Pergamon - Europa · 2009-03-05 · 3310 C.A. PIO et al. approximately 20 km southwest of Aveiro. a small town of ~50,000 inhabitants. The region is characterised by moderate temperatures,

Pergamon Atmospheric Environment Vol. 30, No. 19, pp. 3309-3320, 1996 Copyright © 1996 Elsevier Science Ltd

Printed in Great Britain. All rights reserved PII: S1352-2310(96)00058--1 1352-2310/96 $15.00 + 0.00

SOURCE ASSESSMENT OF PARTICULATE AIR POLLUTANTS MEASURED AT THE SOUTHWEST EUROPEAN COAST

C A S I M I R O A. P I O , L U I S M. C A S T R O , M A R I O A. C E R Q U E I R A ,

I S A B E L M. S A N T O S , F I L I P A B E L C H I O R a n d M A R I A L. S A L G U E I R O

Departamento de Ambiente e Ordenamento, Universidade de Aveiro, 3810 Aveiro, Portugal

(First received 19 July 1995 and in final form 6 February 1996)

Abstract Aerosol particles and gaseous species were measured in air masses transported to the west coast of Portugal, between November 1993 and August 1994. Samples were taken during four monitoring campaigns distributed along the various seasons of the year, integrated in the EC Project: BMCAPE. Aerosol particles were collected with separation in two size fractions and analysed in relation to total mass, water soluble ions, trace elements and black/organic carbon. Local micro-meteorological parameters and air mass backward trajectories were compared with analytical results in order to define characteristic air mass types and to evaluate the origin of pollutants.

Average concentrations on the Portuguese west coast, even in maritime air masses, are higher than values observed in remote oceanic locations. This is probably a consequence of continental European air masses recirculation through the eastern Atlantic Ocean, reinforced by situations of mesoscale transport from the Iberian Peninsula. Principal Component Analysis permitted the identification of five source groups for the fine and coarse aerosol fractions, namely combustion plus road traffic, sea salt spray, secondary aerosol production, soil and possibly non-ferrous metallurgy industries. In the aerosol fine fraction road traffic and combustion contribute on average with 25% of the total fine aerosol mass, while sea spray and secondary production represent 14% and 31%, respectively of the mass loading. Sea spray is by far the major contributor to the coarse fraction with an average of 88% of the suspended coarse aerosol mass. Copyright © 1996 Elsevier Science Ltd

Key word index: Maritime aerosol, Principal Component Analysis, black carbon, trace elements, water soluble ions.

INTRODUCTION

Portugal , a count ry located on the extreme west of Europe, is s trongly influenced by air mass t r anspor t from the Atlant ic Ocean and presents relatively small emissions when compared with industr ial ised regions in the Eu ropean cont inent . As a consequence, a tmo- spheric concent ra t ions at the coast should presum- ably reflect the b a c k g r o u n d levels tha t exist over the cen t re -nor th Atlant ic Ocean, at least when winds blow directly from the sea. However, previous work (Pio et al., 1991a, b) showed tha t concen t ra t ions measured in the outskir ts of Aveiro (a small town on the west coast of Portugal) were much higher t han levels observed in remote areas over the Atlantic, possibly as a consequence of local con t amina t i on or regional/ ' long range t ranspor t .

In order to assess the quali ty of air masses enter ing the European con t inen t from the Atlant ic and integrated in the EC Project: Background Maritime Contri- bution to Atmospheric Pollution in Europe (BMCAPE) , a sampl ing site was establ ished on the western Por- tuguese coast, faraway from pol lu tan t sources. In par- allel with similar measurements t aken at o ther points

on the western seaboard of Europe, more than one hundred , 24-h averaged, measurements of aerosol particles and gaseous compounds were performed dur ing four mon th ly campaigns in each season of the year, between N o v e m b e r 1993 and July 1994. Unt i l now, as far as we know, no o ther extensive da ta of po l lu tan t concent ra t ions in mar i t ime n o n - u r b a n sites in the western coast of the Iber ian Peninsu la are available. Only sporadic measurements , t aken dur ing cruises a long the Por tuguese coast, have been pub- lished (Duce et al., 1975; B u a t - M e n a r d and Chasselet, 1979; V61kening and Heumann , 1990). The measurements provide exper imental informat ion tha t might be used as input in air quali ty m a n a g e m e n t models and for the ca l ibra t ion of emission inventories. They can also be useful as backg round informat ion in studies of mar i t ime/con t inen ta l a tmospher ic chemistry interact ion.

SAMPLING SITE AND MEASUREMENT METHODS

Pollutants were collected at Arefio in the northwestern coast of Portugal (latitude 40 ° 30'N, longitude 8 ° 47' W), at

3309

3310 C.A. PIO et al.

approximately 20 km southwest of Aveiro. a small town of ~50,000 inhabitants. The region is characterised by moderate temperatures, having an annual precipitation of approximately 1000 mm. Rainfall occurs principally between late fall and early spring and is associated with maritime air mass transport from the south sector. During the dry warm season the coastal area is influenced by mesoscale sea breeze circulation with strong winds from the North.

