Study of chemical characteristics of particulate matter concentrations in Riyadh, Saudi Arabia



AtmosphericPollutionResearch6(2015)88Ͳ98

Atm

spheric Pollution



Research www.atmospolres.com



Study of chemical characteristics of particulate matter concentrations in Riyadh, Saudi Arabia BadrAlharbi1,MohammedMujtabaShareef2,TahirHusain2 1 2

NationalCenterforEnvironmentalTechnology,KingAbdulazizCityforScienceandTechnology,P.O.Box6086,Riyadh11442,SaudiArabia FacultyofEngineeringandAppliedScience,MemorialUniversity,St.John’s,NL,A1B3X5Canada

ABSTRACT



ParticulatemattersampleswerecollectedfromseverallocationsduringSeptember2011andSeptember2012in Riyadh, Saudi Arabia. In addition to determining particulate matter (as PM10) concentrations, the samples were analyzed for several metals and ions. PM concentration was approximately 3 times higher than the Country’s ambient air quality standards respectively. Metals and ions contributed to about 21.5% and 16.2% of the PM concentrationsrespectively.Summervs.wintercomparisonshowedthatPMconcentrationswereapproximately 84% higher in summer and the crustal matter species such as Fe, Mn, Ti, Ca+2, Mg+2 increased several folds in summer,primarilyattributedtoduststorms.TheweekdaysPMconcentrationswere17%morethantheweekend concentrations,indicatingweekdayactivitiescontributetotheconcentrations.Theduststormsleadtoover200% increase in the PM and some  elements primarily Al, Fe, Mg and Ca. Spatial comparison at industrial and residentiallocationsrevealedabout60%increaseinPMconcentrationsandsubstantialincreaseinZn,Mn,B,Mg, Fe,andAlandtheionsK+,SO4––,andCl–atindustriallocations.Bivariatecorrelationsamongthemetalsandions demonstratedthatstrongcorrelationexistedbetweenAl,Fe,Mg,KandMnsuggestingacommonoriginforthese species i.e. the crustal mineral aerosols. The correlations among cations and anions implied the presence of compounds in the atmosphere such as CaSO4, (NH4)2SO4, KCl, KSO4, and also to some extent MgSO4. An investigationofionicratiosrevealedthatratiosSO4–2/NO3–,Ca+2/K+,andCa+2/Na+couldbepossibleindicatorsto identify scenarios industrial over residential locations, storm days over no storm days and summer over winter periodsrespectively.



 Keywords:PM10,metalsandioniccomposition,spatialandtemporalindicators,Riyadh

CorrespondingAuthor:

Mohammed Mujtaba Shareef :+1Ͳ709Ͳ771Ͳ2426

:[email protected] 

ArticleHistory: Received:19April2014 Revised:19July2014 Accepted:20July2014

doi:10.5094/APR.2015.011 

1.Introduction  The importance of air pollution research further increases as International Agency for Research on Cancer (IARC), an agency of WorldHealthOrganization(WHO)hasclassifieditascarcinogenic. While air pollution is a complex mixture of many gases and compounds, Particulate Matter (PM) in the air has been particͲ ularlyidentifiedasthemaincomponentcausingthecancer(IARC, 2013). Many studies have revealed an increasing risk of lung cancer, morbidity, mortality and other diseases with increasing levelsofexposure tooutdoorairpollutionandparticulatematter (Dockery,2001;Linetal.,2002;Popeetal.,2002;Brunekreefand Forsberg, 2005; Sioutas et al., 2005; Nieuwenhuijsen et al., 2007; Perez et al., 2012; Fossati et al., 2014; Tao et al., 2014). The presence of particulate matters in atmosphere also impacts the environment by the reduction of visibility, formation of clouds, effectingheattransferintheatmosphere,therebycontributingto theclimatechange(Furutaetal.,2005;Wangetal.,2013).  Understanding the ionic chemistry of the atmospheric PM is important to study its relative effects on human health and environment(Horvath,1996;TsaiandCheng,1999;Schichteletal., 2001;Tsaietal.,2003;Yadavetal.,2003;Leeetal.,2005).Several studies have focused on the detailed analysis of atmospheric aerosols for metals and water soluble ions (Kadowaki, 1976; Wall et al., 1988; Kim and Fergusson, 1994; Kerminen et al., 2001; Venkataramanetal.,2001;Hsuetal.,2008;Shenetal.,2008)and it has been shown that the compositions show significant spatial and temporal variation (Prospero et al., 2002; Reid et al., 2005; Wangetal.,2005;Shenetal.,2009).

Riyadh is the capital and largest city of Saudi Arabia with a population of over 5 million. In recent years, due to strong economic growth, initiation of massive construction projects, expansion of industries, and increase in traffic flow, severely affectedtheatmosphericenvironment,particularlycontamination byatmosphericparticulatematter.Thehotandaridclimateinthe city with events of severe summer dust storms increases enorͲ mously the PM concentration in the atmosphere. While the adverse health effects of the PM are evident, it has been particularly shown that the exposure to the dust caused general health illness, sleep and psychological disturbances in the Riyadh city(Meoetal.,2013).Twoearlierstudieshavealsoidentifiedthat the presence of heavy metal Pb in the atmosphere and was attributedtothetrafficdensityinthecity(El–Shobokshy,1984;Al– Saleh and Taylor, 1994). The impact of dust storms on aerosol optical properties was studied for Saudi Arabia and it was found that the dust storm events significantly changes the optical properties of the aerosol (Maghrabi et al., 2011; Alharbi et al., 2013).ArelativelydetailedstudywasundertakenbyRushdietal. (2013), PM samples were collected from June 2006 to May 2007 fordeterminingitschemicalcomposition.Theresultsshowedthat the PM concentrations were higher for PM10 compared to PM2.5, indicating that the major PM source was local dust. The enrichmentfactorapproachwasusedtocharacterizethechemical composition and it was shown that sulfur and nickel were both enrichedinPM.TheconcentrationofPMwasfoundhigherinyear 2007whencomparedtotheyear2006.  In order to further comprehend the current state of air pollutionanddeterminethelevelsofPMandanalyzeitschemistry,

