Chemical characterization and source apportionment of individual aerosol particles over the North...

Chemical Characterization and Source Apportionmentof Size-Segregated Aerosol Collected at an UrbanSite in Sicily

M. Rinaldi & L. Emblico & S. Decesari & S. Fuzzi &M. C. Facchini & V. Librando

Received: 6 March 2007 /Accepted: 9 June 2007 / Published online: 24 July 2007# Springer Science + Business Media B.V. 2007

Abstract Aerosol samples were collected at Catania(Italy), from 16 March to 13 June 2005. The samplingwas performed using a low pressure five-stage Bernercascade impactor. The samples were analysed for totalaerosol mass, Water Soluble Organic Carbon(WSOC), Total Carbon (TC) and main inorganicionic species. The Water-Insoluble Carbon (WINC)was derived by the difference: TC-WSOC. The

samples share some common features: ammoniumsulphate and carbon-containing species (both solubleand insoluble) are the largest contributors of fineparticle mass, while coarse particles essentiallyconsist of sea-salt, sodium nitrate and unaccountedPM (probably crustal material). The WINC/WSOCratio decreases from the smallest size range to thelarge accumulation mode range (0.42–1.2 μm), whilethe nssSO¼

4 and NHþ4 contribution rises. The water-

insoluble carbonaceous matter is the dominant com-ponent in the smallest particles (0.05–0.14 μm). Weidentified four different aerosol types, correspondingto different sources, contributing to the total particlesload of the investigated urban environment: vehiculartraffic, producing primary carbonaceous insolubleparticles, secondary aerosols, dominating the compo-sition of accumulation mode particles, and marineparticles and mineral dust (both important compo-nents of the coarse aerosol fraction).

Keywords Aerosol characterization .

Catania metropolitan area .Mediterranean Basin .

Size segregated aerosol chemistry . Sourceapportionment . Street canyon . Total carbon .

Urban aerosols .Water soluble organic carbon

1 Introduction

Atmospheric aerosol particles exhibit a wide range ofsizes, from nanometer to micrometer range, while the

Water Air Soil Pollut (2007) 185:311–321DOI 10.1007/s11270-007-9455-4

M. Rinaldi (*) : L. Emblico : S. Decesari : S. Fuzzi :M. C. FacchiniIstituto di Scienze dell’Atmosfera e del Clima-CNR,via P. Gobetti 101,40129 Bologna, Italye-mail: m.rinaldi@isac.cnr.it

V. LibrandoCentro di Ricerca per l’Analisi, il Monitoraggio e leMetodologie di Minimizzazione del Rischio Ambientale,Università di Catania,Viale A. Doria 6,95125 Catania, Italy

V. LibrandoDipartimento di Scienze Chimiche, Università di Catania,Viale A. Doria 6,95125 Catania, Italy

Present address:L. EmblicoEuropean Commission Joint Research Centre-Institutefor the Environment and Sustainability-Transportand Air Quality Unit,Via E. Fermi 1,21020 Ispra, Italy

chemical composition differs greatly among the sizeranges, and even among individual particles within agiven size interval. Particle size is essential fordescribing the interaction between aerosol and solarradiation (radiative effects), as well as the aerosoluptake of water vapour (effects on visibility and cloudformation). However, aerosol properties are also afunction of chemical composition, because the chem-ical constituents of aerosol particles can exhibit verydifferent optical and hygroscopic properties. For thisreason, the concurrent characterisation of particle sizeand chemical composition is necessary to predict theclimate-relevant properties of atmospheric aerosols.

Recent field data on the size segregated chemicalcomposition of aerosol have been made available byfield experiments (Heintzenberg et al. 1998; Putaud etal. 2000; Matta et al. 2003). They show that theorganic and inorganic compound concentrationschange substantially with aerosol particle size, andthat the bulk composition does not provide a realisticdescription of the chemical variability observed inaerosol populations. Furthermore, significant differ-ences in size distributions and chemical compositionscan be observed when comparing aerosol originatingfrom different environments, or aerosols sampledfrom the same environment but in different seasonsof the year (Putaud et al. 2002; Raes et al. 2000) ortransported by different air masses. Further dataconcern the correlation between size distributionsand genotoxic properties (Motta et al. 2006).

