Variations in 7Be concentrations in the atmosphere of Kuwait during the period 1994 to 1998

Activity size distributions of radioactive airborne particles in an arid environment: a case study of Kuwait

Atmospheric radioactive airborne released from several natural and artificial sources can travel for long distances and disperse in different directions. Both the physical and chemical characteristics of the atmospheric aerosols control this movement. The concentrations of ²¹⁰Pb, ²¹⁰Po, ⁷Be, ⁴⁰K and ¹³⁷Cs radionuclides in the ground surface air were determined in three particle sizes (2.4-10.2, 0.73-2.4 and less than 0.73 μm). High-volume air samples were collected from five different locations representing the five governorates of Kuwait using high-volume air samplers connected to a five-stage cascade impactor. The radioactivity concentrations of almost all fallout radionuclides were concentrated on the fine particle size fractions. The cosmogenic ⁷Be radioactivity level in all locations was relatively comparable and varied between 1.16 and 18.38 mBq/m³, with a geometric mean value of 6.80 mBq/m³. ¹³⁷Cs was infrequently recorded with concentration varied between 4 and 14.3 μBq/m³. The geometric mean levels of the ²¹⁰Po and ²¹⁰Pb were 0.899 mBq/m³ and 1.03 mBq/m³, respectively, indicating that anthropogenic sources likely enrich ²¹⁰Po. ⁴⁰K was concentrated on large particle size fractions with a geometric mean value of 2.34 mBq/m³, reflecting the effects of the local dust sources. It was concluded that the radiological hazards due to airborne radioactive inhalation are low and can be negligible, where the annual estimated effective dose is about 64.0 μSv. The radioactive airborne measurements compose the base of estimating the aerosols residence time, resuspension rate of dust, soil redistribution and source apportionment, particularly the ²¹⁰Pb and ²¹⁰Po radionuclides.

Measurements of surface air 7Be concentrations in Saudi Arabia

The main objective of this study is to identify the atmospheric ⁷Be concentrations in 130 surface air samples collected from three stations located in Riyadh, Haql and Khafji cities in Saudi Arabia between November 2012 and April 2014. Monthly variations as well as seasonal patterns of ⁷Be were studied using a medium-volume air sampler and a gamma spectroscopy system equipped with a high-purity germanium (HPGe) detector. ⁷Be exhibited one maximum specific activity in summer and one minimum in winter with average monthly concentrations of 12.4 ± 0.9, 15.4 ± 1.2, and 18.0 ± 1.3 mBq m^-3 in Riyadh, Haql and Khafji, respectively. Overall, the average ⁷Be concentration in the three stations was 12.9 ± 1.0 mBq m^-3, whereas the maximum value of 29.5 mBq m^-3 was registered in Khafji city in August 2013. Besides ⁷Be, measurements indicate observations of ⁴⁰ K, ¹³⁷Cs, ²²⁶Ra radionuclides in surface air samples collected from the three stations. ⁴⁰ K showed measurable concentrations, whereas the concentrations of ¹³⁷Cs and ²²⁶Ra were only detected in a limited number of samples.

7Be atmospheric activity concentration and meteorological data: Statistical analysis and two-layer atmospheric model

Atmospheric activity concentration of ⁷Be in the air was monitored during the period of one year from September 2015 to September 2016 at Ostrava, Czech Republic, with a two-day frequency that is shorter compared to a standard 7-day frequency of routine ⁷Be measurements. Simultaneously, relevant meteorological data (temperature, rainfall amount, precipitation particle size and speed, tropopause height, and PM₁₀ concentrations) and the sunspot number were accumulated. Weighted linear regression analysis applied to the ⁷Be atmospheric activity concentration, the measured meteorological explanatory variables and the sunspot number revealed temperature as the most statistically significant explanatory variable. The tree model proved temperature as the most important explanatory variable and predicted the threshold value separating low and high temperature behavior of ⁷Be at about 13 °C (2-day average). A simple local two-layer (stratosphere and troposphere) atmospheric model was then applied to the data analysis. The model is able to fit the data for a larger accumulation period (6 days).

Large seasonal variations in fine aerosol precipitation rates revealed using cosmogenic 7Be as a tracer

To determine the seasonal variations in the removal efficiency of fine aerosols (PM2.5) in the Northeast Asia, we analyzed ⁷Be data collected for the surface air and precipitation over 20 years in Korea. The ⁷Be activity concentrations in the surface air were relatively higher in spring owing to tropopause folding but lower in summer owing to efficient removal by precipitation. The monthly ⁷Be concentrations decreased as the precipitation amounts increased showing a negative correlation (r² = 0.34) against the precipitation amount. These results indicate that the concentrations of ⁷Be and fine aerosols are mainly controlled by the same washout effect, although the sources are different. The mean depositional velocities of fine aerosols, based on the ⁷Be mass balance model, showed a large seasonal variation, with its maximum value (1.9 cm s^-1) in July and minimum value (0.22 cm s^-1) in March. The ⁷Be depositional velocity reflects the net deposition of fine aerosols excluding moisture effects. Thus, the concentrations of fine aerosols can occur as high as five-fold in the dry season, if the input terms of fine aerosols remain the same. Our results imply that precipitation plays a critical role in the seasonal changes in the concentrations of fine aerosols, providing much clean air in the summer monsoon season in the Northeast Asia.

