Activity concentrations of 226Ra, 228Ra, 210Pb, 40K and 7Be and their temporal variations in surface air

J. Environ. Radioactivity 5 (1987) 445--458

Activity Concentrations of 226Ra, ~ a , ~'°Pb, ~K and 'Be and their Temporal Variations in Surface Air

H. H6tzl and R. Winkler

Institut ffir Strahlenschutz, Gesellschaft f/Jr Strahlen- und Umweltforschung (GSF), D-8042 Neuherberg, Federal Republic of Germany

Received 6 October 1986; revised version received 29 December 1986; accepted 8 January 1987)

A BS TRA CT

Activity concentrations o]' the long-lived natural radionuclides 226Ra, 228Ra, 21°pb, 4OK and of 7Be in surface air were measured twice monthly at a semi-rural location 10 km north of Munich (FRG) ]'or at least three years. For the time interval 1983-1985, all values were )bund to be distributed log-normally, with geometric means (in txBq m -3) of 1.2 ]'or 22°Ra, 0.5 Jor 228Ra, 580¢br 2t°pb, 12 tbr 4°K and 3500for 7Be. Reflecting their common origin, the activity concentrations of 226Ra and 4°K are correlated with surface air dust concentrations (geometric mean 59 tzgm-S). Seasonal variations of 2m pb and 7Be air activity concentrations are established]or the time interval 1978-1985.

The contribution of local soil activity to the air activity concentrations o]" these radionuclides and of natural uranium is discussed. Resuspension factors are found to be of the order of lO-g m-I

INTRODUCTION

During a study of radioactive emissions from coal-fired power plants and their effects on the environment, it was found that, apart from 2~°pb (Rangarajan etal., 1976, 1986), knowledge of the levels of long-lived natural radionuclides and their variability in surface air is fragmentary. From experimentally determined emission data, it was calculated that, in the vicinity of modern German coal-fired power plants, maximum activity concentrations (tzBq m-3) in surface air of, for example, 1-2 for 226Ra and 238U, 0"4 for 2ZSRa, 15 for 21°pb and 4 for 4°K may be expected in addition to

445

446 H. HOtzl, R. Winkler

the corresponding background levels (Chatterjee et al. , 1980). These calculated values are of the same order of magnitude as published surface air concentration data (Welford & Baird, 1967; Hamilton, 1970; Rangarajan et al. , 1976; Kolb, 1978, 1985; Mishra et al., 1978; UNSCEAR, 1982). For example, for 226Ra, a 2.5-28% pollutant contribution to the atmosphere over the United States is estimated to derive from coal-burning power plants (Moore & Poet, 1976).'To assess realistically the contribution of emissions from coal-fired power plants and/or from other technological sources of natural activity to the atmosphere over Western Germany, more information on background levels was needed. Therefore, a programme was started to determine the longer-term activity concentrations of 228Ra, 226Ra and 21°pb from the natural decay series and of the primordial 4°K in surface air at a typical semi-rural location. Moreover, frequency distributions and seasonal and/or long-term variations of the respective levels were studied. Although not emitted by coal-fired power plants, cosmogenic 7Be was included for comparison, particularly as 21°pb and 7Be are often used as tracers in the study of meteorological processes (Marenco & Fontan, 1974) and for investigations on the dynamics of aerosol deposition to ecosystems (Crecelius, 1981).

EXPERIMENTAL

Site description

The sampling station is located at Neuherberg (490 m above sea level, 48°8'N, 11°35'E) about 10 km north of the city of Munich. The location can be described as being typical of semi-rural locations in South Germany. The geological structure of the area comprises quaternary gravel, 8-12 m in depth, overlain with tertiary clays and sands. The main constituent (95%) is carbonate gravel including a crystalline fraction of only 1-2%. The natural environment, mostly grassland, is uncultivated, with some woodland to the north. To the south, at a distance of 1 to 2 km, is the boundary of Munich. Two power plants of low capacity are located at distances of 7 km to the south-east and 24 km to the south. There is a medium capacity power plant (200 MW) 30 km away in the NNE direction. This latter site was the subject of a previous study on emissions of radionuclides and on their distributions in soil around the plant (Bunzl et al., 1984).