Within a given environment, the chemical compo-sition of sub-micrometer particles is generally differ-ent from that of coarse mode particles, due to thedifferent formation mechanisms. Coarse particles aregenerated by mechanical processes and consist of soildust, sea salt, bio aerosol and tyre wear particles.Accumulation mode and smaller particles containprimary particles from combustion sources andsecondary aerosol material (sulphate, nitrate, ammo-nium and secondary organics) formed by gas-to-particles conversion resulting from chemical reactionsin the atmosphere.

In this paper a detailed characterization was carriedout on the size segregated chemical composition ofaerosol samples collected in Catania (Italy), inconditions typical of an urban street canyon. Thisdetailed chemical study showed that it is possible toidentify different aerosol sources, contributing to thetotal particles load, other than vehicular traffic.

2 Sampling and Analyses

Size segregated aerosol samples were collected atCatania (Italy) from 16 March 2005 to 13 June 2005.Samplers were installed at a Municipal EnvironmentalProtection Department monitoring station, located atkerbside near a busy urban street. The samplingfrequency was nearly one sample per week. Thesamplings started in the morning and lasted ten totwelve hours.

Twelve aerosol samples were collected by meansof a Berner cascade impactor, collecting particles infive size fractions between 0.050 and 10 μm, accord-ing to the following equivalent aerodynamic cut-offdiameters at 50% efficiency: 0.05; 0.14; 0.42; 1.2;3.5; 10 μm. Flow rate was 80 L/min.

In order to achieve a full characterization of thewhole aerosol mass collected (Matta et al. 2003) , thesampling substrate consisted of half a Tedlar foil ontop of an aluminium foil.

Tedlar substrates were extracted in water (7 mLmilli-Q water, in an ultrasonic bath for 30 min) andthe whole water-soluble fraction was analysed: inor-ganic ions by ion chromatography and water solubleorganic carbon (WSOC) by total organic carbonanalyzer. The analytical protocol reflects the oneoriginally set up by Matta et al. (2003), but a newTOC analyser was employed: a Multi N/C 2100 ele-mental analyser (Analytik Jena, Germany). The carbonanalyzer was operated in TOC modality: for eachsample two parallel measurements were carried out todetermine inorganic carbon (IC) and total solublecarbon; the difference between the two (TOC=total soluble carbon−IC) was WSOC. Extracts werenot purged in order to avoid loss of volatile organiccompounds.

Total aerosol mass, and Total Carbon (TC) weredetermined on aluminium foils.

The mass was measured by a microbalance(Mettler Toledo, MX5) at 24±1°C and 22% RHbefore and after sampling. The weighing precisionwas ±1 μg and the standard variation of thealuminium blank foils was ±4.6 μg (n=7).

TC was analyzed by a Multi N/C 2100 elementalanalyser (Analytik Jena, Germany) equipped with adouble furnace solid module: for this study, a smallportion of the aluminium foil (about 2 cm2) wasintroduced into the combustion furnace of theinstrument for analysis.

312 Water Air Soil Pollut (2007) 185:311–321

Inside the combustion chamber the sample wasexposed to a temperature of 950°C in a pure oxygenatmosphere, in the presence of a catalyst (CeO2).Under these conditions all carbonaceous matter(organic carbon, carbonate and Elemental Carbon)evolves in CO2 (Cachier et al. 1989; Gelencser et al.2000). TC is determined as total evolved CO2 by anondispersive infrared (NDIR) detector The detectionlimit is 0.2 μg of carbon and the accuracy of the TCmeasurement was better than 5% for 1 μg of carbon.The calibration of the instrument was performed witha liquid standard of potassium hydrogen phthalate.The sampling substrates were prefired at 500°C for4 h to improve the blank signal from the aluminiumfoils.

A blank sample was associated to each samplingrun in order to evaluate the contribution of thesampling substrate to the Total Carbon amount.Average concentration of TC in blank samples was3.3 μgC (on half a foil) with a standard deviation of

0.54; this value was subtracted from all the analysedsamples.

3 Results and Discussion

3.1 Bulk Chemical Composition

Figure 1 reports a comparison between the PM10

concentration, calculated by adding up the aerosolmass on the impactor stages, and the hourly averagedPM10 online measurements performed by the Region-al Environmental Protection Agency (ARPA) for theperiod from 1 March 2005 to 15 June 2005. The twoseries of data show in general a reasonable agreement,although the Berner impactor total mass values were20% lower than the PM10 online measurements onaverage (Fig. 2).

