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Atmospheric Environment 45 (2011) 1015e1024

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Atmospheric Environment

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Gross alpha, gross beta activities and gamma emitting radionuclides compositionof rainwater samples and deposition to ground

C. Dueñas a,*, M.C. Fernández a, E. Gordo a, S. Cañete a, M. Pérez b

aDepartment of Applied Physics I, Faculty of Science, University of Málaga, 29071 Málaga, SpainbDepartment of Radiology and Health Physics, OPHT., and OTL Faculty of Medicine, University of Málaga, 29071 Málaga, Spain

a r t i c l e i n f o

Article history:Received 29 July 2010Received in revised form24 October 2010Accepted 25 October 2010

Keywords:RainwaterRadionuclidesDepositional fluxGross alphaGross beta7Be210PbMediterranean region

* Corresponding author.E-mail address: mcduenas@uma.es (C. Dueñas).

1352-2310/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.atmosenv.2010.10.045

a b s t r a c t

The radiometric composition of bulk deposition samples, collected monthly in a 5 year period (1 January2005 until 31 December 2009) at a site located 30 m a.s.l in Málaga (4�280 800W; 36� 4304000N), are analysedin this paper. Measurement of gross alpha, gross beta, artificial and natural radionuclide activityconcentrations were carried out in 60 bulk deposition samples. We analysed the time series of gross alpha,gross beta 7Be, 210Pb and 40K. The specific activities of gross alpha and gross beta measured in bulkdeposition material are in the range from 0.012e0.32 and 0.045e1.81 Bq l�1 and theirs mean values are:0.11 and 0.59 Bq l�1 respectively. The activity values of 7Be and 210Pb are in the range from 0.65e8.3 and0.05e1.32 Bq l�1 with mean values of 2.5 and 0.41 Bq l�1 respectively. The highest specific activities of 40Kin bulk deposition material were recorded in connection with high altitude Saharan dust intrusion. Thetime variations of the different radionuclide concentrations have been discussed in relation with variousmeteorological factors and themean values have been compared to those published in recent literature forother sites located at different latitudes. To study the deposition, monthly deposition data from a funnelcollector were compared from 2005 to 2009.The monthly range in deposition fluxes for gross alpha variedwidely (0.40e11 Bqm�2month�1) and the average annual deposition is 21 Bqm�2 y�1. Themonthlyfluxesfor gross beta varied (1.3e33.8 Bqm�2month�1) and the average annual deposition is approximately120 Bqm�2 y�1. The total annual deposition fluxes of 210Pb varied between 64.9 and 160.8 Bqm�2 y�1 withamean of 120 Bqm�2 y�1. The annual 7Be depositional flux varied between 432 and 1204 Bqm�2 y�1 witha mean of 676 Bqm�2 y�1. Observed seasonal variations of deposition data are explained in terms ofdifferent environmental features. The atmospheric deposition fluxes of 7Be and 210Pb were moderatelywell correlated with rainfall (r2 of 0.72 and 0.76 respectively) and well correlated one with the other(r2 of 0.79).

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1. Introduction

The deposition of radionuclides on the ground represents animportant factor in environmental radioactivity monitoring and animportant input parameter in radioecological models (Balkanskiet al., 1993; Koch et al., 1996). To predict the long-term radiolog-ical consequences of an accidental deposition of radionuclides tothe ground, it is a prerequisite to know the environmental long-term behaviour of these radionuclides and a relatively largenumber of values is required for statistically meaningful conclu-sions. It is well known that the main part of radioactivity depositionof natural as well as artificial radionuclides from the global nuclearweapons fallout takes place through wet precipitation and dry

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depositions (Dibb, 1989; Todd et al., 1989; Baskaran, 1995; Baskaranet al., 1993; Du et al., 2008). Precipitation scavenging is the removalof particulate matter and gases from the atmosphere throughvarious types of precipitation. The process involves the incorpora-tion of radioactivity into the rain water and the subsequent depo-sition of the material onto the surface of the Earth. The depositionrates which determine the residence time of the material in theatmosphere can affect the downwind surface and airborneconcentration patterns. The removal of radioactive particles andgases from the atmosphere by precipitation scavenging depends oncomplicated microphysical and microchemical processes which areconditional functions both within and outside the natural cloud-bearing layers.

Berylium-7 (half-life 53.29 d) is one of the radionuclidesproduced by spallation reactions of cosmic rays with light atmo-spheric nuclei, such as carbon, nitrogen and oxygen. 7Be is a nuclideas tracer and chronometer in aquatic and atmospheric systems

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e10241016

(Rehfeld and Heimann, 1995). Approximately 70% of 7Be isproduced in the stratosphere, with the remaining 30% produced inthe troposphere. Most of the 7Be that is produced in the strato-sphere does not reach the troposphere except during spring whenthe seasonal thinning of the tropopause takes place at midlatitudes,resulting in air exchange between the stratosphere and the tropo-sphere (Feely et al., 1989; Kim et al., 1998; Graustein and Turekian,1996). 7Be rapidly associates with submicron-sized aerosol parti-cles. Gravitational settling and precipitation processes largelyaccomplish transfer to the surface of the earth. 7Be has becomerecognized as a potentially powerful tool when studying thedescription of environmental processes such as precipitation,wash-out (precipitation scavenging), atmospheric particle deposi-tion and deposition patterns of airborne contaminants(Papastefanou and Ioannidou, 1991; Caillet et al., 2001).