The sampling site is located near the beach, at ~ 300 m from the sea, in a state owned area of fine grain, sandy soil partially covered with grass, shrubs and small pine trees. The site is separated from most nearby houses in the village of Are~o by approximately I km, in order to minimise contamination from local emissions.

Aerosol particles were collected with a high volume sampler, located on the top of a 10 m high tower. The sampler, equipped with a Sierra PMI0 size selective inlet and a Sierra single stage impactor plate to separate particles into two size fractions (0.95 <dp < 10 Ibm; dp < 0.95 llm) (equivalent aerodynamic diameter), was continuously operated for 24-h periods, at a flow rate of 1.13 m 3 min ~. Aerosol samples were collected on pre-treated and washed Whatman QM-A quartz fibre filters (Pio et al., 1991b).

Water soluble ions were analysed by ion chromatography (C1 , NO3, SO ] , MSA-), indophenol-blue spectrophotometry (NH2), potentiometry (H +), and atomic absorption or flame emission spectrophotometry (Ca 2+, Mg 2+. Na + and K+). Trace elements, extracted with a mixture of nitric, perchloric and fluoridic acids, were analysed by flame and/or flameless atomic absorption (Pio et aL, 1989).

The particulate black carbon (BC) and organic carbon (OC) content was determined with a home-made thermo- optical system, based on the thermal desorption/oxidation to CO2 with subsequent determination by non-dispersive in- frared spectrophotometry (Pio et al., 1993). Gaseous species (NH3, HNO3, SO 2 and NO2) were sampled by means of impregnated bi-annutar denuders; after extraction, the ions were analysed by ion chromatography (NOj, NO; , SO42 ) and catalysed blue-indophenol spectrophotometry (NH2) (Pio et al., 1996).

METEOROLOGY AND AIR MASS CLASSIFICATION

The site is provided with a meteorological station that supplies information about wind direction and speed, temperature, relative humidity and solar radi- ation. Isobaric four days backward trajectories (925 hPa) ending at AreS.o were calculated for every 6-h (at 18 h, 24 h, 6 h and 12 h), at the Norwegian Meteorological Institute, in Oslo, and provided by the Norwegian Institute for Air Research. According to the backward trajectories, air masses arriving at AreS.o during sampling campaigns were classified in five main groups of special interest (see Fig. 1):

Mari t ime: If backward trajectories indicate an oceanic origin, without continental contamination, during the previous 4 days. Pure M a r i t i m e samples refer to periods of marit ime air masses with no local contamination, that is, with local wind continuously blowing from the ocean. Contamina ted mari t ime samples refer to marit ime air masses having intermittent periods with local wind direction from land.

Modi f i ed Continental: If backward trajectories show a marit ime origin with final re-circulation through the North of the Iberian Peninsula.

North~Centre Continental: If backward trajectories indicate a continental origin in Europe and transport through the centre of the Iberian Penin- sula.

South Continental: If backward trajectories indicate an African or southern peninsula origin.

Local wind direction data were classified in six sectors of 6 0 amplitude (see Fig. 1). The first sector, SI, refers to the NE wind direction, land side, and is influenced by the industrial area of Estarreja, located at a distance of 40 kin, and by the town of Aveiro. The second sector, $2, is from SE, land side, and is influenced by some main roads and a rural area. The sectors $3 and $6 represent conditions of transition between land and sea and are associated with winds blowing along the coast. Sectors $4, with winds from SW, and $5, with winds from NW, are associated with air masses transported directly from the sea.

RESULTS AND DISCUSSION

A total of 104 samples was collected during four intensive campaigns (17 November to 20 December 1993, and 14 February to 11 March, 9 May to 10 June and 18 July to 12 August 1994).

Air mass trajectories

Measured concentrations and meteorological data were studied in terms of air mass origin and are summarised in Table 1. In Table 2 the most relevant results are compared with concentrations observed in other locations and found in literature. Analysis of our results according to air mass characteristics, shows that maritime samples present the lowest concentrations of all data set, for compounds emitted by anthropogenic sources. However, our maritime samples have values higher than concentrations found in remote oceanic locations. This might be partially a consequence of contamination by local emissions because, associated with some of these samples, intermittent breezes blowing from land were observed.

It is possible to evaluate the contribution of local/ regional emissions by comparing contaminated marit ime and pure maritime samples: local/regional emissions are essentially resultant from road traffic (significant differences in Pb, OC, BC, Zn and NO2), combustion (differences in BC, Se, non-sea salt K + (nssK +)-calculated from the Na ÷ concentration and the sea water K + / N a + ratio, SO2, Ni and V) and secondary formed aerosols (differences in N H 2 , N O 3 - , HNO3), probably resulting from previously referred primary pollutants.