This may be due to a lower impactor collectionefficiency for coarse particles, which are the dominant

Fig. 1 Aerosol mass con-centration (black squares) ofanalysed samples, superim-posed on the hourly averagePM10 measurements (greycircles) performed by theRegional EnvironmentalProtection Agency (ARPA)at the sampling site

Online measurements ARPA Weighed mass

Fig. 2 Air mass concentra-tions measured by theARPA for the samplingdays, averaged over thesampling periods (blackbars) and samples weighedmass concentration (greybars)

Water Air Soil Pollut (2007) 185:311–321 313

fraction of the total mass. The reduction of the collectionefficiency could be the result of the rebound of coarseparticles on the collection substrates (Fujitani et al.2006). Even higher evaporation of semivolatiles (am-monium nitrate and organics) in Berner impactor, dueto higher vacuum, can influence the results. The medianPM10 value for the samples set was 34.9 μg m−3 with aminimum of 17.8 μg m−3 measured on 21 April 2005and a maximum of 64.0 μg m−3 measured on 26 April2005.

The total concentrations of the main chemicalcomponents obtained by summing the concentrations

of the five size intervals for each sample are reportedin Table 1. WSOM and WINCM stand for watersoluble organic matter and water insoluble carbona-ceous matter, respectively.

In order to derive the WINC concentration, twodifferent procedures were followed: for stages from 1to 3 (size interval: 0.05 to 1.2 μm), in which thecarbonate carbon concentration is very low comparedto the total carbon amount, WSOC was subtracteddirectly from TC (WINC=TC-WSOC). For stages 4and 5 (size interval: 1.2 to 10 μm), in which theconcentration of crustal carbonate is not negligible,the inorganic soluble carbon (IC) concentration wasalso measured and then WINC was calculated fromthe equation: WINC=TC−WSOC−IC. In the presentsamples WINC represents the sum of the insolubleorganic carbon and of Elemental Carbon (EC),although a fraction of EC can be recovered by waterextraction (Mayol-Bracero et al. 2002; Gelencser etal. 2000), thus contributing also to WSOC.

Table 1 Main chemical components and total mass (air concentrations are reported in μg m−3)

Date NO�3 nssSO¼

4 NHþ4 Sea salt nssCa2+ Other ions WSOM WINCM Unacc. PM

16/03/05 7.34 5.09 2.91 3.75 1.63 0.25 7.28 11.10 22.18 60.7030/03/05 3.98 3.24 1.37 2.65 0.83 0.13 5.30 7.24 10.67 34.7107/04/05 2.41 4.01 3.33 1.98 0.81 0.21 9.72 11.50 15.73 49.3613/04/05 0.69 1.25 0.35 0.53 0.52 0.09 1.69 9.97 4.45 19.3514/04/05 2.43 2.93 1.18 0.80 0.77 0.10 3.50 7.82 6.67 26.2119/04/05 3.04 3.06 1.02 1.42 0.80 0.13 4.26 6.37 8.78 28.8821/04/05 1.43 1.71 0.44 1.92 0.69 0.22 1.78 6.20 3.69 17.7826/04/05 6.86 4.20 3.96 9.12 1.18 0.12 4.02 10.67 23.90 63.9528/04/05 5.32 4.94 2.51 1.66 0.95 0.17 4.54 10.68 9.28 39.8909/05/05 4.15 3.85 1.62 1.40 0.79 0.25 4.52 10.01 8.88 35.1212/05/05 5.63 4.37 1.69 6.83 1.19 0.19 5.44 8.48 14.92 47.9213/06/05 2.58 3.88 1.40 4.21 0.80 0.09 2.02 7.23 11.13 32.85Min 0.69 1.25 0.35 0.53 0.52 0.09 1.69 6.20 3.69 17.78Median 3.51 3.86 1.51 1.95 0.81 0.15 4.39 9.22 9.98 34.92Max 7.34 5.09 3.96 9.12 1.63 0.25 9.72 11.50 23.90 63.95

Sea salt6%

WINCM26%

Unaccounted29%

nssCa2+

nssSO4=

Other ions0%WSOM

Fig. 3 Median bulk chemical composition of the sample set

Table 2 Statistical summary of size segregated mass concen-trations (μg m−3)

Size range (μm) Min PM Median PM Max PM

0.05–0.14 3.93 5.97 7.750.14–0.42 3.17 5.43 8.950.42–1.2 2.45 9.15 20.391.2–3.5 2.60 7.19 14.933.5–10 2.49 6.97 18.62

In order to include the carbonaceous species in theaerosol mass budget, organic matter concentrationsmust be derived from the measured carbon concen-trations through suitable conversion factors (Turpin etal. 2000). For the WSOM concentration (watersoluble organic matter) a conversion factor of 1.8was used (Matta et al. 2003). By contrast, to calculateWater Insoluble Carbonaceous Matter (WINCM)from WINC a conversion factor of 1.2 was adopted,following the indications of Zappoli et al. (1999).

