Element composition and source apportionment of atmospheric aerosols over the China Sea



AtmosphericPollutionResearch6(2015)191Ͳ201

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spheric Pollution



Research www.atmospolres.com



Element composition and source apportionment of atmospheric aerosols over the China Sea RuojieZhao1,BinHan2,BingLu3,NanZhang1,LinZhu1,ZhipengBai2 1

CollegeofEnvironmentalScienceandEngineering,NankaiUniversity,Tianjin300071,People’sRepublicofChina StateKeyLaboratoryofEnvironmentalCriteriaandRiskAssessment,ChineseResearchAcademyofEnvironmentalSciences,Beijing100012,People’s RepublicofChina 3 YunnanKaisenEnvironmentalProtectionTechnologyCo.,Ltd,Kunming650105,People’sRepublicofChina 2

ABSTRACT



Fourcategoriesofdifferentsizemarineaerosols(PM1.0,PM1.0–2.5,PM2.5–10 andPM10–100)werecollectedfromtheYellow Sea and East China Sea in the spring of 2011 and analyzed for 22 elements by inductively coupled plasma–mass spectrometry(ICP–MS).Theenrichmentfactorsand airmassbackwardtrajectoryanalysiswereusedtoidentifythe potentialsources.Duringthesamplingperiods,twosamplingareaswereinfluencedbyAsianDustonthebasisofAl concentrations (an indicator of mineral dust). Average mass concentrations of particles showed relatively higher valuesintheYellowSeaexceptPM2.5–10.Al,Ba,Ca,Fe,Mg,Ti,Na,K,Pb,Zn,Cr,PandZrwereabundantelementsand theyaccountedformorethan96%ofthetotalconcentrationsofelementsinallsamplesofthetwoareas.Highlevels of trace elements were associated with the airflow from Asia as the air passed over heavily populated and industrializedregionsbeforereachingthenorthwestPacificOcean.Forthecrustalelements,therewerehigherlevels in the East China Sea, while the anthropogenic elements showed higher levels in the Yellow Sea. These results indicated that Asian Dust Storm had more effects on East China Sea during the sampling periods, and Yellow Sea sufferedfrommoreinfluencebyhumanactivities.Sizedistributionanalysisrevealedthatelementsderivedfromcrust and anthropogenic sources tend to reside in fine particles and owing to the long distance away from the land, the concentrationsofanthropogenicelementsinPM2.5wereslightlyhigherintheEastChinaSeathanthoseintheYellow Sea.TheresultsalsosuggestedthattheimpactofAsianDustpresentedadownwardtrendfromwesttoeastandfrom northtosouthingeneral.

 Keywords:YellowSea,EastChinaSea,marineaerosols,traceelements,sizedistribution

CorrespondingAuthor:

Lin Zhu

:+86Ͳ22Ͳ23504379 :+86Ͳ22Ͳ23508807

:[email protected] 

ArticleHistory: Received:19March2014 Revised:18July2014 Accepted:05September2014

doi:10.5094/APR.2015.023 

1.Introduction  In the context of rapid economic development and industrial growth, and the lack of waste control measures in Northeastern Asia, particularly in China, anthropogenic emissions into the atmosphere have had a drastical increase in recent years. Asian Dust Transport (ADT) (Gao et al., 1992a), a long–range transport processofdustadvectedofftheAsiancontinentinthespringtime, deliverssoildustoriginatingfromtheloessanddesertregions,and a variety of atmospheric substances to the adjacent sea and remotewideareasoftheNorthPacific(Duceetal.,1980;Uematsu etal.,1983;Zhangetal.,2001;Parketal.,2004;Nakamuraetal., 2005;Hanetal.,2008).Atmosphericpathwayhasbeenrecognized as an important source for many oceanic chemicals, including Fe (DuceandTindale,1991;Gaoetal.,2001),Al(Kangetal.,2009),Cu (Kocaketal.,2005),Zn(Spokesetal.,2001;Kangetal.,2009),and Pb(Linetal.,2000;Kocaketal.,2005;Kangetal.,2009).Recently, scientists have documented that the concentrations of crustal– originatedmetalsintheatmospheredecreasedexponentiallyfrom the source to downwind regions during the long–range transport (Gaoetal.,1992a;Spokesetal.,2001;Hanetal.,2008).However, itisstillestimatedthat6–12×106tonsofAsiancrustalmaterialsare transferred to the central North Pacific annually (Uematsu et al., 1983).Somenutrientsintheatmospherehavealsobeenfoundto affectmarineecosystemswhenaerosolparticlesaredepositedand dissolvedintheocean(Duceetal.,1991).AeolianironFefluxesin the dust aerosol can enrich the ocean and influence the

