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Atmospheric Environment 80 (2013) 75e84

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Atmospheric Environment

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Mesoscale behavior of 7Be and 210Pb in superficial air along the Gulfof Cadiz (south of Iberian Peninsula)

R.L. Lozano a, M.A. Hernández-Ceballos b, J.F. Rodrigo c, E.G. San Miguel a, M. Casas-Ruiz c,R. García-Tenorio d, J.P. Bolívar a,*aDepartment of Applied Physics, University of Huelva, SpainbRadioactivity Environmental Monitoring, European Commission Joint Research Centre, ITU e Institute for Transuranium Elements, Ispra, ItalycDepartment of Applied Physics, University of Cádiz, SpaindDepartment of Applied Physics II, University of Seville, Spain

h i g h l i g h t s

� Mesoscale analysis of 210Pb and 7Be in air concentrations and bulk deposition.� High mesoscale correlation between 210Pb and 7Be in coastal area.� Similar patterns of 7Be and 210Pb in surface air and depositional fluxes.� Different influence of local winds on 210Pb and 7Be concentrations.

a r t i c l e i n f o

Article history:Received 5 March 2013Received in revised form5 July 2013Accepted 24 July 2013

Keywords:7Be210PbMesoscale variationsComplex and coastal areaEnvironmental radioactivityMonitoring

* Corresponding author. Tel.: þ34 959219793.E-mail address: bolivar@uhu.es (J.P. Bolívar).

1352-2310/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.atmosenv.2013.07.050

a b s t r a c t

210Pb and 7Be activity concentrations in surface air and in bulk deposition have been measured fromNovember 2009 to December 2011 along the Gulf of Cadiz (Southwest of Spain). This area presentsmesoscale variations in its meteorological conditions, with influence of air masses with different origins:maritime, either from the Atlantic Ocean or the Mediterranean Sea and continental, from IberianPeninsula and north of Africa, which make possible this region to be suitable to analyse the mesoscalespatial and temporal variations of atmospheric compounds. The objective of this study is to determine ifthere are differences in 210Pb and 7Be activity concentrations in surface air and in bulk deposition at themesoscale level in this complex area of southwestern Iberian Peninsula taking as reference two sites ofthe same geographical area but influenced by different meteorological conditions.

The temporal evolution pattern of PM10 was different for each site (no correlation between both serieswas found), but the PM10 average concentrations were similar for both locations (differences were notfound at 0.05 significance level). On the other hand, the temporal evolution of 7Be and 210Pb activityconcentrations in surface air show a good correlation between both sites, indicating this fact a similarbehaviour of these radionuclides in the area.

Finally, for each location a strong correlation between 210Pb and 7Be depositional fluxes was alsoobserved, showing that wet deposition plays a key role in the deposition fluxes of both radionuclides. Theaverages depositional fluxes for 7Be and 210Pb are 750 Bq m�2 y�1 and 60 Bq m�2 y�1 in both locations,respectively.

This set of results allows to determine that both radionuclides (7Be and 210Pb) present similar atmo-spheric behaviours, although with mesoscale variations in the magnitude of the values along the entiresouthern coast of the Iberian Peninsula.

� 2013 Elsevier Ltd. All rights reserved.

All rights reserved.

1. Introduction

Natural radionuclides from terrestrial and upper atmosphericsources (e.g., 222Rn, 220Rn, 212Pb, 210Pb, 7Be, 10Be, etc.) and radio-nuclides with anthropogenic origins (85Kr, 137Cs, 90Sr, etc.) arewidely used as tracers to examine atmospheric processes relevant

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e8476

to air quality and climate. Therefore, the long-term measurementsof these radionuclides in aerosols are capable of providing usefulinformation on the atmospheric processes (transport, removal andresidence time) of aerosol species (Jordan et al., 2003).

Beryllium-7 (T1/2 ¼ 53.5 d) is produced throughout the uppertroposphere and lower stratosphere as a product of the spallation ofoxygen and nitrogen nuclei by energetic cosmic rays (Lal et al.,1958). Because of the short average life span and long residencetime of approximately one year of stratospheric aerosols (Kurodaet al., 1962), most of the 7Be nuclei produced in the stratospheredo not readily reach the upper troposphere, except during thespring when a seasonal thinning of the tropopause occurs at mid-latitudes, resulting in air exchange between the stratosphere andthe troposphere. In addition, due to its cosmogenic origin the 7Beconcentration increases with altitude from the surface of the Earth,and its flux to the Earth’s surface shows a latitudinal pattern (Laland Peters, 1967) that is independent of the geography at anyparticular latitude (Turerian et al., 1983). Therefore, the standingcrop of 7Be in the atmosphere should be the same over the oceanand the continent.

The main source of 210Pb (half-life: 22 years) is the radioactivedecay of 222Rn (half-live: 3.8 days) emitted to the atmosphere fromthe earth’s crust; the other artificial sources (burning of coal, use ofphosphate fertilizers, cars engage exhaust, fires) in the air havebeen evaluated as negligible by many authors (Hotzl and Winkler,1987; Jaworowski et al., 1980). The vertical profiles of 222Rn in theatmosphere show the presence of 222Rn up to the tropopause,which serves as a barrier to the Rn gas, except during strongconvective updrafts when some of the 222Rn can reach the lowerstratosphere leading to production of 210Pb (Moore et al., 1977).Highest concentrations of 222Rn are most commonly found in thecontinental boundary layer (3e8 Bq m�3), while it usually de-creases by more than one order of magnitude near the tropopause,with levels around 40 mBq m�3 (Moore et al., 1977; Liu et al., 1984;Kritz et al., 1993). Large variations in 222Rn concentrations in sur-face air have been widely reported, depending of the sources of airmass (Church and Sarin, 2008).