As shown in Table 1, the “Sea salt” concentrationincluded all the ions of marine origin: Na+, Cl−,Mg++, sea-salt SO¼

4 ssSO¼4 ¼ 0:25*Naþ

� �and seasalt

Caþþ ssCaþþ¼ 0:04*Naþð Þ. The concentration ofSO¼

4 and Ca++ exceeding the typical sea salt massratio are called non-seasalt sulphate (nssSO¼

4 ¼SO¼

4 �ssSO¼4 ) and non-seasalt calcium (nssCaþþ¼

Caþþ�ssCaþþ), respectively. “Other ions” is the sumof the ionic species in trace concentrations (K+ andNO�

2 ), while “Unaccounted” is the mass that could notbe accounted for by analysis, and is calculated as thedifference between the weighed mass and the sum ofconcentrations of the analysed chemical components.Figure 3 reports the median bulk chemical compositionof the impactor samples. A considerable fraction of the

aerosol mass consists of carbonaceous species (WSOC+WINCM = 38%), with the insoluble fraction clearlydominating over the soluble one: insoluble carbonaccounts for 68% of all carbonaceous matter. Ammo-nium, nitrate and sulphate together account for 25% ofthe total aerosol mass (4, 10 and 11% respectively),while sea salt accounts for 6%. The unaccountedfraction calculated by the mass balance is alsosignificant, indicating that 29% of PM10 eluded thechemical analyses.

3.2 Size-Segregated Chemical Composition

A statistical summary of air mass concentrations inthe different size ranges is reported in Table 2. Onaverage, 58% of the total mass is distributed in thefine size range (stages 1–3, i.e. PM1,2), even if threesamples show a different behaviour, with the largerpart of the mass accounted for by the coarse sizefraction (16 Mar 05, 12 May 05 and 13 Jun 05).

During the studied period, we observed a signifi-cant variability in the PM size distribution, even ifhalf of the samples shows a mode on the intermediatestage (0.42–1.2 μm) or either on the intermediate andon the fifth stage (3.5–10 μm). Examples of PM size

Table 3 Minimum, median and maximum air concentrations (μg m−3) for nitrate, non-seasalt sulphate and ammonium in the differentimpactor stages

Size range (μm) NO�3 nssSO¼

4 NHþ4

Min Med Max Min Med Max Min Med Max

0.05–0.14 0.00 0.07 0.33 0.17 0.47 0.88 0.07 0.15 0.300.14–0.42 0.02 0.19 0.71 0.59 1.32 1.71 0.20 0.59 0.870.42–1.2 0.08 0.55 1.28 0.36 1.35 2.08 0.08 0.68 2.871.2–3.5 0.26 1.42 3.18 0.07 0.27 0.97 0.00 0.05 0.123.5–10 0.18 1.27 2.85 0.00 0.12 0.45 0.00 0.03 0.06

Table 4 Minimum, median and maximum air concentrations (μg m−3) for sea salt, non-seasalt calcium and the sum of minor ions inthe different impactor stages

Size range (μm) Sea salt nssCa2+ Other ions

0.05–0.14 0.00 0.01 0.19 0.01 0.02 0.05 0.00 0.02 0.060.14–0.42 0.00 0.02 0.05 0.01 0.03 0.07 0.02 0.04 0.070.42–1.2 0.04 0.22 0.59 0.08 0.13 0.18 0.01 0.05 0.101.2–3.5 0.15 0.83 3.68 0.17 0.28 0.48 0.01 0.02 0.073.5–10 0.27 1.01 4.82 0.17 0.36 0.99 0.01 0.02 0.06

distributions will be provided in following sections.The described variability must reflect the interactionof different aerosol sources.