photosynthetic rate of marine phytoplankton (Fung et al., 2000; Gaoetal.,2001).  Studiesonelementalcompositions,inorganicionsandcarbonͲ aceousconcentrationsofaerosolshavebeenconductedonremote islandsinChinaSea(Liuetal.,1998;KaneyasuandTakada,2004; Fengetal.,2007),UlleungIslandintheEast/JapanSea(Kangetal., 2011),JejuIslandnearSouthKoreaintheYellowSea(Chenetal., 1997;Kim etal.,1998;Parketal., 2004;Toppingetal., 2004),by shipboardmeasurementsintheJapan/EastSea(Kangetal.,2009) and China Sea (Gao et al., 1996; Gao et al., 1997; Liu and Zhou, 1999;Nakamuraetal.,2005;Shengetal.,2005;Zhangetal.,2007; Kim et al., 2009) to evaluate the relative importance of source intensities to marine aerosols. These studies have generally defined specific variation trends of aerosol loadings and characͲ teristicsthatarelargelydependentoncontinentalsourcesandthe air mass history. However, there is relatively little information on overallfeaturesofmarineaerosolsintheChinaSea.  The China Sea, surrounded by China, Korean peninsula, and Japanese islands, is in the transport path of the continental pollutantsandAsianDusttothePacificwhennorthwesternwinds prevail. In the past decades environmental deterioration in China made the China Sea extremely sensitive to external ecosystem changes. The atmospheric input has exposed great impact on the environment of this area. It is, therefore, essential to collect aerosolsintheChinaSeainordertohaveacomprehensiveunderͲ standingabouttheinteractionoflandandsea.

©Author(s)2015.ThisworkisdistributedundertheCreativeCommonsAttribution3.0License.

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 Liu et al. (1994) once investigated the size distribution of marineatmosphericparticlesatNear–ChinaOcean,however,most of the previous researchers focused their investigations on the continent (Wang et al., 2005; Wang et al., 2009; Song and Gao, 2011;Panetal.,2013).Thusinthisstudywecarriedoutintensive ship sampling over the Yellow Sea and East China Sea, and collectedfourcategoriesofdifferentsizeparticles:PM1.0,PM1.0–2.5, PM2.5–10 and PM10–100, which provided important data to evaluate the size distribution of the elements. The major objective of this studyistoinvestigatethenatureandsourcesofaerosolsthrough the analyses of their chemical properties, size distribution and transportpath,andtoprovideimportantdatatoevaluatetherole of atmospheric pathways of terrigenous materials in the marine biogeochemicalcycles. 