However, 210Pb does not necessarily decrease with altitude fromthe surface, being its distribution with the altitude highly variableand it is commonly as high near the top of the troposphere as nearthe surface, even sometimes with a reduction at mid-altitudes dueto rainout/washout, but this is dependent on the presence of landmasses, precipitation, etc. Some authors have found that 210Pbconcentrations tend to decrease with altitude in troposphere,measuring the lowest concentrations close to tropopause at 9 km,while in the lower stratosphere the concentrations are little higher(Kownacka, 2002).

Once 7Be and 210Pb have been produced, they are immediatelyattached to sub-micron-sized aerosol particles (Papastefanou andIoannidou, 1995). Due to the high reactivity of these radionu-clides and their different origins, changes in the 7Be/210Pb activityratio has been used as indicator to discriminate between both thecontinental and local sources of aerosols: low values of the ratio(due to high 210Pb levels) reflect a high continental influence, whilehigh ratios indicate a relative isolation from continental sources,showing a maritime influence. Moreover, the temporal and spatialvariations in this ratio reflect both vertical and horizontal transportin the atmosphere (Baskaran, 2011).

It is usual that the characterization of the 210Pb and 7Be aroundtheworld is performed taking as reference one sampling station thatrepresents the behaviour of both radionuclides in a determinatedarea (Rulik et al., 2009). However, there is a lack in the knowledge ofthe local differences in the 7Be and 210Pb behaviour in small areas,which, due to the different origin of both radionuclides, would in-crease the knowledge about local meteorological conditions.

The Gulf of Cádiz (southwestern Iberian Peninsula) is extendedabout 320 km fromCape Saint Vincent (Portugal) to Gibraltar, and itis enclosed by the southern Iberian and northern Moroccan mar-gins, west of Gibraltar Strait. This area highlights by the confluenceof two completely different meteorological areas: Atlantic andMediterranean, being also determined the meteorological condi-tions by the presence of two main orographic elements: the Gua-dalquivir valley and the Strait of Gibraltar. It is very suitable for themeasurement of 210Pb and 7Be in surface air under the influence ofair masses with different origins, i.e., maritime (either from theAtlantic Ocean or the Mediterranean Sea) and continental (fromNorthern Spain and north of Africa). Therefore, the combination ofthese facts suggests that 7Be and 210Pb could present differentbehaviour in this area, and makes this place an optimal site fordetecting the mesoscale differences in the 7Be and 210Pb behaviour.

Therefore, the aim of this study is to provide a detailed analysisabout the mesoscale variations of 7Be and 210Pb concentrations in acomplex area of southwestern Iberian Peninsula. With this pur-pose, the 210Pb and 7Be activity concentrations in surface aerosolsand in bulk deposition samples have been determined at twosampling stations (El Carmen and Puerto Real) during a period ofabout 2.5 years (November 2009eDecember 2011). The differenceshave been investigated based on the relationship between activityconcentrations in surface air and depositional flux of 7Be and 210Pbin each sampling station; deposition velocities of the aerosols ob-tained through 7Be and 210Pb concentrations in the air surfaceaerosols and the total deposition fluxes, and finally, relationshipbetween the 7Be and 210Pb activity concentrations in surface air anddepositional fluxes with temperature and rainfall.

2. Materials and methods

2.1. Study area and sampling

The activity of 7Be and 210Pb has been determined in the PM10fractions of air surface aerosols at two different locations in thesouth-western Iberian Peninsula (Fig. 1); El Carmen (code “EC”)station (located at Huelva city) and Puerto Real (located at Cadiz)station (code “PR”). El Carmen is an urban monitoring stationlocated a certain distance (200 m) from the traffic emission sourcesin Huelva city (37�1600700 N, 6�5502700 W) and approximately 3 kmfrom an industrial chemical complex, while Puerto Real is situatedin an industrial area close to Cádiz city (36�3104900N, 6�1204500W).

The distance between both sampling sites is 100 km and coversthe entire coastal area of the Atlantic coast of Spain. However, whileHuelva city is located in the surroundings of the valleymouth, Cadizcity is closer to the Gibraltar strait. This different location along theGulf of Cádiz determines that the meteorological conditions (wind,temperature, relative humidity, precipitation) over both stationsare different (Castillo Requena, 1989), and therefore, both stationscould be considered sited in different meteorological area. As anexample, Fig. 1b displays the wind roses representative of thewhole period (2000e2007) in each sampling site, being possible toobserve the large differences between both. While in Huelva citydominances the combination of southwesterlyenortheasterly(Guadalquivir valley axis) and north-westerly flows, in Cádizprevalences the arrival of westerlyeeasterly (Strait of Gibraltaraxis). These differences in the wind regime derive in differences interm of temperature, relative humidity as well as in the amount ofrainfall.

Measurements of aerosol and deposition samples were regis-tered in both monitoring sites. The aerosol samples (PM10,AMAD < 10 mm) were collected simultaneously in both monitoringstations with Andersen PM10 high-volume samplers (flow of68 m3 h�1) mounted with quartz microfiber filters QF Scheicher

Fig. 1. a) Definition of the study area indicating the location and the environment of the two reference monitoring stations in the southwestern Iberian Peninsula and b) wind rosescorresponding to Huelva and Cádiz during the period 2000e2007.

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e84 77

and Schuell (25.4 cm � 20.3 cm). The sampling frequency was onefilter for every two weeks with a collection time of 48 h, and asampling period from November 2009 to December 2011.

The total deposition samples (also called “bulk deposition”)were collected by using four drums with a capacity of 200 L and atotal surface area of 4120 � 30 cm2 (1030 cm2 each) from January2010 to December 2011. Collectors were located at 15 m above theground in both monitoring sites.