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

Alharbi et al. – Atmospheric Pollution Research (APR)

89

 Ionic analysis. Anions (Cl–, NO3– and SO4–2) were analyzed using Shimadzu Ion–Chromatography system with CDD–6A conductivity detector and Shim pack IC– A1 column. Mobile phase containing 2.5mM phthalic acid and 2.4mM tris– (hydroxymethyl) aminoͲ methane was used with a flow rate of 1.5mL/min at 40°C. The instrument was calibrated with Dionex anion standard (Dionex SevenAnionstandard,no.057590,ThermoFisherSci.,USA).Each sample analyzed in triplicate and average concentration was recorded.  For cations (NH4+, K+, Mg+2, Na+ and Ca+2), Shim pack IC–C3 (100mmx4.6mm ID) column was used and oxalic acid (3.0mM) mobilephasewithaflowrateof1.0mL/minat40°Cwasapplied. CalibrationwasdonewithDionexsixcationstandard(no.046070, ThermoFisherSci,USA).  Analysisofsilica.AnalysisofSilicawasperformedutilizing5mLof 2.MaterialsandMethods same aqueous extract which was prepared for ionic analysis  followingSilicomolybdatemethod(no.8185)byDR/4000SpectroͲ 2.1.Sampling photometer(Programno.3350)asrecommendedbyHACHCo.USA.   Tocapturethecompletescenario,Riyadhcitywasdividedinto Elemental analysis. Microwave assisted acid extraction was perͲ 16gridsasshowninFigureS1 (seetheSupportingMaterial,SM). Table S1 describes each grid and its classification. The grids were formed following the USEPA Compendium Method IO–3.1 using mainly classified as industrial (predominantly industries in the advanced composite vessels in MDS 2100 microwave digestion area) and residential (largely residential areas). Two mobile staͲ system (CEM Crop, UK). Extracting acid was prepared in a 1L tionswereemployedtocollectthesamplesfromvariouslocations volumetricflask,combininginorderandmixing500mLofdeionized distilledwater,55.5mLofconcentratednitricacidand167.5mLof at different times. Each sampling was performed at each grid for concentrated hydrochloric acid, cooled and diluted to 1L with 24hoursataflowrateof16.67Lpm(1m3/h)onquartzmicrofiber filter discs (47mm) using PQ–100 particulate samplers with PM10 deionizeddistilledwater.After cuttingthefilterpapersinto small pieces, 20mL of extracting acid was added. The microwave inlet (BGI Incorp. USA) and the air inlet was located 2.5m above digestionsystemwasprogrammedto50%power,30psipressure thegroundlevel.Priortosampling,thefilterswerebakedat300– for 30minutes for digestion. Aliquot of digested samples was 550°C for at least 4h to remove any traces of organics. After filtered by Acrodisc syringe filters (0.2μm). Blank samples were sampling, the filters were packed in petri dishes covered with aluminum foil to protect them from sunlight. Filters were condiͲ also run simultaneously. Analysis of elements was carried out following Compendium Method IO–3.4. Targeted elemental tioned in a desiccator at constant temperature (23–25°C) and analysiswasfinallyperformedbyusingICP–OES(Optima–2000DV, relative humidity (40–50%) before and after sampling and the PerkinElmer,USA).Calibrationsofelementswereperformedusing initial and final weight of each filter disks was recorded to ICP Multi Elemental Standard solution VI CertiPUR (Merck Co.) as determineparticulatemasscollectedoverthesamplingperiodand storedinarefrigerator(–1°C). thereferencematerial.Everysamplewasanalyzedintriplicateand  themeanconcentrationofeachmetalwascalculated. ApartfromPQ–100Particulatesamplers,bothmobilestations  equipped with TEOM–1400a (Thermo Fisher Scientific, Inc.) 2.3.Climate ambient Particulate Monitor equipped with Automatic Cartridge  Collection Unit (ACCU) for particulate collection on quartz microͲ During summer the climate conditions in Riyadh city are fiber filter discs (47mm). In one station, the monitor has fitted predominantly hot and dry while winters are cold. During the with PM10 inlet while in the other station the monitor has fitted sampling period, the maximum temperature reached as high as 50°C recorded during July and minimum temperature was about with PM2.5 inlet. The total flow rate in the system was 16.67Lpm and this flow has been bifurcated in two channels. The channel 3°C during December. The average temperature in summer and whichgoestoTEOMunitmaintains3.0Lpmandtheotherchannel winter was 24.5°C and 14.1°C respectively. Highest relative to ACCU unit maintains 13.67Lpm. The PM2.5 samples collected humidity(about47%)occurredinDecemberwhilethelowestvalue of 12% was observed in July. Seasonal variation of wind speed is from ACCU unit were utilized for the analysis of ionic concentraͲ slight, the average summer wind speed occurred in June was tions in addition to samples collected with PQ–100 particulate samplers. For the analysis of elemental concentrations, only 4.4m/s and the month of October recorded as 2.5m/s. Winds PM10 samples collected with PQ–100 particulate samplers were were mainly West–South–Westerly (WSW) during summer and Westerly(W)inwinter. utilized.   2.2.Chemicalanalysis 3.ResultsandDiscussion   Sample extraction. Water soluble ionic components (NH4+, Ca+2, 3.1.PMconcentrationandchemicalcomposition Mg+2,Na+,K+, Cl–, NO3–,SO4–2andSilica) associated with sampled  Atotalof185PMsampleswerecollectedoveraperiodofone particulateweredeterminedbyaqueousextractionmethod.Each year, these samples were analyzed for various metals and ions. samplefilterdiscwascutintopiecesandtakenintopolypropylene Table S2 (see the SM) presents the summary statistics of PM, tube(50mL)separatelycontaining 20mLofdeionizedwater. The metals and ions for summer (April and September), winter tubescontainingsamplesweresonicatedforonehour,andleftfor (October to March), and the average for the whole year. Annual 1hour to settle down the filter fragments, then sonication continued for another 30minutes. After sonication the samples PM concentrations were in the range of 39.7–1803μg/m3 with a weresubjectedtocentrifugationat3000rpminordertosettlethe meanandstandarddeviationof289.24±228.5μg/m3.Theaverage particles and the supernatant extract finally filtered through monthlyvariationofPMandannualaverageareshowninFigure1. Acrodisc(0.45μm)withdisposablesyringe. The annual average PM concentration was over 3 times higher  thantheambientairqualitylimits(80μg/m3)recommendedbythe country’s environmental standards (PME, 2011). The average PM acomprehensivemonitoringprogramwasundertaken.Riyadhcity was divided into 16 grids and the necessary in–situ data and PM samples (as PM10) were collected for about a year (September 2011 toSeptember 2012).The samples were analyzed for twenty metals (As, Co, Te, Mo, V, Ni, Cr, Cu, Cd, Li, Pb, Zn, Mn,B, K, Na, Mg,Fe,Al),fivecations(NH4+,Ca+2,Mg+2,Na+,K+)andthreeanions (Cl–,NO3–,SO4–2).Theobjectivesofthispaperare(1)topresentthe resultsoftheanalysisofmetalandionsofthePMsamples,(2)to study the temporal and spatial variation i.e. summer vs. winter, weekdays vs. weekends and storm days vs. normal days and industriallocationsvs.residentiallocations,(3)toidentifypossible chemicalformsthatmightexistintheatmosphereusingbivariate correlation analysis among the metals and ions, and (4) to investigate the ratios of the ions and correlate to the various scenarios. 