2.Methodology  2.1.Samplecollection  Atmospheric PM samples were collected using a low volume sampler (LVS3, Germany) over the China Sea during March and April,2011.Theactivevolumetricflowcontrolsystemmaintained a constant volumetric flow at a rate of 2.3m3/h. The impactor (Cascade Preseparator, Kalman System Ltd.) allowed aerosol collectionontothreestagesequippedwithsubstrates,andontoa quartz fiber filter (QFF). The cut–offs for each stage were: <1ʅm (base filter), 1–2.5ʅm(Stage 1), 2.5–10ʅm (Stage 2),10–100ʅm (Stage3).Thesamplerswereinstalledonthetoproofofthe“Dong FangHong–2”researchvessel.Toreducethepossibilityofsample contamination, the sampler was turned off when the ship anchoredforotherresearchactivities.DetailedsamplinginformaͲ tion was summarized in Table S2 (see the Supporting Material, SM),alongwiththeshiptracksshowninFigureS1.  Prior to sampling, quartz fiber filters were kept at 650°C for 5htoremoveanyorganiccompoundsthatmaybepresent.Filters wereweightedbyasensitivemicrobalance(MettlerToledo,MX5) withasensitivityof±0.010mg.Priortoweighing, thefilterswere equilibratedin a desiccator atroom temperature over48h.After sampling, the filters were removed from the inlet and put in the plasticsylphon.Afterweighing,thefilterswerestoredinafreezer (atо4°C)untilchemicalanalysis.  2.2.Chemicalanalyses  Thesamplesweresubdividedintotwogroupsaccordingtothe samplingarea:YellowSeaandEastChinaSea(seetheSM,Figure S1). Concentrations of PM1.0, PM1–2.5, PM2.5–10 and PM10–100 were obtained by standard gravimetric methods. Half of each quartz fiber filter was cut into portions for individual analysis for 22 elements(Al,Ba,Ca,Fe,Mg,Zr,Sr,Ti,Na,P,K,V,Cr,Mn,Ni,Cu, Zn, As, Y, Mo, Sn, and Pb). Elements were extracted into acid solutionusingahotplateinthe followingsequence:afterbroken into pieces, filter samples were placed in a vessel of solution container and treated initially by concentrated acid solutions (0.5mL HNO3 and 1mL HF). After placed into a stainless steel vessel and covered, they were then put into an oven for 24h at 190°C (total digestion). Cooling it after taken out, the vessel was boiled to dryness on a hot plate (190°C). This was repeated for anothertime.FivemLHNO3wasaddedintothevessel,andthenit waskeptat130°Cfor3h.Thesolutionwascooledandtransferred into a clean plastic bottle. Three mL of extracted solution was transferred into a TeŇon vial and finally it was diluted to 50mL using distilled water. The extracts were then analyzed by inductively coupled plasma–mass spectrometry (ICP–MS) (IRIS IntrepidII,ThermoElectron).

 2.3.Atmosphericcirculationoverview  BasedonNCEPFNLanalysisdata(1°x1°),averageatmospheric circulation near the ground was analyzed during the observation

periodsoftwoareas(seetheSM,FigureS2).Duringthesampling period over the Yellow Sea, atmospheric circulation changed quicklyandthesourceroutesofairmasseswereverycomplicated. AcoldhighpressuresystemcouldbefoundinShandongPeninsula and Yellow Sea was located in advance of the cold front and controlledbynortheasterlywind.However,weatherwasrelatively stable and the northerly winds prevailed during the sampling period over the East China Sea. Air masses arriving in this region mainlycamefromInnerMongoliaandNorthChinaPlain.  2.4.Qualityassuranceandqualitycontrol  Each filter was weighted 3 times before and after sampling and the average value was used. All the glassware and filters assemblywereacidwashedandovendriedtoavoidcontamination amongsamples.  For elements analysis, calibration was achieved using multi– elementstandardspreparedfromstocksolutionin2%HNO3.The qualityassuranceandqualitycontrolofanalyseswerevalidatedby analyzingtwotypesofstandardreferencematerials(SoilStandard Series:GBW 07408 forocher andGBW07404 for calcareousness, produced by National Research Center for Certified Reference Materials,China).Therecoveredvaluesforallthetargetelements fellintotherangeorwithin5%ofthecertifiedvalues.Indiumwas added to the cooled extracts as an internal standard to monitor analytical drift. Three different concentrations (100ppm, 50ppm, and 1ppm) of V, Fe, Cu, Zn, Cd, Pb and Al were used to protract the standard curves. To check the accuracy of the analysis of the acidic digestions, standard soil materials were pre–treated and analyzed with the same procedure. For most elements, relative analytical errors were less than 10%. Two random filters were chosen and cut into two pieces with about the same area. Pre– treatmentandanalysisweresimultaneouslyconductedforparallel analysis. 2mL HNO3 and 10mL HCl were added into a 100mL bottle, diluted to scale line, to avoid the error of the equipment duringanalyzing. 