Because the prevalent wind at Neuherberg is from the west, neither local domestic pollution from Munich town nor pollution from the above- mentioned power plant should contribute substantially to radioactivity levels at Neuherberg. The mean annual precipitation at Neuherberg, from measurements since 1971, was found to be about 800 mm.

Activity concentrations of 226 Ra, 228Ra, 21° p b , 4° K and 7Be 447

Sampling

At a height of 1.5 m above ground, aerosols (total suspended particulates) were collected on Microsorban filters (54 cm × 89 cm, No. 99/97, Delbag) using a high-volume sampler with an air=flow rate of 600 m 3 h -1. In the absence of any ambient air-flow, it was calculated that particles of up to 30/zm aerodynamic diameter would reach the filter. However, for the average wind speed of 1.5 m s-I prevailing at our sampling site, particles of up to about 15/xm were estimated to be collected.

The filters were changed on the first and fifteenth of each month. In this way, aerosols from about 150000 m 3 air were collected during each sampling period. The air volume was corrected to standard conditions (0°C, 1013 hPa). A more detailed description of the sampling device has been given previously (H6tzl et al. , 1983).

Soil samples were collected to a depth of 2 cm and 10 cm at four different sites in the vicinity of the sampling station using a 5 cm internal diameter core sampler. Each sample consisted of four subsamples. The samples were air-dried, sieved to 2 mm and mixed carefully.

Meteorological data were available from a nearby station of the 'Deutscher Wetterdienst ' (Deutscher Wetterdienst, 1985),.

Procedures

Total air dust concentration is determined by weighing the filters before and after sampling under the same conditions of temperature and humidity. The dust loaded filters are therefore stored for at least one day before reweighing.

All radionuclides are measured by gamma-ray spectrometry. Hence, the dust loaded filters are compressed by means of a hydraulic press at up to 20 tons to give a cylinder of 40 mm diameter and 35 mm height. This procedure assures a highly reproducible geometry.

The data for 7Be and 21°Pb are obtained from our regular fallout measurement programme (H6tzl et al., 1983). For the determination of 226Ra, the samples are sealed in gas-tight perspex boxes and stored for at least two weeks to allow ingrowth to radioactive equilibrium in the 226Ra series. After that time, 226Ra is measured for at least 2500 min via the gamma lines of its daughter products 214pb (295.2,352-0 keV) and 214Bi (609.3 keV) using an anticoincidence-shielded Ge(Li) gamma-ray spectrometer (H6tzl & Winkler, 1981). 228Ra is determined via the gamma lines of the daughter products 212pb (238.6 keV), 2°8T1 (583.1 keV) and 228Ac (911.1 keV) (Powers et al . , 1980).

The lower limit of detection (Harley, 1972; NCRP, 1978) for a counting time of 2500 min was calculated to be 0.1 Bq for ZZ6Ra, 0" 1 Bq for 228Ra and


1 Bq for 4°K, taking into account the interference of overlapping photopeaks from the natural background at the peaks of interest. Any contribution of the filter material was not detectable.

RESULTS AND DISCUSSION

Activity concentrations and frequency distributions

The activity concentrations of 226Ra, 228Ra, 21°pb, 4°K and 7Be--along with the dust concentrations--in the years 1983-1985 are summarized in Table 1. Here the geometric mean, the geometric standard deviation and the range of each nuclide and of the dust concentration are shown. The means, however, are also listed for comparison with other mean values in the literature.

The average ash content of 47% of the air dust at Neuherberg determined by daily measurements in 1973 and 1974 (Bunzl et al., 1976) was confirmed by ashing several compressed filter samples from the year 1985.

By application of the chi-square goodness-of-fit test at the 0.05 level, the frequency distributions for all radionuclides as well as for the dust were proved to be log-normal. The range of the dust concentration at a height of 1.5 m above ground at Neuherberg was found to be 29 to 140/xg m 3 with a geometric mean of 59/zg m -3 related to the total airborne particulate. This value may be related, with some reservation, to the typical values for non-urban areas, which range from 5 to 50/zg m-3, whereas, in areas with considerable domestic and industrial fallout, the particulate concentration varies between 100 and 800/zg m -3 (Junge, 1963).

TABLE 1 Geometric Mean, Geometric Standard Deviation (S.D.), Arithmetic Mean and Range of Natural Radionuclides (/xBq m 3) and Dust Concentrations (gg m-3) in the Years 19&'L-1985

at Neuherberg

Geometric Geometric Mean Range mean S.D.