Alharbi et al. – Atmospheric Pollution Research (APR)

90

 3.2.Temporalvariation  Summer vs. winter. Figure 2 presents the PM comparison for different scenarios including for summer and winter. As observed in the figure, the concentrations were about 84% higher in summer; this is in line with other studies (Contini et al., 2010; Shahsavani et al., 2012; Rushdi et al., 2013). This higher concenͲ trationinsummerisgenerallyattributedtoduststormsthatoccur mostlyduringsummer,increasingthePMconcentration.Moreover, thesmallamountofraininwintermonthsgenerallydampensthe ambient PM concentrations. Some studies (Wang et al., 2005; Pindado et al., 2009) report a higher winter concentrations, the location of the study has no dust storm events and winters experiencenorain.  The significant change of source of PM in summer, as mentionedaboveisfromtheduststorms,thisfactissubstantiated by the increase in the crustal matter species such as Fe, Mn, Ti, Ca+2,Mg+2insummerbyseveralfoldsasillustratedinFigure3.The ions SO4–2, K+, and NH4+ do not show any significant seasonal change while Na+, Cl–, and NO3– show higher average concentraͲ tionsinwinter,sotheseionshaveanoppositetrendwithrespect toPM10concentrationsandcrustalspecies.Increasedconstruction and outdoor activities in the city could be the reason for high concentrations of sodium and chloride in winter. Nitrate is reported to have higher values in winter by other studies as well (Queroletal.,2004;Wangetal.,2005)andgenerallyattributedto the low thermal stability of the nitrate in summer (Contini et al., 2010).OthernoteworthyelementsthatincreaseinsummerareCd, Zn, B, and Na that can be related to the anthropogenic activities that generally increase in summer months. Lithium in winter is foundtobeover12timesthesummervalues,andthereasonfor thisneedstobefurtherinvestigated.

Concentrations(μg/m3)

valueisslightlyhigherthanthevaluesin2006–2007(Rushdietal., 2013)inRiyadh.ThecurrentPMvaluesaregreaterthanthecities in the region such as Jeddah 87μg/m3 in 2011 (Khodeir et al., 2012), Al–Mirfa City in UAE 157μg/m3 in 2009 (Al Katheeri et al., 2012),Tehran100μg/m3in2010(Givehchietal.,2013),Beirutin Lebanon103μg/m3in2007(Salibaetal.,2010)andKuwaitcityin Kuwait 93μg/m3 in 2008 (Brown et al., 2008), while the city of AhvazinIranreportedanaveragevalueof1072μg/m3(Shahsavani etal.,2012).  Table S2 (see the SM) also presents the concentrations of metalsandionswithaverageandstandarddeviations.Theaverage metal and soluble ionic concentrations in PM were about 21.5% and16.2%respectively.Over90%ofthemetalswereCa,Al,Feand Mgandtheions(SO4–2,Cl–,andNH4+together)constituted70%of the total ions. This indicates that the substantial part of the PM concentrationiscomposedofthemetalsofthecrustaloriginand secondary inorganic compounds such as sulfate, chloride and ammonium.Chlorideisgenerallypresentintheatmospheredueto the proximity of the sea, however this is found in high concenͲ trations in Riyadh city which is about 400km away from the sea. Thecontributiontotheaerosolsfromtheseacouldbeignoredin Riyadh as was indicated for Beijing city (Yuan et al., 2004). The presence of chloride in Riyadh air could be from the calcium chloride which is usually used for maintaining unpaved roads and for fortifying road bases for new construction activities. The construction activities were high during sampling period. MoreͲ over, chlorideisalso foundpredominantlynearmotorworkshops (Sulaiman et al., 2005), Riyadh has several such workshops in the vicinity of the city. Coal burning, which is traditionally used for outdoor activities in Riyadh, might also be reason for the high concentrationofchlorideandsodiuminatmosphere.  