3.ResultsandDiscussions  3.1.Overallmassconcentrations  Comparison ofthetotalaverage massconcentrations of four sizefractionsbetweenthetwosamplingareaswasshowninFigure 1. Results indicate that the mass concentrations of aerosols over theYellowSeawerehighercomparedtothoseovertheEastChina SeaexceptPM2.5–10.YellowSeaissurroundedbyChinesemainland andKoreanpeninsula,andmuchclosertothelandthanEastChina Seawhichisarelativelyopensea.Toagreatextent,theaerosolsin the oceans are controlled by inputs from the continental atmosphere, especially for coastal waters. Thus, the geographic position may explain the higher mass concentrations over the YellowSea.  We used the sum of PM1.0 and PM1.0–2.5 to represent the mass concentration of PM2.5. Similarly, PM10 is the sum of PM1.0, PM1.0–2.5 and PM2.5–10. The fine/coarse ratio has commonly been used as a first step in attempting to identify natural and anthroͲ pogenic sources of particles. In the present study, this ratio was 70%intheYellowSeaand51%intheEastChinaSea,respectively. InthepreviousresearchwhichwascarriedoutinBohaiSeainthe spring of 2007, Ji et al. (2011) observed that 57% of PM10 was associated with PM2.5. Coal combustion, mobile vehicles and secondarypollutants(Zhang etal.,2007)are mainlyfoundinfine particles. According to the relevant data from Chinese Statistical Yearbook of 2007 and 2011, the possession of civil vehicles, industrial waste gas emissions and coal combustion in China had increased by 42 million (from 36 to 78), 18818 billion standard cubicmeters(from 33099to 51917),and 370 million tons (from 1839to2209)infouryears, respectively.Therefore,theratio of PM2.5/PM10 was greater in the Yellow Sea than that in Bohai Sea.

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 3.2.Chemicalcharacteristicsofsamples  Figure 2 summarized the mean concentrations for each eleͲ mentinfoursize–differentiatedprofilesofthetwosamplingareas. Total concentrations of elements in PM1.0, PM1.0–2.5, PM2.5–10 and PM10–100 were 3.51, 6.14, 5.59, 5.51ʅg/m3 in the Yellow Sea and 2.98, 6.56, 7.33, 6.54ʅg/m3intheEastChinaSea.These concenͲ trations accounted for 9.5%, 43.5%, 21.3%, 28.1% and 20.6%, 34.4%,26.4%,54.7%ofthemassconcentrationsofPM1.0,PM1.0–2.5, PM2.5–10 and PM10–100 in the two sampling areas, respectively. Al, Ba, Ca,Fe,Mg,Ti,Na,K,Pb,Zn, Cr,P,and Zrwerethe abundant elements and they accounted for more than 96% of the total concentrationsofelementsinallsamples.  When compared by the absolute magnitude of concentraͲ tions, the data could be grouped approximately into four broad categories (Table 1). The elements having the highest concentraͲ tionswereAl,Mg,Ca,TiandFeintheYellowSea,aswellasinthe EastChinaSea,amongwhichAlandFeweretherepresentativeof soil–originated elements, and they followed by sea–salt elements (i.e., Na and K). The observed results were different from that obtainedbyWuetal.(2010)andHanetal.(2010),whofoundthat human activities contributed most to the ambient aerosols. The reason may lie in the difference between sampling sites as their sitesinfluencedmuchmorebyanthropogenicactivities. 

ThelowerratiointheEastChinaSeaindicatedthatanthropogenic airpollutionfromcontinenthadlessinfluenceinthisregion. 

Figure1.ComparisonofPMmassconcentrationsintheYellowSeaandEast ChinaSea.

 

  Table1.ElementconcentrationsintheYellowSeaandEastChinaSea(ng/m3) Concentration YellowSea EastChinaSea