226Ra 1-2 1.54 1-3 <0.2-3-3 228Ra 0.5 1.6 0.6 <(I.3-1.5 21°pb 580 1 "50 670 230-2 250 4°K 12 1.5 12 4-30 7Be 3 500 1 '32 3 630 1 000-7 200 Dust (total) 59 1.41 64 29-140 Dust ash - - - - 47% 15%267%

Activity concentrations of 226Ra, 228Ra, 21°pb, 4°K and 7Be 449

Seasonal and long-term variations

The variations of semi-monthly activity concentrations (/zBq m-3), dust (tzg m -3) and rainfall (mm) within the years 1983 to 1985 are shown in Fig. 1. Where available, annual mean values up to 1983 are included. 226Ra and, with some reservation, 228Ra show a marked seasonal variation, with maxima in summer and minima in winter, whereas 4°K exhibits a more or less constant annual activity level. With regard to variations in dust concentrations, it is striking that distinct peaks in these (summer 1983, spring 1984) seem to be paralleled by peaks in 226Ra, 228Ra, 21°pb and 4°K concentrations. On the other hand, the concentrations of these nuclides exhibit marked troughs coinciding with periods of stronger rainfall due to washout effects in the lower air layers. Similar observations with respect to 21°pb and some other radionuclides have been noted at Toulouse, France (Marenco & Fontan, 1974) and Seattle, USA (Nevissi & Schell, 1978). The 21°Pb maxima in autumn/winter may be attributed to frequent inversion conditions of the surface air layers, resulting in a build-up of radon and its daughters in ground-level air. However, in winter months (December-February), this process can be negated because of the low emanation of radon from the frozen and/or snow-covered soil.

For a six-year period, the 21°pb activity levels (monthly averages) measured at our station were compared with those observed at Brunswick, West Germany (Kolb, 1984). Despite a significant difference between the two medians--Neuherberg: 520 p~Bq m-3; Brunswick: 280/zBq m-3 for the years 1978-1983, due possibly to the different compositions of their air masses, a significant correlation (->99.9%, Spearman rank-correlation coefficient p~ = 0.75) was obtained. Therefore it can be concluded that the correlation must reflect the dominant influence of large-scale weather patterns, and that it occurs despite the effects of the differing local meteorological conditions at the two sampling stations, which are about 600 km apart.

Consistent with our measurements since 1976 (H6tzl et al., 1983), the periodic pattern for 21°pb is generally different from that for 7Be, which reaches regular maximum values in the spring to early summer months because of its different origin, i.e., the cosmogenic 7Be is introduced into the lower atmosphere by lifting of the troposphere during spring.

Correlations

To detect whether there exists a relationship between total dust or rainfall and the activity in ground-level air, we applied a correlation test. Because neither the dust nor the radionuclide concentration showed a normal


40

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Fig. 1. Variation of activity concentrations (/~Bq m-3), dust concentrations (/~g m-3) and rainfall (mm) at Munich-Neuherberg. (Semi-monthly values are from 1983 to 1985, annual

mean values from 1976 to 1982.)

Activity concentrations o f 226 Ra, 228Ra, 2*° pb, 4° K and 7Be

T A B L E 2

S p e a r m a n R a n k - C o r r e l a t i o n s o f R a d i o n u c l i d e s f l D u s t a n d Ra in fa l l

451

7Be 40 K 210 pb 226Ra 228Ra

40 K ***

21°pb n . s . ** 226Ra *** * *

228Ra *** * n .s .

D u s t ( to ta l ) n . s . * . . . . .

R a i n f a l l n . s . * * * ( - ) * * * ( - )

*** n .s .

*(-) n.s.

a C o r r e l a t i o n s b e t w e e n r a d i o n u c l i d e s a re b a s e d on c o n c e n t r a t i o n s pe r un i t m a s s o f a i r b o r n e

d u s t . S ign i f i cance level: *** = 9 9 . 9 % , ** = 9 9 % , * = 9 5 % , n .s . < - 9 5 % , ( - ) = n e g a t i v e

c o r r e l a t i o n .

f requency distribution, the non-parametric Spearman correlation coefficient (two-sided) was calculated for this purpose. The resulting significance levels for these correlations are shown in Table 2. As may be seen, significant positive or negative correlations exist between the dust or rainfall and the activities of 4°K, 21°pb and 226Ra. In the case of 22SRa and 7Be, however , no correlation with either dust or rainfall could be found at the 95% level. It is difficult to understand the reason for the absence of a correlat ion between 228R a and dust or rainfall, respectively, because the local ground is the source of the 228Ra as well as of the 226Ra. However, it has to be pointed out that many of the 228Ra concentration values observed were near or equal to the detection limit. Therefore, the existence of a correlation between =8Ra and dust or rainfall can probably be established only if a greater number of 22SRa values above the detection limit becomes available.