The main source of 210Pb in the atmosphere is 222Rn emanationfrom the ground. 210Pb returns to the earth as dry fallout or iswashed out in rain. As indicated by Winkler and Rosner (2000),whether dry or wet deposition is dominating removal processdepends on the climate. 222Rn daughter nuclides are mainly posi-tive ions, which become associated with polarized air or water oraerosol particles. 210Pb atoms become rapidly fixed to submicron-size aerosols. Since 7Be and 210Pb have different sources ofproduction, a relatively high correlation between their concentra-tions or depositions will provide useful information regarding theirremoval processes from the atmosphere as well informationwhether or not they can be used as independent atmospherictracers (Todd et al., 1989).

Although the large database of deposition fluxes 7Be and 210Pbare available for various regions in the world, the data fromtemperate zones with dry climate at the European Continent,especially from Mediterranean coast are scare ,compared withother regions (Beks et al., 1998; Rehfeld and Heimann,1995). Tatedaet al. (2003) and Ugur et al. (2010) pointed out that careful attentionis needed when making flux estimations in coastal areas dueterrestrial perturbations on the 210Po and 210Pb balances in coastalwaters. It is very important to accurately estimate the 210Pb fluxnear coastal site to obtain reliable sedimentation rates in theregion. The present study involves the measurements of long-termradionuclide concentrations in rainwater and deposition fluxes tothe ground surface. Samples were analysed for activity concentra-tions of natural as well as artificial radionuclides. Here we presenttemporal variations in the deposition of atmospheric radionuclides

Fig. 1. The map of sa

in the monitoring station at Malaga (Mediterranean Sea Coast) overa 5-year period (2005e2009).

The objectives of this study, therefore, are: a) to carry out a studyby collection monthly bulk deposition samples to know thetemporal variations of gross alpha, gross beta and gamma radio-nuclides in rainwater in combination with meteorological datawould help us to elucidate the causes of variations of theirconcentrations. b) to explain the highest specific activities of 40K inbulk deposition material in connection with high altitude Saharandust intrusion. c) to evaluate the deposition of ground of grossalpha, gross beta and the radionuclides 7Be and 210Pb and discusson meteorological factors controlling the deposition of theseradionuclides.

2. Material and methods

2.1. Sampling site and collection samples

The sampling site is one of the environmental radioactivitymonitoring network stations operated by the Spanish NuclearSecurity Council (CSN), under a cooperative agreement with theUniversity of Málaga through the Environmental RadioactivityResearch Group. The sampling site is situated 14 m above theground, on the flat roof of the SCAI building, University of Malaga,see, Fig. 1. The site, where the measurements were carried out, is inthe north-west of the city (4�280 800W; 36� 4304000N), 5 km awayfrom the coastline. The mean of yearly precipitation is 550 mm.

Samples were collected monthly using a collector that it isslightly tilted stainless steel tray 1 m2 in area and polyethylenevessels of 50 or 25 litre capacities for rainwater sample reservoir.Since the rain collector was always exposed to the atmospherecontinuously, the sum of dry and wet fallout (equal to bulk depo-sition) was collected. At the end of each month, if there was notrain, the collector was rinsed with acidulated water until a samplevolume of at least 6.8 l was achieved. Then the liquid samples wereacidified with hydrochloric acid to a pH lower than 1 to minimizesorption of radionuclides to the container wall. The surfacewas alsocleaned with distilled water to avoid contamination between eachcollection period. The rinses were combined with the rainwatersample (Ioannidou and Papastefanou, 2006; Kim et al., 2000).Samples were not filtered prior to evaporation and the measure-ments include the dust load or solids in the rainwater.

mpling location.

Table 1Statistical summary of the radiometric data collected from January 2005 tillDecember 2009.

Gross a(Bq l�1)

Gross b(Bq l�1)

7Be(Bq l�1)

40K(Bq l�1)

210Pb(Bq l�1)

N of cases 60 60 60 27 60Arit. mean 1.10E�01 5.90E�01 2.50Eþ00 2.45E�01 4.06E�01Geo. mean 8.10E�02 4.10E�01 2.10Eþ00 2.02E�01 3.30E�01Maximum 3.20E�01 1.80Eþ00 8.30Eþ00 8.40E�01 1.32Eþ00Minimum 1.20E�02 4.50E�02 6.50E�01 7.50E�02 5.00E�02Std. deviation 7.70E�02 4.80E�01 1.65Eþ00 1.72E�01 2.70E�01Std error 1.00E�02 6.20E�02 2.13E�01 3.30E�02 3.50E�02Variation coefficient 72% 82% 66% 70% 65%Skewness (GI) 2.8 3.4 4.6 3.9 4.5

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e1024 1017

2.2. Analytical and counting procedures

Monthly precipitation and dry fallout samples usually containvery low levels of radionuclides. At the Environmental Radioac-tivity Laboratory the radiometric methods for the monitoring ofradionuclides in the bulk depositional samples are based ongamma-spectrometry and proportional counting.

To determine the monthly gross beta activity in the liquidsamples an appropriate volume of the original sample (300 ml) wasevaporated to dryness. The residue was transferred quantitativelyto a pre-weighted ribbed stainless-steel planchet (5 cm of diam-eter) and dried.