0–10

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102–103

103–104

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Ba,Zr,Ti,P,V,Cr,Ni,Zn,Mo,Pb

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 3.3.Sourceapportionment  Air Mass Backward Trajectory analysis. The trace metals in aerosols have three important sources, including crustal, anthroͲ pogenic,andoceanicsources(sea–saltgeneration)(Chesteretal., 2000).TheconcentrationofAloftenactsasanindicatorofmineral dust (Hsu et al., 2010) because Al is one of the most common elementsfoundincrustalsources.Hsuetal.(2008)haveproposed a criterion of 2.8ʅg/m3 Al in ambient PM10 as an indication of a significant AsianDust event.TheAlconcentrations in PM10inthis studywere4.4ʅg/m3intheYellowSea,and6.8ʅg/m3intheEast China Sea, over 60% and 140% higher than the criterion, respecͲ tively. A similar Al level was observed in a previous study which reportedthattheAlconcentrationsinthecaseofhigh–dustevents rangedfrom3.05to9.69ʅg/m3(Kangetal.,2011).YellowSeaand East China Sea belong to the mid–latitude and they are on the primary pathway of dust transport, so the Al concentrations in thoseareasarestronglyaffectedbythedustactivitiesinthespring (Gao et al., 1997). However, the sampling location of Hsu et al. (2008) is Taiwan, which is part of the low–latitude region and far away from the dust sources and their transport path. As a result, the influence of desert dust on this location is considerably less thanthatinnorthernChina.Therefore,thetwosamplingareasare heavilyinfluencedbyAsianDustonthebasisofAlconcentrations.  Numerous aerosol characterization studies have generally highlighted specific trends of aerosol loadings and characteristics that are largely dependent on the air mass history (Mukai and Suzuki, 1996; Topping et al., 2004; Kang et al., 2009; Kang et al., 2011). Thus, to identify the possible sources of mineral dust, we obtained two–day backward trajectories over the Yellow Sea

(StationS06)andEastChinaSea(StationP09andE04)duringthe samplingperiods(Figure3).  Air mass trajectories arriving to the Yellow Sea were very disorderly and came from all directions as illustrated in Figure 3. Theycouldberoughlyclassifiedintothreegroups.Thefirstgroup was the trajectories having the long–range transport from the Chinese mainland, accounting for 38% of the trajectories. The second group whichaccountedfor 37%of the trajectories mainly included the trajectories originating from the offshore areas in KoreaandChina.Therestofthetrajectorieswerefrom the open sea including short–range transport from the East China Sea. However, air trajectories exhibited obvious regularity during the sampling periods of the East China Sea (Figure 3). We found that 92%ofthe airtrajectoriescametothe EastChina Sea were from the Inner–Mongolia, Mongolia and North China Plain, which was consistent with the location of Ulleung Island (Kang et al., 2011). Thus, we can hypothesize that the Asian Dust Storm was more effective on East China Sea during the sampling periods. FurtherͲ more, the above analysis agreed with the average atmospheric circulationdefinedinSection2.3.  Comparing the elemental concentrations between two areas (Figure2),itwasfoundthatasignificantgeographicalcharacterisͲ ticcorrelatedwellwiththevariabilityofairmasses.Concentrations of crustal elements such as Al, Fe, Ti, and Zr were higher in each particlesizeintheEastChinaSeathanintheYellowSea,whilethe Ba and Y showed comparable concentrations in both regions. Moreover, there was an exception for another crustal element, Mn,whichwashigherintheYellowSea.Itwaslikelythat,partof Mn in the Yellow Sea was from high–temperature combustion of manganese rich fuel enhancers or smelting (Spokes et al., 2001).