A study of temporal variations of 7Be and 210Pb concentrations and their correlations with rainfall and other parameters in the South West Coast of India

As a part of establishing a regional database on natural radioactivity, the atmospheric concentrations of ²¹⁰Pb and ⁷Be were measured over a three and half year period (2014-2017) in Mangalore and Kaiga in the South West Coast of India. A total of 99 air samples, collected in the different months of the year, were analysed in this study. The mean activity concentrations of ⁷Be and ²¹⁰Pb were found to be 5.5 ± 3.1 mBq m^-3 and 1.1 ± 0.73 mBq m^-3, respectively. Both the radionuclides exhibited strong seasonal variations, with maximum concentration of ⁷Be occurring in the summer and that of ²¹⁰Pb in the winter season. The concentration of both the radionuclides was minimum in the rainy season. Higher ²¹⁰Pb concentration during winter was attributed to the ingression of continental air masses due to the wind regime from the North East. The sunspot number index of the solar activity also plays an important role in the increase and decrease of ⁷Be concentration in the air. A clear trend of increased and lowered concentration of ⁷Be with lower and higher solar activity (low and high sunspot number), respectively, in accordance with the 11-year solar cycle, was observed in this study. The temporal variation of PM₁₀ concentration was also studied and it showed maximum value in the winter and minimum in the rainy season with an average of 56.9 μg m^-3. Statistically significant positive correlation was observed between the PM₁₀ and ²¹⁰Pb activity concentration, whereas a weak correlation was observed between PM₁₀ and ⁷Be. This is due to the fact that ⁷Be is largely associated with sub-micrometer size particles, whereas PM₁₀ is contributed by larger sizes. The dependence of the activity concentrations of ⁷Be and ²¹⁰Pb with meteorological parameters such as rainfall, temperature, and humidity was studied through linear regression analysis. A significant correlation was observed between ⁷Be and ²¹⁰Pb concentrations with rainfall intensity (with identical correlation coefficients), which suggested that the removal mechanisms of these two radionuclides were similar. ⁷Be showed a strong correlation with temperature, whereas ²¹⁰Pb with humidity. A comparison of the data obtained in the present study for the South West Coast of India with the global literature values of ⁷Be and ²¹⁰Pb in aerosols showed that the values did not reflect the well-known latitudinal dependence of the ⁷Be tropospheric fluxes. Overall, the study provides an improved understanding of the correlation and variability of ²¹⁰Pb and ⁷Be concentrations in the atmosphere in the South West Coast of India.

Atmospheric deposition fluxes of 137Cs associated with dust fallout in the northeastern Arabian Gulf

For many years, monitoring and determining the radioactivity of ¹³⁷Cs in the environment has considerable interest. This paper presents monitoring ¹³⁷Cs deposition fluxes during the period from 2009 to 2011. Dust fallout samples were collected from ten locations in Kuwait, and ¹³⁷Cs concentrations were determined using ultra low spectrometry system. The average of the annual atmospheric deposition fluxes of ¹³⁷Cs was 4.3, with an extreme value reaching 50 Bq m^-2. The monthly deposition rates of ¹³⁷Cs were attributed to seasonal increases in the spring. ¹³⁷Cs deposition fluxes showed a significant relationship with dust deposition and precipitation rates, where the correlation between the monthly dust fallout and the ¹³⁷Cs deposition fluxes and precipitation rates were approximately 0.95 and 0.81, respectively. The spatial monthly distribution of ¹³⁷Cs fluxes showed high rates in the southeastern part of Kuwait while the lowest rates were recorded along the coastlines. A strong correlation was observed between the annual ¹³⁷Cs and ⁴⁰K deposition rates considering that both radionuclides deposition were governed by similar conditions. It was concluded that long-range transport from the northwestern areas along with the effects from local dust washout and the site specify played a major role in controlling the rate of ¹³⁷Cs deposition. The estimated annual effective dose equivalent due to external and internal exposures was insignificant and can be ignored. It is worthwhile to continue investigating the source origin of ¹³⁷Cs in Kuwait to enhance understanding of the radiological hazards in the country.