Tables 3, 4 and 5 present the minimum, medianand maximum air concentrations of the main chemicalaerosol components for the different size intervals,while Fig. 4 illustrates the median chemical compo-sition of the sample set. The main components of thefine fraction (size range between 0.05 and 1.2 μm) areWSOM, WINCM, NHþ

4 and nssSO¼4 , with median

percentage contribution to the total mass of 17, 36, 7and 16% respectively. On the other hand, NO�

3 (20%)and sea salt (14%) dominate the coarse fraction(particles between 1.2 and 10.0 μm). The presenceof nitrate in the coarse fraction is typical of the marineenvironment, where gaseous nitric acid absorbs ontoNaCl particles, providing NaNO3 (Pio and Lopes1998; Coe et al. 2006). Moreover, all the analysedsamples show a Cl+/Na− ratio sensibly lower than 1.8,the sea salt ratio, indicating a displacement of chlorinedue to the above mentioned reaction (Seinfeld andPandis 1998).

In stages 1 and 2 (size interval 0.05–0.42 μm)almost the whole mass was speciated, while for largerparticles a substantial amount of the mass wasunaccounted by chemical analysis: the uncharacter-ized mass was 17% of the total in the fine fraction,concentrated almost entirely in the third stage; ahigher percentage of unaccounted material character-ises the coarse fraction (median 44%).

The increase of the unaccounted for mass withparticle size can be attributed to inorganic insolublematerials of crustal origin, not detected by theanalytical techniques employed. The linear regressionstatistical analysis supports this remark, showing agood correlation between the unaccounted for fractionand non-seasalt Calcium, considered as a tracer of theaerosol crustal component (for stages 4 and 5 R2=0.777 and 0.944, respectively).

The concentration of WINCM decreased from thefirst to the third impactor stage (that is, increasingparticles size), while WSOM, nssSO¼

4 and NHþ4

concentration increased. WINCM is the dominantcomponent in the fraction 0.05–0.14 μm, with a

Table 5 Minimum, median and maximum air concentrations (μg m−3) for WSOM, WINCM and the unaccounted for mass in thedifferent impactor stages

Size range (μm) WSOM WINCM Unacc.

0.05–0.14 0.28 0.96 2.15 3.18 3.90 5.64 0.00 0.00 1.160.14–0.42 0.42 1.15 2.41 1.30 2.10 2.89 0.00 0.17 1.350.42–1.2 0.24 1.28 3.78 0.63 1.12 2.40 0.37 3.17 11.291.2–3.5 0.24 0.50 1.03 0.39 0.56 1.02 1.12 2.71 5.733.5– 10 0.09 0.29 0.69 0.27 0.50 2.35 1.42 3.27 9.16

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

NO3 nssSO4 NH4 Sea salt nssCa

Other ions WSOM WINCM Unacc.

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

Fig. 4 Median size segregated chemical composition and relative chemical composition of the sample set

median percentage of 70% (3.9 μg m−3), thenreducing its contribution through size intervals 0.14–0.42 μm (2.1 μg m−3, 37%) and 0.42–1.2 μm(1.12 μg m−3, 13%), down to 0.5 μg m−3 for thelargest particles, corresponding to 7% of the mass.

WSOM median air concentration increases fromthe 0.05–0.14 μm size range (0.96 μg m−3) to the0.42–1.2 μm size range (1.28 μg m−3), and thendecreases to a minimum for the largest particles(0.29 μg m−3). NHþ

4 and nssSO¼4 show a similar

trend in all the analysed samples, with the minimumin the 3.5–10 μm size range (median air concentra-tion: 0.03 and 0.12 μg m−3 for NHþ

4 and nssSO¼4 ,

respectively) and maxima for particles in the 0.42–1.2 μm size interval (0.68 and 1.35 μg m−3). Similar

trends, increase of the solubility of the carbonaceousfraction and a concurrent increase of SO¼

4 and NHþ4

concentration as increasing of size, within thesubmicronic range, have already been observed inother urban environments (Matta et al. 2003 andreferences therein).

3.3 Aerosol Source Apportionment

In order to achieve a better understanding of thesample set variability and of the interaction betweenthe different particles sources in the investigatedenvironment, some case study have been considered.