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 TheconcentrationsofNaandKwerehigherintheYellowSeathan thoseintheEastChinaSea,exceptforNainPM2.5–10,whereasthe gapwasnotasobviousasthecrustalmetals.Thisresultsuggested that the bubble injection of atmospheric sea salt in the marine environmentcouldcontributetomostoftheatmosphericNaandK intwosamplingareas.Incomparison,theMgandCa,whichwere alsohighintheseawaterexceptforsoil,showeddifferentfeatures. ThehigherconcentrationsofMgwerefoundintheEastChinaSea, whiletheCapresentedhigherlevelsintheYellowSea.Thesemay resultfromthecouplingoftheseawaterandterrestrialsubstances, and some fraction of Ca may originate from the anthropogenic emissionsintheYellowSea(Zhangetal.,2007).Inaddition,Zn,Pb, V, As, Ni, and Cr (anthropogenic metals) shared the similar features, which showed relatively higher concentrations in the Yellow Sea, indicating that anthropogenic source played an important role. Heavy fuel–oil combustion probably is the most important anthropogenic source of atmospheric V (Gao et al., 1992b; Wang et al., 2013). Aerosol lead (Pb) is almost exclusively anthropogenic in origin, resulting from the high–temperature combustion of coal (Dod et al., 1986) and leaded fuels in vehicle engines. Zn is also primarily anthropogenic in origin, e.g. peat combustion in power stations. There are several large ports and industrialcitiesinChinaandKorealocatedclosetotheYellowSea, therefore,inaccordancewiththeaboveanalysisofairmasses,the input of pollutants to this region was considerable in addition to the dust sources and detecting higher concentrations of anthropogenicmetalsinthisregionwasnotsurprising.  Calculation of enrichmentfactors(EFs).Theelements inaerosols arederivedfromvarioussourcessuchasEarth’scrust,oceans,and many anthropogenic processes (e.g. fossil fuel burning, waste incineration, processing of ores etc.). The marine enrichment factors(EFs)ofelementshasbeenusedasanattempttoevaluate thestrengthofnon–marinesourcesonobservedconcentrationsof elements.  TheenrichmentfactorforanyelementXrelativetoseawater isdefinedby:  EFs(X)=(X/Y)aerosol/(X/Y)seawater (1)  whereEFs(X)istheenrichmentfactorofX,Yisareferenceelement forseawater,(X/Y)aerosolistheconcentrationratioofXtoYinthe aerosolsamples,and(X/Y)seawateristheaverageconcentrationratio of X to Y in the seawater, based on the book Chemical Oceanography(Rileyetal.,1975).Sodium(Na)waschosenasthe reference element for the enrichment factor calculations in this study.IfEFs(X)approachestounity,whentheseawaterislikelythe predominant source for element X, and these are termed as the non–enrichedelements(NEEs).Incontrast,anEFs(X)valueof>100 is considered to indicate that a significant proportion of an element has a non–marine source, and these are referred to the anomalouslyenrichedelements(AEEs).  TheEFsvaluesofelementsfortheYellowSeaandEastChina Sea were depicted in Figure 4. On the basis of these data, the metals could be divided into two distinct groups: (1) Ca, Mg, Sr, and K (10100).SincetheEFsingroup(2)were2–6ordersofmagnitude ashighasingroup(1),elementsCa,Mg,SrandKweresupposed to slightly enriched or non–enriched due to the non–marine sources, which demonstrated that seawater was an important source.Among these enriched elements, crustalelements (Al,Fe, Cr, Ti and Y) emerged with higher EFs than some anthropogenic elements (Zn, Pb, V, Cu, As, and Cr) in both areas, indicating the strong effect of Asian Dust. Furthermore, higher EFs of crustal elements were found in the East China Sea than those in the Yellow Sea, while the EFs of anthropogenic elements presented lower values in the East China Sea. As previously discussed, this findingsuggestedthattherewasalargeranthropogenicinfluence intheYellowSea.