Elements such as AI, Cr, Cd, Fe and Mn, specially in the fine fraction, do not vary appreciably in concentration between pure and contaminated marit ime air masses, which might indicate a long range transport from continental emissions, with recirculation over the ocean. The ratio fine/coarse fraction for these

Source assessment of particulate air pollutants 3311

:Ocean :

Modif ied

I h ' l i I m , n

Fig. I. Sampling site localisation, local wind direction classification and air mass categorisation, based on four day backward trajectories.

elements is higher in maritime than in continental air masses, which reinforce the conclusion about their origin because during transport the coarse particles will sediment more than the fine particles and the ratio fine/coarse will increase. Therefore, maritime air masses with a higher fine/coarse fraction ratio are probably associated with long range transport and a significant atmospheric residence time.

Despite the levels of black carbon (BC) being higher in continental air masses, the ratio BC/OC in the fine fraction is lower (_~ 25%) when compared to maritime air masses ( - 35%). This "relative enrichment" of BC compared to organic carbon (OC), in the maritime air masses probably results from the volatilisa- tion of particulate OC or a less efficient condensation of volatile organics over the ocean, where the concentrations of gaseous organic compounds are lower.

Maritime air masses clearly present lower values of NH4 + showing that in the oceanic air masses the neutralisation of nitric and sulphuric acidity is essentially made by NaC1 (through HCI degassing), because of the absence of NHa. The inter-comparison between modified continental and contaminated maritime samples can give indications about the contribution from emissions in the North of the Iberian Peninsula. In modified continental air masses the values of secondary aerosol compounds are significantly increased with respect to contaminated maritime, showing that during transport over the north of the Iberian Penin- sula sulphur and nitrogen compounds emitted by anthropogenic sources have time to suffer oxidation and gas/particle conversion. The fine/coarse fraction

ratio of compounds emitted by anthropogenic sources is lower in continental than in maritime air masses because deposition effects during long range transport over the ocean are more effective for coarse particles. For naturally emitted compounds, such as Na +, Ca 2 + and Mg 2+, the fine/coarse fraction ratio is higher in continental than in maritime air masses.

Contribution from the ocean is significant in every sample, irrespective of wind direction, as a result of the proximity of the sea and of the 10/~m sampler cut off that prevents the sampling of very big particles emitted locally from the splash of sea waves (more dependent on the wind direction). There is a relevant difference in the ratio fine/coarse fractions for Na+, Ca 2 +, Mg 2 +, Fe and Mn, between the North and the South Peninsula continental air masses with the last presenting higher values, probably as a result of more effective contribution in the fine fraction of long range transported soil emissions, namely from African emitted dust by the Sahara desert.

Comparison of measured concentrations with aerosol levels in other locations, with the objective of determining the degree of atmospheric contamination in this region, is difficult, due to the great variability of levels measured on coastal, remote and rural areas. Trace elements in pure maritime air masses agree, in general, with measurements taken in oceanic cruises passing along the Portuguese coast (Duce et al., 1975; Buat-Menard and Chesselet, 1979) and are similar to results from rural areas in industrialised European countries. Our values are higher than measurements taken near the Portuguese coast during another Cruise


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3314 C. A. PIO et al.

Table 3. Principal Component (PC) pattern, for Varimax rotated components, applied to the fine fraction (dp < 0.95/~m) aerosol constituent concentrations

PC1 PC2 PC3 PC4 PC5 Traffic/Comb. Marine Sec. Aerosol Soil N.F. Met.? Communal.

NO3 0 . 9 5 0.92 OC 0.93 0.89 BC 0.91 - - - - 0.86 K + 0 . 8 9 - - - - 0.82 Pb 0 . 8 3 . . . . 0.70 PM 0.77 - - 0.47 0.86 Zn 0.74 - - 0.34 0.69 Se 0.65 -- 0.53 N H ~ - 0.60 - - 0.70 - 0.86 Ni 0.57 --- 0.48 0.59 Mg 2 + 0.94 - 0.89 Na + 0.87 0.79 C1 0.46 0.76 - 0.86 Ca 2+ 0.48 0.50 -- 0.41 0.65 SO42 - - - 0.94 0.92 H + - - 0.71 - 0.51 AI -- 0.81 0.27 0.74 Mn - - - 0.76 0.66 Cr - - 0.59 0.44 Fe 0.33 0.28 0.58 0.53 As . . . . . 0.87 0.78 Cu 0.39 - - - 0.64 0.66 V 0.46 - - 0.33 0.40 Cd 0.38 - - 0.33 0.34

Eigenvalues 7.29 2.87 2.42 2.64 1.65 16.87 % of tot. variance explained 30.38 11.94 10.10 10.98 6.90 70.29

Note. Presented only factor loadings with absolute values larger than 0.25. Factor loadings greater than or equal to 0.70 in bold. OC--organic carbon; BC black carbon; PM--particle mass.

experiment , but are in general agreement with higher values observed dur ing the same exper iment in regions fur ther nor th , near the Eu ropean cont inen t (V61kening and Heumann , 1990). All these results taken in the N o r t h e r n Atlant ic are significantly higher than measurements ob ta ined in the Southern Hemi- sphere, showing the existence of a s t rong cont inenta l con t amina t i on in the oceanic t roposphere between the E u r o p e a n and the Amer ican continents .