A first case is the 13 April sample. The sampleshowed a monomodal size distribution centred on the

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

Fig. 5 Size segregated chemical composition and relative chemical composition of the sample collected on 13 April 2005

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

Fig. 6 Size segregated chemical composition and relative chemical composition of the sample collected on 28 April 2005

0.05–0.14 size interval, and was characterized by lowbulk mass concentration (19.35 μg m−3). Meteoro-logical data provided by the Sicilian EnvironmentalProtection Agency show that the day before thesampling (12 April 2005) was a rainy day (precipita-tion of 11 mm of water), and that during the samplingperiod, wind blew constantly from west to east, thatis, from inland to the sea, in contrast to all the othersamples collected during sea breeze regime. Figure 5shows the size segregated chemical composition andthe relative size segregated composition of thissample: the chemical size segregated characteristicsare quite different to the median characteristicsdescribed above. In the coarse fraction, nitrateconcentrations as low as 0.26 and 0.18 μg m−3 weremeasured respectively in 0.42–3.5 and 3.5–10 μmsize ranges, while similar, very low, concentrations

(0.15 and 0.27 μg m−3) were registered for sea salt aswell.

In the fine fraction, low NHþ4 , nssSO

¼4 and WSOM

concentrations were also detected. Conversely,WINCM concentrations are similar to those detectedin all the other samples (5.64, 2.34 and 1.14 μg m−3

for particles in 0.05–0.14, 0.14–0.42 and 0.42–1.2 μmsize ranges, respectively). The lowering of the con-centrations observed in the accumulation and coarsemodes is probably due to scavenging by rainfallduring the day before the sampling and by winddirection, blowing eastward, thus keeping the relativecontribution of the sea spray low compared to theurban aerosol load.

The figure shows that the meteorological condi-tions described above did not affect the WINCMconcentration, suggesting that the insoluble carbona-

COARSE

-3 nssSO4

Fig. 7 Air mass concentration trends of nssSO4= and WSOC in coarse and fine fraction

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

0.05-0.14 0.14-0.42 0.42-1.2 1.2-3.5 3.5-10

Size range [µm]

Fig. 8 Size segregated chemical composition and relative chemical composition of the sample collected on 12 May 2005

ceous fraction was emitted by a strong local source.This is consistent with the WINCM size distribution,centred on the smallest size range (0.05–0.14 μm), inwhich fresh particles from fossil fuel combustionsources are recovered (Seinfeld and Pandis 1998;Kleeman et al. 2000; Longley et al. 2003). Therefore,given the sampling site characteristics, it can beargued that WINCM is composed of primary freshlyemitted particles due to traffic-related sources.

Figure 6 shows a typical sample characterized by amonomodal distribution centred on the 0.42–1.2 μmsize interval (28 April 2005): NHþ

4 , nssSO¼4 and

WSOM account for 49% of the weighed mass in the0.05–1.2 μm size range and for 31% of the total(PM10) weighed mass. Impactor stages 2 and 3roughly cover the accumulation mode (size intervalbetween 0.14–1.2 μm). In all the samples, particlescollected in these stages were characterized by morewater-soluble organic compounds, plausibly originat-ed by oxidation in the atmosphere and condensationof vapours formed by photo-chemical reactions.Typical components of secondary aerosol are detectedin these stages (NHþ

4 , nssSO¼4 , and NO�

3 ) in all thesamples collected in Catania from March to June2005, with increasing concentrations from the 0.14–0.42 μm stage to the 0.42–1.2 μm one. Moreover, asdepicted in Fig. 7, WSOM is qualitatively wellcorrelated with nssSO¼

4 , in both the fine and coarse

fraction, thus suggesting that also WSOM originatedprevalently from gas-to-particle conversion processes.

The coarse mode is clearly dominated by sea sprayaerosol (both fresh or processed by anthropic emittednitric acid) and by mineral derived particles. Thecoarse fraction, accounting for less than 50% of thetotal mass for the majority of the samples, is thereforestrongly influenced by natural sources, sea spray andmineral dust, although a contribution by trafficresuspension is also possible (Almeida et al. 2006).Figure 8 shows a sample characterized by mass modecentred on the 3.5–10.0 μm size range.

Given the above remarks, it is possible to try toquantify the contribution of each source to the totalparticles load in the sample set. To achieve this someassumptions are required: the “mineral dust” contri-bution can be obtained by considering all theunaccounted for fraction to be of crustal origin, andadding to that the mass contribution of nss Calcium.The aerosol water content contribution to the unac-counted for fraction was considered negligible,having weighed on hydrophobic sampling substrates(aluminium foils) at very low relative humidity(22%).