To investigate whether a correlation exists between the various radionuclides, we again applied the rank-correlation test of Spearman. However, for this purpose, we could not use the nuclide activity concentrations in /zBq m 3 of air, because these are also a function of the mass of dust. Any resulting correlation would therefore be trivial. However, by evaluating the activities in terms of activity per unit mass of airborne particulate, this dependence on dust mass is eliminated and an unambiguous rank- correlat ion coefficient can be calculated (Sachs, 1974). Table 2 lists the significance levels for each tested correlation, the 95% level being set as the minimum criterion and all data being shown regardless of whether a correlat ion was found to exist or not. An observed correlation between two radionuclides of different origins is probably due to similar seasonal variation patterns of their concentrations in air. This is not surprising because the same meteorological parameters, especially washout of air-


masses in the lower atmosphere, are responsible for these variations. No correlation could be found between 7Be and 21°pb as expected for the above-mentioned reasons. For these two nuclides we investigated the influence of meteorological parameters during the period 1978 to 1985 by consideration of the stagnation index (Bayer. Landesamt, 1985). This meteorological parameter takes into account horizontal and vertical exchange processes and the washout of aerosols in the lower atmosphere. It includes the daily maximum of the mixing height, the daily average wind speed and the daily sum of precipitation. The range of the index is 10 to 100, where a decreasing value means an increasing exchange of air. To illustrate the typical behaviour of 7Be and 2mpb together with the stagnation index, we pooled the monthly mean values from eight years (1978-1985) into an overall mean value for each month (Fig. 2).

As is evident from this figure, the seasonal variation of 2~°pb is in phase with the stagnation index. 2~°Pb shows distinct minima in spring/summer months, corresponding to higher air mixing and/or washout processes, i.e., low values of the stagnation index. The maxima in autumn/winter months are apparently coincident with high values of the index. 7Be follows a

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1985.

Activity concentrations o f 226 Ra, 228Ra, 21° pb, 4° K and 7Be 453

pattern similar to that of fallout fission products from nuclear weapons tests, with a maximum in early summer due to the stratospheric subsidence mechanism (Abe & Abe, 1984). Relative to 21°pb and the stagnation index, 7Be exhibits a seasonal behaviour completely opposite in phase.

To investigate whether, in fact, a correlation exists between the stagnation index and 7Be or 21°Pb air concentrations, systematic variations due to the seasonal cycle must be eliminated. Otherwise a common cause correlation due to chronological order could not be excluded. Therefore, the mean monthly values had to be de-trended before calculation of the correlation. By applying polynomial fits of the third order to each seasonal cycle, only deviations of the means from the fitted curves were taken into account in calculating the correlation coefficients. In this way it was found that 21°Pb air concentrations are strongly correlated with the stagnation index (->_99%, Pearson's linear correlation coefficient rp = 0.743; n = 12). On the other hand, no influence of this ground-level meteorological parameter on 7Be air concentrations was detectable (rp = - - 0 - 2 0 5 ) . Analogous results were obtained by de-trending the data using fourth order polynoms.

Resuspension

It is obvious that local surface soil particles may account for the natural radionuclides resident in ground-level air. Therefore, it seems appropriate to compare the specific activities in air with those of the local soil in order to estimate the component of resuspended ground dust. In Table 3 the average specific activities per unit mass of air dust (total and ash) and of local soil are summarized. For comparison, the specific activities of the escaping fly ash from a medium capacity coal-fired power plant are included in the table. The specific activity of 238U was taken from a single measurement of 141 g air dust obtained from a filter device which ran from May 1984 to July 1985. As can be seen from the Table, the escaping fly ash has a mean specific activity which is at most a factor of 10 higher than that of the air at Neuherberg. Taking dispersion into account, any measurable increase in air activity at the sampling station is therefore believed to be undetectable.