Source apportionment o f the total aerosol data set

In a fur ther a t t empt to assess the sources respon- sible for the observed pol lut ion levels, Pr incipal C o m p o n e n t with Var imax ro ta t ion and Mul t i l inear Regression Analysis were applied to the aerosol con- s t i tuents alone, and in associat ion with gaseous concent ra t ions and meteorological data , to all sets of results and to mar i t ime samples, separately. In the total aerosol da ta set, five principal componen t s were identified for the fine fract ion results (dp < 0.95 #m), which explained approximate ly 70% of all the variance observed (see Table 3).

Pr incipal C o m p o n e n t 1 (PC1) correlates with const i tuents BC, O C and Pb, character is t ic of road traffic emissions, and with K, Ni and V, traces f rom o ther combus t ion processes. This principal c o m p o n e n t in- eludes an i m p o r t a n t variabil i ty for zinc. Zinc also

correlates well with road traffic emissions in the coarse fract ion (see Table 5), which agrees with the results of H u a n g et al. (1994), tha t indicated zinc as a new potent ia l marke r element for mo to r vehicle emissions, since leaded gasoline consumpt ion has been decreasing nowadays. The existence of a small corre la t ion between PC1 and chloride suggests tha t a fraction of fine chloride mass may have an origin in road traffic emissions as compounds such as PbBrC1. W h e n the results are studied together with meteorological da ta and gaseous concent ra t ions (Table 4), this principal c o m p o n e n t correlates quite well with NO2, a c o m p o u n d character is t ic of road traffic and com- bust ion processes. Corre la ted with PC1 is also local wind direct ion from SE, land side, and low wind intensities and temperatures , which might be a consequence of an increase in the con t r ibu t ion of nearby emissions from domest ic fireplaces and of a less effective dispersion by the wind.

PC2 explains most of Na +, Mg 2+ and C1- variance and is associated with mar ine emissions. Curiously, sea wind direct ions do not correlate strongly with this source as would be expected. Tha t might be explained by the s t rong influence of mar ine emissions (particles below 10 #m) as a result of the sampl ing site proximity from the sea border, and therefore the presence of sea spray, whatever the wind direct ion observed. The


Table 4. Principal Component (PC) pattern, for Varimax rotated components, applied to the fine (dp < 0.95 /~m) fraction aerosol constituent concentrations, gaseous species and meteorological parameters

PCI PC2 PC3 PC4 PC5 Traffic/Comb. Marine Sec. Aerosol Soil N .F . Met.'? Communal.

BC 0.93 - - 0.91 Pb 0.91 0.89 NO3 0.89 0.85 OC 0 . 8 8 0.26 0.85 NO2 0.84 - 0.76 TimeS2 0.63 - 0.32 0.61 NH3 0.58 - 0.31 0.47 0.67 Avg. DT - 0.52 0.26 0.52 0.71 SO~ - - 0.89 - 0.83 HNO 3 - 0.28 0.83 - 0.79 H + 0.78 - 0.64 N H + - - 0 . 7 8 - - 0 . 7 1

PM 0.41 - 0.70 0.75 SO2 - 0.63 - - 0.47 Trajectory 0.30 0.51 0.26 0.44 M g2 + 0 . 8 9 - - 0.84 Na ~ 0.83 - ~ 0.75 CI 0.79 - - 0.72 Ca 2 + 0.40 0.56 - 0.49 0.73 TimeS6 - 0.25 -- 0.10 TimeS4 0.33 - 0.12 TimeS3 . . . . 0.05 Times 1 - - 0 . 1 2

Cd 0.41 0.33 . . . . 0.31 Avg. RH . . . . . 0.77 0.64 As 0.61 0.47 Solar Rad. - 0.34 ..... 0.60 0.52 Zn 0.44 . . . . . 0.56 0.59 ( 'u - 0.33 0.56 0.47 AI 0.75 - - 0.57 Mn ~ -- 0.26 0.67 - - 0.54 ( ' r -- 0.60 - - 0.38 t e 0.42 0.60 0.37 0.70 Ni - - - - 0.37 0.43 - - 0.39 K + 0.32 0.36 - - 0.26 Sc 0.47 - - 0.28 - 0.36 - - 0.46 V . . . . . . . . . 0.12 Avg. WS - 0.31 0.36 -- 0.40 - 0.41 TimeS5 - - - - 0.10 PREC. - . . . . . 0.33 - 0.15