The analytical procedure used to determine the monthly grossalpha activity level was that of coprecipitation of 0.5 l of samplewater. This method consists of the selective precipitation ofradium isotopes followed by a coprecipitation of the actinoids(Suárez et al., 2000). Once they were precipitated, they wereseparated by filtration. The samples were kept in a desiccator for5 days after sample preparation and were then counted in orderto ensure the complete decay of 222Rn daughter. The gross alphaactivity was measured by a solid ZnS (Ag) scintillation counter.The gross beta activity was measured with a gas flow propor-tional counter of the low-background multiple detector type withfour sample detectors (CANBERRA HT-1000). All the calculationswere carried out using the appropriate density thicknesscorrections for efficiencies to convert the alpha and betameasurements to specific activities with estimates of errorat �1.96s. Since the levels of radioactivity found in environ-mental samples are low, long counting times, of approximately1000 min per sample were necessary. Detailed description ofthe analytical procedure calibration process has been given(Dueñas et al., 1997).

To determine the monthly depositional flux of 7Be and 210Pbfrom the funnel collector, a volume of 6 l was evaporated at 80 �Cdown to approximately 1 l and then transported to a Marinelligeometry container. This large sample size was required because ofthe low activity of the samples. The Marinelli containers werecounted using an intrinsic germanium coaxial detector made beCANBERRAwith an relative efficiency about 30% to the efficiency ofa 300�300 NaI(Tl) at 25 cm distance. Typical resolution (full-width athalf-maximum) is about 1.3 keV at 46 keV and 2 keV at 1.33 MeV.Careful calibration was carried out using water standardsample containing known amount of radioisotopes such as 152Eu,133Ba, 60Co, and 137Cs uniformly distributed and sealed in Marinellicontainers, the same design as those used for the rainwatersamples resolution previously described (Dueñas et al., 1999).Samples were counted for 25e48 h to achieve a higher precision.Owing to the low activity level of most samples, for quality controlinstrumental and reagent blanks were measured frequently.Furthermore, for quality control for gamma-spectrometric analysiswe participated in international and national intercomparisonanalyses.

The standard meteorological data: rainfall, duration of rainfall,number of dry days and number of wet days were obtained by theMeteorological Institute located 500 m away from the samplingsite.

Back-trajectories at 12 UTC were calculated with the HybridSingle-Particle Lagrangian Integrated Trajectory (HYSPLIT) 4.0dispersion model (Draxler and Rolph, 2003, http://www.arl.noaa.gov/ss/models/hysplit,htlm). Five day back-trajectories at sixdifferent altitudes (300, 500, 1000, 1500, 3000, 5000 m a.s.l.) wereobtained on some days of the studied events .In addition, 0e72 hforecast of dust loading in the atmosphere and deposition wereobtained with the Dust Regional Atmospheric Model (DREAM)(http://www.bsc.es/projects/earthscience/DREAM/index.psp).

3. Results and discussion

3.1. Statistical analyse and uncertainties of measurements

Table 1 summarises the main statistical variables calculated forthe gross alpha and gross beta activities as well as for the measuredgamma emitting radionuclides (7Be, 210Pb and 40K) over the wholesampling period: 1 January 2005 until 31 December 2009. Allactivities are given in Bq l�1. The measurements were performedonce the short-lived radon daughter had decayed. The highestconcentration was of 8.3 Bq l�1 obtained for 7Be while the lowestmeasured concentration was in the order of 50mBq l�1, obtainedfor 210Pb. The artificial radionuclides investigated were below theminimum detectable activity (MDA).

The measuring uncertainties were very variable depending onthe nuclide studied. On the one hand, measured concentrationof 7Be were associated with the lowest uncertainty, in the order of8%. On the other hand, the 40K concentrations were associated withthe largest uncertainties, in the order of 14%. The mean measure-ment uncertainties for the gross alpha and gross beta activitieswere calculated to be (see Table 1) approximately 9 and 11%.

Due to the value of skewness (GI), gross alpha, the gross betaactivities and specific activities of 7Be, 40K and 210Pb in rainwatershould fit approximately to log normal distribution. The geometricmean was used in further analysis and comparisons as the maincharacterization factor for gross alpha, gross beta and specificactivities of 7Be, 40K and 210Pb.

3.2. Temporal variations of gross alpha and gross beta activitiesof rainwater samples

A total of 60 monthly bulk deposition samples corresponding toa different number of events were collected from January 2005 toDecember 2009. To give an illustration of the data, Fig. 2 shows thetime series of themonthly gross-alpha and beta specific activities insamples. The specific activities of gross alpha and gross betameasured in bulk deposition material are in the range (0.012e0.32)and (0.045e1.81) Bq l�1 with their mean values of 0.11 and0.59 Bq l�1 respectively. To give an illustration of the data, Fig. 2shows high activities of gross alpha and gross beta in May, June,July and August. The minima gross alpha and beta activities areregistered in winter months while the maximum ones are funda-mentally registered in spring-summer months. The difference inrainfall between wet and dry months leads to a marked contrast inrainfall samples. The specific concentrations of radionuclides areexpected to be higher during drier months as the build-up of theseradionuclides in the air due to lower removal by precipitation willresult in higher specific concentrations.

A strong linear correlation (r¼ 0.85) was found between themonthly measured gross alpha and gross beta activities. This result

Fig. 2. Monthly variations of gross alpha and gross beta activities in rainwater during 2005e2009.

