Science of the Total Environment 424 (2012) 182–192

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Science of the Total Environment

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Natural versus anthropogenic inhalable aerosol chemistry of transboundary EastAsian atmospheric outflows into western Japan

Teresa Moreno a,⁎, Tomoko Kojima b, Xavier Querol a, Andrés Alastuey a, Fulvio Amato c, Wes Gibbons d

a Institute of Environmental Assessment and Water Research, Spanish Research Council (IDÆA-CSIC), C/Jordi Girona 18-26, 08034 Barcelona, Spainb Department of Earth and Environmental Sciences, Kumamoto University, 2-39-1, Kurokami, Kumamoto 860-8555, Japanc TNO Climate, Air and Sustainability, Princetonlaan 6, PO Box 80015, 3508 TA Utrecht, The Netherlandsd AP 23075, Barcelona 08080, Spain

⁎ Corresponding author. Tel.: +34 934006100; fax: +E-mail address: teresa.moreno@idaea.csic.es (T. Mor

0048-9697/$ – see front matter © 2012 Elsevier B.V. Alldoi:10.1016/j.scitotenv.2012.02.060

a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 October 2011Received in revised form 20 February 2012Accepted 24 February 2012Available online 22 March 2012

Keywords:Transboundary aerosolsSW JapanKosaMetalliferous sulphate PM10

Coal emissions

The eastward transport of aerosols exported from mainland Asia strongly influences air quality in the Japa-nese archipelago. The bulk of the inhalable particulate matter (PM10) in these intrusions comprises eithernatural, desert-derived minerals (mostly supermicron silicates) or anthropogenic pollutants (mostly submi-cron sulphates), in various states of mixing. We analyse PM10 collected in Kumamoto, SW Japan, during threecontrasting types of aerosol intrusions, the first being dominated by desert PM which became increasinglymixed with anthropogenic components as time progressed, the second being a relatively minor event mixingfine, distal desert PM with anthropogenic materials, and the third being dominated by anthropogenic pollut-ants. Whereas the chemistry of the natural mineral component is characterised by “crustal” elements (Si, Al,Fe, Mg, K, Li, P, Sc, V, Rb, Sr, Zr, Th, lanthanoids), the anthropogenic component is rich in secondary inorganiccompounds and more toxic metallic elements (NH4

+, SO42−, As, Pb, Cd, Cu, Zn, Sn, Bi, Sb, and Ge). Some desert-

dust (Kosa) intrusions are more calcareous than others, implicating geologically different source areas, andcontain enhanced levels of NO3

−, probably as supermicron Ca(NO3)2 particles produced by chemical reactionbetween NOx pollutants (mostly from industry and traffic) and carbonate during atmospheric transport. Theoverall trace element chemistry of aerosol intrusions into Kumamoto shows low V/Rb, low NO3

−/SO42−, en-

hanced As levels, and unfractionated La/Ce values, which are all consistent with anthropogenic sources in-cluding coal emissions rather than those derived from the refining and combustion of oil fractionates.Geographically dispersed, residual sulphatic plumes of this nature mix with local traffic (revealed by OCand EC concentrations) and industrial emissions and dissipate only slowly, due to the dominance of submi-cron accumulation mode PM which is atmospherically persistent, and raise questions over the chronic healtheffects of breathing finely respirable sulphatic aerosol containing enhanced amounts of toxic metals.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

One of the greatest air pollution challenges facing the globalcommunity this century is the vast cloud of contaminating atmo-spheric particles currently suspended in the atmosphere over EastAsia (Liu and Mauzerall, 2007; Ohara et al., 2007). This particulatemegaplume reduces average annual air quality across an area cover-ing over 3 million sq km (Fig. 1) and is of particular concern with re-gard to its effects on atmospheric visibility, climate change andhuman health (e.g. Saikawa et al., 2009). Much of the anthropogeniccomponent of this suspended particulate matter (PM) is derivedfrom air pollutant emissions in China (Chan and Yao, 2008; Aikawaet al., 2010). Transboundary regional atmospheric outflows of thesematerials regularly intrude neighbouring areas such as the Korean

34 934110012.eno).

rights reserved.

Peninsula and Japan, adding to local pollutants, and have been tracedcrossing the Pacific Ocean to contaminate North America (Prosperoet al., 2003; Liu et al., 2008; Fairlie et al., 2010). The problem is par-ticularly acute during spring, when dust intrusions from the desertsof northern China and southern Mongolia move southeast to en-counter anthropogenic pollutants over lowland China (Fig. 1). Theresulting chemically complex air masses are loaded with both natu-ral and anthropogenic PM and commonly move away on trans-boundary migration paths across the epicontinental seas east of theChinese mainland (Guo et al., 2004; Ma et al., 2004; Wang et al.,2004; Lasserre et al., 2008; Zhang et al., 2010; Takahashi et al.,2010). Driven by rapidly moving cold fronts (Uno et al., 2004),these heterogeneous transboundary PM intrusions can cross frommainland China to the Korean Peninsula or western Japan in lessthan 24 h and impose sudden, and sometimes dramatic, changes inair quality (Chung and Kim, 2008).

A proliferation of recent research articles has provided much de-tailed information on the structure of the atmosphere containing

Gobi Desert

Kumamoto(monitoring site)

Hong Kong

Shanghai

BeijingTak

limak

an BadainJaran

HexiCorridor

Highly contaminatedinnerzone

MiddlezoneSO4

2- > 7.5µg/m3

annual averageOuterzoneSO4

2- > 2.5µg/m3

annualaverageDesert dust transport paths

TokyoSeoul

Pyongyang

Hanoi

Taipei

Wuhan

Anthropogenic pollutants

a

1000 km

b

50 µgPM10/m3

Coarsening Index= 3.6%

39 µgPM10/m3

Coarsening Index= 0.9%

53 µgPM10/m3

Coarsening Index= 1.5%

mineral dustsulphate

26-27 Aprilsample K260410

11-12 Maysample K110510

20-21 Maysample K200510

c

d

Fig. 1. Location map (1a) and contrasting settings each of the three aerosol intrusions sampled during the Kumamoto campaign (1b–d). Fig. 1a: Overview of the huge area affectedby East Asian anthropogenic aerosol megaplume, with mean surface concentrations of airborne SO4

2−recalculated from modelling data of Aikawa et al. (2010) combined with pub-lished monitoring data (e.g. Querol et al., 2006; Ianniello et al., 2011). The monitoring site in Kumamoto lies on the island of Kyushu in SW Japan, in the area most frequently visitedby transboundary PM outflows from the west. The main source areas of springtime desert dust intrusions into the area are also shown (Wang et al., 2004). Fig. 1b: direct hit fromdesert PM (Kosa), pushing sulphatic pollutants ahead and aside of the storm. Fig. 1c: Peripheral influence of minor dust storm to the north, combined with contamination by a wide-ly dispersed anthropogenic pollutant cloud. Fig. 1d: Desert dust storm grazing past Kyushu and dragging concentrated belt of metalliferous sulphatic pollutants into SW Japan.Coarsening Index refers to the number of supermicron PM10 compared to the number of PM10>0.3 μm (CI0.3=% N 1–10 μm/N 0.3–10 μm). See text for details.

183T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

these mixtures of natural and anthropogenic PM over East Asia,boosted especially by the 2001 Asian Pacific Regional Aerosol Char-acterization Experiment (ACE-Asia) (e.g. Uno et al., 2003; Seinfeldet al., 2004; Zhang et al., 2004; Kim et al., 2005; Park et al., 2005and references therein). Important contributions to our chemical un-derstanding of atmospheric PM in East Asia again include ACE-Asiadata (e.g. Arimoto et al., 2004; Satake et al., 2004) but also detailedobservations on individual airborne particles (e.g. Zhang et al.,2003, 2006; Kojima et al., 2006; Tobo et al., 2009) as well as manystudies on transboundary secondary inorganic compounds (e.g.Nishikawa et al., 1991; Shimohara et al., 2001; Mori et al., 2003;Trochkine et al., 2003; Zhang et al., 2004; Uno et al., 2007; Aikawaet al., 2010; Fairlie et al., 2010; Kong et al., 2010a, 2010b). Some pa-pers have additionally investigated the presence of metalliferousparticles of technogenic origin within Asian atmospheric aerosols(e.g. Kim et al., 2003; Arimoto et al., 2004), although overall mostchemical data published so far provide only partial analyses of PMsize fractions (e.g. Kong et al., 2010a, 2010b). Another limitation,particularly with respect to human health studies, is that somepast publications on East Asian PM chemistry have referred only toTotal Suspended Particulate Matter (e.g., Okuda et al., 2008; Yuanet al., 2008; Kim et al., 2009) rather than specifically the inhalablefraction (i.e. b10 μm: PM10, Cheng et al., 2005; Chan et al., 2008).In this paper we present a new PM10 dataset on transboundaryEast Asian PM including a full analytical suite of major and trace el-ements, secondary inorganic compounds (SIC), and both elementaland organic carbon (EC, OC). Analysis and interpretation of thesedata are integrated with meteorological information, data on air-borne particle size and number, and chemical forecasting results(CFORS: Uno et al., 2003, 2004; Satake et al., 2004). The airbornePM10 samples were collected at Kumamoto in Kyushu, SW Japan

during springtime (April–May 2010) prior to, during and after exoticdust intrusions swept eastward from the Asian mainland. The resultsoffer insight into the complex atmospheric mixing processes andchanges in air quality that occur within transboundary receptorareas lying immediately downstream from East Asian aerosoloutflows.