Eigenvalues 6.72 3.50 5.12 3.05 2.99 2 t .38 % of tot. variance cxplained 16.80 8.76 12.79 7.62 7.47 53.44

Note. Presented only factor lodings with absolute values larger than 0.25. Factor loadings greater than or equal to 0.70 in bold. OC--organic carbon; BC--black carbon; PM--particle mass; TimeS/--period of the day with wind direction from sector Si; Avg. WS--average wind speed; Avg. DT--average dry temperature; Avg. RH--average relative humidity; Trajectory qualitative evaluation of backward trajectories (higher for continental air masses).

c o m p o n e n t is howeve r associa ted wi th wind speed,

which obv ious ly increases the f o r m a t i o n of sea spray.

PC3, wi th high factor load ing for N H 4 ~, SO42- and

H + (Table 3), identifies clearly a s econda ry aerosol

f o r m a t i o n process , tha t is also associa ted wi th pre-

cu r so r gases ( H N O 3 and SO2) and meteoro log ica l

condi t ions f avourab le for s econdary aerosol fo rma-

tion, such as h igher t empera tu res , absence of precipi-

t a t ion and low wind intensit ies (Table 4). Cor re la ted

with this c o m p o n e n t are con t inen ta l air masses and

local wind di rect ion f rom nor th , t r a n s p o r t i n g emis-

s ions f rom densely p o p u l a t e d coastal areas in Aveiro

and O p o r t o . M S A is also corre la ted wi th this corn-

p o n e n t indicat ing tha t a fract ion of the SO 2- m a y

result f rom D M S oxidat ion. However , it was not

poss ible to identify a single c o m p o n e n t associa ted

wi th M S A - and S O ~ - or SO2, even when nssSO~

ins tead of SO 2- was cons idered in PC analysis.

Fe, Ca, M n and A1 correlate well wi th PC4, which

therefore represen ts a soil con t r ibu t ion . Associa ted

wi th this pr incipal c o m p o n e n t are also Ni and Cr tha t

usual ly are emit ted du r ing fuel c o m b u s t i o n (Semb and

Pacyna , 19861. NH3, local wind with land origin and

Con t inen ta l air masses present h igh cor re la t ion coeffi-

cients wi th this c o m p o n e n t , a t tes t ing the responsibi l -

ity of land emissions.


Table 5. Principal Component (PC) pattern applied to the coarse fraction (0.95 < d r < 10 #m) aerosol constituents concentrations for all samples

PC 1 PC2 PC3 PC4 Traffic/C. + Soil Marine Sec. Aeros. N.F. Met.? Communal.

OC 0.91 - 0.84 Zn 0.87 - - 0.77 Pb 0 . 8 5 ~ - 0.75 BC 0.81 0.72 Fe 0.81 0.26 - - 0.79 NO3 0.68 - 0.39 0.28 0.71 Cd 0.66 . . . . 0.44 A1 0.65 0.42 - 0.60 V 0.57 - - 0.40 0.49 Mn 0.53 - - 0.41 0.46 NH + 0.52 - 0.70 0.82 Na ÷ - - 0.96 - - 0.94 Mg 2 + --- 0.96 - - 0.94 CI - - 0.95 0.94 K + 0 . 8 3 - - 0.71 C a 2 + 0.42 0.79 -- 0.25 0.86 PM -- 0.70 - 0.52 SO~ - ~ 0.26 0.87 0.85 MSA - - - - - 0.87 0.82 Se - - - - 0.72 0.26 0.62 Cu -- - - - - 0.72 0.55 As 0.35 - -- 0.61 0.51 H + 0.25 - - - - - 0.55 0.39 Cr - - 0.25 - - 0.15

Eigenvalues 6.26 5.09 3.21 1.63 16.19 % of tot. var. expl. 26.1 21.2 13.4 6.8 67.5

Note . Presented only factor loadings larger than 0.25. Factor loadings greater than or equal to 0.70 in bold. OC--organic carbon; BC--black carbon; PM--particle mass.

Finally, PC5 identifies possibly non-ferrous industrial emissions and is correlated mainly with As, and Cu and might be a consequence of pyrite smelt ing emissions from central peninsula Spanish smelters.

F o u r pr incipal componen t s were identified in the coarse fraction. PC1 represents bo th soil (Fe, Mn, Ca and A1) and road traffic emissions (Pb, Zn, BC, OC). W h e n gas concent ra t ions and meteorological condi- t ions are considered in Pr incipal C o m p o n e n t Analysis (results no t shown), these two types of sources may be roughly separated, in road traffic emissions associated with NO2 and soil emissions associated with NH3 concent ra t ions , local wind direct ion from land and low relative humidity. The second Principal Compo- nent is clearly associated with mar ine emissions, as in the fine fraction.