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e10241018

indicates that the main source of alpha and beta emitters in rain-water is the same. The atmospheric radioactivity is known to bedominated by the naturally occurring short-lived particulate decayproducts of gaseous radon and in view of the 5 day decay periodallowed for rainwater samples before counting, the shortest-livedradon descendants would have decayed to negligible levels. Thismeans that only 210Po would contribute significantly to themeasured gross-alpha activity while 210Pb, and to less extent 210Bi

Fig. 3. Monthly specific activities of 7Be and

(half-life¼ 5.01 days), would contribute to the gross-beta activity.Nonetheless, 210Po concentrations are much lower than that of itsancestor, 210Pb. The ratio between the geometric means calculatedfor alpha and beta activities was close to 0.19 (see Table 1). Values ofthe ratio 210Po/210Pb measured at various locations around theworld (Chamberlain, 1991; Kim et al., 2008; Ugur et al., 2010)resembles the average ratio Aa/Ab of the rainfall samples collectedin Málaga. This leads us to asses that 210Po constitutes the main

210Pb in rainwater during 2005e2009.

Table 2Annual minimum, maximum and sum values for monthly amounts of rainfall,maximum and minimum values for rainfall duration and the sum of annual numberof wet days (nw).

Year Rainfall amount (mm) Sum Rainfall duration (min) nw

Maximum Minimum Maximum Minimum

2005 84 0.8 239.6 3363 110 542006 160.3 0.5 476.1 2300 20 582007 126.7 0.1 351 1670 10 662008 96.5 3.4 313.6 1270 310 702009 188.5 0.1 435.2 3680 10 59

Table 3Linear correlation studies between the specific activities of gross alpha, gross betaand the studied radionuclides with some parameters.

Gross-alpha(Bq l�1)

Gross-beta(Bq l�1)

7Be(Bq l�1)

40K(Bq l�1)

210Pb(Bq l�1)

The amount of rainfall(mm)

�0.55 �0.54 �0.17 �0.06 �0.36

Rainfall duration (min) �0.62 �0.62 �0.24 �0.13 �0.42Number of dry days 0.69 0.68 0.15 0.12 0.42Number of wet days �0.68 �0.67 �0.16 �0.13 �0.40

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e1024 1019

source of alpha-activity. The ratio between the geometric meanscalculated for gross beta and 210Pb in rainwater was closed to 0.80(see Table 1). Therefore approximately 80% of beta activity isattributable to 210Pb.

3.3. Variability of specific activities of gamma radionuclidesin rainwater samples

The radionuclides present in all samples are: 7Be and 210Pb.Fig. 3 displays the specific activities of 7Be and 210Pb during themeasurement period. The specific activities of 7Be exhibit theirmaximum values in the months of summer and spring. The highervalues of 7Be may be due to a low amount of rains in the summer(dry period) and the rapid exchange of aerosols between strato-sphere and troposphere by contraction of tropopause in the springseason. The highest value of specific activity of 7Be occurs in May(2009) and the lowest occurs in December (2009). The specificactivity of 210Pb shows minimum values in winter and autumn andmaximum values in summer and spring. The highest value ofspecific activity of 210Pb occurs in July (2006) and the lowest occursin December (2005).

Table 2 displays the annual minimum and maximum values ofrainfall, the annual minimum and maximum values of rainfallduration, the sum of monthly amounts of rainfall and the sum ofannual number of wet days for the measurement period. Theminimum annual rainfall value was 239.6 mm (2005) and themaximum value was 476.1 mm (2006). The total amount of rainfallduring the studied period was 1815.5 mm corresponding toa number of 307wet days. The annual amount of precipitation from2005 to 2009 was lower than the average annual amount ofprecipitation in Málaga, which has been 550 mm, averaged for 5decades (Ortega and Sanchez, 1976). The climate in our samplingsite is temperate, with contrasting wet (approximately Octo-bereApril) and dry (approximately MayeSeptember) seasons.Although the timing of the seasonal transitions varies from year to

Fig. 4. Monthly precipitation data observed in Málaga during 2005e2009.

year, on average approximately 96% of the annual rainfall occursbetween October and April (inclusive), see Fig. 4. In Fig. 4 the boxand whisker diagrams of the amount of rainfall through the fiveyears are represented. The vertical box encloses the middle 50%.The median is the horizontal line inside the box and the crossrepresents the mean value. Vertical lines, called whiskers extendfrom each end of the box. Values that fall beyond the whiskers areplotted as individual points. Far outside points (outliers) aredistinguished by a special character (A point with aþ through it).Outliers are point more than three interquartile ranges below thelower quartile or above the upper quartile. There are variousoutliers in January, April, October, November and December. Pre-vailing wind directions at this station are from the NW, generallybringing dry air, and from SE, bringing maritime, humid air.

Taking into account the local features of precipitation in Málaga,with heavy rain events followed by long dry periods, four differentparameters have been considered: rainfall amount, rainfall dura-tion, number of dry days and number of wet days.

Table 3 shows the correlation coefficient between specificactivities and those parameters. All specific activity data sets shownegative correlations with the number of wet days, the rainfallduration and the amount of rainfall. A positive correlation hasbeen found with the number of dry days. The coefficients rangebetween �0.06 and 0.69 indicating relatively weak relationshipbetween the variables. The weak relationship in this study suggeststhat radionuclide activities at our site might be controlled by theinteractions of complex processes, such as source and scavengingintensity. The highest correlation coefficients have been foundbetween gross alpha and beta activities and the number of dry andwet days. Based on the available data and the low dependenciesfound between the different variables, no predictive model couldbe built.