2.2. Processing of the samples

2.2.1. Aerosol filtersEach atmospheric filter was weighed before and after the sam-

pling, and the mass of the aerosol collected by the filter was calcu-lated by subtracting the blank filter mass from the total massdetermined after collection. Next, the filter was dissolved by wetdigestion with strong acids (6 mL of 65% HNO3, 2 mL of 37% HCl and15 mL of 40% HF), evaporated to dryness, and then, 10 mL of HClO4was added, and the solution was again evaporated to dryness. Thedigestion process was completed with another acid attack using10 mL of HNO3, which was evaporated to dryness again. Then,10 mL

of 2% HNO3 was added to the solution and then divided into threealiquots, which were weighed with a precision of 1 mg. One of thisaliquot (5 mL) was measured by gamma-ray spectrometry in a wellGe detector for determining 210Pb and 7Be. This aliquot was quan-titatively transferred into a 5-mL gamma spectrometry vial. No los-ses of 7Be and 210Pb occurred during the evaporation and transfer ofthe solution into the counting vial (Lozano et al., 2011) (Fig. 2).

2.2.2. Bulk depositionAt the end of the collection period (one month), the collectors

were emptied into a container, and their walls were rinsed twicewith 50 mL of 8 M HNO3. The addition of acid prevents theadsorption of particle reactive radionuclides onto the polyethylenedrum surfaces. The obtained bulk sample is evaporated to dryness.Then, the residue is dissolved with a mixture of strong acids (6 mLof 65% HNO3, 2 mL of 37% HCl, 15 mL of 40% HF) and finally re-dissolved in dilute 5% HNO3 (5 mL) before it is quantitativelytransferred into a 5-mL gamma spectrometry vial. If there is notwet deposition during period sampling, the collector is cleanedtwice by adding diluted nitric acid (10%), and then the same pre-vious methodology is applied that with rainfall.

Feb-10 Apr-10 Jun-10 Oct-10 Jan-11 Mar-11 May-11 Sep-11 Oct-110

10

20

30

40

50

60 El Carmen Puerto Real

PM10

(ug

m-3)

Fig. 3. The temporal evolution of the PM10 concentrations collected at the El Carmenand Puerto Real monitoring sites from November 2009 to December 2011.

Fig. 2. Pre-treatment and the radiochemical procedure applied to the aerosol filters.

Table 1Statistical values in air for PM10, 7Be and 210Pb at the El Carmen and Puerto Real sitesduring the period from November 2009eDecember 2011.

Station El Carmen Puerto Real

PM10

(mg m�3)

7Be(mBq m�3)

210Pb(mBq m�3)

PM10

(mg m�3)

7Be(mBq m�3)

210Pb(mBq m�3)

Average 30.2 5.1 0.53 25.8 5.2 0.49St. Dev. 1.8 0.4 0.07 1.5 0.4 0.06Maximum 49.8 10.7 1.39 49.0 11.4 1.28Minimum 10.7 2.1 0.08 13.3 2.8 0.03P10 17.4 2.8 0.15 17.8 3.2 0.13P50 30.3 4.9 0.47 23.3 5.0 0.48P90 44.9 7.2 1.17 37.7 7.7 1.06

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e8478

2.3. 7Be and 210Pb gamma spectrometry measurement

The 7Be and 210Pb measurements were performed by thedetection of the gamma emissions of energies 477.7 keV (intensity10.3%) and 46.5 keV (intensity 4.05%), respectively. The detectorused was a well Ge detector (Canberra) with a full-width at half-maximum (FWHM) of 1.33 keV at 122 keV (57Co) and 2.04 keV at1332 keV (60Co) and a peak/Compton ratio of 56.2/1. The detectorwas coupled to a multichannel analyser and shielded with a 10-cmlead shield. To avoid interferences from the X-rays from the Pb ofthe shield, a 2-mm-thick layer of Cu lines the shield. The full energypeak efficiency calibration for the peaks of interest was conductedusing a solid RGU-1 Standard Reference Material (IAEA, 1987) witha known amount of 238U (4940 � 30 Bq kg�1), which is in secularequilibrium with its daughter products. Absorption correctionswere made for the measurements of 210Pb or 7Be following themethod described in Appleby et al. (1992).

The quality assurance of radioanalytical measurements wasregularly ensured through participation in intercomparison exer-cises organized by the International Atomic Energy Agency (IAEA-MEL), as well as the periodic measurement of certified referencematerials that we have in our laboratory (IAEA-326 black soil; NIST-1646a estuarine sediment, etc.).

3. Results and discussion

This section describes the PM10, 7Be and 210Pb behaviour in thesouth-western Iberian Peninsula based on the data obtained fromthe aerosol (Section 3.1) and bulk deposition samples (Section 3.2)from the period of November 2009 to December 2011 in the ElCarmen (EC) and Puerto Real (PR) stations.

3.1. Surface air aerosols

The statistical results (average, maximum and minimum, andstandard deviation of the mean) obtained from both monitoringstations for PM10, 7Be and 210Pb are shown in Table 1.

3.1.1. Aerosol mass concentration (PM10)The temporal evolution of the PM10 concentration (Fig. 3) varied

across both sites but with different patterns, indicating this fact thatPM10 is mainly regulated by the local meteorological conditions, i.e.,

the wind regime and the types of the surrounding soils of moni-toring stations. The PM10 concentration was found to be in therange of 10e50 mg m�3 at El Carmen, while in Puerto Real, the in-terval was smaller (14e49 mg m�3), showing here a more uniformtemporal evolution than in EC. At both sites, the PM10 concentra-tions did not exceed the objective for the 24 h daily value of50 mg m�3 established by the European Union Air Quality Stan-dards, or the mean annual value of 40 mg m�3.