Figure1.OverallannualandmonthlyaveragePMconcentrations.



Alharbi et al. – Atmospheric Pollution Research (APR)

91

PM10Concentrations(μg/m3)



 Figure2.ComparisonofPMconcentrationsunderdifferentscenarios.



Concentrations(μg/m3)

(a)

Mg++

K+

Concentrations(μg/m3)

(b)

Na+

NH4+

NO3Ͳ

ClͲ

Ca++

SO4ͲͲ

Figure3.Temporalcomparison(summervs.winter)(a)metalsandionswithconcentration<1.4,(b)metalsandionswith concentration>1.4.

Alharbi et al. – Atmospheric Pollution Research (APR)

92

  Weekday vs. weekend. Out of 185 days of sampling 25 were weekend days (Friday). A decrease of 17% in PM concentrations (Figure2)wasobservedduringtheweekends.Similartrendswere reported by Contini et al. (2010) (reduced by 19%) and by Morawska et al. (2002) (reduced by 70%). This indicates the presenceofanthropogeniccontributionsparticularlythevehicular trafficduringweekdays.TheaveragesofmetalsandionicconcenͲ trationsoftheweekdaysandtheweekendswerealsocomparedas illustratedinFigure4.GenerallyNa+,K+,NO3–andSO4–2 arehigher during weekdays indicating that these ions are from human activitiesduringweekdays.  September 2012 vs. September 2011. To get an understanding of state of air quality over a period of one year the average concentration of PM for September 2011 and September 2012 were compared (Figure 2). It is clear from the figure that the PM concentrations were over 2 times (207% increase) in September 

2012 when compared to September 2011. This shows that PM concentration increased tremendously over one year. In addition to increase in dust storm events, emissions from vehicles, and increaseinconstructionactivitiescouldbeprimaryreasonsforrise. ThesimilarincreaseinconcentrationswasalsoreportedbyRushdi etal.(2013).Particularly,itwasobservedthattheconcentrations ofNO3–,Mg,Fe,andAl,increasedin2012,whencomparedtothe concentrations in 2011 (Figure 5). The increase in NO3–, which is primarilyconsideredtobefromvehicularexhaust,couldbedueto theincreaseinthetrafficovertheyear,verywellsupportedbythe factthatthecity is expandingatarapidpace. Mg,Fe,andAl are thecrustalelementsandtheirincreasecouldbeattributedtothe increasingeventsoftheduststorms.Interestingly,NH4+,V,Cr,Cu, Li,PbandK+decreasedintheyear2012.Theincreasingeventsof duststorm(thatincreasesthecrustalelementsandsubduesother elements)couldbethereasonforthedecreaseoftheseelements.

Concentrations(μg/m3)

(a)

Mg++

K+

Concentrations(μg/m3)

(b)

Na+

NH4+

NO3Ͳ

ClͲ

Ca++

SO4ͲͲ

Figure4.Temporalcomparison(weekdayvs.weekend)(a) metalsandionswithconcentration<1.4,(b) metalsandionswithconcentration>1.4.

 

Alharbi et al. – Atmospheric Pollution Research (APR)

93



Concentrations(μg/m3)

(a)

K+

Concentrations(μg/m3)

(b)

NH4+

NO3Ͳ

ClͲ

SO4ͲͲ

Figure5.Temporalcomparison(Sep2011vs.Sep2012)(a)metalsandionswithconcentration<0.8,(b)metalsandionswithconcentration >0.8.

 Duststormvs.noduststormdays.Duringtheperiodofstudy,15 dust storm events were reported, all of them in the summer months. The samples were collected during these days. Figure 2 presentsacomparisonbetweenstormandnostormdaysforPM, thestormdaysareclearlymorethandouble(over200%increase) of the no storm days. The ionic concentrations increased during theduststormdaysexceptNO3–whichwaslessduringthestorm daysasillustratedinFigure6.CrustalelementssuchasAl,Fe,Mg, and Ca increased significantly during the storm events, and this phenomenon is also shown by other studies (Shen et al., 2009; Shahsavanietal.,2012).NO3–remainsalmostthesameindicating automobileemissionsasapotentialanthropogenicsource.  3.3.Spatialvariation  Industrial vs. residential locations. The average of samples from industrial(35samples)andresidential(71samples)werecompared to see the variation of PM and its chemical composition. The PM comparison is shown in Figure 2 and the metal and ionic compaͲ

risons are presented in Figure 7. The industrial area showed an increase of over 60% in PM concentration, showing that there is substantialcontributiontoPMbyindustries.ThemetalsZn,Mn,B, Mg,Fe,andAlthehigherionsareK+,SO4–2,andCl–werehigherin industrial locations. Riyadh is a metropolitan city and has a refinery, cement plant and power plants that generate emissions andthereasonforthisincreaseinconcentrationscouldbedueto these emissions. The concentration of NO3– is higher in the residentialareasagainprovingthefactthatthesearecomingfrom vehicularactivitieswhicharemoredenseintheresidentialareas.  3.4.Bivariateanalysis  Bivariatecorrelations wereperformedamong metals,cations and anions. The correlation coefficients (r) of the combinations (see the SM, Table S3) were calculated after establishing the statistical significance. These coefficients allow obtaining inforͲ mation about the possible common sources. Strong correlation (r>0.9) exists between Al, Fe, Mg, K, and Mn. This suggests a