In order to asses the secondary production contri-bution, nssSO¼

4 , NHþ4 , WSOM and fine NO�

3 massconcentrations were summed, while WINSOC wasconsidered directly as the “primary production from

Sample

mineral dust fresh marine particles modified marine particles

secondary processes primary from traffic

Fig. 9 Contribution of theidentified sources to totalPM in the sample set

traffic”. Finally, calculating the Na−/Cl+ ratio, anestimation was obtained of the mass of freshlyemitted sea salt and of processed marine particles(coarse NO�

3 mass was included within the agedmarine particles mass).

Figure 9 shows the results of the said calculations.The figure suggests a relatively constant contributionfrom dust sources and much more variable contribu-tions from marine particles and from primary versussecondary pollution sources.

4 Conclusions

Chemical mass closure was almost achieved in thefine fraction (stages 1, 2 and 3 of the impactor,corresponding to particles smaller than 1.2 μm aero-dynamic diameter), while in the coarse fraction(stages 4 and 5, up to 10 μm) a median value of44% of the mass turned out to be uncharacterized, dueto the presence of crustal derived insoluble inorganicspecies not detected by the analytical techniquesemployed.

The main fine fraction components are WINCM,WSOM, nssSO¼

4 and NHþ4 , with WINCM dominating

the first stage (0.05–0.14 μm), with the lattercomponents increasing their concentrations in thefine size interval. In the coarse fraction, sea salt andNO�

3 are the dominant components with the unac-counted for fraction corresponding to 44% of themass. The presence of nitrate in the coarse fraction,together with a lower Cl+/Na− as compared to thetypical sea salt ratio, suggests that gaseous nitric aciddisplaces sodium chloride.

The chemical component air concentrations andsize distribution characteristics allow the identifica-tion of different aerosol sources contributing to thetotal particle load. The first source identified isvehicular traffic, mainly producing primary carbona-ceous insoluble particles. By contrast, secondaryaerosol dominates the 0.14–1.2 μm size interval, withWSOM, ammonium sulphate and nitrate as maincomponents. Organic matter is more soluble in thismode, indicating the presence of more oxidizedfunctional groups, plausibly due to the ageing oforganic matter, or to the gas-to-particle conversion ofsemi-volatile organic compounds.

Given the life-time of such aerosol components,regional sources, beside local traffic gaseous emis-

sions, have to be considered, such as a contributionfrom other cities in the Catania metropolitan area andGulf, Augusta petrochemical plant, sea traffic emis-sions (Zanini et al. 2005), and the Mt. Etna naturalvolcanic emissions (Allen et al. 2006).

Thus, submicron aerosol particles collected in thisexperiment are a mixture of small insoluble particlesderived by traffic emissions (aerodynamic diameterbetween 0.05 and 0.14 μm) and of larger particles ofdifferent origin and more aged.

Finally, modified (e.g., nitrate-containing) sea-saltparticles and mineral dust are the dominant compo-nents of coarse particles in the urban environmentinvestigated.

While insoluble carbon particles originated bylocal traffic emissions constantly occur in the sam-ples, the concentrations of secondary, organic andinorganic components, as well as that of sea-saltparticles, vary among samples, according to thedifferent wind regimes and occurrence of regionalpollution episodes in the central Mediterranean Basin.

Acknowledgements This work was supported by MIUR,Rome, COFIN 2004, Project “Functional and StructuralCharacteristics of Atmospheric Particulate Organic Matter inUrban Areas”.

References

Allen, A. G., Mather, T. A., McGonigle, A. J. S, Aiuppa, A.,Delmelle, A., Davison, B., et al. (2006). Source, sizedistribution, and downwind grounding of aerosols fromMount Etna. Journal of Geophysical Research, 111, D10302.

Almeida, S. M., Pio, C. A., Freitas, M. C., Reis, M. A., &Trancoso, M. A. (2006). Source apportionment of atmo-spheric urban aerosol based on weekdays/weekend vari-ability: Evaluation of road re-suspended dust contribution.Atmospheric Environment, 40, 2058–2067.

Cachier, H., Bremond, M. P., & Buat-Menard, P. (1989).Determination of atmospheric soot carbon with a simplethermal method. Tellus, 41B, 379–390.

Coe, H., Allan, J. D., Alfarra, M. R., Bower, K. N., Flynn, M.J., McFiggans, G. B., et al. (2006). Chemical and physicalcharacteristics of aerosol particles at a remote coastallocation, Mace Head, Ireland, during NAMBLEX. Atmo-spheric Chemistry and Physics, 6, 3289–3301.