2. Methodology

Data were obtained in April and May 2010 at the top of a nine-storey building within the Kumamoto University precinct on the is-land of Kyushu in Western Japan. Kumamoto, with c. 731,000 inhab-itants (2010 data), lies near the western Japanese coastapproximately midway between Tokyo (c. 1000 km ENE) and Shang-hai (c. 1000 km WSW). The city is built on low, alluvial groundbacked by forested hills and, with only light and service industries,is not impacted by any nearby heavy industrial point sources, makingit an excellent location to observe the arrival of transboundary dustintrusions. The monitoring site is located in the eastern part of thecity and can be classified as an urban background site influenced tosome extent by road traffic emissions from a city centre arterialroad 1400 m to the west and a minor (although frequently traffic con-gested) two-lane road crossing the University area.

The site was equipped with a SIBATA HV-1000F high volumesampler (60 m3/h) for collecting of particles. We used an optionaldevice for the sampler that is provided by the manufacturer andcan exclude particles larger than 10 μm. Quartz fibre filters(ADVANTEC QR-100) were conditioned (30–40% relative humidityduring 48 h) and weighed before and after sampling to determine24 h PM10 concentrations by standard gravimetric procedures(with sampling starting at 18:00 JT). Once the gravimetric

184 T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

determination was performed the filters were treated and analysedfor the determination of the chemical composition of PM10. Onequarter of each filter was acid digested (HF:HNO3:HClO4, with amixture of 2.5:1.25:1.25 ml, kept at 90 °C in a Teflon reactor during6 h, driven to dryness and re-dissolved with 1.25 ml HNO3 to makeup a volume of 25 ml with water) for the chemical analysis usingICP-AES and ICP-MS. Another ¼ of each filter was water leached(6 h at 60 °C, preceded by incubation in an ultrasound bath for10 min, in 50 ml sealed PVC bottles) for the determination of solu-ble ion concentrations by ion chromatography (sulphate, nitrateand chloride) and ion selective electrode (ammonium), allowingan average detection limit for the analysed components of25–30 ng/m3. A (1.5 cm2) portion of the remaining half of each fil-ter was also used for the determination of organic and elementalcarbon (OC and EC, respectively) by a thermal–optical transmissiontechnique (Birch and Cary, 1996) using a Sunset Laboratory OCECAnalyser with the EUSAAR-2 standard temperature programme.The accuracy of the equipment is 0.1 μg OC/m3, 0.2 μg EC/m3, andthe detection limit 0.2 μg/m3 for both OC and EC. The sum OC+EC is Ctotal. The OM+EC (organic matter plus elemental carbon)value was obtained after applying a 1.6 factor to the OC concentra-tions (Turpin et al., 2000).

SiO2 and CO32− were indirectly determined on the basis of empirical

factors (Al∗1.89=Al2O3, 3∗Al2O3=SiO2 and 1.5∗Ca+2.5∗Mg=CO32−,

see Querol et al., 2001a). Blank field filters were used for every stockpurchased for sampling and analysed in the same batches of their re-spective filter samples. The corresponding blank concentrationswere subtracted from each sample. To assure the quality of the ana-lytical procedure a small amount (5 mg) of the NIST-1633b (fly ash)reference material loaded on a ¼ quartz micro-fibre filter was alsoanalysed. Detection limit and accuracy of the techniques were esti-mated as 0.18 ng/m3 and 1–3% respectively for ICP-AES, and0.007 ng/m3 and 0–7% respectively for ICP-MS. The detection limitsfor Zr and Hf are higher (0.05 ng/m3). Particle number-size distribu-tion at the sampling site was measured by an optical particle counter(OPC), less than 2 m apart from the high volume sampler. The OPC(RION, KC-01D1) has 5 channels, counting numbers of particles>0.3, >0.5, >1, > , and >5 μm at an interval of 10 min. Mass concen-tration of atmospheric sulphate was monitored using the Model 5020Sulfate Particulate Analyzer (SPA) (Thermo Electron). Integrated sul-phate mass measured by the SPA during the sampling period of each fil-ter correlateswell (R2=0.89)with the sulphatemass determined by ionchromatography, except for one filter. The SPA data indicate temporalvariation of sulphate concentration in the atmosphere over the Kuma-moto area, which we used to identify the timing of pollutant intrusions.

In order to characterise the daily atmospheric scenarios impactingon PM levels, the pathways of air-masses into the Kumamoto areaduring the monitoring period were assessed using the HYSPLIT-model (Draxler and Rolph, 2003), with vertically modelled transportback-trajectories being calculated for 5 days at 500, 1000 and1500 m above sea level. In addition dust and sulphate maps forecast-ed by the Chemical Weather Forecasting System (CFORS) wereobtained from the website of the National Institute for EnvironmentalStudies (http://www-cfors.nies.go.jp/~cfors/). CFORS numerically cal-culates distributions of Asian dust and anthropogenic sulphate aero-sols every 3 h, the results being uploaded on the website every day.The system is reported to have accurately reproduced many impor-tant features observed during ACE-Asia (Uno et al., 2004; Satake etal., 2004), and is widely referred to as a source of real-time informa-tion on movements of dust and pollution clouds over Asia. Finally,weather conditions (wind velocity and direction, precipitation, rela-tive humidity and ambient temperature) were also obtained fromthe Kumamoto Meteorological Observatory, located about 2 kmwest of the sampling site, to provide a better understanding of morelocal atmospheric patterns and their influence on the dispersion oflocal pollution sources.

3. Pollution episodes

Three contrasting types of high PM component events involvingmixtures of natural desert particulates and anthropogenic pollutantswere sampled during the 2010 monitoring campaign in Kumamoto(Figs. 1b–d). The first of these took place over the week of 26 Aprilto 3 May and involved a direct hit from a desert-derived aerosolcloud travelling ESE across the Chinese mainland and out into theEast China Sea. This was a classic Japanese Kosa event (Kosa, “yellowsand” in Japanese, refers to the long-range transport of atmosphericparticles originating from the desert areas of China and Mongoliathat reach the western Pacific Region, including Japan), with back-trajectory analyses indicating the origin of the dust storm centredon the Badain Jaran Desert, a well documented prominent aeolianPM source in Northern China (Ma et al., 2004; Wang et al., 2004).These desert particulates had been lofted high into the free tropo-sphere and driven across to SW Japan behind a rapidly movingrainy cold front, pushing a high-sulphate aerosol cloud rich in pollut-ants ahead and aside of the storm (Fig. 1b). In Kumamoto the rainyfront passed during the night and early morning of the 26–27 April,bringing in its wake reduced atmospheric visibility associated witharrival of the dust storm intrusion. Having reached Japan, eastwardprogress of this frontal dust wave slowed as a wedge of warm oceanicair mixed with pollutant SIC from SE China pushed north, splitting theintrusive PM mass which initially declined in intensity over Kyushubefore the arrival of a second dust wave. This second desert aerosolwave, this time sourced mainly from the Inner Mongolian Plateau,swept southeastwards across Kyushu and out to sea. No furtherfresh dust intrusions were received from the northwest as an inter-mingled, ageing cloud of natural and anthropogenic transboundaryaerosols spread across much of the NW Pacific region. One of themore concentrated remnants of this cloud, still rich in mineral PM,hung over the ocean south of Kyushu for two days before driftingback across the island, inducing a third PM10 event. The fluctuationsin air quality induced by these successive events are recorded by PM10

24-hour mass measurements which rose three times to 50 μg/m3

or more as the three more concentrated aerosol waves passed overKumamoto.