Alharbi et al. – Atmospheric Pollution Research (APR)

94

 commonoriginforthesespeciesi.e.thecrustalmineralaerosol,as also reported by Contini et al. (2010). Similar strong relationships werefoundbetweenAs,Co,CdandLi.Thesemetalsaremostlikely ofanthropogenicorigin,maybefromcertainindustriesexistingin theCity.Thesecondlevelofcorrelation(r>0.8)wasfoundbetween theheavymetalsAs,VandNi,again suggestingtheirorigincould betheindustries.StrongcorrelationalsoexistsbetweenVandTe that indicates the presence of compound vanadium ditelluride in the atmosphere. Vanadium is generally emitted as a result of emissions from oil combustion and can be ascribed to the automobileemissions.  Todeterminethepossiblechemicalformsofthecomponents that might exist in the atmosphere, bivariate correlations were made among cations and anions (see the SM, Table S4). This methodwasalsousedbyothersimilarstudies(Continietal.,2010; Shahsavani et al., 2012). Correlation between Ca+2 and SO4–2 suggests an origin of calcium sulfate, primarily from cement 

industries.Nitrateandchloridealsohasacorrelationindicatingthe possible common origin. These correlations indicate the presence of various chemical compounds that might possibly exist in the atmosphere such as CaSO4 (r=0.64 between Ca+2 and SO4–2), (NH4)2SO4,(r=0.40betweenNH4+andSO4–2)andtocertainextent KCl,KSO4withr=0.3.  3.5.Indicatorsforvariousscenarios  Ratios of ions have been used in many studies to identify possibleindicatorsforrelativeimportanceofvarioussourcesinthe atmosphere (Wang et al., 2005; Shahsavani et al., 2012). To determine the possible indicators, the average of the ionic ratios for all the ions have been calculated for scenarios; industrial vs. residential, storm period vs. no storm period and summer vs. winter.The ratioswhichhavethehighestdifferencebetweenthe meansarethendeterminedandpresentedinTable1.

Concentrations(μg/m3)

(a)

K+

Mg++

Concentrations(μg/m3)

(b)

Na+

NH4+

NO3Ͳ

ClͲ

Ca++

SO4Ͳ

Figure6.Temporalcomparison(duststormvs.normal)(a)metalsandionswithconcentration<1.4,(b)metalsandionswithconcentration >1.4.



Alharbi et al. – Atmospheric Pollution Research (APR)

95



Concentrations(μg/m3)

(a)

Mg++

K+

Concentrations(μg/m3)

(b)

Na+

NH4+

NO3Ͳ

ClͲ

Ca++

SO4ͲͲ

Figure7.Spatialcomparison(industrialvs.residentiallocations)(a)metalsandionswithconcentration<1.4,(b)metalsandionswith concentration>1.4.

 Table1.Ionicratiofordifferentscenarios 

SO4–2/NO3–

Cl–/NO3–

K+/Mg+2

Mean

Range

Mean

Range

Mean

Range

Industrialarea Residentialarea

5.53 4.50

0.75–54.30 0.34–96.63

45.81 2.37

1.61–170.2 0.99–4.73

4.04 2.70

0.61–29.47 0–24–34.19

 Duststormdays Noduststormdays

15.86 7.24

SO4–2/Na+ 15.07–16.6 0.82–68.49

7.36 3.74

NO3–/Na+ 5.36–9.49 0.01–67.42

9.27 7.77

Ca+2/K+ 5.38–13.62 0.01–25.07

 Summer Winter

16.48 1.39

Ca+2/Na+ 2.26–75.11 0.004–3.49

31.26 17.51

SO4–2/K+ 3.0–1167.3 1.43–128.8

19.57 6.89

SO4–2/Na+ 0.45–985.2 0.01–22.4

 In case of spatial comparison of industrial and residential location,itwasfoundthattheratiosSO4–2/NO3–,K+/Mg+2,andCl– /NO3– have the highest differences. The mass ratio of SO4–2/NO3– has been used as an indicator of the relative importance of

stationary vs. mobile sources of sulfur and nitrogen in the atmoͲ sphere(Arimotoetal.,1996;Yaoetal.,2002;XiaoandLiu,2004). Predominanceofsulfateovernitrateinthiscasecanbeattributed to the emissions from the stationary sources i.e. industries. With

Alharbi et al. – Atmospheric Pollution Research (APR)

96

 the existenceof refinery, powerplants and cementfactory inthe industrial area, the emissions of sulfate and chloride are obvious. Dominanceofnitrateoversulfatecanbeinferredfortheresidential areaswheretheemissionsfromtheautomobilesarehigher.  Theratiosfortheduststormdaysversusnostormdayshave been evaluated and it was found that SO4–2/Na+, NO3–/Na+ and Ca+2/K+exhibitedhighestdifference.TheratioofCa+/Na+wasalso identifiedtobeaduststormindicatorbyRushdietal.(2013)and Shahsavani et al. (2012). It is evident that dust storms increase tremendouslytheCa+2concentrationintheatmosphere.  Inordertodeterminetheseasonalidentifier,theratiosofions were calculated for summer and winter. Ca+2/Na+, SO4–2/K+, and SO4–2/Na+havethehighestdifference,thisisalmostsimilartothe duststormidentifiersastheduststormsoccur mostlyin summer season. The presence of sulfate as indicator can be ascribed probablytotheincreasingindustrialactivityinsummerseason. 

