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Atmospheric Environment 52 (2012) 98e108

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Atmospheric Environment

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Study of present-day sources and transport processes affecting oxidised sulphurcompounds in atmospheric aerosols at Dome C (Antarctica) from year-roundsampling campaigns

Silvia Becaglia,*, Claudio Scarchillib, Rita Traversia, Uri Dayanc, Mirko Severia, Daniele Frosinia,Vito Vitaled, Mauro Mazzolad, Angelo Lupid, Silvia Navae, Roberto Udistia

aDepartment of Chemistry, University of Florence, Sesto Fiorentino, Florence I-50019, Italyb ENEA/UTMEA-TER, S. Maria di Galeria, Roma I-00123, ItalycDepartment of Geography, Hebrew University of Jerusalem, Jerusalem 91905, Israeld ISAC CNR, Bologna I-40129, Italye INFN, Sesto Fiorentino, Florence I-50019, Italy

a r t i c l e i n f o

Article history:Received 18 April 2011Received in revised form27 July 2011Accepted 28 July 2011

Keywords:MSASulphateAerosolAntarctic PlateauTransport processesBiogenic aerosol

* Corresponding author. Tel.: þ39 0554573350; faxE-mail address: silvia.becagli@unifi.it (S. Becagli).

1352-2310/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.atmosenv.2011.07.053

a b s t r a c t

A year-round study, which was conducted from November 2004 to November 2007, of atmosphericoxidised sulphur compounds (methanesulphonic acid (MSA) and sulphate) was carried out in the eastAntarctic Plateau at Dome C (75� 060 S, 123� 200 E, 3220 m a.s.l. and 1100 km away from the nearestcoast). The two sulphur-derived species exhibit a seasonal cycle characterised by maxima in the summerfrom November to March. Size-segregated sampling performed with Andersen 8-stage impactorsrevealed that SO4

2� and MSA have different size distributions in early summer (November) in comparisonwith mid-late summer (February). In November, the size distribution exhibited two distinct modes, theaccumulation (0.4e0.7 mm) and the micrometric mode (1.1e2.1 mm), which is in contrast to Februarywhen only the accumulation mode was observed. The two modes exhibited different speciation; in thefinest mode, sulphate and methanesulphonate were present primarily in the acidic form, whereas theywere present primarily as sodium or ammonium salts in the micrometric mode. The different sizedistributions and speciation patterns in the two months are related to different transport pathways fromoceanic areas to the central Antarctic Plateau. In the early summer months, air masses came primarilyfrom the Indian Ocean and lingered for a long time over the Antarctic continent. The transport of sulphurcompounds is related to sea spray aerosols and the resulting condensation of H2SO4 and MSA over seasalt particles to form sodium salts. In contrast, a rapid transport of H2SO4 and MSA formed above theboundary layer over oceanic areas leads to higher concentrations of the acidic species in the fine fractionof aerosols reaching Dome C in February relative to other summer months.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Aerosol studies carried out at internal sites in Antarctica arefocused on improving our knowledge of present-day sourceintensity, transport efficiency and atmospheric pathways of atmo-spheric particles reaching these remote sites. Understanding theproperties and behaviours of Antarctic aerosols is essential in thestudy of the cycles of natural compounds, as well as in the inter-pretation of past climates based on Antarctic ice core data.

: þ39 0554573385.

All rights reserved.

Chemical aerosol measurements in Antarctica are sparse and aremainly limited to coastal areas (Minikin et al., 1998; Legrand et al.,2001; Jourdain and Legrand, 2002); few aerosol data are availablefrom the central Antarctic regions.

Sulphur aerosols formed from the oxidation of dimethylsulphide (DMS) emitted by phytoplankton play an important role inthe Earth’s albedo; this phenomenon is particularly true in theSouthern Hemisphere (Gondwe et al., 2003) because these oceanicregions have not yet been disturbed by anthropogenic SO2 emis-sions and remain dominated by natural DMS emissions frommarine biota.

The oxidation products of DMS are methanesulphonic acid(MSA) and sulphate. In contrast to sulphate, MSA is exclusivelyformed by photo-oxidation of DMS. MSA records extracted from

Fig. 1. Map of Antarctica with the sampling site (Dome C) and the coastal site Dumont D’Urville.