3.4.Comparisonofatmosphericelementswiththeotheroceanic regionsinEastAsia  For comparison, we summarized previous literature on the mass concentrations for selected metals from several oceanic regions in East Asia as shown in Table 2. Although the sampling periods were not identical among the observed sites, an overall view of air pollution levels could be gained from the inter–site comparisons.  The concentrations of elements in this study were much higherthanthoseattheremoteislands(namelyAmamiandMiyako, aerodynamicdiameter<2ʅm)oftheEastChinaSea(Kaneyasuand Takada, 2004). This result accorded with the concentration/ distance model developed by Gao et al. (1992b). The Yellow Sea and East China Sea in this study were more strongly affected by mineralmaterialfromthedustregionthantheotherregionalseas based on the comparison of their atmospheric Al concentrations, although their sampling time (spring) was also part of Asian Dust period theoretically (Table 2). The other elements also showed similarresults,exceptsomeanthropogenicmetals(e.g.Zn,Pb,As) whichdisplayed comparable(Hsu et al.,2004) or opposite results (Wuetal.,2010;Wangetal.,2013).Theapparentlyhigherlevelsof Zn in the offshore island (Wu et al., 2010) may reflect the differences in the source strengths for air pollution (Gao et al., 1992b).  When compared with the research in Bohai Sea (Ji et al., 2011), it was noticed that the mass concentrations of particles in Bohai Sea were considerably larger than those collected in the present research, and the concentrations of elements showed great variability. Since it was presented by annual values in the BohaiSea,thehigherlevelsof Al,Fe,Ca,Mg,andTiinthis study suggested that large quantities of dust moved from land to the oceaninspring.Meanwhile,thehigherMn,Cu,ZnandPblevelsin BohaiSeawereattributedtothecontributionofthecitiesaround. The comparison indicated that the impact of Asian Dust had obvious regional characteristics and the dust aerosol concentraͲ tions presented a downward trend from west to east and from northtosouthingeneral.  3.5.Sizedistributionsoftheelements  The concentrations of trace species which were present in atmosphericaerosolsvariedstronglywithparticle–size.Routinely, PM2.5 and PM2.5–10 are the research focus. Therefore, Figure 5 depictspercentagesofPM2.5(the sumof PM1.0andPM1.0–2.5) and PM2.5–10foreachelement.  Crustal dust particles are produced through weathering and mechanicalwinderosionwhichprimarilygenerateslarge–sizeparͲ ticles (Gillette and Walker, 1977; Gillette and Dobrowolski, 1993; Gaoetal.,1997)andcoarseparticlestendtodominateADS(Asian DustStorm)episodes.Somestudiesonlandalsosummarizedthat crustal metals are more abundant in the coarse particles (Hsu et al.,2004;Caoetal.,2008;Panetal.,2013).Nevertheless,thismay notbethecaseintheocean.Spokesetal.(2001)observedthatAl occurredprimarilyascoarse–modeinthenortheastAtlanticOcean aerosol, however, the size segregation between coarse and fine fractions was 1ʅm. Liu et al. (1994) collected aerosol samples at Near–China Ocean and found that crustal metals (Al, Si, and Fe) peakedataround1.2ʅmdiameter.ThestudyofGaoetal.(1997) found that the Al concentration on aerosol particles between 1.1 and 3.3ʅm accounted for 65% of the total Al. Likewise, from the results of this study, it could be concluded that crustal metals, including Al, Ba, Fe, Ti, Mn, and Zr were found to have higher percentages in PM2.5 than PM2.5–10 in two sampling areas, suggesting that the particle size distributions of dust had shifted towardsmallersizesbecauseofthelong–rangetransportfromthe continent. 

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Figure3.Two–daymultiplebackwardtrajectoriesduringthesamplingperiodsforYellowSea:(a)StationS06(29March–8April2011),andEastChina Sea:(b)StationP09and(c)E04(19–29March2011).ThebackwardtrajectorieswerecalculatedusingtheHybridSingle–ParticleLagrangianIntegrated Trajectory(HYSPLIT)modeloftheU.S.NationalOceanographicandAtmosphericAdministration/AirResourcesLaboratory(NOAA/ARL)witharchived meteorologicaldatafromtheGlobalDataAssimilationSystem(GDAS)dataproducts(http://www.ready.noaa.gov/HYSPLIT_traj.php).Themodel calculatedtrajectoriesatstartingaltitudesof500 mAMSLofthesamplingarea,taggedat6 hintervals.

  

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Figure4.EnrichmentfactorsoftraceelementsrelativetoNafortheYellowSeaandEastChinaSea.

 Sea salt aerosols are produced at the ocean surface by the burstingofbubblesresulting fromtheentrainmentofairinduced by wind stress. Huang et al. (2003) obtained that Na and K in atmosphere were present in the form of coarse particles (>0.45ʅm). Likewise, Na, Mg and K were also higher in PM1.0–2.5 and PM2.5–10 in this study. This finding correlated well with the measurementsinapreviousresearch,whichreportedthat98%of the sea salt were concentrated in the coarse particles (>1ʅm) (Shaojin et al., 1993). Moreover, K displayed comparable size distributions whereas Na showed larger distributions in fine particlesintheYellowSeathanEastChinaSea,indicatingthatNa couldbeslightlyinfluencedbyanthropogenicsourcesintheYellow Sea.Inparticular, fraction ofCa in PM1.0ofYellowSea accounted for more than 20% and was the highest proportion of all the elementsinPM1.0,andtheabundanceofCaintheEastChinaSea was also relatively higher than the other metals in PM1.0. Calcite (CaCO3)isthemostcommonmineralinsoilandcarbonatecanalso beformedinfineparticleslikePM2.5andPM1.0,whichmayresultin thehighcontentsofCainPM1.0(Caoetal.,2008).  Sizedistributionofanthropogenicelements(Zn,Pb,V,Cu,As, andCr)alsorevealedstrongeraccumulationinPM2.5.Onepossible reasonisthatlargerparticlesareremovedfromtheatmosphereby deposition during their transport while the fine particles can be transportedwiththeairmasses(Huangetal.,2003).Furthermore, owingtolongdistancefromtheland,theanthropogenicelement concentrations in PM2.5were slightlyhigher inthe East ChinaSea thanthoseintheYellowSea.  ItisworthnotingthatthedistributionofSrshowedthelargest mode in the PM1.0 fraction. Hsu et al. (2004) measured the size distribution of elements in Taipei during ADS (Asian Dust Storm) episodesandfound thatSrwasfoundto residepredominantly in thecoarsemode(PM2.5–10);thisfindingisconsistentwiththestudy in the Venice Lagoon by Toscano et al. (2011). Therefore, further analysis is required from our current observation to clarify this 

