 0.18 97.63

Fig. 5. The upper row represents secondary electron images of tephra glass shards in samples of Icelandic (Ey) volcanic ashes and Prague (19, 21) settled dust material.Middle and bottom rows are back scattered electron images of polished tephra glass grains. Bar scale in all SEM images is 10 lm.

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Table 2Bulk chemical analyses of homogenized dust samples 19, 21 and BG and ash samples Ey, 55, 56 and 57. The data of major elements presented it wt% were obtained by classicalwet analysis and minor elements in mg kg�1 were analyzed with ICP-MS. Not analyzed (n.a.) means that there was no additional homogenized material for Fe2O3/FeO and P2O5

determination available. Concentrations of Fe2O3 (tot.) marked by asterisk, samples 55, 56 and 57, were calculated as a sum of Fe2O3 and FeO.

Praha-Suchdol (mixed dust sediments) Eyjafjallajökull area (ash fall sediments)

19 21 BG Ey 55 56 57

(%)SiO2 43.88 47.13 56.17 61.23 60.73 59.35 58.71TiO2 0.56 0.54 0.69 1.59 1.27 1.44 1.45Al2O3 7.16 7.31 9.97 12.71 13.88 14.11 13.92Fe2O3 (tot.) 5.61 3.93 4.99 8.81 7.97⁄ 8.60⁄ 8.73⁄

Fe2O3 n.a. n.a. n.a. n.a. 3.18 3.27 3.14FeO n.a. n.a. n.a. n.a. 5.11 5.66 5.91MnO 0.09 0.09 0.11 0.24 0.21 0.21 0.21MgO 1.72 1.26 1.66 2.23 2.35 3.15 3.64CaO 4.51 7.48 2.89 4.92 4.24 4.73 4.96Na2O 0.88 0.91 0.89 4.63 5.12 4.85 4.75K2O 1.62 1.67 1.82 1.92 2.31 2.05 1.97P2O5 n.a. n.a. n.a. n.a. 0.23 0.24 0.24Loss on ignition (1000 �C) 33.56 29.03 19.92 1.11 0.66 0.39 0.36Total 99.59 99.34 99.11 99.39 99.29 99.45 99.26

(mg/kg)Li 22.4 22.5 30.5 11.64 18.43 16.55 15.86Be 1.34 1.60 2.08 3.00 4.10 3.74 3.4Sc 8.10 7.06 9.96 14.71 10.71 13.05 12.84V 73.7 62.4 87.7 80.0 80.3 99.6 102.0Cr 81.6 170.44 89.8 37.1 59.1 100.3 107.4Co 11.11 12.41 15.99 13.08 13.69 19.08 21.05Ni 50.3 80.4 53.8 10.28 38.7 66.1 79.7Cu 160 89.1 146 32.4 25.2 32.7 33.4Zn 915 785 3193 155 158 157 154Rb 58.0 57.7 71.7 35.7 50.0 45.2 44.2Sr 138 137 136 306 237 276 287Y 20.1 16.70 23.1 58.1 72.8 68.1 65.8Zr 202 144 174 383 640 578 551Nb 12.53 9.05 15.48 65.7 85.1 77.7 72.5Cs 3.71 3.55 5.26 0.38 0.64 0.49 0.51Ba 1009 466 649 370 506 422 414La 25.7 25.3 37.7 48.9 56.8 53.0 50.9Ce 48.8 46.7 64.7 110 125 117 112Pr 5.49 4.84 6.65 13.79 15.15 14.39 13.79Nd 21.8 18.75 25.2 58.5 62.2 59.6 57.3Sm 4.39 3.61 4.94 13.21 13.94 13.45 12.98Eu 0.91 0.79 1.10 3.90 3.71 3.62 3.56Gd 4.26 3.50 4.65 13.43 14.40 13.76 13.36Tb 0.65 0.53 0.69 2.04 2.29 2.17 2.08Dy 3.58 3.01 3.99 11.48 12.84 12.29 11.79Ho 0.73 0.58 0.80 2.18 2.49 2.33 2.27Er 2.13 1.71 2.39 6.26 7.25 6.91 6.55Tm 0.30 0.25 0.33 0.83 0.99 0.92 0.87Yb 2.04 1.65 2.25 5.29 6.50 6.00 5.74Lu 0.30 0.24 0.33 0.78 0.95 0.87 0.83Hf 6.25 4.36 5.24 10.61 15.18 13.90 12.94Ta 0.77 0.53 0.80 3.63 4.95 4.59 3.99Pb 71.9 89.9 210 11.35 8.50 13.38 13.39Th 6.01 5.79 7.71 4.75 7.60 6.73 6.45U 2.03 1.95 2.48 1.58 2.41 2.14 2.20206Pb/207Pb 1.1632 1.1554 1.1582 1.1971 1.2221 1.2232 1.2200± 0.0030 0.0030 0.0030 0.0040 0.0033 0.0055 0.0050208Pb/206Pb 2.103 2.104 2.102 2.054 2.028 2.023 2.027± 0.007 0.007 0.006 0.008 0.005 0.008 0.006