Table 1Aerosol sampling parameters.

Samplingperiod

Timeresolution

Flow rate(Lmin�1)

Collectedaerosol size

Filters/membranes

PM10 Dec 04eDec 07 1e4 days 38.3 <10 mm Teflon

Dekati4-stages

Jan 06eDec 07 4 days 29.0 >10 mm Policarbonate2.5e10 mm Policarbonate1.0e2.5 mm Policarbonate<1.0 mm Teflon

Andersen8-stages

Dec 04eNov 06 7 days 28.3 9e10 mm Policarbonate5.8e9 mm Policarbonate4.7e5.8 mm Policarbonate3.3e4.7 mm Policarbonate2.1e3.3 mm Policarbonate1.1e2.1 mm Policarbonate0.7e1.1 mm Policarbonate0.4e0.7 mm Policarbonate

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108 99

Antarctic ice cores have been used to investigate past bio-productivity of the Southern Ocean (Legrand and Feniet-Saigne,1991; Legrand et al., 1991; Wolff et al., 2006) and to reconstructthe past extent of sea-ice (Welch et al., 1993; Curran et al., 2003).However, interpretation of MSA ice core records is still ambiguous,due to the complex processes that control the atmosphericformation of MSA (Davis et al., 1998; Preunkert et al., 2008),atmospheric transport processes towards the sampling site relatedto Southern Hemisphere circulation modes (Becagli et al., 2009)and possible post-deposition losses from snow layers (Wagnonet al., 1999; Weller et al., 2004; Traversi et al., 2009).

Atmospheric records of sulphur aerosols are needed to under-stand further these issues. Multiple year-round atmosphericrecords of sulphur aerosols (sometimes completed from DMS data)are scarce both at coastal Antarctic sites (Minikin et al., 1998;Jourdain and Legrand, 2001; Preunkert et al., 2007) and at innerAntarctic Plateau sites where they are mainly restricted to theaustral summer (Arimoto et al., 2001, 2004; Piel et al., 2006; Udistiet al., 2004). The only year-round records were obtained at Dome Cfor only one year (Preunkert et al., 2008) and at Kohnen Station forthe years 2003e2005 (Weller and Wagenbach, 2007) with a two-week resolution.

In this study, we report on the longest high-resolution, year-round record to date of oxidised sulphur compounds (MSA andsulphate) obtained in the central Antarctic Plateau at ConcordiaStation; the study was 3 years in length with a 1e4 day resolution.The seasonal cycles of these sulphur species are interpreted asa function of meteorological conditions leading to the delivery ofoxidised sulphur compounds to Dome C. Furthermore, the sizedistribution of sulphur species, as well as overall chemical compo-sition and backward trajectories, allowed the identification ofsource areas, atmospheric transport conditions and pathways andrelated chemical speciation (acidic or salt form) of polar aerosols.

2. Sampling, instrumentation and methods

Year-round aerosol samplings were carried out beginning inDecember of 2004 at the Concordia Station (Dome C, central Ant-arctica, 75� 060 S, 123� 200 E, 3220 m above sea level), which islocated 1100 km away from the nearest coast in the inner AntarcticPlateau (Fig. 1). The sampling site was located at the edge of the“clean area” approximately 700 m away from the Concordia Italian-French base and was upwind with respect to the dominant winddirection (south-west).

Sampling was carried out using PM10 cut-off head, Dekati4-stage and Andersen 8-stage impactors; the sampling parametersare summarised in Table 1. Filter holders were prepared prior tosampling under a laminar flow hood and brought to the sampling

Fig. 2. Methanesulphonate and sulphate time evolution in the PM10 sampled at DomeC from December 2004 to December 2007. Red dots represent PM10 bulk sampling.Blue and green dots are related to the concentrations in PM10 reconstructed bysumming the concentrations of the stages collecting aerosol fractions with aero-dynamic diameter lower than 10 mm by Dekati 4-stages and Andersen 8-stagesimpactor respectively. Analytical errors for MSA and SO4

2� chromatographicmeasurements are reported as horizontal bars (For interpretation of the references tocolor in this figure legend, the reader is referred to the web version of this article.).