The relative importance of the coarser, crustally-derived “geologi-cal” component to the suspended PM load during this first pollutionepisode is revealed by the data on particle numbers and size fractions.Most atmospheric rock forming mineral dust particles are silicatesthat are typically supermicron in diameter and thus (together withsea salt) constitute the bulk of aerosol mass. In contrast, in terms ofparticle number it is the submicron sized nucleation and accumula-tion mode carbonaceous and SIC particles which dominate. Ambientaerosol size distributions in East Asia therefore typically show bimod-al sub- and supermicron peaks at around 0.4–0.7 μm and 4–6 μm(Kanai et al., 2003; Chan and Yao, 2008). With this in mind, ourdata on particle number (N) allows us to separate N>0.3 μm fromN>1 μm. We have found that the difference between these two,expressed as % N>1 μm/N>0.3 μm and referred to here as the Coars-ening Index (CI0.3 where 0.3 refers to the minimum submicron PMsize counted), provides a useful indication of the relative importanceof coarser “natural” supermicron PM as compared to submicron aero-sols. Thus Coarsening Index refers to the number of supermicronPM10 compared to the number of PM10>0.3 μm (CI0.3=% N1–10 μm/N 0.3–10 μm). Aerosol populations with CI0.3>2.5% are op-erationally classified as coarse, those with CI0.3=1.25–2.5% are medi-um, and those with CI0.3b1.25% are fine. In the case of the pollutionepisode described above, the average CI0.3 was high at 3.0%(Fig. 1b), reaching peaks of 3.6% in response to the arrival of fresh de-sert PM during the first and second dust wave events and reflectingthe abundance of supermicron-sized crustal PM.

The second pollution episode recorded by our 2010 dataset(11–14 May) was produced by a brief encounter with a desert dust

185T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

intrusion passing eastward to the north of Kumamoto as it crossedthe Sea of Japan from the Korean Peninsula to central Honshu(Fig. 1c). Kyushu was affected only by the southern edge of thisdust storm as it brushed past the island, so 24-hour average PM10

levels stayed below 40 μg/m3. Low CI0.3 values (0.9–1.0%) indicate amuch finer average particle size due not only to the absence of coars-er crustal PM but also the presence of anthropogenic aerosols. CFORSpredictions show the arrival of a widely dispersed area of trans-boundary pollutants swept into Kyushu from the Asian mainlandand mixing with the southern margin of the dust storm (Fig. 1c).These pollutants however failed to intrude much further into Japandue to the development of a blocking low pressure system centredeast of Hokkaido. Instead, the remains of the diluting aerosol cloudwere blown back across Kyushu and west into the East China Seathen away north as a clean mass of fresher, colder air arrived fromthe NE.

The final pollution episode sampled during this study was themost anthropogenic in character. In this case once again the mainfocus of the desert dust storm lay to the north of Kyushu, grazingthe north of the island on 20–21 May. However, the sulphate cloudlying to the south of the storm was unusually concentrated, havingbeen constricted by southerly winds to occupy a narrower east–westband than had occurred in the previous episode (Fig. 1d). Underthese conditions although PM10 mass values rose to >50 μg/m3 inKumamoto, CI0.3 values remained only moderate at around 1.5%,less than half the value seen during the desert dust waves of thefirst pollution event recorded the previous month. Furthermore,despite a brief atmospheric cleansing during the following day, alow pressure system developed over the Korean Peninsula anddragged a new wave of mixed crustal and anthropogenic materialeastwards into Kyushu (Fig. 2). Whereas the crustal component ofthis new intrusion was aged and diluted (the same particles havingreturned from initial dispersal into the NW Pacific back across theKorean Peninsula and down through China) the anthropogenic pol-lutants included a new plume of fresh contaminants derived directlyfrom SE China. The arrival of this pollutant mass produced the mostanthropogenic signature of the entire campaign, with PM10 levelsrising to 52 μg/m3 but CI0.3 values falling to 0.9%.

Finally, three additional 24-hour samples were taken to character-ise relatively clean background atmospheric conditions that existedimmediately before the first pollution episode (25–26 April), be-tween the first and second episode (7–8 May), and immediately

20th May23

Background 24-25th MaySO4

2- 4,6 18,6NH4

+ 1,4 6,3NO3

- 1,1 5,6Pb 10,6 61Bi 0,2 1,2Tl 0,1 0,5As 1,2 5,6Cd 0,3 1,1Zn 32 137Ge 0,2 0,8V 2,1 5,8Cr 1,5 3,8Ni 1,6 3,8Sn 1,1 2,8Cu 4,8 9,2Sb 1,3 2,5

1000 km

anth

rop

og

enic

po

lluta

nts

Kumamoto

Fig. 2. Map showing track of desert dust storm depicted on Fig. 1d, passing eastwards intotransported from the Asian mainland. The result produced the most anthropogenically conshowing the consequent striking increase in pollutants as compared to background (calculin μg/m3 (SIC) and in ng/m3 (metals).

after the third episode (25–26 May). Both PM10 loading and CI0.3 forthese days were predictably low (19–25 μg/m3 and 0.9 respectively).In summary, the first pollution event sampled was the longest, mostcomplex and dominated by desert PM which became increasinglymixed with anthropogenic components as time progressed. The sec-ond episode was a relatively minor event mixing fine, distal desertPM with anthropogenic materials, whereas in the third episode an-thropogenic pollutants were dominant. The following section reportson the chemical data from each of these episodes, comparing themwith each other and with the cleaner background days.

Weather conditions recorded at the Kumamoto MeteorologicalObservatory during the campaign indicate very similar patterns dur-ing the whole period suggesting a low effect on the pollution events.Thus temperatures were very homogeneous (increasing from April toend of May) with average temperatures of 20 °C. Daily wind patternswere also very similar, being predominant from a SW–W directionand reaching up to 8 m/s speed but rarely exceeding 3 m/s. Finallyrain was uncommon and only registered on the 25–26 of April(b 15 mm) and 21–22 of May (b50 mm), although such precipita-tion did not affect importantly the levels of PM10 that were notbelow 42 μg/m3 those days.

4. Geochemical results

The marked segregation between coarser natural particles andfiner anthropogenic aerosols is confirmed by linear regression be-tween PM number (N) and chemical data which allows separationinto mineral particles (mostly clays, quartz and carbonate) andmore anthropogenic PM such as SIC and pollutant metals (details onthe data used for such analyses are shown in the supporting informa-tion, Table S1). Mineral aerosols show a strongly positive correlationbetween mass and number only in the coarsest fractions, with R2 ex-ceeding 0.90 for N>5 μm, 0.80 in N>2 μm, 0.50 in N>1 μm, and fall-ing below 0.10 in N>0.3 (Fig. 3). The same calculation performed on(NH4)2SO4 shows exactly the opposite, with good correlations onlypresent for the size fractions that include submicron particles(Fig. 3). Trace elements are likewise strongly segregated in their pref-erence for the coarser or finer fractions. In the case of typically crustaltrace elements, such as Sc, Ti, Se, and Rb, these always show the bestcorrelations only between mass and N>2 μm. In contrast, the highestcorrelation coefficients between mass and particle number for metal-lic anthropogenic pollutants such as Cu, Zn, Sb, As, Cd, Sn, Tl, Pb and Bi

Kumamotomonitoring site

24-25th May

fresh pollutants(SIC+metals)

desert dust

+ ageing

pollutants

22nd May

rd May

the Sea of Japan then back anticlockwise to mix with a cloud of fresh pollutants beingtaminated day of the Kumamoto 2010 campaign (24–25 May) with the adjacent tableated as an average of samples K250410, K070510, and K250510). Concentration units

R² = 0.907

R² = 0.8778

R² = 0.514

R² = 0.8682

R² = 0.9776

1

10

100

1,000

10,000

100,000

1,000,000

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0

> 0.3µm (NH4)2 SO4 X 2

> 1µm mineral

> 2µm mineral

> 5µm mineral

> 0.5µm (NH4 )2 SO4 X 2

Par

ticl

e n

um

ber

(co

un

ts/li

ter)

PM10 (µg/m3)

Fig. 3. Particle number (OPC: counts/liter) plotted against PM10 mass for coarser(>1 μm) mineral PM and finer (>0.3 μm) ammonium sulphate size fractions. Correla-tion coefficients for OPC data including submicron mineral and supermicron sulphatePM all have R2b0.2, demonstrating that most silicate mineral particles are coarse andmost anthropogenic aerosols are fine. There are no OPC data for sample K250410,and samples K270410 and K280410 have been omitted because they are anomalouslyrich in coarse marine (NaCl) PM10.