T. Navrátil et al. / Aeolian Research 9 (2013) 191–202 199

processes (potato-shaped, porous particles of mullite-like compo-sitions and weathered silicate-magnetite microspherules), parti-cles typical for urban locations derived from constructionactivities and from street dust re-suspension (powdered or weath-ered concretes, bricks and mortar, fragmented paintwork, fuel–oilcombustion cenospheres, glass and rock wool, anthophyllite asbes-tos fibers and transport abrasion particles). Similar particles wereidentified by a number of previous works by their morphologyor structure (cf. Tervahattu et al., 2006; Sharonova et al., 2008;Goodarzi and Sanei, 2009).

3.4. Comparative tephra fall samples from the Eyjafjallajökull area

The main difference between the samples of tephra fall col-lected near the Eyjafjallajökull volcano (apart of sampling location)was the time of sampling. The Ey sample includes only volcanic ashparticles emitted during relatively early stage of eruption, until themorning of 15 April 2010. Samples 55, 56 and 57 represent the lateperiods of Eyjafjallajökull eruption. All the proximal tephra fallnear Eyjafjallajökull used for this study (Ey, 55, 56 and 57) exhib-ited a broad polydispersion of particle diameters from 1 to 100 lm.

200 T. Navrátil et al. / Aeolian Research 9 (2013) 191–202

Virtually all these samples have features in common: (1) a highpercentage of fine ash that probably fell as larger particle aggre-gates and disaggregated during transport of the sample, but (2) ageneral lack of �10 lm particles (Fig. 3).

The early deposited Ey ash sample was of different mineralogi-cal composition than that of late ash fall samples 55, 56 and 57.The major mineral phases identified in Ey by XRD were plagioclase,augite, irregularly interstratified montmorillonite–chlorite–micastructure, amphibole and a zeolitic mineral phase. There wasclearly also a large proportion of glass, lack of calcite and kaolinite,but small amounts of quartz. The late-deposited ash (samples 55,56, and 57) did not contain quartz, calcite, or clay minerals; insteadtheir phase composition was dominated by plagioclase, augite anda spinel-group mineral, most probably close to ulvospinel, and for-steritic olivine. In addition to these minerals, hydrogarnet wasidentified in sample 55. Volcanic glass shards are darker coloredand have thin bubble walls in late samples (56 and 57) comparedto the earliest deposits (Ey) (Fig. 5). The EPMA compositions ofindividual tephra glasses correspond to the data for early ashdeposits reported by Sigmarsson et al. (2011). The glasses in earlydeposited ashes showed a great variability of compositions, bothamong the different shards and even within them. These shardsare composed on average of ca. 60 wt% of SiO2 and 17 wt% ofAl2O3, respectively, and FeO, CaO, Na2O, and MgO were well repre-sented (Table 1). The glass morphology was diversified. Roughlyequal proportions of shards were classifiable as massive types withrare bubbles, then types with small and more or less scatteredspherical bubbles and, finally, also very frothy types where thelarge, spherical and/or slightly elongated vesicles were separatedonly by thin walls (Fig. 5). The massive glasses of early origin typ-ically showed high-silica and iron-rich stripes, alternatively,whereas the vesicular glasses of late origin contained thin lathsof plagioclases. In general, the feldspatic and ferroan/ferric-silicaglasses were present in amounts reaching 25–35 wt% of the totalglass amount. In samples 55–57, there were small but visibleamounts of pyroxene (aegirine, augite, diopside, hedenbergite)and amphibole, with crystal fragments dominating euhedral crystals.In the context of these mineralogical insights into the composition ofreference samples from Iceland, it should be noted that the olivinesdelivered and deposited in Prague were more frequently of fayaliticthan forsteritic composition (EDS). These observations merely dem-onstrate how complex the magma mixing and aerial ash historywas (cf. Schumann, 2010; Sigmarsson et al., 2011).