The linear correlation between 7Be specific activity and rainfallis poor (r¼�0.17). However, other investigators reported signifi-cant correlations between 7Be specific activity and the amount ofprecipitation (Olsen et al., 1985). Canuel et al. (1990) suggested thatthe specific activity of 7Be in rainfall may be higher during the driermonths and periods characterized by short- duration precipitationevents. A poor correlation has also been reported by Brown et al.

Fig. 5. Monthly variations of activities of 40K in rainwater during 2005e2009.

Table 4Correlation analysis of the measurement of activities (Gross alpha, gross beta, 7Be,210Pb, 40K) in bulk samples.

Gross alpha Gross Beta 7Be 40K 210Pb

Gross alpha 1 0.85 0.46 0.50 0.65Gross Beta 1 0.57 0.44 0.707Be 1 0.11 0.7540K 1 0.22210Pb 1

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e10241020

(1989), Todd et al. (1989) and Benitez-Nelson and Buessler (1999),who suggested that the dilution is not the only process thatcontrols the 7Be specific activity in rainwater. With reference to210Pb, significant correlation between specific activity of 210Pb andthe amount of rainfall reported for places such Oak Ridge-Tennesse(Olsen et al., 1985) and Pacific Northwest (Nevissi, 1985).However,similar observations as in our sampling site have been reported inareas where large portions of precipitation are derived from heavyrain events, e.g., Galveston-Texas (Baskaran et al., 1993), ChesapeakBay (Kim et al., 2000), Izmir (Ugur et al., 2010).

3.4. 40K in rainwater samples

According to Hernandez et al. (2005) and Karlsson et al. (2008)the concentrations of 40K and 137Cs have been previously associatedwith the arrival of coarse re-suspended material (PM10, particulatematter with a diameter below 10 mm) from the African continent.The artificial radionuclide 137Cs was below theminimumdetectableactivity (MDA) during the measurement period while specificactivity of 40K show up when dust intrusion arrives in Málaga,Fig. 5. The specific activity of 40K varied between 0.075 Bq l�1 inFebruary (2006) and 0.84 Bq l�1 in October (2008) with an averageof 0.245 Bq l�l .The highest values occur in July (2005), June (2006),July (2007), October (2008) and July (2009) coinciding with eventsof African dust intrusions in Málaga. High specific activity of 40K isdue to its presence in terrestrial crustal materials that are sus-pended during wind storms in North Africa. 3D atmospheric back-trajectories confirmed the African origin of the air masses duringthe dust intrusion and located the most probable aerosol sourcearea within the Southern Algeria- North-Eastern Sahara region.Fig. 6 shows the back-trajectories and map of atmospheric dustloads during a typical example of this type of events whichoccurred in October 2008. The back-trajectories showed that theseair masses mostly crossed over Morocco, North-Eastern Sahara,Algeria and Libya. 210Pb and 7Be activities in rainfall have been notobserved to increase in connectionwith the long-range transport ofaerosols from Africa, see Table 4. This table displays a Pearsoncorrelation analysis performed to gross alpha, gross beta, 210Pb, 7Beand 40K data measured in the bulk deposition (collected monthlyfrom January 2005 to December 2009). The strongest correlation,0.85, was observed between the gross alpha and beta activities. 40Kactivities correlated with gross alpha and beta, while 210Pb activi-ties correlated well with 7Be and with gross beta and alpha.

Fig. 6. Back-trajectories (top row) and DREAM model results obtained for some days w

However, this is currently under investigation and further analysisis required to explain the behaviour of these two nuclides.

3.5. Deposition to ground and annual depositional fluxes

Table 5 summarises the main statistical variables calculated forgross alpha, gross beta, 7Be and 210Pb atmospheric deposition fluxesover the whole sampling period: 1 January 2005 until 31 December2009. Due to value of the skewness (GI), the deposition alpha, thedeposition beta flux and 7Be and 210Pb depositions fluxes should fitapproximately to log normal distributions. The measuring uncer-tainties were variable depending on the nuclide studied. On the onehand, beta depositions were associated with the lowest uncer-tainty, in the order of 9%. On the other hand, the 7Be depositionswere associated with the largest uncertainties, in the order of 16%.The mean measurement uncertainties for the gross alpha and 210Pbdepositions were calculated to be (see Table 5) approximately 14%.The mean uncertainty for gross beta deposition was 10%.

The monthly data of gross alpha, gross beta, 7Be and 210Pbdeposited during the exposure time (depositional flux), expressedin Bqm�2, are reported in Tables 6a and 6b. The sample type withthe number of rain events for each period (given in parenthesis)and the rainfall amount can also be found .In this table ninecollection periods, all of which are during the summer months,corresponding to dry deposition only, can be seen during summermonths. The term “dry deposition” refers to periods when precip-itation is not occurring.

The monthly fluxes varied widely for gross alpha(0.40e11 Bqm�2month�1) and the average annual deposition is21 Bqm�2 y�1. The annual average of gross alpha is comparablewith the findings in literature for 210Po (Tateda et al., 2003; Tatedaand Iwao, 2008; Ugur et al., 2010). Themonthly fluxes for gross beta

ithin a sampling week (2008-09-08-2008-09-15) when a dust intrusion occurred.

Table 5Statistical summary of the deposition data.