186 T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

always occur in the finest fraction. Given the clear dominance of nat-ural mineral dust and sulphatic anthropogenic aerosols, the chemicalcontrasts between these two groups are now explored further in acomparison between each of the three PM intrusion episodes sam-pled during the 2010 campaign.

4.1. Transboundary aerosol intrusion 1: Natural>anthropogenic

Atmospheric conditions in Kyushu on 25 April were quiet, anticy-clonic and low in suspended PM mass (19 μg/m3), as the first aeoliandust outflow from mainland Asia was gathering momentum, movingrapidly across central China and out to sea (Fig. 1b). Immediately priorto arrival of the dust storm in Japan CFORS data indicate the lingeringpresence of an aged, diluted, sulphatic air mass derived mainly fromprevious eastward aerosol migrations. Light winds in Kumamoto, orig-inating from inland, favoured the addition of local pollutants to theseregional background pollutants, with minimal marine influence. Thegeochemical data for this day (Sample K250410, Tables 1a and 1b)correspondingly demonstrate a dominance of carbonaceous particles(40% of total measured particulate matter: PM10) and SIC (34%PM10)over mineral dust (24%PM10) andmarine PM (2%PM10), with campaignmaximum values for elemental carbon (EC=0.9 μg/m3) recording thepresence of locally-derived traffic emissions. Given the low mass ofthe collected sample most major and trace element concentrationsare also subdued, although exceptions are provided by several metals,notably Cu and Sb (Table 1a). The presence of suchmetals is highlightedby normalising data to PMmasswhich reveals relatively elevated levels(per μg/g) of other similarly anthropogenic metallic elements such asZn, Cd, As, and Sn.

Analysis of the filter collected the following day (sample K260410,Tables 1a and 1b) provides an excellent example of the suddenchange in atmospheric PM levels and chemistry produced by the ar-rival of a Kosa dust storm into SW Japan. The amount of mineraldust now composes 64% of the total PM10 (64%∑PM10), with a corre-sponding increase in the concentrations of “crustal” major and traceelements characteristic of rock forming minerals found in soils andsedimentary rocks, namely Al, Fe, Ca, Mg, K, Li, Sc, Ti, Mn, Co, Rb, Sr,Y, Nb, Cs, Th and the lanthanoid series (REE). The rise in Ca, Mg, andSr is especially marked, indicating a notable presence of carbonatemineral particles. In contrast the six technogenic metallic pollutantspreviously mentioned rise relatively little or not at all, with Cu andSb concentrations actually falling despite the jump in PM10 massfrom 20 to 50 μg/m3. Another difference is that whereas C and NH4

+

concentrations fall, SO42− and NO3

− levels both rise, presumably in

response to new anthropogenic pollutants driven into Kyushu bythe dust storm (Table 1a). Such opposite trends suggest a differencein grain size, with SO4

2− and NO3− being preferentially concentrated

in the coarse size.The following two 24-hour samples (K270410 and K280410) re-

cord the rapid dissipation of the first dust wave arrival, with the min-eral dust loading falling to b50%PM10. The consequent drop in PM10

mass (from 49.7 to 37.3 μg/m3) is offset by increasing SIC(32%PM10) and NaCl content (7%PM10) as warm, low-level oceanicair briefly arrives into Kyushu from the south (Table 1a and 1b).This tendency is reversed by the arrival of the second crustal dust in-trusion from the NW (sample K290410; 56 μg/m3), cutting off thesupply of southern marine air and returning mineral PM levels tothose attained during the first dust wave arrival (>60%PM10). Despitethis similarity in overall mass, however, the chemical composition ofthis new intrusion is markedly less calcareous (Table 1a: Al2O3 levelsmore than double whereas Ca concentrations actually fall slightly),revealing that not all desert-derived mineral aerosol intrusions intoJapan have the same crustal chemistry. The response of the threeSIC concentrations to the arrival of the second dust wave is initiallymuted. However, the following day, with mineral PM already onceagain in rapid decline as the desert dust cloud drifts south of Kyushu,SIC all rise sharply to a new peak (NO3

− 4 μg/m3, SO42− 10 μg/m3, NH4

+

3 μg/m3), raising PM10 to over 60 μg/m3. Atmospheric concentrationsof the more toxic metallic trace elements (Ni, Cu, Zn, Ge, As, Se, Cd, Sn,Sb, Tl, Pb, Bi) also peak the day after the second Kosa dust wave, coin-ciding with the peak in SIC and presumably likewise recording the ar-rival of fresh new pollutants from the Asian mainland in the wake ofthe second desert dust intrusion.

There is a clear tendency towards increased mixing of the naturaland anthropogenic components as time progresses, demonstrated bythe greater concentrations of SIC present during the first (21%PM10)and second (26%PM10) desert dust arrivals (Table 1b). By the penulti-mate sampling day SIC levels have climbed to 35%PM10 within a re-gional pollutant cloud by now dispersed over the entire Japanesearchipelago. The spatial inhomogeneity of this persisting cloud, vari-ably enriched in natural and anthropogenic particles, is recorded bythe chemical data of the final sample (K020510) in which mineralPM10 suddenly doubles in mass and exceeds 60%∑PM10 for thethird time. An overview of the fluctuations in atmospheric PM chem-istry during this first pollution episode is graphically represented inFig. 4. On this figure siliceous and calcareous crustal PM are repre-sented by Al2O3 and Ca respectively, with Al2O3 recording the triplepeak of each successive dust wave whereas only the first dust wave(K260410) is calcareous. Also clear is the overall rise in SIC levels,and the tendency for these pollutants to rise especially in the wakeof a desert dust intrusion, a lack of synchronisation best displayedby sample K300410. Also apparent on Fig. 4 is the local traffic Cpeak of initial background conditions (K250410), the intrusion of ma-rine air recorded by higher Na levels (K270410 and K290410), andthe initial strong rise in NO3

− levels which we associate in part withthe presence of supermicron Ca(NO3)2 particles (K260410). WhereasNH4

+ follows a similar concentration pattern to that of SO42−, presum-

ably due to the presence of abundant ammonium sulphate particles,NO3

− levels fall below those of NH4+ towards the end of the pollution

episode suggesting preferential depositional loss of the coarser ni-trate component.

4.2. Transboundary aerosol intrusion 2: Natural ≈ anthropogenic

The chemical evidence for intermingling between natural and an-thropogenic aerosols is particularly manifested during the secondpollution episode (11–13 May) which involved the arrival of a pe-ripheral desert aerosol storm brushing eastwards across northernKyushu reaching PM10 values up to 38.7 μg/m3 (Fig. 1c and Tables1a and 1b). Under this type of “glancing blow” Kosa episode the

Table 1aDaily, average, maximum, and standard deviation values for elemental concentrations in the PM10 analysed in gravimetric filters in Kumamoto during April–May 2010. PM and major element concentrations are in μg/m3, trace elementalconcentrations in ng/m3.

K250410 K260410 K270410 K280410 K290410 K300410 K010510 K020510 K070510 K110510 K120510 K130510 K200510 K210510 K240510 K250510 Average Max. St. dev.

μg/m3

PM10 19.38 49.72 42.87 37.29 55.98 61.47 36.45 62.52 25.14 38.67 27.48 28.86 52.57 50.97 51.80 18.82 41.25 62.52 14.41Cnm 4.97 2.64 1.82 2.18 2.23 2.70 3.07 2.19 4.16 4.19 2.71 4.13 4.26 6.88 3.07 2.16 3.33 6.88 1.35OM+EC 7.65 5.45 3.74 4.17 4.31 4.84 5.31 4.59 6.60 6.81 4.33 6.64 6.93 11.26 4.96 3.42 5.69 11.26 1.95OC 4.22 2.92 2.01 2.37 2.42 2.69 3.02 2.60 3.67 3.89 2.37 3.80 3.88 6.51 2.64 1.88 3.18 6.51 1.15EC 0.89 0.78 0.52 0.39 0.43 0.53 0.48 0.43 0.73 0.59 0.54 0.56 0.72 0.84 0.74 0.41 0.60 0.89 0.16CO3

