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Atmospheric Environment 80 (2013) 75e84Contents lists avaiAtmospheric Environment
journal homepage: www.elsevier .com/locate/atmosenvMesoscale behavior of 7Be and 210Pb in superficial air along the Gulfof Cadiz (south of Iberian Peninsula)
R.L. Lozano a, M.A. Hernndez-Ceballos b, J.F. Rodrigo c, E.G. San Miguel a, M. Casas-Ruiz c,R. Garca-Tenorio d, J.P. Bolvar 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 Cdiz, SpaindDepartment of Applied Physics II, University of Seville, Spainh 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.: 34 959219793.E-mail address: email@example.com (J.P. Bolvar).
1352-2310/$ e see front matter 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.atmosenv.2013.07.050a 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 m2 y1 and 60 Bq m2 y1 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) 75e8476to 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 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 Earths 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 earths 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 m3), while it usually de-creases by more than one order of magnitude near the tropopause,with levels around 40 mBq m3 (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 Cdiz (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 (371600700 N, 65502700 W) and approximately 3 kmfrom an industrial chemical complex, while Puerto Real is situatedin an industrial area close to Cdiz city (363104900N, 61204500W).
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 Cdiz 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 Cdizprevalences 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 h1) 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 Cdiz during the period 2000e2007.
R.L. Lozano et al. / Atmospheric Environment 80 (2013) 75e84 77and 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 mLof 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
60 El Carmen Puerto Real
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...