Fig. 3. Panel a: 5 days back-trajectories arriving at 4000 m over Dome C at 00, 06, 12, 18 synoMSA. Air mass velocity along the path is represented by different colors over the back-trajaltitude along each 5 days back-trajectories arriving at 4000 m over Dome C at 00, 06, 12, 18and MSA. Red points show when air mass altitude results lower than the mixing layer one alegend, the reader is referred to the web version of this article.).

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108100

site in polyethylene bags. After sampling, filters were stored in pre-cleaned Petri dishes that were frozen until analysis. Field filterblanks were regularly obtained during the sampling period. Half ofeach filter was extracted with 10 mL of ultrapure water (18 MUMilli-Q) in an ultrasonic bath for 20 min. Blank concentrations werebelow the detection limit for methanesulphonate (i.e., CH3SO3

�) andwere not significant for SO4

2�.Methanesulphonate and sulphate analysis was performed by

ion chromatography under working conditions summarised else-where (Becagli et al., 2011; Udisti et al., 2004). For sulphate andMSA, the uncertainty is mainly determined by the ion chroma-tography accuracy, which is typically 5%.

The air mass backward trajectories were calculated using theHYSPLIT Lagrangian model, which was developed by NOAA andAustralia’s Bureau of Meteorology. The model was initialised withNCEP-NCAR reanalysis data fields using a regular 2.5� � 2.5� lon-gitudeelatitude grid. Five-day back trajectories were computedfour times per day arriving at synoptical hours (00-06-12-18 UTC)and at 500, 1000, 1500, 2000, 3000 and 4000 m above the Dome Csite. Uncertainties in the resulting trajectories were caused by bothnumerical truncations in the calculation algorithm and resolutionerrors, due to the limited resolution of themeteorological dataset inspace. It was possible to estimate the total error on the order of1500 km after five days (15e30% of the travel distance) (Scarchilliet al., 2010).

The anomaly field for atmospheric parameters, such as geo-potential height at 500 mb (GP500), surface pressure (SP) zonal andmeridional wind at 300 and 500 mb (U300, U500, V300 and V500respectively), precipitable columnar water and specific humiditywere derived from NCEP Reanalysis data provided by the NOAA/OAR/ESRL PSD (http://www.esrl.noaa.gov/psd//).

3. Results and discussion

The temporal evolution of MSA and SO42� in the atmospheric

aerosol (PM10) in the course of three years of sampling is reportedin Fig. 2. This sampling is the longest high-resolution record to date

ptic hours (UTC time) during days related to high measured concentration of SO42� and

ectory. Panel b: Time sequences of air mass (black lines) and mixing layer (blue lines)synoptic hours (UTC time) during days related to high measured concentration of SO4

2�

t the same time and position (For interpretation of the references to color in this figure

Fig. 4. Surface pressure (a), 500 mb Geo Potential Height (GHP) pressure (b), 500 mb air temperature (c), columnar precipitable water (d), surface dew point (e), specific humidity (f),500 mb (g) and 300 mb (h)GPH zonalwind composite anomaly (respect to Long TermMean 1968e1996) for the 20 sampling days (29-12-04; 10-01-05; 16-01-05; 01-02-05; 15-01-06;21-01-06; 22-01-06; 27-01-06; 04-02-06; 05-02-06; 07-02-06; 08-02-06; 09-02-06; 21-02-06; 23-02-06; 24-02-06; 01-12-06; 16-01-07; 28-01-07; 13-02-07) characterised by thehighest concentration of sulphur oxidised compounds. The aerosol sampling site is shown as black cross in the pictures a, b, c, d, e, g, h and its latitude as a dashed line in picture f.

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108 101

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108102

of oxidised sulphur compounds in atmospheric aerosols of thecentral Antarctic Plateau.

The SO42� and MSA concentrations in PM10 that are reported in

Fig. 2 arise from bulk PM10 sampling and from impactor samplings(both Dekati 4-stage and Andersen 8-stage) by summing SO4

2� and

Fig. 5. Methanesulphonate (plots on the left) and sulphate (plots on the right) time evolutioequivalent diameter) is reported in each plot.

MSA concentrations in the stages collecting particles with anaerodynamic diameter less than 10 mm. In periods of overlappedsampling (PM10 and impactors are represented by red and bluedots, respectively), a good correspondence is found for bothmarkers in bulk PM10 and PM10 reconstructed by Dekati 4-stage.

n in the 8 stages of Andersen impactor. The collected aerosol size range (aerodynamic

Fig. 6. MSAsize distribution in the tree selected events in late summer (end of JanuaryeFebruary, plots on the left) and the tree selected in early summer (November, plots on the right).