2− 0.72 5.29 3.58 2.87 3.16 2.63 2.15 4.22 1.19 1.44 0.99 1.19 1.70 2.33 1.55 0.66 2.23 5.29 1.33SiO2 2.37 13.47 9.06 7.30 15.82 13.75 8.39 17.63 3.49 5.90 3.89 4.51 4.64 6.77 3.92 1.49 7.65 17.63 4.99Al2O3 0.79 4.49 3.02 2.43 5.27 4.58 2.80 5.88 1.16 1.97 1.30 1.50 1.55 2.26 1.31 0.50 2.55 5.88 1.66Ca 0.30 2.20 1.41 1.07 1.06 0.83 0.78 1.49 0.53 0.47 0.37 0.47 0.65 0.89 0.55 0.14 0.83 2.20 0.53Fe 0.31 1.38 1.01 0.84 1.59 1.41 0.92 1.75 0.44 0.65 0.47 0.53 0.59 0.78 0.54 0.17 0.84 1.75 0.47K 0.19 0.86 0.61 0.56 0.93 0.91 0.63 1.05 0.27 0.44 0.30 0.30 0.55 0.55 0.63 0.12 0.56 1.05 0.28Na 0.19 0.67 1.44 1.29 0.88 0.87 0.44 0.71 0.20 0.57 0.25 0.24 0.25 0.28 1.20 0.55 0.63 1.44 0.41Mg 0.11 0.79 0.58 0.50 0.63 0.56 0.39 0.79 0.16 0.29 0.18 0.19 0.29 0.40 0.29 0.18 0.40 0.79 0.22Cl 0.15 0.39 1.14 1.12 0.61 0.33 0.41 0.40 0.26 0.16 0.13 0.17 0.09 b d.l. 0.50 0.21 0.40 1.14 0.33NO3

− 0.64 2.50 3.42 2.95 3.18 3.81 1.73 2.30 0.90 1.98 0.41 0.89 2.21 1.09 5.60 1.66 2.20 5.60 1.37SO4

2− 4.63 5.13 5.90 6.06 6.70 9.65 8.12 10.54 3.01 8.76 3.55 5.20 16.12 13.15 18.56 6.15 8.20 18.56 4.46nss-SO4 4.60 5.05 5.73 5.90 6.59 9.55 8.06 10.46 2.99 8.69 3.52 5.17 16.09 13.12 18.41 6.08 8.13 18.41 4.45NH4

+ 1.44 1.29 1.31 1.54 1.96 2.80 2.41 2.69 1.04 2.98 2.31 1.76 7.33 3.99 6.31 1.62 2.67 7.33 1.80

ng/m3

Li 0.23 1.82 1.22 1.01 1.85 1.78 1.16 2.24 0.42 0.77 0.47 0.56 0.84 0.96 1.01 0.21 1.03 2.24 0.62Be 0.01 0.08 0.07 0.06 0.11 0.10 0.07 0.12 0.04 0.06 0.04 0.04 0.05 0.06 0.05 0.03 0.06 0.12 0.03Sc 0.07 0.49 0.33 0.25 0.49 0.52 0.27 0.68 0.09 0.17 0.08 0.14 0.13 0.22 0.11 0.00 0.25 0.68 0.20P 21.72 37.20 31.63 23.02 49.44 45.11 32.75 53.04 26.88 27.30 19.46 25.01 40.36 42.04 34.63 13.57 32.70 53.04 11.25Ti 27.10 124.45 88.41 71.38 148.75 136.17 83.52 170.51 40.64 57.86 38.85 49.73 47.90 68.91 44.03 14.05 75.77 170.51 46.31V 2.02 7.00 3.94 3.49 5.94 7.63 5.09 7.55 2.34 4.57 2.05 3.20 2.97 3.26 5.82 2.00 4.31 7.63 1.98Cr 0.98 3.20 2.38 2.19 3.24 3.60 2.37 3.86 1.74 2.19 1.21 3.04 1.88 2.62 3.82 1.74 2.50 3.86 0.89Mn 7.58 35.89 25.82 23.92 42.39 41.69 27.91 46.04 14.28 20.79 15.10 17.70 19.32 24.80 24.67 7.47 24.71 46.04 11.77Co 0.12 0.65 0.42 0.34 0.61 0.58 0.39 0.73 0.20 0.30 0.19 0.26 0.24 0.33 0.31 0.10 0.36 0.73 0.19Ni 1.16 2.83 1.89 1.89 2.46 3.08 2.29 2.99 1.92 2.37 0.98 2.21 1.80 2.21 3.78 1.58 2.22 3.78 0.72Cu 6.02 4.93 3.97 4.86 5.35 7.62 6.45 6.25 6.12 5.27 4.03 4.48 7.27 7.09 9.22 2.31 5.70 9.22 1.67Zn 22.81 38.47 28.52 43.54 48.77 79.40 55.79 55.08 37.10 51.10 38.08 37.95 60.12 53.86 136.57 35.76 51.43 136.57 26.50Ga 0.16 0.96 0.64 0.58 1.03 1.20 0.73 1.27 0.24 0.47 0.30 0.34 0.73 0.60 1.19 0.23 0.67 1.27 0.37Ge 0.11 0.39 0.24 0.17 0.30 0.44 0.41 0.21 b d.l. b d.l. 0.20 0.25 0.53 0.39 0.81 0.56 0.36 0.81 0.19As 0.97 2.10 1.28 1.98 2.43 3.65 2.57 3.14 1.37 2.63 1.54 1.91 3.26 2.26 5.61 1.36 2.38 5.61 1.15Se 0.40 0.86 0.83 0.77 0.96 1.65 1.23 1.19 0.57 1.06 0.58 0.63 0.49 1.15 0.66 0.34 0.83 1.65 0.35Rb 0.57 3.80 2.77 2.57 4.30 4.17 2.93 4.95 1.08 1.90 1.26 1.32 2.33 2.35 3.07 0.81 2.51 4.95 1.32Sr 1.60 13.43 9.12 6.94 10.07 9.44 6.64 12.98 2.64 4.27 2.33 2.95 4.85 6.69 5.59 1.53 6.32 13.43 3.83Y 0.15 0.84 0.60 0.47 0.84 0.78 0.55 0.97 0.32 0.41 0.20 0.41 0.31 0.46 0.47 0.27 0.50 0.97 0.24Zr 0.96 3.33 2.52 2.06 4.42 4.20 2.64 4.64 1.87 2.48 0.49 2.38 1.38 2.47 2.56 1.74 2.51 4.64 1.17Nb 0.15 0.88 0.65 0.50 0.99 1.04 0.58 1.14 0.27 0.39 0.27 0.37 0.33 0.59 0.34 0.13 0.54 1.14 0.32Mo b d.l. 0.35 2.75 2.10 2.24 2.58 2.65 2.48 2.64 3.20 b d.l. 4.49 2.03 2.71 5.65 4.78 2.90 5.65 1.32Cd 0.21 0.36 0.27 0.34 0.38 0.72 0.54 0.59 0.26 0.40 0.26 0.26 0.57 0.44 1.06 0.30 0.44 1.06 0.22Sn 1.03 1.09 0.93 1.22 1.24 2.14 1.88 2.05 1.37 1.35 1.22 1.33 1.93 2.15 2.82 0.88 1.54 2.82 0.55Sb 1.57 1.27 0.65 0.99 1.30 1.86 1.58 1.44 1.61 1.51 1.10 1.24 2.45 2.63 2.49 0.76 1.53 2.63 0.59Cs 0.05 0.39 0.30 0.32 0.47 0.49 0.35 0.50 0.13 0.23 0.16 0.16 0.31 0.27 0.54 0.13 0.30 0.54 0.15Ba 7.34 26.10 17.96 15.78 25.97 26.17 18.05 32.68 10.47 16.74 9.25 9.50 13.38 16.87 13.17 4.28 16.48 32.68 7.89La 0.17 1.13 0.84 0.67 1.25 1.23 0.81 1.38 0.35 0.57 0.35 0.46 0.40 0.65 0.60 0.20 0.69 1.38 0.38Ce 0.58 2.86 2.09 1.84 3.16 2.98 1.90 3.56 0.96 1.46 0.87 1.03 1.06 1.66 1.57 0.43 1.75 3.56 0.96Pr 0.03 0.25 0.18 0.13 0.28 0.24 0.15 0.31 0.06 0.12 0.07 0.08 0.08 0.13 0.09 0.03 0.14 0.31 0.09Nd 0.14 1.12 0.80 0.60 1.21 1.06 0.68 1.34 0.29 0.48 0.28 0.36 0.33 0.52 0.39 0.12 0.61 1.34 0.39Sm 0.03 0.24 0.17 0.13 0.25 0.22 0.14 0.28 0.07 0.10 0.06 0.09 0.07 0.11 0.09 0.04 0.13 0.28 0.08Eu 0.02 0.05 0.04 0.04 0.06 0.05 0.04 0.06 0.03 0.03 0.03 0.03 0.03 0.04 0.03 0.02 0.04 0.06 0.01