Samples 55–57 were dominated by crystalloclastic fragmentswithout adhered fine particles, but these were frequently abundantin sample Ey.

The volcanic ash samples from Iceland typically had very lowLOI ranging from 0.36% to 1.11% (Table 2) due to their prevailingly

30 40 50 60 70

SiO (wt.%)2

0

10

20

30

40

ProxDist

MINERALS

Ol

Fig. 6. Electron microprobe analyses of silicate mineral grains (left) and glasses (right) inrepresent olivines, pyroxenes and amphiboles, and feldspars. It is clear that several minerApril chemically match the proximal volcanic dust particles. Dist - Prague samples; Pro

mineral character and very low organic content. The concentra-tions of SiO2, Al2O3 and CaO obtained from the bulk sample digest,which averaged 60.0%, 13.7% and 4.7% from four samples, did notdiffer too much from the averaged values for northern hemispheredust-storm dusts (e.g., 60.0%, 14.1% and 3.9%, respectively; cf. Gou-die and Middleton, 2006). This small difference suggested difficul-ties in discerning volcanic signatures from the major elementcomposition. All the ash samples from Eyjafjallajökull eruptionhad increased contents of TiO2, Al2O3, Fe (expressed as Fe2O3

tot.), MnO and MgO when compared to BG as well as to samples19 and 21 (Table 2). The major difference occurred with the evi-dent abundance of sodium. Far more important was that therewere remarkable differences between the proximal and distal sam-ples, which were identified by means of ICP-MS analyses of volca-nic ash and mixed settled dusts and BG from Prague. According tothese analyses, the samples from Icelandic ash falls (Ey and 55–57)possessed relatively high amounts of Sr, Zr, rare earth elements(REE; especially MREE), and Hf and Ta, but abundances of Cr andNi were not increased. The sample Ey was even significantly de-pleted in terms of Cr and Ni (Table 2). The slightly enhanced MREEcontents can be explained by enrichment of purely volcanic ashsamples in P2O5 (phosphates). This signature occurred in spite ofthe almost total absence of pollen in the Eyjafjallajökull samples– the most common carrier of phosphorus in settled dusts withinlocal latitudes (�50�N) (Doskey and Ugoagwu, 1989; Tsukudaet al., 2005). Due to the local anthropogenic contribution of partic-ulate matter, settled dust samples 19, 21 and especially BG exhib-ited significantly enhanced concentrations of Cu, Zn and Pb(Table 2).

4. Final synthesis

The most significant evidence of volcanic ash particles deposi-tion in Prague-Suchdol was the morpho-textural properties ofnumerous individual tephra glass shards and mineral grains suchas whole pyroxene crystals (Fig. 4). Mineral grains are accessorycomponents of distal ash deposits but they represent unique andwell recognizable markers of volcanic ash contribution. Surpris-ingly, the sizes of the mineral crystals and also massive vitricshards often exceeded the equivalent diameter of 10 lm sphericalparticles. Abundance of these particles in distal sediment dustdeposits is much greater than would be generally expected forlong-distance transport. Chemical compositions of individual sili-cate minerals determined by EPMA in Iceland volcanic ash samplesoverlap with the analysis of similar particles in Prague settleddusts (Fig. 6 – left panel). Similar overlap of individual glass shardsanalysis was found for tephra glasses (Fig. 6 – right panel). This evi-dence supports the hypothesis of Eyjafjallajökull volcanic ash being

30 40 50 60 700

10

20

30

40

ProxDist

GLASS

SiO (wt.%)2

studied dust samples. Three principal compositional trends among silicate mineralsal as well as glass grains from settled dust samples collected in Prague on 19 and 21x - Icelandic samples.