Fig. 7. Sulphate sizedistribution in the tree selected events in late summer (endof JanuaryeFebruary, plots on the left) and the tree selected inearly summer (November, plots on the right).

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108 103

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108104

The slight differences are due to differences in time resolutionbetween the samplings and the analytical error affecting themeasurements (as represented by vertical bars in the plots). Incontrast, SO4

2� and MSA concentrations that were reconstructed byAndersen 8-stage (represented by green dots) were always lowerthan values obtained from the other samplings; this finding wasespecially true in the summer months.

A previous study performed with a 12-stage impactor in thesame site (Jourdain et al., 2008) showed thatMSA and SO4

2� reachedtheir highest concentrations in the accumulationmode between 0.1and 0.7 mm; this aerosol mode is only partially sampled by theAndersen 8-stage impactor, which loses aerosol particles withaerodynamic diameters of less than 0.4 mm. These particles werecaptured by the Teflon filter used for bulk PM10 and Dekati 4-stagesamplings. In fact, although these filters have a nominal porosity of

Fig. 8. Ionic balance in each of 8 stages of Andersen impactor for the tree selected events at ton the right).

2 mm, their efficiency is higher than 99.6% for aerosol particles with0.3 mm equivalent aerodynamic diameter, due to their microstruc-ture (cross Teflon fibres).

Despite this limitation, this joined record allows us to drawseveral conclusions regarding the seasonal pattern and size distri-bution of oxidised sulphur compounds in relation to transportprocesses.

Due to their common source from biogenic productivity, a clearseasonal cycle with summer maxima from October to March isvisible for both markers. Examining at the summer maxima indetail, a composite shape with higher concentrations in Novemberand February than during the central portion of the summer(DecembereJanuary) is noticed. This minimum in midsummerconcentrations is more evident in theMSA profile. A previous study(Preunkert et al., 2008) showed that this DecembereJanuary

he end of JanuaryeFebruary (plots on the left) and the tree selected in November (plots

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108 105

minimum is probably due to the weakened advection of sulphuraerosols from oceanic areas and DMS photochemistry during thepathway towards inland Antarctica, which may result in the fav-oured formation of SO2 (which is subsequently oxidised to SO4

2�)with respect to MSA.

The highest concentrations of SO42� and MSA were recorded in

February; back-trajectories related to the 20 days recording thehighest concentration of such markers suggest a transport of airmasses from altitudes higher than themarine boundary layer in theSouthern Atlantic Ocean as shown in Fig. 3. This finding isconfirmed by the weakening of the summer Antarctic polar high inthe surface pressure field, with negative anomalies in the centralAntarctic Plateau (Fig. 4a) coupled with the large anomalous ridgein GP500 field (Fig. 4b) intruding from Antarctic Peninsula towardsEast Antarctica, thereby driving moist and hot air masses (Fig. 4cand d) from the Bellingshausen-Amundsen Sea coastal areastowards the central Antarctic Plateau via the Ross Ice Shelf(Scarchilli et al., 2010). This observation is further confirmed byboth the weakening of the zonal wind component over the lat-itudinal band of Dome C and the eastern coasts of the continent at300 and 500 mb and the strengthening of the dipole anomaly overthe Peninsula and the western part of the continent as going up to300mb (Fig. 4g and h). However, the decrease of the dew pointtemperature pattern and the specific humidity zonal mean(0�e180� E) with respect to their long-term means (Fig. 4e and f,respectively) suggests a prevalent dry deposition of thesecompounds.

Fig. 9. Air mass back trajectories for the tree selected events at the end of JanuaryeFebruawith NCEP-NCAR reanalysis data fields with a regular 2.5� � 2.5� longitude-latitude grid. Fiv(00-06-12-18 UTC) and at 1000, 2000, and 4000 meters above Dome C site.