(continued on next page)

187T.M

orenoet

al./Science

oftheTotalEnvironm

ent424

(2012)182

–192

Table1a

(con

tinu

ed)

K25

0410

K26

0410

K27

0410

K28

0410

K29

0410

K30

0410

K01

0510

K02

0510

K07

0510

K11

0510

K12

0510

K13

0510

K20

0510

K21

0510

K24

0510

K25

0510

Ave

rage

Max

.St.d

ev.

ng/m

3

Gd

0.05

0.23

0.17

0.12

0.24

0.21

0.14

0.26

0.08

0.12

0.06

0.09

0.08

0.12

0.10

0.05

0.13

0.26

0.07

Tb0.01

0.03

0.02

0.02

0.03

0.02

0.02

0.03

0.01

0.01

0.01

0.01

0.01

0.02

0.01

0.01

0.02

0.03

0.01

Dy

0.03

0.15

0.11

0.09

0.15

0.14

0.10

0.17

0.06

0.08

0.04

0.08

0.06

0.08

0.09

0.05

0.09

0.17

0.04

Ho

0.01

0.03

0.02

0.02

0.03

0.03

0.02

0.03

0.01

0.01

0.01

0.01

0.01

0.02

0.02

0.01

0.02

0.03

0.01

Er0.01

0.07

0.05

0.04

0.07

0.06

0.04

0.08

0.02

0.03

0.02

0.03

0.02

0.04

0.03

0.02

0.04

0.08

0.02

Tmbd.l.

0.03

0.02

0.02

0.03

0.03

0.02

0.03

0.02

0.02

bd.l.

0.02

0.02

0.02

0.02

bd.l.

0.02

0.03

0.00

Yb0.01

0.07

0.05

0.04

0.08

0.07

0.05

0.09

0.03

0.04

0.02

0.03

0.03

0.04

0.04

0.02

0.04

0.09

0.02

Lubd.l.

0.02

0.02

bd.l.

0.02

0.02

0.02

0.02

bd.l.

bd.l.

bd.l.

bd.l.

bd.l.

bd.l.

bd.l.

bd.l.

0.02

0.02

0.00

Hf

bd.l.

0.12

0.11

0.09

0.17

0.17

0.11

0.20

0.10

0.11

0.02

0.12

0.07

0.11

0.11

0.09

0.11

0.20

0.04

Ta0.04

0.16

0.12

0.13

0.16

0.43

0.10

0.16

0.13

0.03

0.07

0.09

0.05

0.22

0.05

0.02

0.12

0.43

0.10

W0.62

0.76

0.57

0.38

1.52

1.26

2.24

0.79

3.14

1.31

4.50

2.85

2.28

5.21

1.36

0.60

1.84

5.21

1.45

Tl0.05

0.13

0.14

0.17

0.19

0.29

0.23

0.21

0.14

0.14

0.13

0.20

0.30

0.19

0.48

0.08

0.19

0.48

0.10

Pb9.71

19.16

16.75

20.35

22.50

33.58

26.51

24.41

10.14

18.60

13.65

12.78

35.00

24.57

61.43

11.99

22.57

61.43

12.86

Bi0.16

0.36

0.23

0.37

0.37

0.54

0.43

0.43

bd.l.

0.41

0.41

0.39

0.93

0.79

1.23

0.31

0.49

1.23

0.28

Th0.07

0.55

0.37

0.28

0.53

0.49

0.33

0.64

bd.l.

0.24

0.13

0.19

0.20

0.28

0.23

0.10

0.31

0.64

0.17

U0.06

0.23

0.17

0.13

0.17

0.17

0.14

0.22

bd.l.

0.14

0.07

0.14

0.13

0.15

0.19

0.13

0.15

0.23

0.05

188 T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

mineral dust burden is lighter and finer than that of the “direct hit”described previously. However, the passing of a dust intrusion tothe north typically sweeps transboundary pollutants into SW Japan(Fig. 1c) and so sulphate concentrations increase (rising in this caseto 9 μg/m3). Such sulphate levels are similar to those reached towardsthe end of the previous pollution episode described above (Table 1a),with stagnating anticyclonic conditions prevailing locally in bothcases. There is little Ca or Na but, in addition to SO4

2−, there are en-hanced levels of NH4

+ and NO3−, consistent with the presence of sub-

stantial amounts of ammonium compounds in suspension. As seenpreviously, the SIC particles are accompanied by typical anthropogen-ic metals/metalloids such as Zn, Cu, As, Sn and Sb, this being especial-ly apparent when data are normalised to PM10 mass (per μg/g).Overall levels of SIC in this scenario are similar to those of mineraldust (33–41% PM10, Table 1b) with both components declining rapid-ly from an initial high as eastward passage of the aerosol intrusion(K120510) is blocked and pushed westwards back across Kyushu(K130510) into the Yellow Sea.

4.3. Transboundary aerosol intrusion 3: Anthropogenic > natural

The meteorological setting during the third phase of the samplingcampaign favoured the transport of unusually high levels of pollut-ants into SW Japan (20–24 May). Once again the initial eastward pas-sage of a dust storm to the north dragged sulphatic air across the EastChina Sea into Kyushu (as seen in the previous episode), but this timethe pollutant cloud was contained by a southerly airstream whichinhibited its dispersal over the ocean and so maintained high ambientPM10 concentrations (>50 μg/m3) over Kumamoto (compare Fig. 1cand d). Under these conditions SIC particles were strongly dominant(reaching 60%PM10) whereas the mineral PM10 loading failed to riseabove normal background levels as the dust storm stayed further tothe north (sample K200510). Sulphate concentrations rose to an un-precedented 16 μg/m3 accompanied by peaks in metalliferous ele-ments such as Pb and Sb, and NH4

+ recorded a campaign maximumof 7 μg/m3.

The next filter sample (K210510) records the stagnation of thismetalliferous, sulphatic air mass, increasingly mingling with mineralPM drifting in from the NW, and with local traffic emissions. Thismore composite character, chemically similar to the mix observedduring intrusion event 2, is demonstrated by the decline in SIC(41%PM10) and a rise in both mineral dust (32%PM10) and carbona-ceous PM (25%PM10). Over the following two days clean atmosphericconditions returned to Kyushu as the pollutant cloud was pushednorthwards around the intensifying depression centred on SouthKorea. This storm swept the diluted remains of the former desertdust intrusion anticlockwise over Russia and down across the YellowSea to mix with a fresh anthropogenic pollutant cloud dragged rapid-ly eastward from east central China (Fig. 2). Sample K240510 demon-strates the dramatic impact of this new transboundary pollutantcloud on air quality in Kumamoto (Fig. 2), with SIC aerosols compris-ing 66%PM10 as opposed to only 19%PM10 residual mineral particles.Sulphate and ammonium ion concentrations rise to 19 μg/m3 and6 μg/m3 respectively, and campaign maxima are attained by NO3

−

(6 μg/m3) and a wide array of the more toxic metallic pollutants(Ni, Cu, Zn, Ge, As, Mo, Cd, Sn, Tl, Pb and Bi: Table 1a). The notablejump in NO3

− concentrations repeats that seen at the beginning ofthe campaign (K260410) and seems to characterise the arrival of rap-idly transported fresh pollutants from the Chinese mainland, al-though in this case the nitrate content is more associated withincreased Na (coarse in size) and NH4

+ (fine in size) rather than Ca(Table 1a).

The final PM sample analysed during the Kumamoto 2010 cam-paign (K250510) records the advection of clean air from the northinto Kyushu, resulting in an abrupt fall in PM10 concentrations backto the background levels seen at the beginning of sampling one

0

2

4

6

8

10

12

µg/m

3

Na Ca Al2O3 OC+EC NO3 NH4+ SO4

localtrafficpeak

calcareous dustintrusion

siliceous dustintrusion

mixed crustal+

sulphate cloud

arrival of freshanthropogenic pollutants

marine air intrusion

250410 260410 270410 280410 290410 300410 010510 020510

PM10/SO4

Fig. 4. Daily variations in PM10 chemistry prior to and during the first transboundaryaerosol event (25 April to 2 May 2010) affecting Kumamoto. Stagnant atmosphericconditions produced an initial C peak (traffic emissions) on 25 April. Arrival of thefirst, relatively calcareous desert dust wave resulted in silicate and carbonate peaks(represented by Al2O3 and Ca) accompanied by a sharp rise in NO3

− (26 April). Subse-quent minor marine PM peaks (Na) on 27–28 April were followed by the arrival of anon-calcareous dust intrusion (Al203 peak on 29 April), behind which arrivednew pollutants (30 April). The final PM peak (2 May) recorded the passing of a sul-phate+silicate airmass in the increasingly mixed aerosol outflow, with PM10/SO4

values having declined from 10 to 6. See text and Tables 1a and 1b for details.