With regard to error limits, the specific activities of both radium isotopes in soil correspond to those in dust ash but not to those in total dust. This seems to confirm the observation of Kolb (1985) that a considerable fraction of aerosols comprises organic material whose specific activity is markedly less than that of soil dust. On the other hand, 238U, as well as 4°K, in dust ash is found to be in excess and it may therefore be concluded that both nuclides are also constituents of airborne organic material such as pollen or soot.

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Activity concentrations of 226 Ra, 22S Ra, 2t° Pb, 4° K and 7Be 455

In soil, 238U and 226Ra are apparently in disequilibrium, a result which at first sight is difficult to understand in view of their common genetic origin. It is reported, however, that 226Ra in soils is generally greatly in excess of 238U because of its deposition from percolating soil water by ion-exchange on to clays and organics or as a result of preferential leaching of 238U from soil (Ivanovich & Harmon, 1982). With regard to specific activities in soil, no difference between the upper (0-2 cm) and the 2-10 cm layer was observed for all nuclides.

Whether the activity levels of the nuclides under investigation are increased by pollution from anthropogenic sources may also be revealed by con- sidering the resuspension factor, which is defined as

concentration per m 3 of air [Bq .m-3] K[m 1] = total deposition per m 2 of ground area [Bq. m 2]

(Moore & Poet, 1976; Linsley, 1978; Sehmel, 1980). This factor has been shown to be useful, especially in localized situations,

as a simple means of characterizing the relationship between surface and airborne contamination, though it does not take account of many parameters such as meteorological conditions, nature of the surface, types of soil, and vegetation and effects of weathering of the surface deposit. For undisturbed, uncultivated soil sites, the resuspension factor is of the order of 10 -9, whereas, for newly deposited material on cultivated, fertilized areas, it increases up to 10-5 (Bennett, 1976; Moore & Poet, 1976). From the results of our measurements of air activity concentrations (Table 1) and of specific activities in the upper layer (0-2 cm) of soil (Table 3), the following resuspension factors (m -l) w e r e calculated: 226Ra: 1-2- 10 -9, 228Ra: 1.0. 10 -9, 23sU: 3"2 • 10 -9, 4°K: 3-2- 10 9and 21°pb: 5.0. 10 -7.

From the 238U data measured at Sutton, UK (Hamilton, 1970), a resuspension factor of 5 • i0-9 was derived (Bennett, 1976), where the soil down to a depth of 1 cm was considered to contain resuspensible activity. Bennett (1976) also reported a resuspension factor of 1.10 Sm-t for 238U derived from air concentration measurements at New York (Welford & Baird, 1967). However, an undetermined amount of industrial material was also included in this material. For 226Ra, Moore & Poet (1976) reported a resuspension factor of 1.3.10-9 m 1 for aged deposits in the top 1 cm of soil in Colorado and Kansas, USA. Our factor is in good agreement with this value. Furthermore, our values for 22SRa and 4°K are of the same order of magnitude. However, no other resuspension factor data for 228Ra or 4°K could be found in the literature. Except for 2~°Pb, the resuspension factors are typical of those for material that has been deposited and weathered for long periods of time in a natural unpolluted environment.


For 21°pb, the high value of 5 .10 7m-~ can obviously be traced to its different origins, as described above; and, thus, for this nuclide, it is inappro- priate to use the resuspension factor to predict elevated concentrations from industrial or other anthropogenic sources. To determine whether there was an increase in 2t°pb concentrations in surface air from anthropogenic sources during the last decade, we carried out a trend analysis, calculating the Spearman rank-correlation coefficient for successive annual medians from 1976 to 1985. No statistically significant increase (_<_90%) in surface air 21°pb concentrations could be found.

CONCLUSION

- - M e a n surface air concentrations from at least 1983 to 1985 at Neuherberg, a location 10 km north of Munich, West Germany, were found to be (geometric mean p, Bq/m3): 226Ra: 1-2,228Ra: 0-5, 2~°pb: 580, 4°K: 12 and 7Be: 3500.

- -Semi-month ly concentration values of all radionuclides under investigation are log-normally distributed.