Fujitani, Y., Hasegawa, S., Fushimi, A., Kondo, Y., Tanabe, K.,Kobayashi, S., et al. (2006). Collection characteristics oflow-pressure impactors with various impaction substratematerials. Atmospheric Environment, 40, 3221–3229.

Gelencser, A., Hoffer, A., Molnar, A., Krivacsy, Z., Kiss, G., &Meszaros, E. (2000). Thermal behaviour of carbonaceousaerosol from continental background site. AtmosphericEnvironment, 34, 823–831.

Heintzenberg, J., Muller, K., Birmili, W., Spindler, G., &Wiedensohler, A. (1998). Mass-related aerosol propertiesover Leipzig basin. Journal of Geophysical Research, 103,13125–13135.

Kleeman, M. J., Schauer, J. J., & Cass, A. (2000). Size andcomposition distribution of fine particulate matter emittedfrom motor vehicles. Environmental Science & Technology,34(7), 1132–1142.

Longley, I. D., Gallagher, M. W., Dorsey, J. R., Flynn, M., Allan,J. D., Alfarra, M. R., et al. (2003). A case study of aerosol(4.6 nm<Dp<10 mm) number and mass size distributionmeasurements in a busy street canyon in Manchester, UK.Atmospheric Environment, 37, 1563–1571.

Matta, E., Facchini, M. C., Decesari, S., Mircea, M., Cavalli, F.,Fuzzi, S., et al. (2003). Mass closure on the chemicalspecies in size-segregated atmospheric aerosol collected inan urban area of the Po Valley, Italy. Atmosphericchemistry and Physics, 3, 623–637.

Mayol-Bracero, O. L., Guyon, P., Graham, B., Andreae, M. O.,Decesari, S., Facchini, M. C., et al. (2002). Black carbon,organic carbon and water soluble organic compounds inbiomass smoke particles over the Amazon Basin. Journalof Geophysical Research, 107, 8091.

Motta, S., Librando, V., Minniti, Z., Federico, C., & Saccone, S.(2006). Identification of genotoxic compounds in the airborneparticulate matter endowed by small aerodynamic diameter inthe city of Catania (Italy). Journal of Analytical, Environmen-tal and Cultural Heritage Chemistry, 96(9–10), 537–542.

Raes, F., Bates, T., McGovern, F., & van Liedekerke, M.(2000).The 2nd aerosol characterization experiment (ACE-2):General overview and main results. Tellus, 52B, 111–125.

Pio, C. A, & Lopes, D. A. (1998). Chlorine loss from marineaerosol in a coastal atmosphere. Journal of GeophysicalResearch, 103(D19), 25263–25272.

Putaud, J.-P., Van Dingenen, R., Dell’Acqua, A., Raes, F.,Matta, E., Decesari, S., et al. (2002). Size-segregatedaerosol mass closure and chemical composition. MonteCimone (I) during Minatroc. Atmospheric Chemistry andPhysics Discussions, 3, 4097–4127.

Putaud, J. P., Van Dingenen, R., Mangoni, M., Virkkula, A.,Raes, F., Maring, H., et al. (2000). Chemical mass closureand assessment of the origin of the submicron aerosol inthe marine boundary layer and the free troposphere atTenerife during ACE-2. Tellus, 52B, 141–168.

Seinfeld, J. H., & Pandis, S. N. (1998). Atmospheric chemistryand physics—from air pollution to climate change. NewYork: Wiley Interscience.

Turpin, B. J., Saxena, P., & Andrews, E., (2000). Measuringand simulating particulate organics in the atmosphere.Atmospheric Environment, 34, 2983–3013.

Zanini, G., Pignatelli, T., Monforti, F., Vialetto, G., Vitali, L.,Brusasca, G., et al. (2005). The MINNI project: Anintegrated assessment modeling system for policy making.In A. Zerger & R. M. Argent (Eds.), MODSIM 2005International Congress on Modelling and Simulation (pp.170–176. ISBN: 0-9758400-2-9). Modelling and Simula-tion Society of Australia and New Zealand.

Zappoli, S., Andracchio, A., Fuzzi, S., Facchini, M. C.,Gelencsér, A., Kiss, G., et al. (1999). Inorganic, organicand macromolecular components of fine aerosol in differentareas of Europe in relation to their water solubility.Atmospheric Environment, 33, 2733–2743.

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