During the sampling period, the average aerosol mass concen-tration (PM10) registered at El Carmen station was 30.2 � 1.8mg m�3, which was slightly higher than that obtained one at PuertoReal (25.8 � 1.5 mg m�3) (Table 1). These differences in the PM10values could be related with the differences in the industrial ac-tivities adjoining these sites and with the different wind regimeobserved over both sampling areas. The uncertainties of the meansare indicated as the standard deviation of the average ¼ Sx/N

1/2,where N is the number of measurements and the significance levelof the tests are given at a 95% confidence level. Thus, the mean ofthe PM10 concentrations was not significantly different betweenthe two sampling sites at the confidence level of 95%. These valueswere comparable to those obtained in previous studies in the samearea (Lozano et al., 2011), and in other coastal areas of similarlatitude (Chung and Chen,1998; Dueñas et al., 2011). The 10, 50 and90 percentiles have also been obtained for both data series(Table 1). P50 is close to the average value, indicating this fact agood symmetry in the frequency distributions for both locations.Moreover, PM10 in both stations follows normal distributions.

A weak correlation (R2 ¼ 0.11) between PM10 concentrations inboth sampling stations have been found. This fact indicates thatPM10 concentrations depend on local meteorological conditions.The linear regression model gave:

PM10PR¼ ð0:46� 0:21Þ$PM10EC

þ ð17� 6Þ

0

2

4

6

8

10

12

14 El Carmen Puerto Real

7 Be (m

Bq m

)

a)

Feb-10 Apr-10 Jun-10 Oct-10 Jan-11 Mar-11 May-11 Sep-11 Oct-11

R2 = 0.64

Feb-10 Apr-10 Jun-10 Oct-10 Jan-11 Mar-11 May-11 Sep-11 Oct-110,0

0,4

0,8

1,2

1,6

2,0

2,4 El Carmen Puerto Real

210 Pb

(mBq

m)

R2 = 0.72

b)

Fig. 5. Temporal evolution of a) 7Be and b) 210Pb activity concentrations at the ElCarmen and Puerto Real monitoring stations from November 2009 to December 2011.

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e84 79

The parameters of the regression are not significantly differentfrom zero at 95% confidence level. However, if each year isconsidered separately, in 2010, the relationship of PM10 betweenboth stations is very low (R2 ¼ 0.001), while a stronger relationshipis found for PM10 in 2011 (R2 ¼ 0.23). This finding could be justifiedby considering the great differences in rainfall between both sta-tions during 2010, and the high correlation with rainfall during2011 (Fig. 4). Fig. 4 shows the monthly total rainfall and the meantemperature values at the meteorological stations of Moguer (3 kmaway from El Carmen) and Jerez de la Frontera (10 km away fromPuerto Real). This variation between stations is an example of in-fluence of local meteorological conditions on the PM10 concentra-tions in the sampling sites.

3.1.2. 7Be and 210Pb activity concentrationsAs can be observed from Table 1, the 7Be activity concentrations

determined in both of the sampling sites are similar. The mean 7Beactivity concentration was 5.1 � 0.4 mBq m�3 at El Carmen and5.2 � 0.4 mBq m�3 at Puerto Real, presenting the following mini-mum and maximum values at El Carmen (2.1 and 10.7 mBq m�3)and Puerto Real (0.04 and 11.4 mBq m�3). Statistical tests for vari-ances (Fisher’s tests) and averages (Student’s t test) did not showsignificant differences at a 0.05 significance level between bothsampling stations. In addition, and as it could be expected, similarpercentiles (P10, P50 and P90) have been obtained for both dataseries (Table 1).

On the other hand, the mean activity concentrations of 210Pbwere 0.53 � 0.07 mBq m�3 at El Carmen, and 0.49 � 0.06 mBq m�3

at Puerto Real, which do not show significant differences. Themaximum (1.28 and 1.39 mBq m�3) and minimum (0.08 and0.03 mBq m�3) values were quite similar in both stations (Table 1).The P10, P50 and P90 percentiles are similar for both samplingstations (Table 1). Statistical tests (0.05 significant level) show thatthe variance and the average for both stations do not present anysignificant differences. The statistical parameters obtained arecomparable with results published previously for coastal sites(Dueñas et al., 2009; Baskaran, 2011).

In contrast to PM10, these similar statistical values were alsoconditioned by the analogous temporal evolution of the 210Pb and7Be activity concentrations observed between both monitoringsites (see Fig. 5).

The similarities in the temporal variability of these radionu-clides in both sampling sites are confirmed by the goodness of thelinear fittings obtained between both stations:

7BePR ¼ ð0:74� 0:11Þ7BeEC þ ð1:5� 0:6Þ�R2 ¼ 0:64

�

0

50

100

150

200

250

Rainfall-El Carmen Rainfall-Puerto Real

Jan 10 Jun 10 Dec 10 Jun 11

Temp-El Carmen Temp- Puerto Real

5

10

15

20

25

30

Nov 11

Rai

nfal

l (m

m)

Temperature (ºC

)

Fig. 4. Monthly total rainfall and mean temperature values at the El Carmen andPuerto Real sites during the sampling period (January 2010 to November 2011).

210PbPR ¼ ð0:74� 0:07Þ210PbEC þ ð0:12� 0:05Þ�R2 ¼ 0:72

�

The 7Be concentrations ranged from 2 to 8 mBq m�3, and themaximum concentrations were observed during the late spring andsummer periods (Fig. 5a), which reached up to 12 mBq m�3. Thetemporal evolution of the 7Be can be influenced by different phe-nomena such as changes in the atmospheric production rates dueto the solar activity, strong stratosphere-troposphere exchanges, oradvection of 7Be along the latitude (Aldahan et al., 2001). In thisway, this seasonal evolution is in agreement with the air exchangebetween the stratosphere and the troposphere by the thinning ofthe tropopause at mid-latitudes during the spring.