Deposition alpha(Bqm�2month�1)

Deposition beta(Bqm�2month�1)

7Be deposition(Bqm�2month�1)

210Pb deposition(Bqm�2month�1)

N of cases 60 60 60 60Arit. mean 1.78Eþ00 9.48Eþ00 7.30Eþ01 1.01Eþ01Geo. mean 1.30Eþ00 7.54Eþ00 4.05Eþ01 6.39Eþ00Maximum 1.10Eþ01 3.38Eþ01 5.19Eþ02 5.28Eþ01Minimum 3.97E�01 1.35Eþ00 4.02Eþ00 1.17Eþ00Std. deviation 1.95Eþ00 7.01Eþ00 9.35Eþ01 1.11Eþ01Std. error 2.52E�01 9.05E�01 1.21Eþ01 1.44Eþ00Variation coefficient 1.10Eþ02 7.39Eþ01 1.28Eþ02 1.10Eþ02Skewness (GI) 1.00Eþ01 5.46Eþ00 8.71Eþ00 7.22Eþ00

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e1024 1021

varied (1.3e33.8 Bqm�2month�1) and the average annual depo-sition is approximately 110 Bqm�2 y�1.The monthly fluxes for 7Be(4e519 Bqm�2month�1) and the average annual deposition is676 Bq m�2 y�1 .This value is a little bigger than 605 Bqm�2 y�1

derived from Brost et al. (1991) of a global model of 7Be depositionover land .It should be noted that the value by Brost et al. is derivedfrom part of themodel (36�N) for which there are few experimentaldata mainly for the Mediterranean region. The monthly fluxesvaried widely for 210Pb (1.2e52.8 Bqm�2month�1) and the averageannual deposition is 120 Bqm�2 y�1. The worldwide average 210Pbdeposition is 73e110 Bqm�2 y�1 (Beks et al., 1998). According toUgur et al. (2010), the 210Pb atmospheric deposition fluxes 40�N inthe Mediterranean varied between 81e120 Bqm�2 y�1. The annualbulk depositional flux of 210Pb can be compared to other stationssuch as Galveston e Texas (172 Bqm�2 y�1) over 3 years (Baskaranet al., 1993); Portsmouth-Massachusetts (158 Bqm�2 y�1 over 2

Table 6aMonthly bulk depositions of gross alpha, gross beta, 7Be, 210Pb (Bqm�2) over years 2005

Collection period Sample type rain events Rainfall (mm) Gross alp

Jan/05 Bulk (3) 2.30Eþ00 5.00E�01Feb/05 Bulk (9) 8.40Eþ01 1.10Eþ00Mar/05 Bulk (10) 6.72Eþ01 3.00Eþ00Apr/05 Bulk (1) 8.90Eþ00 6.00E�01May/05 Bulk (3)) 8.00E�01 8.00E�01June/05 Bulk (1) 0 1.30Eþ00Jul/05 Dry 0 6.00E�01Aug/05 Bulk (1) 8.00E�01 8.00E�01Sep/05 Bulk (2) 8.00E�01 1.00Eþ00Oct/05 Bulk (9) 2.40Eþ01 9.00E�01Nov/05 Bulk (9) 4.57Eþ01 1.40Eþ00Dec/05 Bulk (6) 5.10Eþ00 5.00E�01Jan/06 Bulk (9) 6.43Eþ01 1.30Eþ00Feb/06 Bulk (7) 2.57Eþ01 1.00Eþ00Mar/06 Bulk (5) 8.66Eþ01 7.20Eþ00Apr/06 Bulk (4) 2.39Eþ01 4.20Eþ00May/06 Bulk (4) 1.39Eþ01 2.20Eþ00Jun/06 Bulk (2) 1.00Eþ00 1.90Eþ00Jul/06 Bulk (2) 5.00E�01 1.20Eþ00Aug/06 Bulk (1) 2.90Eþ00 8.00E�01Sep/06 Bulk (2) 1.82Eþ01 1.10Eþ00Oct/06 Bulk (5) 3.00Eþ01 6.00E�01Nov/06 Bulk (10) 1.60Eþ02 7.00E�01Dec/06 Bulk (7) 4.88Eþ01 3.70Eþ00Jan/07 Bulk (5) 2.11Eþ01 1.60Eþ00Feb/07 Bulk (8) 2.91Eþ01 2.10Eþ00Mar/07 Bulk (3) 5.30Eþ00 1.50Eþ00Apr/07 Bulk(13) 1.27Eþ02 7.00E�01May/07 Bulk (8) 2.22Eþ01 9.00E�01Jun/07 Dry 0 1.20Eþ00Jul/07 Dry 0 1.50Eþ00Aug/07 Bulk (1) 1.00E�01 1.90Eþ00Sep/07 Bulk (7) 3.62Eþ01 3.90Eþ00Oct/07 Bulk (6) 4.06Eþ01 2.10Eþ00Nov/07 Bulk (5) 1.81Eþ01 9.00E�01Dec/07 Bulk (10) 5.16Eþ01 3.90Eþ00

years (Benítez-Nelson and Buesseler, 1999); Geneva-Switzerland(150 Bqm�2 y�1 over 1 year, Caillet et al., 2001).