- -Accord ing to their common origin from soil, 226Ra and 4°K air concentrations are correlated at the 99.9% significance level with air dust concentrations. Though 22SRa also has its common source in the local ground, no correlation was found at the 95% level. The resuspension factors are of the order of 10-gin ~, typical of material that has been deposited and weathered for a long time in natural, unpolluted environments.

--2"~Pb is strongly correlated with the stagnation index, a meteorological parameter which takes account of the horizontal and vertical air exchange processes and washout of aerosols in the lower atmosphere. For 2J°pb a resuspension factor of 5 • 10 7m-I was obtained, reflecting its origin in surface air as a daughter product of radon.

--226Ra, 2~°Pb and 7Be show marked seasonal variations. 226Ra concentrations show maxima in summer and minima in winter. The maxima for 2~°pb in autumn/winter are attributed to frequent inversion conditions in the surface air layers. The periodic pattern for VBe, reaching regular maximum values in the spring to early summer months, is generally different from that for 21°pb.

- - A n increase in 21°pb concentrations in surface air as a result of anthropogenic inputs during the last decade was not found. A similar analysis for the other nuclides is not yet possible because of the restricted observation time (1983 to 1985).

Activity concentrations of ee6Ra, eeeRa, 21°pb, 4°K and 7Be 457

A C K N O W L E D G E M E N T

The authors would like to thank Mr H. Haimerl for technical assistance and Dr K. Bunzl for stimulating discussions.

R E F E R E N C E S

Abe, M. & Abe, S. (1984). Worldwide distribution of the 7Be concentration in the atmosphere. Nat. Inst. Radiol. Sci. Ann. Report NIRS-24, 74.

Bayer. Landesamt f/jr Umweltschutz (1985). Lufthygienische Jahresberichte 1978- 1985.

Bennett, B. G. (1976). Transuranic element pathway to man. In Transuranium nuclides in the environment, Proc. Symp., San Francisco 1975, IAEA-SM-199/ 40, IAEA, Vienna, 367-83.

Bunzl, K., Schmidt, W. & Schultz, W. (1976). Untersuchung der Luft auf Schwebstoffe, Blei, Cadmium, Zink und andere Metallspuren. Gesellschaft ffir Strahlen- und Umweltforschung, Neuherberg.

Bunzl, K., H6tzl, H., Rosner, G. & Winkler, R. (1984). Spatial distribution of radionuclides in soil around a coal-fired power plant: 21°pb, 21°po, 226Ra, 232Th, 4°K emitted with the fly ash and 137Cs from the worldwide weapon testing fallout. Sci. Total Environ., 38, 15-31.

Chatterjee, B., H6tzi, H., Rosner, G. & Winkler, R. (1980). Untersuchungen iiber die Emission yon Radionukliden aus Kohlekraftwerken. GSF-Report S-617, Gesellschaft fiir Strahlen- und Umweltforschung, Neuherberg.

Crecelius, E. A. (1981). Prediction of marine atmospheric deposition rates using total 7Be deposition velocities. Atmosph. Environ., 15,579-82.

Deutscher Wetterdienst (1985). Agrarmeteorologische Monatsberichte fiir Bayern, AMBF Weihenstephan, ISSN 0172-4312,

Hamilton, E. I. (1970). The concentration of uranium in air from contrasted natural environment. Health Phys., 19, 511-20.

Harley, J. H. (ed.) (1972). HASL-Procedures, HASL-300, US Atomic Energy Commission, New York, Section D-08-01.

H6tzl, H. & Winkler, R. (1981). The GSF-anticoincidence-shielded Ge(Li) gamma-ray spectrometer and its application to the analysis of environmental samples, IAEA-SM-252/59. In Methods of low-level counting and spectrometrv, Vienna, IAEA, 77-91.

HOtzl, H., Rosner, G., Winkler, R. (1983). Radionuclide concentrations in ground level air and precipitation in South Germany from 1976 to 1982. GSF°Report S-956, Gesellschaft f/Jr Strahlen- und Umweltforschung, Neuherberg.

Ivanovich, M. & Harmon, R. S. (eds) (1982). Uranium series disequilibrium: applications to environmentalproblems. Oxford, Clarendon Press, 53 pp.

Junge, C. E. (1963). Air chemistry and radioactivity. New York, Academic Press, 250 pp.

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Documents

Activity concentrations of 226Ra, 228Ra, 210Pb, 40K and 7Be and their temporal variations in surface air