Since most of the 210Pb is originated from the 222Rn emanatedfrom terrestrial surface, its concentration in air can be expected tobemore influenced than 7Be by the local meteorological conditions,such as temperature, atmospheric pressure, precipitation or soilmoisture, that affect the emanation rate of 222Rn from ground.However, with a small difference, the determination coefficient for210Pb is higher than for 7Be, as can be observed in Fig. 5. This resultis not expected. Analysing the temporal evolutions of 7Be in bothstations, the obtained R2 value could be associated with the evo-lution registered at the beginning and at the end of the period,coinciding with the largest differences in temperature and rainfall.In fact, without these values, the R2 for 7Be is equal to 0.89. Fig. 5bshows that the highest 210Pb concentrations were obtained fromMay to October, which can be attributed to the lower amount ofscavenging (only by dry deposition) that occurs during the dryperiod, which is coincident with this period in this geographicalarea. It is also necessary to highlight the low values found during2010 in the wintertime (DecembereFebruary), which might be dueto the high levels of rainfall registered during these months(approximately 700 mm).

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e8480

These statistical values for the 210Pb and 7Be datasets in bothmonitoring sites show that the gulf of Cádiz presents values of bothradionuclides spread in a similar range that could be associatedwith the influence of similar synoptic conditions. These results arein agreement with the proximity between both monitoring sta-tions. However, as we have mentioned above the surface windregime is different in each site. With the aim to go deeper in theinfluence of surface winds on 210Pb and 7Be concentrations, Fig. 6displays the correlation of the data with wind direction. As refer-enced of wind data, the wind direction average during each sam-pling period was taken to carry out the analysis.

The results firstly showed the difference in surface winds be-tween them, confirming the wind differences between both. PuertoReal registered a more variable arrival of surface flows than at ElCarmen site. Whilst at Puerto Real was observed a dominance ofsoutheasterly winds, with some episodes with arrival of northerly,northwesterly and southwesterly flows, at El Carmen the surfacedynamic presented a main advection along the westeeast axisduring the periods, with more occurrence of westerly flows.

This difference between surface winds was reflected on 210Pb and7Be concentrations. Regarding 7Be activity, at Puerto Real wasobserved awider range of surface winds in favour to high 7Be values,

Fig. 6. Wind roses of 7Be and 210Pb activity concentrations obtained

being associated the highest values with the arrival of easterly flows.However, at El Carmen the highest values of 7Bewere observed underthe advection of westerly winds. On the other hand, the highest 210Pbvalues at Puerto Real were registered with the arrival of northern-northeastern winds (continental pathway), registering less influencethe advection of the other wind components over concentrations. AtEl Carmen site was similar the impact of westerly and easterly windson 210Pb concentrations. These results indicated similar influence ofmaritime and continental flows. The relevance that maritime flowshave in the 210Pb concentrations is actually being studied. Overall,these results reaffirmthedifferencesbetweenbothsites regarding theinfluence that local winds have on 210Pb and 7Be concentrations.

As it was previously mentioned 7Be/210Pb activity ratio in sur-face air has been used to track the origin of the air mass for eachsite. The main statistical parameters for 7Be/210Pb in each of thesampling sites are shown in Table 2. The standard deviation and theaverage for both stations do not present significant differences at95% of confidence significant level. Both average activity ratios arealso comparable to the ratios obtained in previous studies, such asin Málaga, Spain (4.5e25.7; Dueñas et al., 2009) or in Belgrado,Republic of Serbia (1.7e12.7; Todorovic et al., 2005), located at thesame latitude and in coastal areas.

during the sampling periods at Puerto Real and El Carmen sites.

Table 2Statistical values in air for 7Be/210Pb at the El Carmen and Puerto Real sites during theperiod November 2009eDecember 2011.

Station El Carmen Puerto Real

7Be/210Pb 7Be/210Pb

Average 13.5 21.2St. Dev. 1.7 5.5Maximum 58.5 147.7Minimum 2.3 3.1P10 4.9 5.9P50 11.5 11.6P90 21.7 28.1

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e84 81

Fig. 7a displays the temporal evolution of 7Be/210Pb activity ra-tios in aerosols collected in the El Carmen and Puerto Real sitesduring the sampling period. The determination coefficient in thecorrelation in this activity ratio between sampling station is R2 ¼0.67 (Fig. 7b).

Fig. 7a shows seasonal 7Be/210Pb mean activity ratios evolution.It can be observed that both stations have the same evolutionpattern. In general, the maximum values of 7Be/210Pb activity ratioswere registered during high temperature periods. This findingcould be explained considering that during the summer time, thelargest stratospheric injections of 7Be are produced due to the highturbulence that exists in the upper troposphere. In contrast, the7Be/210Pb minima were observed during the winter months.Assuming a similar scavenging for both, the minimum must havebeen produced from the low injection of 7Be from the stratosphere

Fig. 7. a) Seasonal 7Be/210Pb mean activity ratios evolution and b) Correlation between 7BeNovember 2009 to December 2011.

into the upper troposphere during the months with a lower solarradiation (wintertime) (Rogers and Nielson, 1991). During thesummer time the convection mixes 210Pb upwards and 7Be down-wards, leading to a peak in the 7Be/210Pb activity ratio because bythis process, 7Be tends to increase, while 210Pb tends to be reduced(�Simon et al., 2009).