Both the maximum flux of 7Be and gross beta occurred in April2007 and maximum flux of gross alpha and 210Pb occurred inOctober 2008 and in December 2009 respectively. The minimumflux of gross alpha and gross beta occurred in December 2009 andOctober 2006 respectively. The minimum fluxes of 7Be and 210Pboccurred in June 2005 and August 2008 respectively. The fluxesof 7Be and 210Pb are changed in the same tendency of variousmonths. These results suggest seasonal character of deposition flux.Fig. 7 displays seasonal fluxes of gross alpha, gross beta, 7Be and210Pb. The fluxes show a marked seasonal variation with highervalues in winter and autumn months and lower values in springand summer .The sampling area has hot and dry summers due to itsMediterranean characteristics. Both fluxes are correlated (r¼ 0.89),Fig. 8 suggesting that their removal behaviour from the atmosphere

e2006 and 2007.

ha (Bqm�2) Gross beta (Bqm�2) 7Be (Bqm�2) 210Pb (Bqm�2)

3.30Eþ00 1.10Eþ01 2.20Eþ006.20Eþ00 9.20Eþ01 5.90Eþ009.00Eþ00 7.20Eþ01 2.02Eþ015.40Eþ00 2.90Eþ01 6.00Eþ008.70Eþ00 3.30Eþ01 6.80Eþ009.40Eþ00 3.40Eþ01 5.00Eþ007.60Eþ00 4.00Eþ00 1.70Eþ007.40Eþ00 1.90Eþ01 2.20Eþ003.00Eþ00 1.30Eþ01 1.60Eþ008.20Eþ00 3.60Eþ01 8.40Eþ001.08Eþ01 7.30Eþ01 3.20Eþ002.20Eþ00 1.60Eþ01 1.70Eþ003.40Eþ00 9.70Eþ01 3.20Eþ001.50Eþ00 6.40Eþ01 1.50Eþ001.92Eþ01 3.03Eþ02 1.73Eþ011.43Eþ01 9.80Eþ01 1.86Eþ011.25Eþ01 6.00Eþ01 6.80Eþ009.30Eþ00 3.20Eþ01 5.70Eþ007.20Eþ00 3.30Eþ01 6.60Eþ003.50Eþ00 4.00Eþ00 2.50Eþ009.80Eþ00 5.50Eþ01 1.10Eþ011.40Eþ00 4.10Eþ01 7.50Eþ002.04Eþ01 3.05Eþ02 3.68Eþ011.11Eþ01 5.70Eþ01 1.66Eþ014.20Eþ00 4.10Eþ01 8.40Eþ001.08Eþ01 8.60Eþ01 1.23Eþ017.10Eþ00 3.20Eþ01 9.40Eþ003.38Eþ01 5.20Eþ02 5.07Eþ016.00Eþ00 6.40Eþ01 8.70Eþ009.90Eþ00 3.50Eþ01 4.40Eþ005.50Eþ00 1.10Eþ01 3.80Eþ009.70Eþ00 1.40Eþ01 3.90Eþ002.42Eþ01 5.30Eþ01 1.96Eþ011.31Eþ01 1.09Eþ02 8.70Eþ006.00Eþ00 3.80Eþ01 4.60Eþ002.71Eþ01 2.01Eþ02 2.63Eþ01

Table 6bMonthly bulk depositions of gross alpha, gross beta, 7Be, 210Pb (Bqm�2) over years 2008e2009.

Collection period Sample type rain events Rainfall (mm) Gross alpha (Bqm�2) Gross beta (Bqm�2) 7Be (Bqm�2) 210Pb (Bqm�2)

Jan/08 Bulk (6) 2.06Eþ01 1.40Eþ00 8.90Eþ00 3.15Eþ01 7.40Eþ00Feb/08 Bulk (9) 3.38Eþ01 3.80Eþ00 2.21Eþ01 1.08Eþ02 1.76Eþ01Mar/08 Bulk (5) 1.90Eþ01 7.00E�01 4.20Eþ00 4.30Eþ01 9.70Eþ00Apr/08 Bulk (8) 2.30Eþ01 1.40Eþ00 5.10Eþ00 4.20Eþ01 4.20Eþ00May/08 Bulk (7) 3.40Eþ00 1.20Eþ00 8.50Eþ00 3.60Eþ01 3.90Eþ00Jun/08 Dry 0 1.30Eþ00 9.00Eþ00 1.00Eþ01 1.90Eþ00Jul/08 Dry 0 1.20Eþ00 5.50Eþ00 7.00Eþ00 1.60Eþ00Aug/08 Dry 0 1.30Eþ00 5.80Eþ00 4.90Eþ00 1.20Eþ00Sep/08 Bulk (5) 5.20Eþ01 2.00Eþ00 1.07Eþ01 1.38Eþ02 1.20Eþ01Oct/08 Bulk (12) 9.65Eþ01 1.10Eþ01 3.02Eþ01 1.64Eþ02 2.90Eþ01Nov/08 Bulk (11) 4.33Eþ01 1.10Eþ00 5.80Eþ00 4.20Eþ01 9.00Eþ00Dec/08 Bulk (7) 2.20Eþ01 4.00E�01 4.30Eþ00 1.40Eþ01 3.10Eþ00Jan/09 Bulk (10) 2.37Eþ01 1.70Eþ00 6.10Eþ00 4.10Eþ01 5.50Eþ00Feb/09 Bulk (8) 9.11Eþ01 5.00E�01 1.44Eþ01 1.83Eþ02 2.46Eþ01Mar/09 Bulk (7) 5.76Eþ01 9.10Eþ00 2.14Eþ01 2.09Eþ02 2.57Eþ01Apr/09 Bulk (6) 2.20Eþ01 7.00E�01 2.40Eþ00 2.70Eþ01 5.80Eþ00May/o9 Bulk (4) 2.70Eþ00 1.60Eþ00 1.02Eþ01 7.20Eþ01 7.60Eþ00Jun/09 Bulk (1) 1.00E�01 1.20Eþ00 5.10Eþ00 1.60Eþ01 2.50Eþ00Jul/09 Dry 0 1.20Eþ00 5.50Eþ00 1.00Eþ01 1.50Eþ00Aug/09 Dry 0 1.20Eþ00 5.50Eþ00 1.00Eþ01 4.10Eþ00Sep/09 Bulk (6) 1.05Eþ01 9.00E�01 4.90Eþ00 4.40Eþ01 2.60Eþ00Oct/09 Bulk (5) 2.50Eþ01 8.00E�01 4.90Eþ00 2.70Eþ01 6.20Eþ00Nov/09 Bulk (3) 1.40Eþ01 6.00E�01 4.90Eþ00 9.00Eþ00 3.50Eþ00Dec/09 Bulk (11) 1.89Eþ02 4.00E�01 1.16Eþ01 3.07Eþ02 5.28Eþ01