Fig. 7. REE distributions (UCC (McLennan, 2001) and Lu normalized shapes),logarithmic axis. The simulation based on mixing of Icelandic ash and backgroundPrague dust components gives proxies to �10% contents of volcanic ash with thepeak Prague deposition events.

T. Navrátil et al. / Aeolian Research 9 (2013) 191–202 201

incorporated into Prague settled dusts. Similar trends were also ob-served for several non-silicate oxide minerals corresponding toeither spinel group or ilmenite group phases.

All the methods used as proxies to estimate the proportions ofEyjafjallajökull volcanogenic components in Prague settled dustsled to similar conclusions (optical microscopy, EDS/EPMA and geo-chemical examination; cf. Fig. 2). The estimates of volcanic ashcontribution to the total mass of settled dust should be consideredwith caution due to possible error caused by combination of in-volved methods which could reach about ±2% (or more). Therefore,we tested the estimated accuracy by application of a mixing modelonto REE distributions (Fig. 7). The UCC and Lu normalized REE dis-tributions for Eyjafjallajökull ash samples showed a very differentshape compared to BG and mixed settled dusts 19 and 21 (Fig. 7).The Eyjafjallajökull ash samples had low abundances of LREE, a po-sitive Eu anomaly and elevated MREE. However, the loosely fittingshape resembling the REE distributions of 19 and 21 was simulatedusing 10% Eyjafjallajökull and 90% BG. Hence, it was confirmed thatthe percentage proportions of Eyjafjallajökull ash in Prague settleddusts between 19 and 22 April were actually about 10%, i.e., at lev-els which were also reached early on 16 April but were never againas high after the 22–24 April decline. A total absence of errant Ey-jafjallajökull particles in Prague settled dusts was not found untilthe end of May. The available data was not extensive enough to al-low making definitive conclusions regarding (1) the complex andmultifaceted evolution of magma in an erupted volcano and emit-ted volcanic ash, (2) the sorting and mixing of particulate matter inatmosphere, and finally, (3) variable parameters during dust depo-sition episodes. Thus, there remain many unanswered questionsand challenges which may perhaps be elucidated by comparingseveral concurrent studies on the Eyjafjallajökull 2010 event.

5. Conclusions

Meteorological conditions in Prague favored the deposition ofatmospheric particulate matter in the period from 16 to 25 April

2010, with a peak in deposition on 21 April 2010. Daily particulate mat-ter deposition samples collected on 19 and 21 April 2010 were ana-lyzed by various methods, and the presence of volcanic particles wasdemonstrated in detail. The contribution of distal volcanic materialto the total sample mass was small (�10%) and the most significant evi-dence came from EDS and XRD methods. Besides the morphologicalsimilarities of single mineral grains and tephra glasses, the overlappingdata from EPMA analyses were the most convincing evidence of volca-nogenic admixture in distal settled dust samples. The geochemicalsignals in settled dust compositions were hardly detectable due tothe character of Prague’s local deposition background, but some evi-dence was gathered by comparing REE patterns.

Acknowledgments

The monitoring of Prague settled dust during the 2010Eyjafjallajökull eruptions was supported by the Czech GrantIAAX00130702 (particulate matter) and research plan RVO67985831 and MSM0021620855 (transport of matter). Thanksare due to a number of individuals and organizations who helpedin this research: A. Langrova, V. Bohmova, Z. Korbelova, J. Jaburk-ova, K. Jurek, M. Jarosova, J. Schwarz, V. Zdimal, D. Rimnacova, O.Sebek, M. Vonaskova, R. Skeril, M. Salek, M. Setvak, L. Kucerova,Z. Charvat, V. Rapprich, J. Haloda, M. Gersl, V. Jankovska, J. Malek– all from the Czech Republic. S.R. Gislason collected sample Eyand J. Malek collected samples 55, 56 and 57. Special thanks goto T. Thordarson, S.R. Gislason, and G. Larsen. We thank D.W. Hard-ekopf for careful reading and language corrections within the finalversion of the manuscript.

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