4.Conclusions  OneyeardatacollectedinRiyadhcityrevealedthattheannual average PM concentration was over 3 times higher than the country’sairqualitylimits.Theseconcentrationswerehigherthan the most of the neighboring cities in the region. Metals and ions contributed to about 21.5% and 16.2% of the PM concentrations respectively. Over 90%of the metalswere Ca, Al,FeandMg and theionsSO4–2,Cl–,NH4+togetherformed70%ofthetotalions.This indicates that the substantial part of the PM concentration is composed of the metals of the crustal origin and secondary inorganiccompoundssuchassulfate,chlorideandammonium.  Summer vs. winter comparison showed that PM concentraͲ tionswereabout84%higherinsummerandprimarilyascribedto dust storms thatoccurfrequently during summer. Crustal species such as Fe, Mn, Ti, Ca+2, Mg+2 increased several folds in summer signifying the contribution of dust storms to PM. The nitrate is reportedtohavehighervaluesinwinterandcouldbeduetothe low thermal stability of the nitrate in summer. The elements Cd, Zn, B, and Na were shown to have significantly higher values in summer. A decrease of 17% in PM concentrations was observed duringtheweekendsindicatingweekdayactivitiesincreasethePM concenͲtrations. Generally the ions Na+, K+, NO3– and SO4–2 are higher during weekdays. The average PM concentrations in September2012weremorethandoublecomparedtoSeptember 2011,indicatinganincreaseoftheseconcentrationsinRiyadhatan alarming rate. The species that increased during the same comparisonwereNO3–,Mg,Fe,andAl.TheincreaseinNO3–,which isprimarilyconsideredtobefromvehicularexhaust,couldbedue to the increase in the traffic over the year and the increase of crustal elements are due to increasing events of dust storms. Events of the dust storms lead to over 200% increase in the PM andsomemetalselementsprimarilyAl,Fe,MgandCa.  Spatial comparison at industrial and residential locations showed about 60% increase in PM concentrations at industrial locations, attributed to the presence of refineries, power and cement plants in addition to other industries that significantly contributetothePMconcentrations.TheelementsZn,Mn,B,Mg, Fe, and Al and the ions K+, SO4–2, and Cl– were reported to be higher at industrial locations, while the NO3– was higher in the residentialareas,mainlyduetovehicularemissions.  Bivariate correlations among the metals and ions showed strong correlation existed between Al, Fe, Mg, K and Mn, suggesting a common origin for these species i.e. the crustal mineral aerosols. Correlation was also strong between As, Co, Cd and Li, suggesting a common origin, probably anthropogenic. The correlations implied the presence of various chemicalcompounds intheatmospheresuchasCaSO4,(NH4)2SO4,KCl,KSO4,CdSO4and

alsotosome extentMgSO4.StrongcorrelationbetweenVandTe advocatesthepresenceofvanadiumditellurideintheatmosphere.  Theaveragesoftheionicratiosforalltheionswerecalculated for various scenarios. The three most possible indicators for scenarioindustrialvs.residentialwereSO4–2/NO3–,K+/Mg+2,andCl– /NO3–. The ratios Ca+2/K+, Ca+2/Na+, Cl–/Ca+2 were good indicators for storm days and the ratios Ca+2/Na+, SO4–2/K+, and SO4–2/Na+ could significantly identify the seasonal variation i.e. summer vs. winter. 

Acknowledgements  We gratefully acknowledge the financial support of King Abdulaziz City for Science and Technology (KACST) under grant number32–594. 

SupportingMaterialAvailable  Map showing the locations of sampling stations (Figure S1), Description of grids (Table S1), Summary statistics of particulate matter and chemical components (Table S2), Correlation coeffiͲ cients (r) among metals (Table S3), Correlation coefficients (r) amongions(TableS4).Thisinformationisavailablefreeofcharge viatheinternetathttp://www.atmospolres.com 

References  AlKatheeri,E.,AlJallad,F.,AlOmar,M.,2012.Assessmentofgaseousand particulate pollutants in the ambient air in Al Mirfa City, United Arab Emirates.JournalofEnvironmentalProtection3,640–647. Alharbi,B.H.,Maghrabi,A.,Tapper,N.,2013.TheMarch2009dusteventin Saudi Arabia precursor and supportive environment. Bulletin of the AmericanMeteorologicalSociety94,515–528. Al–Saleh,I.A.,Taylor,A.,1994.Leadconcentrationintheatmosphereand soil of Riyadh, Saudi–Arabia. Science of the Total Environment 141, 261–267. Arimoto,R.,Duce,R.A.,Savoie,D.L.,Prospero,J.M.,Talbot,R.,Cullen,J.D., Tomza, U., Lewis, N.F., Jay, B.J., 1996. Relationships among aerosol constituents from Asia and the North Pacific during PEM–West A. JournalofGeophysicalResearch–Atmospheres101,2011–2023. Brown, K.W., Bouhamra, W., Lamoureux, D.P., Evans, J.S., Koutrakis, P., 2008. Characterization of particulate matter for three sites in Kuwait. JournaloftheAir&WasteManagementAssociation58,994–1003. Brunekreef, B., Forsberg, B., 2005. Epidemiological evidence of effects of coarse airborne particles on health. European Respiratory Journal 26, 309–318. Contini, D., Genga, A., Cesari, D., Siciliano, M., Donateo, A., Bove, M.C., Guascito, M.R., 2010. Characterisation and source apportionment of PM10 in an urban background site in Lecce. Atmospheric Research 95, 40–54. Dockery, D.W., 2001. Epidemiologic evidence of cardiovascular effects of particulateairpollution.EnvironmentalHealthPerspectives109,Suppl. 4,483–486. El–Shobokshy, M.S., 1984. A preliminary–analysis of the inhalable particulate lead in the ambient atmosphere of the city of Riyadh, Saudi–Arabia.AtmosphericEnvironment18,2125–2130. Fossati, S., Baccarelli, A., Zanobetti, A., Hoxha, M., Vokonas, P.S., Wright, R.O., Schwartz, J., 2014. Ambient particulate air pollution and microRNAsinelderlymen.Epidemiology25,68–78. Furuta, N., Iijima, A., Kambe, A., Sakai, K., Sato, K., 2005. Concentrations, enrichment and predominant sources of Sb and other trace elements in size classified airborne particulate matter collected in Tokyo from 1995to2004.JournalofEnvironmentalMonitoring7,1155–1161. Givehchi, R., Arhami, M., Tajrishy, M., 2013. Contribution of the Middle EasterndustsourceareastoPM10levelsinurbanreceptors:Casestudy ofTehran,Iran.AtmosphericEnvironment75,287–295.