The secondary aerosol fo rmat ion is identified by PC3 and correlates with HNO3, temperature , conti- nenta l air mass origin, low wind speed and lack of precipitat ion. Associated with this c o m p o n e n t are Se, V and Mn, elements character is t ic of combus t ion emissions, tha t may suggest the ma in source respon- sible for the secondary aerosol formation. As observed in the fine fraction, MSA is also correla ted with this component .

PC4 in coarse, as well as PC5 in the fine fraction, possibly identifies non-ferrous industr ial emissions

and is correlated mainly with As and Cu. To assess quant i ta t ively the con t r ibu t ion of each source group to the total aerosol load, Mul t i l inear Regression Analysis (MLRA) was applied to the experimental data, using as dependent variables a tmospher ic concent ra t ions and as independent variables the principal componen t factor scores, calculated by in t roducing a fictitious sample with null concent ra t ions for all variables in the PCA (Thurs ton and Spengler, 1985). M L R A permits to conclude that , on the average, the largest con t r ibu t ion to the aerosol mass in the fine fract ion (see Table 6) is road traffic and combus t ion emissions (25%), sea spray (14%) and secondary pro- duct ion (31%). In the coarse fract ion (Table 7) mar ine con t r ibu t ion is much more significant (88%) than all o ther sources.

The sea spray source group compounds (Na +, K +, Mg 2+, Ca 2÷, C1 ) have origin mainly on mar ine emissions as expected, principally in the coarse fraction. However, in the fine fract ion there is an impor- t an t influence of soil emissions, p robab ly result ing from long range t ransport . Potass ium, in the fine fraction, has a significant con t r ibu t ion tha t results from combus t ion emissions. C1- presents, part icular ly in the fine fraction, a "negat ive" emission for the secondary aerosol fo rmat ion component , which is explained by the volat i l isat ion of the sea salt chloride

Source assessment of particulate air pollutants

Table 6. Multilinear Regression Analysis applied to the absolute factor scores determined by Principal Component Analysis of the fine fraction (dp < 0.95/~m) aerosol constituent concentrations

3317

Const. Traf./Comb. Marine Sec. Aer. Soil N . F . Met. r

PM 24 25 14 31 - l 6 0.77 Na * 25 1 46 6 18 4 0.88 Mg z+ 19 4 72 0 13 - l l 0.95 Ca 2~ 19 30 0 45 9 0.95 K ~ 12 45 4 6 36 - 2 0.82 C1 30 99 - 3 2 40 -31 0.93 SO~ 5 5 70 8 13 0.98 MSA 50 3 - 15 33 1 28 0.70 NH,2 23 1 59 9 10 0.96 NO3 99 7 9 8 - 2 1 0.94 OC 69 7 15 11 - 2 0.97 BC 0 58 13 7 14 7 0.94 Pb 54 16 5 21 5 0.95 Zn 28 5 9 19 41 0.94 Mn 9 -- 1 6 5 69 13 0.8 l Fe --6 24 21 86 --18 0.85

Note. Values are presented as percentage of mass attributed to each source, r multiple correlation coefficient. OC --organic carbon; BC--black carbon; PM particle mass.

Table 7. Multilinear Regression Analysis applied to the absolute factor scores determined by Principal Component Analysis of the coarse fraction (0.95 < dp < 10/~m) aerosol constituent

concentrations

Const. Traf./C, + soil Marine Sec. Aer. N, F. Met. r

PM 9 1 88 3 - 1 0.72 Na + 8 - 2 94 0 0 0.98 Mg 2+ - 2 104 - 2 0 0.99 Ca 2 + 11 17 73 - 2 1 0.94 K + 2 86 12 0 0.96 CI 9 - 3 104 - 11 0 0.97 SO~, - 1 24 79 - 1 0.98 MSA- 42 - 13 - 30 100 0 0.88 NH2 50 - 54 111 - 2 0.93 NO3 28 41 - 3 32 2 0.77 OC 25 79 - 14 12 - 1 0.87 BC 43 97 30 - 8 - 2 0.85 Pb 6 97 - 4 3 - 1 0.92 Zn 108 - 6 4 0 0.87 Mn 17 32 17 34 0 0.65 Fe 70 24 14 2 0.92

Note. Values are presented as percentage of mass attributed to each source, r--mult iple correlation coefficient. OC organic carbon; BC--black carbon; PM--par t ic le mass.

tha t occurs in the p resence of H N O 3 and s e c o n d a r y su lphur ic acid aerosol . Pb , BC, O C and Zn main ly result f rom r o a d traffic emiss ions . M S A is a s soc ia ted wi th s e c o n d a r y fo rma t ion , bu t a large f rac t ion of M S A var iabi l i ty is no t exp la ined by the five C o m p o - nents , sugges t ing tha t a n o t h e r c o m p o n e n t of na tu ra l

s e c o n d a r y ae roso l p r o d u c t i o n was n o t ident i f ied by the P C analys is t echnique .