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e10241022

are relatively similar It further indicates that these nuclides tworadionuclides cannot be used as independent air mass tracers atleast for the areas similar to Málaga. Some scattering of data pointsalong the regression line could be the result of other processes.

We have performed a correlation study to identify parametersassociated with fluctuations of deposition to ground. The fourparameters have been considered: rainfall amount, rainfall dura-tion, number of dry days and number of wet days. Table 7 shows thecorrelation coefficient between monthly deposition fluxes andthose parameters. There is not a statistical relationship betweengross alpha deposition flux and the rainfall duration and thenumber of dry days at the 95% or higher confidence level since the pvalues in all cases are greater or equal to 0.05. On the contrary, there

Fig. 7. Seasonal variations of gross alpha, gross b

is statistically a relationship between gross alpha deposition fluxand the amount of rainfall and the number of wet days. There is alsoa statistical relationship between the gross beta, 7Be and the vari-ables 210Pb deposition fluxes and all the parameters at the 99%confidence level. The correlation coefficients indicate a relativelyweak relationship between the variables with the exception for thedeposition fluxes of 7Be and 210Pb.In the majority of studies,a moderate correlation between the deposition fluxes of radionu-clides and rainfall is observed. Such relationships have beencommonly observed and explained by the fact the rainfall consti-tutes themajor depositional pathway of the radionuclides (Benitez-Nelson and Buesseler,1999; Caillet et al., 2001; Du et al., 2008; Uguret al., 2010). The behaviour of depositions of gross alpha, beta 7Be

eta, 7Be, 210Pb activities during 2005e2009.

Fig. 8. Deposition flux of 7Be is plotted against the deposition flux of 210Pb.

Table 7Linear correlation studies between of deposition fluxes of gross alpha, gross beta 7Beand 210Pb and some parameters.

Grossalphadeposition

Grossbetadeposition

7Bedeposition

210Pbdeposition

The amount of rainfall(mm)

0.38 0.68 0.85 0.87

Rainfall duration (min) 0.35 0.64 0.64 0.68Number of dry days �0.41 �0.66 �0.60 �0.60Number of wet days 0.43 0.67 0.60 0.62

C. Dueñas et al. / Atmospheric Environment 45 (2011) 1015e1024 1023

and 210Pb suggests that the amount rainfall is the main process toremove the aerosols from the atmosphere (Sugihara et al., 2000).

4. Conclusions

We have evaluate a time series of radioactivity concentrations inrainwater and atmospheric deposition fluxes for gross alpha, grossbeta, 7Be and 210Pb obtained for five years (2005e2009). Seasonalvariations have been observed. The minima specific activities ofradionuclides are registered in winter months while the maximumones fundamentally in springesummer months.

Specific activity data sets for the radionuclides show negativecorrelations with the number of wet days, the rainfall duration andthe amount of rainfall. A positive correlation has been foundwith the number of dry days. The correlation coefficient rangesbetween �0.003 and 0.69 indicating a relatively weak relationshipbetween the variables. The highest concentrations of 40K in bulkdeposition material were recorded in connection with very intensehigh African dust intrusions.

Mean values of annual deposition fluxes of gross alpha, grossbeta, 7Be and 210Pb are: 21, 11, 676 and 106 Bqm�2 y�1 respectively.The depositional fluxes of radionuclides in this coastal site (Málaga)have relatively low value, in particular 210Pb, probably reflectingsignificant input of marine air. The depositional fluxes of 7Beand 210Pb are correlated indicating that removal behaviour from theatmosphere is relatively similar. A positive correlation has beenfound between the deposition fluxes and amount of rainfall, therainfall duration and the number of wet days. A negative correla-tion has been found with the number of dry days. There isa statistically relationship between 7Be and 210Pb deposition fluxesand the amount of rainfall. This study suggests that continuousmonitoring of radioelement fluxes is necessary to examine bothepisodic and long-term changes in annual and seasonal atmo-spheric fluxes .The option of having some additional coastal

sampling stations permanently in the Mediterranean Sea is desir-able. The flux information in this area should be important inmodelling mechanisms controlling atmospheric transport, mixingand deposition of trace elements.

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