3.2. Bulk deposition

3.2.1. 7Be and 210Pb fluxesThe atmospheric flux of 7Be and 210Pb were calculated based on

the bulk deposition of these radionuclides through the followingexpression:

F ¼ ASt

�Bqm�2 month�1

�

, where A is the activity (Bq) measured in the collected sample, S isthe surface area (m2) of the collector and t is the duration ofdeployment (months in this study).

The collection interval, the depositional fluxes of 7Be and 210Pbfor the monthly bulk deposition (wet þ dry), and the activity ratio7Be/210Pb between January 2010 and November 2011 are displayedin Table 3 for the two studied locations.

The rainfall and the temperature play a key role in the wet anddry deposition processes. During the sampling period the temper-ature ranged from 12 to 27 �C (Fig. 4). From this figure, it can beobserved that although the patterns of the temperature and therainfall were similar at both stations, the daily average temperature

/210Pb activity ratios in aerosols collected in the El Carmen and Puerto Real sites from

Table 4Determination coefficients obtained from linear fits between 210Pb and 7Be fluxesand mean temperature and total rainfall in each sampling period November 2009eDecember 2011.

Station Puerto Real El Carmen

7Be 210Pb 7Be 210Pb

Precipitation 0.1767 0.0032 0.0001 0.0249Temperature 0.1945 0.0138 0.0036 0.0189

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e8482

was always 1e2 �C higher in the areas surrounding the Puerto Realstation than in the El Carmen station. However, the rainfall wasslightly higher in the El Carmen station. A clear, wet period fromOctober to April with very little rainfall in the remaining months isidentified in this figure. It is also worth noting the large differencesin the rainfall between the two sites at the beginning of the sam-pling period (JanuaryeFebruary 2010, Fig. 4). This fact couldgenerate big differences in the radionuclide fluxes between bothlocations.

With the aim to determine the correlation between 210Pb and 7Befluxes with temperature and rainfall linear fit were made using thevalues of fluxes, mean temperature and total rainfall for each sam-pling period. Table 4 shows the corresponding determination co-efficients (R2) of thementioned linear regression. Theobtainedvaluesindicated that therewasnot a significant correlationneither between210Pb and 7Be fluxes and rainfall or temperature. However, for thetemperature a very high correlation between both stations is ob-tained: TEC (�C)¼ (0.5� 0.6)þ (0.897� 0.003) TPR (�C), R2¼ 0.976. Inthe case of rainfall, as it is expected, a smaller correlation is obtained:REC (mm) ¼ (�1 �10) þ (1.22 � 0.14) RPR (mm), R2 ¼ 0.777.

The monthly depositional flux of 7Be are very similar for bothmeasuring stations, ranging at El Carmen station (Table 3) from 1.1 to186 Bq m�2 month�1 (average of 63 � 12 Bq m�2 month�1), while arange of 8.4e204 Bq m�2 month�1 (average of 66 � 11 Bq m�2

month�1)was found for thePuertoReal station. In the caseof 210Pb, therange was from 0.23 to 14.9 Bq m�2 month�1 (average of 5.8 � 0.9Bq m�2 month�1) at El Carmen and from 1.08 to 9.9 Bq m�2 month�1

(average of 4.1�0.6 Bqm�2month�1) at Puerto Real.Minimumfluxeswere found during the dry months when no rainfall was registered.

Furthermore, the strong correlation between the monthlydepositional fluxes of 7Be and 210Pb in El Carmen (R2 ¼ 0.76) and inPuerto Real (R2 ¼ 0.81) sites clearly suggests a similar depositionalprocess for both radionuclides that is independent of each samplingstation.

The mean depositional flux for 7Be is similar for both stations;740 � 160 and 760 � 120 Bq m�2 y�1 in El Carmen and Puerto Real,respectively. These values are lower than those found in wet cli-mates as St. Petersburg (1468 Bq m�2 y�1) (Baskaran and

Table 3The sampling time, number of days, bulk depositional fluxes of 7Be and 210Pb, and activityDecember 2011.

Date in Date end Days 7Be flux (Bq m�2 month�1)

EC PR

03/01/10 01/02/10 28 98 � 3 105 � 401/02/10 01/03/10 30 11.1 � 0.401/03/10 01/04/10 30 174 � 5 129 � 401/04/10 01/05/10 30 186 � 6 72 � 301/05/10 01/06/10 30 39.1 � 1.8 23.3 � 0.801/06/10 01/07/10 30 30.7 � 0.9 24.1 � 0.901/07/10 01/08/10 30 20.4 � 0.6 8.4 � 0.401/08/10 01/09/10 30 36.7 � 1.1 16.8 � 0.601/09/10 01/10/10 30 35.5 � 1.3 80 � 301/10/10 02/11/10 31 e 83 � 302/11/10 01/12/10 29 1.15 � 0.21 204 � 701/12/10 04/01/11 33 38.0 � 1.3 74 � 304/01/11 01/02/11 27 80 � 3 53.2 � 1.801/02/11 01/03/11 30 40 � 3 50.9 � 1.801/03/11 31/03/11 30 7.1 � 0.3 59.7 � 2.031/03/11 02/05/11 32 149 � 4 64.3 � 2.331/05/11 02/06/11 34 e 96 � 302/06/11 05/07/11 33 89 � 3 20.9 � 0.805/07/11 02/08/11 27 26.4 � 0.9 91 � 302/08/11 01/09/11 29 119 � 401/09/11 04/10/11 33 34.6 � 1.1 8.4 � 0.304/10/11 09/11/11 35 62.4 � 2.0 85 � 309/11/11 06/12/11 27 45.5 � 1.4 31.2 � 1.1

Swarzenski, 2007), but the precipitation in these locations issignificantly higher than in the studied stations (dry climate).However, data presented in this study are quite comparable withother similar nearby areas (Dueñas et al., 2001) (amount of rainfallis half that in Huelva or Cadiz), or in an analogous climatology, suchas Tessaloniki (Greece), where themeasured fluxes ranged between483 and 841 Bq m�2 y�1 (Papastefanou and Ioannidou, 1991).Several studies have shown that 7Be fluxes are latitudinallydependent, but it is the rainfall the main factor regulating the fluxof natural radionuclides over the earth surface (Kulan et al., 2006).