3.1. Methanesulphonate and sulphate aerosol size distributionin selected events

By observing the temporal evolution of MSA and SO42� in the

different size classes sampled with the Andersen 8-stage impactor(Fig. 5), we noticed that higher concentrations were recorded inseveral spikes at the end of January and February in the finest sizeclasses for both sampled years. Examining the data in greater detail,we also observed some concentration spikes in the size classes1.1e2.1 mm in November with values in the same order of magni-tude as the values for the finest mode.

As observed from the size distribution data of 3 events inFebruary and 3 events in November for MSA (Fig. 6) and SO4

2�

(Fig. 7), sulphur compounds have different size distributions in thetwo periods.

In February, MSA and SO42� present a single mode at 0.4e0.7 mm

with the highest concentrations recorded over the whole year.Previously, some authors (Virkkula et al., 2006) reported thatsulphate in the Aitken mode region centred at about 0.1 mm andexhibited one or two accumulation modes between 0.3 and 0.7 mm.As already discussed, with the 8-stage impactor used in this study,we could not sample aerosol fractions with aerodynamic diametersof less than 0.4 mm; therefore, even if the accumulation mode wasdetermined to have a higher concentration than the finest mode(Virkkula et al., 2006; Jourdain et al., 2008), only a portion of theaccumulation mode was sampled with the devices used in thisstudy.

ry calculated by HYSPLIT Lagrangian model (Draxler, 2003). The model was initialisede-day back trajectories were computed four times per days arriving at synoptical hours

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108106

To understand which MSA and sulphate species are present inthe different size classes, we can examine the single stage ioniccomposition (Fig. 8). In all of the events selected in February, the0.4e0.7 mm fraction was primarily composed of H2SO4 and MSAand consistently contained a low concentration of neutralisingspecies (sea salt and crustal e Naþ, Kþ, Mg2þ and Ca2þ). In contrast,in the slightly coarser size fraction (0.7e1.1 mm) and in the micro-metric fraction (1.1e2.1 mm), SO4

2� and methanesulphonate werecounterbalanced by NH4

þ such that they were present as ammo-nium salts ((NH4)2SO4 and NH4MS). Primary species from sea sprayand crustal aerosol and NO3

� concentrations were negligible withrespect to biogenic markers.

In November, SO42� and MS� size distributions fell in the

micrometric mode (1.1e2.1 mm) at concentrations similar to orhigher than the accumulation mode. The species having primarysources (Naþ, Mg2þ, etc) and NO3

� were present at higher concen-trations in November; this result was especially the case in themicrometric mode and confirmed the presence of different speci-ation in November relative to February. In early summer(November), sulphate and methanesulphonate were generally notpresent in acidic forms in the finest fraction but were counter-balanced by Naþ, NH4

þ and, to a lesser extent, by other primarycations, such as Mg2þ, Ca2þ and Kþ, such that the prevailing speciesin all of the aerosol fractions were sodium and ammonium salts.The different size distributions and chemical speciation patternsare probably related to differences in source locations or transportprocesses between the two periods.

Fig. 10. Air mass back trajectories for the tree selected events in November calculated by Hreanalysis data fields with a regular 2.5� � 2.5� longitudeelatitude grid. Five-day back trajeUTC) and at 1000, 2000, and 4000 meters above Dome C site.

Regarding source areas, although biogenic activity and DMSproduction have already begun under the sea ice in November, thenearest ice-free oceanic areas that are suitable for the exchange ofDMS from the sea to the atmosphere are in the Indian Ocean sectorfacing Wilkes Land. However, the sea ice extent reaches itsminimum in February, and all oceanic areas around Antarctica aresubsequently potential sources for DMS emission.

From backward trajectories analysis (Figs. 9 and 10), one can seethat all of the selected events are characterised by the followingtwo features: low altitude trajectories moving around the centralAntarctic Plateau and high altitude (2000e4000 m over groundlevel) trajectories coming from the oceanic sector. The latter areinvolved in the transport of sulphur compounds at Dome C. Indeed,as shown by Davis et al. (1998), when frontal systems pass over theAntarctic Ocean, rapid vertical motion brings DMS from the marineboundary layer to high elevation layers (buffer layer) where DMS isoxidised to H2SO4 and MSA. Several field and kinetic studies (Sciareet al., 2000; Legrand et al., 2001; Bardouki et al., 2002) have shownthat in the Antarctic marine boundary layer, the heterogeneousreactions producing H2SO4 and, especially, MSA are more efficientthan gas-phase reactions. Conversely, the heterogeneous reactionsin the buffer layer are negligible, due to the low water content inthis atmospheric layer (Davis et al., 1998). In the selected events inFebruary, the high elevation backward trajectories show two mainprovenance directions (Ross Sea or Indian Ocean and from themid-east Antarctic Plateau to areas of the American Highlands) thatboth deliver air masses at high speed to Dome C. Due to the rapid