Source apportionment of maritime aerosol samples

In an a t t e m p t to get m o r e i n f o r m a t i o n a b o u t the sources and p rocesses respons ib le for the ae roso l l oad in the a t m o s p h e r e over the At lan t i c ocean , P C A was app l ied to 52 samples col lec ted w h e n all the four day b a c k w a r d t ra jec tor ies h a d m a r i t i m e origin, i ndepen -

den t ly of the local w ind d i rec t ion (pure plus con- t a m i n a t e d mar i t i me samples , in Tab le 1).

In Table 8 the resul ts for the fine aerosol f rac t ion are p resen ted . The soil c o m p o n e n t o b s e r v e d previously in P C analys is app l ied to all samples , d i sap- pears , s h o w i n g tha t soil inf luence in the fine f rac t ion is ma in ly the result o f con t inen t a l t r anspor t , since even in s amples wi th local w ind b l owi ng f rom land the soil inf luence is n o t visible.

T h e o t h e r 4 P r inc ipa l C o m p o n e n t s were ident i f ied as fol lows. PC1, as in the to ta l P C analysis , identif ies r o a d traffic a n d c o m b u s t i o n emiss ions and is c lear ly co r re l a t ed wi th local w i n d d i r ec t ion f rom SE. T h a t migh t sugges t a s ignif icant inf luence of local road traffic a n d c o m b u s t i o n emiss ions , inc reased du r i ng


Table 8. Principal Componen t pattern applied to the fine fraction aerosol constituents concentrations, gaseous species and meteorological parameters, observed during maritime air mass periods

PC 1 PC2 PC3 PC4 Traffic/Comb. Marine Regional L .R. Trans. Communal .

Na + 0.81 - 0.26 0.74 K + 0 . 8 5 0.81

Mg z + - - 0.76 - 0.26 0.70 Ca 2 + 0.34 0.77 - 0.26 0.79 N H ~ 0.62 0.37 0.44 0.75 H + - - 0.29 0.34 0.21 CI- 0.79 - 0 . 3 3 0.78 NO~- 0 . 8 8 0.78 SO,~- 0.31 0.45 0.50 0.57 AI 0.39 - 0 . 2 9 0.38 Cd - - 0.46 - 0 . 5 6 0.58 Pb 0.83 ~ 0.72 Cu 0.52 0.34 Cr - - 0.05 Fe - - 0.46 - 0 . 2 7 0.33 Mn -- 0.54 0.41 0.52 Ni 0.44 0.40 0.38 V 0.27 0.36 0.60 0.56 Zn 0.35 0.44 0.33 As - 0.76 0.57 Se -0 .31 0.53 0.37 PM 0.73 0.39 -- 0.70 BC 0.76 . . . . . . 0.59 OC 0.93 0.88 MSA - --0.27 0.46 0.58 0.65 NH 3 0.52 0.35 HNO3 0.27 0.70 0.33 0.69 N O 2 0 . 8 9 - 0.81

SO2 0.49 0.49 0.53 TimeSl --~ 0.65 0.43 TimeS2 0.77 - 0.67 TimeS3 .... 0.51 0.31 TimeS4 - 0.27 - 0.75 0.68 TimeS5 - - - 0.25 0.09 TimeS6 - 0.27 - - 0.77 0.67 Avg. WS - 0 . 2 9 - 0 . 6 2 0.56 Avg. DT --0.38 0.54 0.43 0.67 Avg. RH -0 .38 0.24 Solar Radiat. - 0 . 33 0.37 0.65 0.83 Precipitation 0.54 0.35

Eigenvalues 7.75 4.23 5.61 4.37 21.96 % of tot. var. 19.4 10.6 14.0 10.9 54.9

Note. Presented only factor loadings larger than 0.25. Factor loadings greater than or equal to 0.70 in bold. OC- -o rgan ic carbon; BC--b lack carbon; PM--par t i c le mass; TimeSi--per iod of the day with wind direction from sector Si (see Fig. 1); Avg. WS--average wind speed; Avg. DT -average dry temperature; Avg. RH average relative humidity.

w in t e r p e r i o d s a n d s h o w s t h a t a f r ac t ion o f the ob-

s e rved levels in c o m p o u n d s s u c h Pb , BC, V, Ni , a n d

O C h a v e local c o m b u s t i o n or igin .