The annual mean depositional flux of 210Pb was 70 � 12 and48� 7 Bqm�2 y�1 at El Carmen and Puerto Real, respectively, whichare also very similar to those published for other sites in Spain:34 Bqm�2 y�1 in Cabo de Gata (Almeria, SE Spain), 85 Bqm�2 y�1 inSan Felipe (East Spain), and 61 Bq m�2 y�1 in Port Vendres at NESpain (García-Orellana et al., 2006). Conversely, the values found inthis study were lower than those found for the other latitudes withhigher amounts of rainfall, comprised between 30 and 40 Northlatitude (Baskaran, 2011), and for other coastal systems, such asGalveston, Texas, where the annual mean depositional flux of 210Pbbased on a 3-year atmospheric depositional flux was approximately171 Bq m�2 y�1 (Baskaran et al., 1993).

On the other hand, 7Be/210Pb activity ratios in bulk depositionranged from 4.5 to 23.3 in El Carmen (mean of 10.1 �1.2) and from7.0 to 30.6 in Puerto Real (mean of 15.7 � 1.6) (Table 3). These av-erages show significant differences at 95% confidence level. Thesedifferences could be an indicative that a fraction of the air massesreaching PR are significantly different from those arriving at EC site,

ratio 7Be/210Pb at the El Carmen (EC) and Puerto Real (PR) sites from January 2010 to

210Pb flux (Bq m�2 month�1) 7Be/210Pb

EC PR EC PR

8.1 � 0.4 5.55 � 0.24 12.0 � 0.7 18.9 � 1.00.84 � 0.11 13.2 � 1.710.9 � 0.4 6.07 � 0.23 16.0 � 0.7 21.3 � 1.18.0 � 0.4 3.73 � 0.18 23.3 � 1.3 19.4 � 1.13.3 � 0.3 1.26 � 0.10 11.8 � 1.2 18.4 � 1.6

2.74 � 0.15 1.74 � 0.11 11.2 � 0.7 13.9 � 1.03.80 � 0.17 1.19 � 0.10 5.4 � 0.3 7.1 � 0.74.40 � 0.20 2.33 � 0.13 8.3 � 0.5 7.2 � 0.54.9 � 0.3 8.5 � 0.3 7.3 � 0.5 9.4 � 0.5

e 5.21 � 0.22 e 15.9 � 0.90.23 � 0.15 9.0 � 0.4 4.5 � 3.0 22.7 � 1.25.17 � 0.21 3.15 � 0.16 7.3�0.4 23.3 � 1.410.7 � 0.5 3.50 � 0.17 7.5 � 0.4 15.2 � 0.92.4 � 0.8 1.66 � 0.10 17 � 5 30.6 � 2.2

1.47 � 0.16 2.98 � 0.13 4.8 � 0.6 20.0 � 1.110.3 � 0.3 4.56 � 0.19 14.5 � 0.6 14.1 � 0.8e 9.9 � 0.4 e 9.7 � 0.514.9 � 0.5 2.99 � 0.16 6.0 � 0.3 7.0 � 0.54.94 � 0.23 5.61 � 0.3 5.3 � 0.3 16.2 � 0.913.3 � 0.5 9.0 � 0.44.2 � 0.3 1.08 � 0.12 8.3 � 0.6 7.8 � 0.93.3 � 0.2 4.5 � 0.2 16.4 � 1.3 19.0 � 1.23.0 � 0.2 2.3 � 0.1 16.8 � 1.2 13.7 � 0.9

a) b)

0,00,20,40,60,81,01,21,41,61,82,02,2

7Be 210Pb - Puerto Real

Dep

ositi

on v

eloc

ity (c

m s

-1)

0,00,20,40,60,81,01,21,41,61,82,02,2

7Be 210Pb - El Carmen

Dep

ositi

on v

eloc

ity (c

m s

-1)

Jan 10 Jun 10 Dec 10 Jun 11 Nov 11 Jan 10 Jun 10 Dec 10 Jun 11 Nov 11

Fig. 8. Evolution of the total deposition velocity for 7Be and 210Pb at the a) El Carmen and b) Puerto Real sites between January 2010 and November 2011.

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e84 83

as it can be expected since PR is close to the Gibraltar Strait(interaction zone between Atlantic Ocean and the MediterraneanSea).

It is interesting to note that although there is not a linear cor-relation between the 7Be/210Pb ratios measured at both stations(slope¼ 0.45� 0.27; intercept¼ 11�3, R2¼ 0.13), these ratios tendto decrease in both sites during the summermonths, which has alsobeen observed in other studies (McNeary and Baskaran, 2003;Hirose et al., 2004; Dueñas et al., 2005).

3.3. Deposition velocity of aerosols

Deposition rates are usually characterised by the parameter‘deposition velocity’. In fact, the deposition velocity (Vd) is a usefultool for describing the transfer of radionuclides from the atmo-sphere to the Earth’s surface. The average total deposition velocityfor a given radionuclide (here 7Be, and 210Pb) is calculated using thefollowing relationship:

Vd ¼ FAair

where Vd is the deposition velocity (m s�1), F is the total depositionflux (Bq m�2 s�1) and Aair is the mean activity concentration in theground level air (Bq m�3).