Table1b

Type

ofep

isod

e,pa

rticle

numbe

r-size

distribu

tion

andmainch

emical

compo

nentspe

rsample.

Sample

K25

0410

K26

0410

K27

0410

K28

0410

K29

0410

K30

0410

K01

0510

K02

0510

K07

0510

K11

0510

K12

0510

K13

0510

K20

0510

K21

0510

K24

0510

K25

0510

Episod

eBG

EP1

EP1

EP1

EP1

EP1

EP1

EP1

BGEP

2EP

2EP

2EP

3EP

3EP

3BG

PM10(μm/m

3)

1950

4337

5661

3663

2539

2729

5351

5219

Particle

numbe

r-size

distribu

tion

—OPC

N>0.3μm

–50

943

1279

015

533

5062

686

9773

697

9714

239

651

1220

1574

993

6554

117

0394

1233

8619

8809

8237

3N>1μm

–18

5541

543

317

9822

6813

1729

7630

711

4172

864

325

1819

9717

0271

3CI

0.3(%

)–

3.6

3.2

2.8

3.6

2.9

1.8

3.1

0.8

0.9

1.0

1.0

1.5

1.6

0.9

0.9

Mainch

emical

compo

nents—

ICP(%

)Crus

tal

2464

5447

6253

4661

3734

4037

2332

1919

OM

+EC

4012

813

89

157

3421

2328

1625

1120

SIC

3420

3032

2635

3529

2542

3433

6041

6655

Marine

23

77

33

32

22

22

11

44

Tracemetals

11

11

11

11

11

11

11

11

BG:airqu

alityba

ckgrou

ndco

nditions

;EP

1-3:

Airpo

llution

episod

es1to

3.CI:Co

arsening

Inde

x(see

text).

189T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

month before (K250410). There are, however, subtle chemical differ-ences between these “before” and “after” background samples, thelatter being relatively much less carbonaceous but notably richer inSIC and marine aerosols (Table 1b). The lack of time available forany build-up of local traffic emissions explains the low levels of C inthis final sample, the analysis of which instead represents the chem-istry of air advected across the Sea of Japan (hence the higher levels ofmarine PM) mixing with the diluted remnants of the anthropogenicSIC-rich pollution event affecting Kyushu the previous day. The lin-gering presence of this pollution event can be discerned by mass nor-malising the PM10 data, revealing the persistence of relatively highlevels (per μg/g) of many anthropogenic metallic elements such asNi, Ge, As, Mo, Cd, and Sn. Despite the “clean” nature of the air, interms of PM mass, it is still contaminated with anthropogenic metals.

0.1

1

10

100

Na Cl Al2O3 Ti/10 CO3 OC+EC NO3 NH4 SO4 Pb As Cd

µg

/m3

RESIDUAL BACKGROUND

(NH4)2 SO4

MARINE CRUSTAL ANTHROPOGENIC POLLUTANTS

K250410 pre-intrusion urban background

K260410 calcareous dust intrusion

K270410 marine air intrusion

K290410 siliceous dust intrusion

K240510 anthropogenic aerosol intrusion

Fig. 5. Variations in natural (marine and crustal) PM components compared to anthro-pogenic pollutants. Five samples are shown, each being characterised by a differentpeak: marine (K270410), calcareous crustal (K260410), siliceous crustal (K290410),urban background with residual sulphate PM and local traffic (K250410), and anthro-pogenic transboundary sulphate (K240510).

190 T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

5. Discussion and conclusions

The main chemical variations between PM10 samples collectedduring the 2010 campaign are illustrated by the five examples plottedin Fig. 5. The chemistry of PM10 derived dominantly from natural(dust and marine) sources is represented on this figure by samplesK260410 (calcareous desert dust: high CO3), K290410 (siliceous de-sert dust: high Al2O3, Ti/10), and K270410 (marine: high NaCl). Theobservation that some Kosa aeolian dust intrusions into Japan aremore calcareous than others we attribute to the geology of the sourceareas. In the case of the more calcareous dust wave (K260410), withCa concentrations exceeding 2 μg/m3 (and with correspondinglyhigh Mg and Sr: Table 1a), back-trajectory data indicate the mainsource area to be the Badain Jaran desert (Fig. 1a) in western InnerMongolia, an area known for calcareous surface deposits of probablepedogenic origin and peculiar for its high number of saline lakes, de-spite the extreme aridity (Yang, 2006). This is the fourth largest de-sert in the world and (along with the adjacent Hexi Corridor)provides one of three main sources of dust storms in China (Fig. 1a),the others being the Taklimakan Desert to the west, and the centralInner Mongolian Plateau to the east (Wang et al., 2004), so Kosa intru-sions travelling from this region into Japan are common (Mori et al.,2002). In contrast, the dust wave arriving three days later(K290410), characterised by abundant silicates but 50% less Ca-content, was sourced in the central Inner Mongolian Plateau. We sug-gest that a lack of calcareous surface sediment available for atmo-spheric resuspension in this more easterly source provides anexplanation for the more siliceous chemistry of the second dustwave. This conclusion is supported by the fact that in Beijing, muchcloser to source than Kumamoto, similar differences in the Ca-content of desert dust outflows have also been observed, with morewesterly-derived storms (from Badain Jaran and Taklimakan) beingmore calcareous than those from the central Mongolian Plateau(Yuan et al., 2008).

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Wuhan PM10

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FCC oil refinery PM10

Coal slag

CoalCoal light DF

Coal medium DFCoal heavy DF

uncontaminated

crustal PM

sulphatic PM

mixed PM

coal combustion

3

3

Fig. 6. Ternary AsCeLax2 diagram depicting the mixing line between uncontaminatedcrustal compositions and urban PM highly contaminated by coal combustion and in-dustrial emissions in the city of Wuhan, China (see Fig. 1a and Querol et al., 2006).The least anthropogenically contaminated Kumamoto samples (K260410, K270410,K290410) plot closest to upper continental crustal compositions (UCC; Taylor andMcLennan, 1995) and the clean tropospheric PM10 (from Izaña in the Canary Islands:Alastuey et al., 2005), whereas the most anthropogenic contaminated samples(K200510, K240510, K250510) plot closest to the Wuhan samples. Also plotted are an-alyses of coal, coal slag, light, medium and heavy density fractions extracted from coal(Querol et al., 2001b), with the heavy density fraction (DF) containing toxic volatile el-ements such as As (numbers in black circles are only for legend). For comparison weinclude data from PM10 contaminated by Fluid Catalytic Converter (FCC) oil refineries(La-rich) and the ceramic industry (Ce-rich) (Moreno et al., 2010).

An exceptional (x4) rise in NO3− concentrations coincides with the

arrival of the calcareous dust intrusion on 26 April, supporting a pre-viously observed correlation between NO3

− and Ca in Kosa outflowsinto Japan (Matsumoto et al., 2003). Nitrate in the atmosphere isformed from reactions involving NOx and HNO3, and its relativelyhigh volatility (compared to sulphate) favours evaporation fromsmaller aerosols and deposition onto larger mineral PM (Geng et al.,2009; Lim et al., 2011). Given the low Na levels and lack of any ac-companying rise in NH4

+ on 26 April, we suggest that NO3− in this

first dust wave is mainly present as supermicron-sized calcium ni-trate following reaction between calcite and NOx or HNO3 during at-mospheric transport (e.g. Chan and Yao, 2008). The presence ofnitrate in relatively coarse mode PM is also consistent with themarked decline in NO3

− concentrations towards the end of the firsttransboundary intrusion (compare NO3

− and NH4+ on Fig. 4) as dry

or wet deposition from the ageing dust cloud winnowed out thecoarser SIC particles.