YSPLIT Lagrangian model (Draxler, 2003). The model was initialised with NCEP-NCARctories were computed four times per days arriving at synoptical hours (00-06-12-18

S. Becagli et al. / Atmospheric Environment 52 (2012) 98e108 107

transport of air masses, these high altitude trajectories probablyrepresent long distance transport and source arise from areaslocated as far north as 50�S.

The selected events in November are characterised by highaltitude trajectories coming from ice-free areas of Indian Ocean andspending a significant amount of time over the Antarctic ice sheet(Fig. 10). Indeed, the synoptic conditions in November are charac-terised by high zonal winds along the whole atmospheric columnover the Indian Ocean, which have the effect of promoting theformation of primary sea spray aerosols that are transported at highelevation towards Dome C along the same trajectories as sulphurcompounds. During transport over the Antarctic Plateau, absorp-tion of newly formed H2SO4 andMSA in the gas phase over primarysea spray aerosols distributed in the micrometric aerosol fractionleads to the formation of Na2SO4 and NaMS (Fig. 8).

4. Conclusions

The year-round atmospheric record of oxidised sulphurcompounds obtained at Dome C reveals that two oxidised sulphurspecies, MSA and SO4

2�, exhibit a seasonal cycle characterised bymaxima in summer (NovembereMarch). The highest concentra-tions for both these species were measured in November andFebruary. Size-segregated sampling performed with Andersen 8-stage impactors reveals that SO4

2� and MSA have different sizedistributions in early summer (November) in comparison withmid-late summer (February). In November, the size distributionexhibits two modes: the accumulation mode (0.4e0.7 mm), andthe micrometric mode (1.1e2.1 mm). In contrast, only the accu-mulation mode is present in February. Additionally, the two modesexhibit different speciation patterns. Sulphate and meth-anesulphonate are present primarily in acidic forms in the finestmode, whereas they are present primarily as sodium or ammo-nium salts in the micrometric mode. The different size distribu-tions and speciation patterns in the two months are related todifferent transport pathways from oceanic areas to the centralAntarctic Plateau. In the early summer, air masses arise mainlyfrom Indian Ocean where the sea ice margin is close to the coastand DMS sea-water/atmosphere exchange can occur. GaseousDMS is easily transported to high elevation atmospheric layers(buffer layer) where it is oxidised into H2SO4 and MSA, primarilythrough gas phase reactions. In November, high velocity zonalwinds over the coastal areas allow the transport of sea sprayaerosols at high elevation; in addition, air mass back trajectoriesdemonstrate that air masses spend more time over the continentin November relative to late summer. Both these factors allow thecondensation of newly formed H2SO4 and MSA in the gas phaseover sea salt particles and the development of a mode in themicrometric fraction forming sodium salt.

In February, by contrast, the gas to particle conversion of H2SO4and MSA during transport appears to be dominant during the rapidtransport of air masses at high elevation coming from highly bio-productive oceanic sectors located as far north as 50�S. Thisphenomenon leads to the highest concentrations of the acidicspecies over the whole year with a distribution mode in the finefraction of aerosols reaching Dome C.

Additional year-round studies of chemical composition span-ning multiple years are needed to provide a statistically reliableevaluation of the main transport processes delivering oxidisedsulphur compounds to the central Antarctic Plateau. Such studieswould help illuminate interannual variability in summer concen-trations of these components in relation to variations other thansource intensity in transport circulation modes affecting theSouthern Hemisphere.

Acknowledgments

This research was performed in the framework of the Air-Glacs1181 “Station Concordia” project, which was funded by theMIUR through the Italian “Programma Nazionale di Ricerche inAntartide” (PNRA). The field operations benefited from the supportof the French-Italian Concordia Station.

This paper is a contribution to the HOLOCLIP project, which isfunded by the European Science Foundation. This is HOLOCLIPpublication no. 3.

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