There are several advantages of using 7Be and 210Pb to deter-mine the total deposition velocities: 7Be and 210Pb activity con-centrations can be easily determined; the production rates of 7Beand 210Pb at any given site remain constant over long periods oftime; and the size distributions of 7Be and 210Pb in aerosols are verysimilar to those of other particulate contaminants of interest and,therefore, can be used to determine the fluxes of these contami-nants into the Earth’s surface from a knowledge of the depositionvelocities of these nuclides and the concentration of these con-taminants in the air (McNeary and Baskaran, 2003; Dueñas et al.,2004).

The temporal evolution of the deposition velocity for 7Be and210Pb is shown in Fig. 8 for both stations; the values obtained for210Pb were slightly lower than those obtained for 7Be. The resultsfor the 7Be deposition velocity present a similar mean in bothsampling sites; average deposition velocity for 7Be was 0.52 �0.10 cm s�1 and 0.46 � 0.12 cm s�1 in Puerto Real and El Carmen,respectively. Meanwhile, for 210Pb the average deposition velocitywas also similar in both sites; 0.28 � 0.05 cm s�1 and 0.33 � 0.12cm s�1 in Puerto Real and El Carmen, respectively. Statistical testsfor the variance and for the average of the deposition velocity at a0.05 significance level indicated that there were no significantdifferences in the deposition velocities of each radionuclide

between the two stations. However, in both stations, depositionvelocity for 7Be was slightly higher than the 210Pb one, factdemonstrated by the corresponding statistical tests at 95% of sig-nificance level. The fact that deposition velocities obtained for eachradionuclide (7Be or 210Pb) are quite similar in both stations ratifiesthe hypothesis that both 7Be and 210Pb travel by attaching to par-ticles of similar size, and for that they will be affected by similardeposition processes (Winkler et al., 1998).

The correlation between the deposition velocity of 7Be versus210Pb in both stations has been analyzed, registering very low deter-mination coefficients; R2¼ 0.10 at El Carmenwith 7Be¼ (0.41�0.23)210Pb þ (0.32 � 0.14), and R2 ¼ 0.04 at Puerto Real with 7Be ¼(0.3 � 0.6) 210Pb þ (0.46� 0.15).

Because atmospheric aerosols are removed mainly by drydeposition in the summer period (June, July, August and September,when there is no rain or rainfall is minimal), a lower depositionvelocity is expected thanduring the rest of the year (rainy season). Inthis sense, the obtained average summer deposition velocities were0.16 � 0.06 cm s�1 at Puerto Real for 7Be and 0.15 � 0.04 cm s�1 for210Pb, which are much less than those obtained in the rainy season(0.99 � 0.15 cm s�1 for 7Be and 0.31 � 0.08 cm s�1 for 210Pb). For ElCarmen station, similar results are obtained for the dry seasondepositionvelocity: 0.24�0.05 cms�1 for 7Be and0.15�0.05 cms�1

using 210Pb, whereas in rainy season is obtained 1.0� 0.3 cm s�1 for7Be and 0.8� 0.3 cm s�1 for 210Pb. These results indicate that, as it isexpected, the atmospheric cleaning is more intensive during therainy period.

4. Summary and conclusions

The ranges of PM10 mass concentrations are similar in bothstations. Nevertheless, slightly lower values were registered inPuerto real (mean of 30.2 � 1.8 mg m�3 at El Carmen and25.8 � 1.5 mg m�3 at Puerto Real). The differences in the industrialactivities adjoining to these sites and also to the wind regime couldbe responsible of this variations. 7Be and 210Pb activity concentra-tions varied between 2.1 mBqm�3 and 11.4 mBqm�3 and 0.03 mBqm�3 and 1.48 mBq m�3, respectively. A strong correlation betweenthe activity concentrations of both radionuclides (7Be versus 210Pb)at each sampling station was found.

The average monthly depositional flux of 7Be and 210Pb (fromJanuary 2010 to November 2011) ranged between 1.1 Bq m�2

month�1 and 204 Bq m�2 month�1 and 0.23 Bq m�2 month�1 and14.9 Bq m�2 month�1 respectively, being this differences associatedto the amountofmonthly precipitation and thedifferentwind regimeover each sampling area. The average annual bulk depositional fluxesof 7Be (740 � 160 and 760 � 120 Bq m�2 y�1 in El Carmen and inPuerto Real, respectively) and 210Pb (70�12 Bqm�2 y�1 in El Carmen

R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e8484

and 48 � 7 Bq m�2 y�1 in Puerto Real) are similar to the values thathavebeenpublished for areaswith the same latitude and climatology.The seasonal depositionalfluxes aremainly controlled by the amountof precipitation, althoughseasonal factors alsoaffect the 7Beand 210Pbconcentrations.

The depositional fluxes of 7Be and 210Pb are well correlated inboth of the studied locations (Cadiz and Huelva); thus, it is clearthat both nuclides cannot be used as two independent atmosphericair mass tracers. This high correlation has also been found in othercontinental and coastal areas from the Mediterranean Sea to otherregions throughout the world.

The deposition velocities of the aerosols for each radionuclide(7Be and 210Pb) were similar for both of the studied sites, withaverages of 0.49 � 0.11 cm s�1 (7Be), 0.30 � 0.12 cm s�1 (210Pb).During the dry period (June to October), the deposition velocitieswere between 2 and 4 times lower than those for the rainy season.

By considering all of the results of this study and taking intoaccount the different meteorological conditions, we can concludethat both radionuclides (7Be and 210Pb) present similar atmosphericbehaviours along the entire southern coast of the Iberian Peninsula.Therefore, this study can be taken as reference to redistribute thepoints of the national sampling network in order to increase theknowledge of the spatial and temporal evolution of 7Be and 210Pb inthe Iberian Peninsula.

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