P C 2 r e p r e s e n t s m a r i n e ae ro so l e m i s s i o n s . I n th is

ana ly s i s C1- is m o r e a s s o c i a t e d wi th th i s c o m p o n e n t

t h a n in to ta l d a t a set ana lys i s . T h i s p r o b a b l y re su l t s

f r o m the less s ign i f i can t ac id ic a t t a c k to the sea sal t

pa r t i c l es wi th the c o n s e q u e n t ch lo r ide vola t i l i sa t ion .

B e c a u s e the soil i n f luence is r e d u c e d the c o r r e l a t i o n

b e t w e e n C a 2 + a n d th i s c o m p o n e n t i n c r e a s e d signifi-

c a n t l y as well as the i m p o r t a n c e o f the c o m p o n e n t to

the to ta l s u s p e n d e d m a s s .

T h e s e c o n d a r y ae ro so l f o r m a t i o n c o m p o n e n t is n o t so s t r o n g l y c o r r e l a t e d wi th H + a n d SO4 z , as it was in

the to ta l d a t a set ana lys i s , s h o w i n g a s m a l l e r c o n t a m i -

n a t i o n o f m a r i t i m e ai r m a s s e s . W h e n a n a l y s e d wi th

i n c l u s i o n o f local m e t e o r o l o g i c a l d a t a (Table 8) th is

c o m p o n e n t s e e m s to be d iv ided in two g r o u p s , one ,

(PC3), well c o r r e l a t e d wi th l a n d w i n d d i r ec t i on f r o m

N E - - t i m e S l - - w i t h h i g h t e m p e r a t u r e s a n d low wind

speeds , w h i c h pos s ib ly h a s local or ig in , a n d a n o t h e r

a s s o c i a t e d wi th s o m e t race e l emen t s , w h i c h is no t

i n f luenced by local d a t a a n d m i g h t be r e s u l t a n t of l ong d i s t a n c e t r a n s p o r t f r o m the N o r t h o f E u r o p e


(PC4). PC analysis of the marine aerosol coarse fraction showed also a reduced influence of Soil originated species, but not so significant as in the fine fraction.

CONCLUSION

Measurements permit to say, as a general conclusion, that average concentrations at the Por- tuguese west coast are higher than values observed in remote oceanic locations, principally when winds are blowing from land and air masses have a continental origin. Concentrat ions of trace compounds associated with anthropogenic emissions are lower in air masses coming directly from the ocean with a marit ime origin, than in continental air masses. However, even in these conditions, the minimum observed levels are higher than results obtained from measurements taken in the middle of the Atlantic Ocean, or at coastal sites in more remote regions.

The study of marit ime air masses with and without local land wind direction consideration (in Table 1: contaminated and pure marit ime air masses; and in Table 8) allowed to conclude that, by comparison with long range transport, local sources are important for road traffic and combustion emissions. Local sources contribute more significantly to the measured levels of Pb, OC, BC and fine nssK +, gaseous species and part of secondary formed aerosols, and less significantly to the levels of fine Ni and V. Otherwise we may conclude that trace elements as Cd, Cr, Mn, Fe and AI, in the fine fraction mainly result from long range transport. These results are in accordance with Semb studies (Semb and Pacyna, 1986) which esti- mated V, Ni and Pb emissions to be the Portuguese most significant contribution to the global European emissions. (The higher values of the Portuguese to European emissions ratio were found in these compounds.)

The observed high concentration values in maritime air are probably a consequence of recirculation effects of European continental air masses through the eastern Atlantic Ocean, reinforced by situations of mesoscale transport associated, for example, to sea and land breezes resulting from low pressure centres formed over the Iberian Peninsula during summer months. A third contribution to the measured high levels ,night be local contaminat ion of marit ime air masses by ships navigating along the coast. The western coast of Portugal is crossed each day by an important number of ships transporting goods and combustible between northern Europe and the Medi- terranean, African and Asian regions.

Principal Component Analyses can reasonably separate and identify the major sources of atmospheric aerosol collected in Arefio. Five source groups were identified for the fine and coarse aerosol fractions, namely, combustion plus road traffic, sea salt spray, secondary aerosol production, soil and possibly non- ferrous metallurgy industries.

In the aerosol fine fraction road traffic and combustion contribute on the average with 25% of the total fine aerosol mass, while sea salt spray and secondary production represent 14% and 31%, respectively, of the mass loading. Sea spray is by far the major con- tr ibutor to the coarse fraction with an average of 88 % of the suspended coarse aerosol mass.

Acknowledgements--The authors wish to thank the JNICT Junta Nacional de Investiga¢fio Cientifica e Tec- nol6gica for their helpful support to this project. This work was also supported by EC project EV5V-CT92-0094: "Back- ground Maritime Contribution to Atmospheric Pollution in Europe".

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Pergamon - Europa · 2009-03-05 · 3310 C.A. PIO et al. approximately 20 km southwest of Aveiro. a small town of ~50,000 inhabitants. The region is characterised by moderate temperatures,