Alharbi et al. – Atmospheric Pollution Research (APR)

97

 Horvath,H.,1996.BlacksmokeasasurrogateforPM(10)inhealthstudies. AtmosphericEnvironment30,2649–2650. Hsu, Y.C., Lai, M.H., Wang, W.C., Chiang, H.L., Shieh, Z.X., 2008. Characteristicsofwater–solubleionicspeciesinfinePM(2.5)andcoarse particulate matterPM(10–2.5)in Kaohsiung,southern Taiwan.Journalof theAir&WasteManagementAssociation58,1579–1589. IARC (International Agency for Research on Cancer), 2013. Outdoor Air Pollution a Leading Environmental Cause of Deaths, http://www.iarc. fr/en/media–centre/iarcnews/pdf/pr221_E.pdf,accessedinJune2014.

Querol,X.,Alastuey,A.,Viana,M.M.,Rodriguez,S.,Artinano,B.,Salvador, P.,doSantos, S.G.,Patier,R.F.,Ruiz,C.R.,delaRosa,J.,delaCampa, A.S., Menendez, M., Gil, J.I., 2004. Speciation and origin of PM10 and PM2.5inSpain.JournalofAerosolScience35,1151–1172. Reid,J.S.,Piketh,S.J.,Kahn,R.,Bruintjes,R.T.,Holben,B.,2005.ASummary of First Year Activities of the United Arab Emirates, Unified Aerosol Experiment: UAE2, NRL/MR/7534—05–8899, Naval Research Laboratory.

Kadowaki,S.,1976.Sizedistributionofatmospherictotalaerosols,sulfate, ammonium and nitrate particulates in the Nagoya area. Atmospheric Environment(1967)10,39–43.

Rushdi, A.I., Al–Mutlaq, K.F., Al–Otaibi, M., El–Mubarak, A.H., Simoneit, B.R.T., 2013. Air quality and elemental enrichment factors of aerosol particulate matter in Riyadh City, Saudi Arabia. Arabian Journal of Geosciences6,585–599.

Kerminen, V.–M., Hillamo, R., Teinila, K., Pakkanen, T., Allegrini, I., Sparapani,R.,2001.Ionbalancesofsize–resolvedtroposphericaerosol samples: Implications for the acidity and atmospheric processing of aerosols.AtmosphericEnvironment35,5255–5265.

Saliba,N.A.,ElJam,F.,ElTayar,G.,Obeid,W.,Roumie,M.,2010.Originand variabilityofparticulate matter(PM10and PM2.5) massconcentrations over an Eastern Mediterranean city. Atmospheric Research 97, 106– 114.

Khodeir, M., Shamy, M., Alghamdi, M., Zhong, M.H., Sun, H., Costa, M., Chen,L.C.,Maciejczyk,P.,2012.Sourceapportionmentandelemental composition of PM2.5 and PM10 in Jeddah City, Saudi Arabia. AtmosphericPollutionResearch3,331–340.

Schichtel,B.A.,Husar,R.B.,Falke,S.R.,Wilson,W.E.,2001.Hazetrendsover the United States, 1980–1995. Atmospheric Environment 35, 5205– 5210.

Kim, N.D., Fergusson, J.E., 1994. The concentrations, distribution and sources of cadmium, copper, lead and zinc in the atmosphere of an urban–environment.ScienceoftheTotalEnvironment144,179–189. Lee,C.G.,Yuan,C.S.,Chang,J.C.,Yuan,C.,2005.Effectsofaerosolspecies onatmosphericvisibilityinKaohsiungCity,Taiwan.JournaloftheAir& WasteManagementAssociation55,1031–1041. Lin, M., Chen, Y., Burnett, R.T., Villeneuve, P.J., Krewski, D., 2002. The influence of ambient coarse particulate matter on asthma hospitalization in children: Case–crossover and time–series analyses. EnvironmentalHealthPerspectives110,575–581. Maghrabi,A.,Alharbi,B.,Tapper,N.,2011.ImpactoftheMarch2009dust event in Saudi Arabia on aerosol optical properties, meteorological parameters,skytemperatureandemissivity.AtmosphericEnvironment 45,2164–2173. Meo, S.A., Al–Kheraiji, M.F.A., AlFaraj, Z.F., Alwehaibi, N.A., Aldereihim, A.A., 2013. Respiratory and general health complaints in subjects exposed to sandstorm at Riyadh, Saudi Arabia. Pakistan Journal of MedicalSciences29,642–646. Morawska, L., Jayaratne, E.R., Mengersen, K., Jamriska, M., Thomas, S., 2002. Differences in airborne particle and gaseous concentrations in urbanairbetweenweekdaysandweekends.AtmosphericEnvironment 36,4375–4383. Nieuwenhuijsen, M.J., Gomez–Perales, J.E., Colvile, R.N., 2007. Levels of particulate air pollution, its elemental composition, determinants and health effects in metro systems. Atmospheric Environment 41, 7995– 8006. Perez, L., Tobias, A., Querol, X., Pey, J., Alastuey, A., Diaz, J., Sunyer, J., 2012.Saharandust,particulatematterandcause–specificmortality:A case–crossover study in Barcelona (Spain). Environment International 48,150–155. Pindado,O.,Perez,R.M.,Garcia,S.,Sanchez,M.,Galan,P.,Fernandez,M., 2009.CharacterizationandsourcesassignationofPM2.5organicaerosol inaruralareaofSpain.AtmosphericEnvironment43,2796–2803. PME (Presidency of Meteorology and Environment), 2011, Environmental Standards – Ambient Air Quality Standards, http://www.pme.gov.sa/ en/En_EnvStand19.pdf,accessedinNovember2013. Pope, C.A., Burnett, R.T., Thun, M.J., Calle, E.E., Krewski, D., Ito, K., Thurston, G.D., 2002. Lung cancer, cardiopulmonary mortality, and long–term exposure to fine particulate air pollution. JAMA–Journal of theAmericanMedicalAssociation287,1132–1141. Prospero, J.M., Ginoux, P., Torres, O., Nicholson, S.E., Gill, T.E., 2002. Environmental characterization of global sources of atmospheric soil dustidentifiedwiththeNimbus7TotalOzoneMappingSpectrometer (TOMS)absorbingaerosol product. Reviewsof Geophysics40, art.no. 1002.