result,althoughitmaybeassociatedwiththemineralphaseofthe elementinsmallparticles(Caoetal.,2008). 

4.Conclusions  Resultsregardingthechemicalanalysisofaerosolssampledin the Yellow Sea and East China Sea were presented using various analytical techniques. The atmosphere received large amounts of naturalandanthropogenicmaterialsfromtheAsiancontinent.The high concentrations of elements in the aerosols were associated withtheairmassesthatwerefrequentlytransportedfromeastern China. The influence of Asian Dust had obvious regional characͲ teristicsandatrendofdecreasingaerosolconcentrationstowards eastandsouthwasobserved.Thiswasprimarilyattributedtothe increasingdistancefromthedustsourceregion.  Theextentofthechangeofatmosphericelementsvariedwith elementsandlocationsduringthesamplingtime.Inbothareasthe elements having the highest concentrations were crustal metals, which revealed obvious influence from Asian Dust. The crustal elementsexhibitedasharpincreaseinconcentrationfromYellow SeatoEastChinaSea,whiletherelativelyhigherconcentrationsof anthropogenicmetalswereobservedintheYellowSea.According to the air mass backward trajectories obtained in this study, air masses in the East China Sea were primarily from northwest, in other words, these were also the trajectories of the dust storm seeneveryspringintheEastAsia.However,itwasfoundthatthe origins of air masses in the Yellow Sea did not show single rules. Therefore, the atmosphere was also under the influence of the industrial areas around the Yellow Sea except for the Asian sand storm. The lower and higher EFs for crustal and anthropogenic elements in the Yellow Sea, respectively, manifested that there were more inputs of anthropogenic pollutants in the Yellow Sea andmoredustpollutionintheEastChinaSea.Inparticular,theEFs of Ca, Mg, Sr, and K indicated seawater was an important source forthem.

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 (a)

(b)

 Figure5Sizedistributionsoftheelements(a) intheYellowSea,(b) EastChinaSea(%).

 Theanthropogenicelements(Zn,Pb,V,Cu,AsandCr)showed higher distribution in fine particles because of the removal of coarse particles by dry deposition during long–range transport in the atmosphere, while the sea salt elements displayed higher percentages in PM1.0–2.5 and PM2.5–10. In addition, the element Sr showed a largest mode in the PM1.0 fraction, which needs to be furtherevaluated.Thehigherpercentagesofcrustalsourcemetals in PM2.5, including Al, Ba, Fe, Ti, Mn, and Zr indicated that the particlesizedistributionsofdusthadshiftedtowardssmallersizes becauseofthelong–rangetransportfromthecontinent. 

Acknowledgments

 TheauthorswouldliketoextendtheirgratitudetotheNOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model (http://www.ready.noaa.gov/ HYSPLIT_traj.php)usedinthispublication. 

SupportingMaterialAvailable

 Themethoddetectionlimits(MDLs)oftheanalyzedelements are presented in Table S1. Regional map and ship tracks for the cruises over the Yellow Sea and East China Sea, and detailed information of each site can be found in Figure S1 and Table S2. FigureS2summarizestheaverageatmosphericcirculationnearthe ground during the observation periods of two areas. These information are available free of charge via the internet at http://www.atmospolres.com. 

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