With respect to the submicron size particles, most of which will becarbonaceous or sulphatic, pre-campaign background (K250410) at-mospheric conditions show a carbon peak, with a campaign maxi-mum for levels of EC presumably reflecting the presence of trafficemissions (Table 1a). The concentrations of carbonaceous aerosolsin this sample (OM+EC=7.65 μg/m3) lies within the 5–10 μg/m3

range typical of, for example, European background urban/suburbanmonitoring stations (e.g. Viana et al., 2007). Less comparable with Eu-rope are the background sulphate concentrations in Kumamoto, thesebeing relatively high due to the lingering residue of a previous sul-phatic intrusion, with the PM10/SO4 value of 4.2 being around halfthat of a typical European urban background ambient (Fig. 4). Evenlower values of background PM10/SO4 (3.1) are registered in ourdata after the immediate passing of the anthropogenic aerosol intru-sion at the end of the campaign (sample K250510, Table 1a). Geo-graphically dispersed, residual sulphatic plumes of this nature mixwith local traffic and industrial emissions and dissipate only slowly,due to the dominance of submicron accumulation mode PM whichis atmospherically persistent. The presence of such contaminatedbackground air masses over Japan, regularly replenished by newtransboundary intrusions from the west, has unfortunately becomeincreasingly common over the last decade, leading to what Lasserreet al. (2008) have recently described as “a regional situation ofquasi-permanent pollution”.

Given the current persistence of this pollution cloud over Japan,affecting atmospheric chemistry even on “clean” background dayswhen PM levels are low, it is interesting to compare aspects of the at-mospheric geochemistry of this regional pollution cloud with otherareas within and outside Asia. In particular, the metalliferous trace el-ement chemistry of the Kumamoto samples provides insight into theorigin of the anthropogenic component in these Asiatic aerosol intru-sions. Levels of V are consistently low, with V/Rb values averagingonly 1.7 (range 1.3–3.5) which rules out significant contaminationby the combustion of V-rich fuels such as heavy fuel oils and petcoke(Moreno et al., 2010). Similarly, the lack of any enrichment in La rel-ative to heavier lanthanoid elements (La/Ceb0.5 in all samples) elim-inates the possibility of an important contribution from FluidCatalytic Converter (FCC) oil refinery plumes (Moreno et al., 2008),this being also in agreement with the results previously shown onthe principal component analysis grouping V with the mineralgroup. In contrast, coal deposits typically show unfractionated La/Cevalues and low V so that the composition of fly ash PM10 releasedfrom coal burning power stations is close to upper crustal composi-tions, with La/Ceb0.5 and V/Rbb2.5 (Querol et al., 1995), closely sim-ilar to the geochemical signature of the Kumamoto samples. Similarly,low NO3

−/SO42− values in the Kumamoto samples (0.1–0.3 during the

more anthropogenic pollution episodes 2 and 3) are muchmore char-acteristic of coal emissions than those derived from the combustion ofoil fractionates (Kong et al., 2010a, 2010b).

191T. Moreno et al. / Science of the Total Environment 424 (2012) 182–192

Another characteristic of coal combustion is the release of metallicelements such as As, Cd, Pb, Sb, and Zn which volatilize in the flamezone then condense immediately after combustion by homogeneousnucleation to form ultrafine aerosols (10–30 nm) which subsequentlygrow by heterogeneous agglomeration and become concentrated infly ash (Ninomiya et al., 2004; Meij and Vinkel, 2007). Arsenic isone of the more toxic of these volatile metallic components and pro-vides a useful geochemical tracer element. Our Kumamoto PM10 sam-ples contain a range of 1.0–5.6 ng/m3 of As which, while still wellbelow the annual average target value in Europe (6 ng/m3: EuropeanDirective 2004/107/EC; average urban background concentra-tionb0.5 ng/m3; Putaud et al., 2004), nevertheless demonstrates no-table enrichment when compared to uncontaminated crustalconcentrations (e.g. Upper Crustal Enrichment Factor As/Li=39).

In Fig. 6 we introduce a ternary AsCeLax2 diagram to illustrate thisAs-enrichment in our samples (see Moreno et al., 2006 for other ap-plications of triangular diagrams to atmospheric chemical variations).The least polluted aerosol sample on this figure is provided by PM10

collected from the monitoring station of Izaña, located high in thefree troposphere in the Canary Islands (Alastuey et al., 2005). In con-trast, the most contaminated PM10 samples are those collected during2003/4 inWuhan City, China (Querol et al., 2001b), which contain av-erage As levels up to 70 ng/m3 attributed to a mixture of metallurgicaland coal emissions. The Kumamoto samples, displaying no lanthanoidfractionation, lie on a mixing line between the Izaña andWuhan sam-ples (Fig. 6), with the most crustal compositions corresponding to thearrival of the dust waves during the first PM intrusion (samplesK260410, K270410, K290410). The most anthropogenically contami-nated Kumamoto samples collected during Intrusion 3 plot close tothe As apex (K200510 and K240510). For comparison, we also plotthe natural composition of coal compared with its different constitu-ents separated into different densities (Querol et al., 1995). The light-est coal fraction (and the refractory slag) contains mostly silicatemineral matter and so plots close to crustal compositions (UCC). Incontrast, the heaviest coal fraction, which includes the bulk of theheavy metal content as sulphides, plots adjacent to the As apex andrepresents the volatile material released during combustion. For com-parison on Fig. 6 we also add PM10 samples contaminated by La dur-ing FCC oil refining, and by Ce in ceramic industrial emissions(Moreno et al., 2008; 2010).

The likely imprint of coal combustion emissions on the chemistryof sulphatic East Asian transboundary aerosol outflows into the Pacif-ic area is not surprising, given that recent estimates of SO2 emissionsfrom China indicate around 50% emanate from power plants (Aikawaet al., 2010; Ianniello et al., 2011). China is currently the top producerand consumer of coal, burning nearly half the entire annual globalsupply to meet over 70% of domestic energy needs and manufacturearound 60% of all Chinese chemical materials (Dai et al., in press).Many of the main coal combustion emission sources are clusteredclose to the coast of central China, between Shanghai and Tientsin(Zhao et al., 2008), and the resulting pollutants are regularly trans-ported eastwards to deliver the dominant source of sulphate overthe Northern Pacific region (Liu et al., 2008; Fairlie et al., 2010).

Given the widespread impact on human health of air pollution re-lated to coal combustion and heavy industry within China (Kan et al.,2007; Saikawa et al., 2009), concerns are increasingly being raisedabout similar effects being exported to neighbouring receptor coun-tries. Many of these concerns have focussed more on the pulmonarytoxicity and corresponding acute effects of PM inhalation, especiallyon asthmatic patients (e.g. Ichinose et al., 2005; Ueda et al., 2010;Watanabe et al., 2010), or on the potential transport of active bioaer-osols between countries (e.g. Chen et al., 2010). However, the great-est health problem is more likely to be related to premature deathsfrom cardiovascular and respiratory diseases resulting from long-term exposure to elevated levels of inhalable PM (Liu et al., 2009).In this context, as our data clearly demonstrate, it is salient to note

that there are great chemical differences between the natural and an-thropogenic aerosol components arriving in Japan from MainlandAsia. It is unlikely that the inhalation of coarse silicate mineral dustduring a Kosa event has the same chronic health impact as a persis-tent haze of finely respirable sulphatic aerosol containing enhancedamounts of toxic metals. A further complication, again illustrated bythe three events described in this paper, are the spatial and temporalvariations between the transport paths and arrival of mineral dustwaves and fresh pollutants, followed by progressive mingling of thetwo components. This raises the possibility of synergistic interactionsbetween the different components producing a change of inhalationtoxicity with time as the mixed pollution cloud ages and decays. Itis also possible that antagonistic (offsetting) interactions between at-mospheric constituents can occur, neutralising for example acidicspecies and therefore reducing overall toxicity. It is unfortunate thatthe striking physicochemical bimodality and inhomogeneity betweennatural and anthropogenic PM in East Asian transboundary aerosolintrusions greatly complicates epidemiological and toxicology study,but this is the reality. As we can also see in many other studies of am-bient aerosol chemistry, the Kumamoto dataset highlights the limita-tions associated with legal air quality standards based only on PMmass rather than chemical composition.

Acknowledgements

This work was supported by the Generalitat de Catalunya (CUR-DIUE: BE-DGR 2010), partly by the Grant-in-Aid for Scientific Re-search (No. 17684026), and by the Invitation Fellowship Programfor Research of the Japan Society for the Promotion of Science (No.11019). One of the authors (TK) thanks Drs. D. Zhang and T. Nagatanifor cooperation with air monitoring in the Kumamoto area.

Appendix A. Supplementary material

Supplementary data to this article can be found online at doi:10.1016/j.scitotenv.2012.02.060.

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