Shahsavani, A., Naddafi, K., Haghighifard, N.J., Mesdaghinia, A., Yunesian, M.,Nabizadeh,R.,Arhami,M.,Yarahmadi,M.,Sowlat,M.H.,Ghani,M., Jafari, A.J., Alimohamadi, M., Motevalian, S.A., Soleimani, Z., 2012. Characterization of ionic composition of TSP and PM10 during the Middle Eastern Dust (MED) storms in Ahvaz, Iran. Environmental MonitoringandAssessment184,6683–6692. Shen,Z.X.,Cao,J.J.,Arimoto,R.,Han,Z.W.,Zhang,R.J.,Han,Y.M.,Liu,S.X., Okuda, T., Nakao, S., Tanaka, S., 2009. Ionic composition of TSP and PM2.5 during dust storms and air pollution episodes at Xi'an, China. AtmosphericEnvironment43,2911–2918. Shen, Z.X., Arimoto, R., Cao, J.J., Zhang, R.J., Li, X.X., Du, N., Okuda, T., Nakao, S., Tanaka, S., 2008. Seasonal variations and evidence for the effectiveness of pollution controls on water–soluble inorganic species intotalsuspendedparticulatesandfineparticulatematterfromXi'an, China.JournaloftheAir&WasteManagementAssociation58,1560– 1570. Sioutas, C., Delfino, R.J., Singh, M., 2005. Exposure assessment for atmospheric ultrafine particles (UFPs) and implications in epidemiologic research. Environmental Health Perspectives 113, 947– 955. Sulaiman, N., Abdullah, M., Chieu, P.L.P., 2005. Concentration and composition of PM10 in outdoor and indoor air in industrial area of BalakongSelangor,Malaysia.SainsMalaysiana34,43–47. Tao, Y., Mi, S.Q., Zhou, S.H., Wang, S.G., Xie, X.Y., 2014. Air pollution and hospital admissions for respiratory diseases in Lanzhou, China. EnvironmentalPollution185,196–201. Tsai, Y.I., Cheng, M.T., 1999. Visibility and aerosol chemical compositions near the coastal area in Central Taiwan. Science of the Total Environment231,37–51. Tsai,Y.I.,Lin,Y.H.,Lee,S.Z.,2003.Visibilityvariationwithairqualitiesinthe metropolitan area in southern Taiwan. Water Air and Soil Pollution 144,19–40. Venkataraman, C., Sinha, P., Bammi, S., 2001. Sulphate aerosol size distributions at Mumbai, India, during the INDOEX–FFP (1998). AtmosphericEnvironment35,2647–2655. Wall, S.M., John, W., Ondo, J.L., 1988. Measurement of aerosol size distributions for nitrate and major ionic species. Atmospheric Environment(1967)22,1649–1656. Wang, J., Hu, Z.M., Chen, Y.Y., Chen, Z.L., Xu, S.Y., 2013. Contamination characteristics and possible sources of PM10 and PM2.5 in different functionalareasofShanghai,China.AtmosphericEnvironment68,221– 229. Wang, Y., Zhuang, G.S., Tang, A.H., Yuan, H., Sun, Y.L., Chen, S.A., Zheng, A.H., 2005. The ion chemistry and the source of PM2.5 aerosol in Beijing.AtmosphericEnvironment39,3771–3784.

Alharbi et al. – Atmospheric Pollution Research (APR)

98

 Xiao, H.Y., Liu, C.Q., 2004. Chemical characteristics of water–soluble components in TSP over Guiyang, SW China, 2003. Atmospheric Environment38,6297–6306.

Yao,X.H.,Chan,C.K.,Fang,M.,Cadle,S.,Chan,T.,Mulawa,P.,He,K.B.,Ye, B.M., 2002.The water–solubleioniccompositionofPM2.5 inShanghai andBeijing,China.AtmosphericEnvironment36,4223–4234.

Yadav,A.K.,Kumar,K.,Kasim,A.M.B.H.A.,Singh,M.P.,Parida,S.K.,Sharan, M., 2003. Visibility and incidence of respiratory diseases during the 1998hazeepisodeinBruneiDarussalam.PureandAppliedGeophysics 160,265–277.

Yuan, H., Wang, Y., Zhuang, G.S., 2004. MSA in Beijing aerosol. Chinese ScienceBulletin49,1020–1025.