7Be concentration in the near-surface layer of the air in Bialystok (north-eastern Poland) in the years 1992-2010

Weekly measurements of air ⁷Be concentrations (n = 769) were performed in the years 1992-2010 in Bialystok (north-eastern Poland) using gamma spectrometry. The arithmetic mean (AM) concentration of ⁷Be was 2.51 mBq m^-3, and the median (M) was 2.24 mBq m^-3 (range 0.47-7.81 mBq m^-3). The observed ⁷Be concentrations were within the range of levels recorded in Europe. Typical seasonal variability was observed. Concentrations of ⁷Be in the warm season (May, June, July) were almost twice as high as those in the cold season (November, December, January). A correlation was found between weekly ⁷Be concentrations and mean weekly values of relative humidity, temperature, and wind speed throughout the observation period. Pearson's correlation coefficients were -0.63, p < 0.001; 0.477, p < 0.001; -0.288, p < 0.001, respectively. The correlation coefficient between sunspot number and mean annual ⁷Be concentrations in the air in the years 1992-2010 was -0.609.

7Be in soil, deposited dust and atmospheric air and its using to infer soil erosion along Alexandria region, Egypt

This study investigated the radioactivity behavior of ⁷Be in surface soil, airborne and deposited dust along Alexandria region in Egypt. The results obtained were used to predict scavenging processes of ⁷Be from surface soil to infer soil erosion and land vulnerable to accelerated sea-level rise. The areal activity concentrations of ⁷Be in surface soil were investigated in 30 undisturbed sites and ⁷Be inventories were determined via deposited dust in 10 locations. Results of the former were found to be ranged from 78 Bq/m² to 104 Bq/m². High levels were observed in western sites associated with high dust deposition rate. On the other hand, low levels were found in the eastern sites, those may be attributed to scavenging processes such as land erosion toward the direction to the sea. The effective removal rates of ⁷Be were calculated using the box-model, showing a broad special trend of inventories generally decreasing eastwards. The scavenging rates were ranged between 3.13 yr^-1 in western sites to 5.34 yr^-1 in eastern ones which denote that the east of the city suffers from rapid soil erosion. The airborne ⁷Be was monthly monitored along the period from October 2014 to September 2015 through one site located at the mid of the city. The results revealed lower values in winter and autumn than in summer and spring ranged between 6.2 mBq/m³ and 10.5 mBq/m³. These levels are comparable with that in other world regions and the seasonal variations are associated with the prevailing climatic conditions in Alexandria region.

Influence of long-range atmospheric transport pathways and climate teleconnection patterns on the variability of surface 210Pb and 7Be concentrations in southwestern Europe

The variability of the atmospheric concentration of the ⁷Be and ²¹⁰Pb radionuclides is strongly linked to the origin of air masses, the strength of their sources and the processes of wet and dry deposition. It has been shown how these processes and their variability are strongly affected by climate change. Thus, a deeper knowledge of the relationship between the atmospheric radionuclides variability measured close to the ground and these atmospheric processes could help in the analysis of climate scenarios. In the present study, we analyze the atmospheric variability of a 14-year time series of ⁷Be and ²¹⁰Pb in a Mediterranean coastal city using a synergy of different indicators and tools such as: the local meteorological conditions, global and regional climate indexes and a lagrangian atmospheric transport model. We particularly focus on the relationships between the main pathways of air masses and sun spots occurrence, the variability of the local relative humidity and temperature conditions, and the main modes of regional climate variability, such as the North Atlantic Oscillation (NAO) and the Western Mediterranean Oscillation (WeMO). The variability of the observed atmospheric concentrations of both ⁷Be and ²¹⁰Pb radionuclides was found to be mainly positively associated to the local climate conditions of temperature and to the pathways of air masses arriving at the station. Measured radionuclide concentrations significantly increase when air masses travel at low tropospheric levels from central Europe and the western part of the Iberian Peninsula, while low concentrations are associated with westerly air masses. We found a significant negative correlation between the WeMO index and the atmospheric variability of both radionuclides and no significant association was observed for the NAO index.

Cosmogenic 22Na, 7Be and terrestrial 137Cs, 40K radionuclides in ground level air samples collected weekly in Kraków (Poland) over years 2003-2006

A low background gamma spectrometer with an Etruscan, 2500 years old lead shield and a muon veto detector were applied to study ²²Na and ⁷Be activity concentration in ground level air aerosol samples collected weekly over the years 2003–2006 in Kraków. Each sample was formed with ca 100 000 m³ of passed air, collected with two parallel ASS-500 high volume air samplers. The results for ⁴⁰K and ¹³⁷Cs are also presented for reference and comparison. Presented frequency distributions for activity concentration and correlation between the obtained results are discussed. The activity concentration results confirmed seasonal variation of activity to be different for all the investigated radionuclides. Moreover, the seasonal variation in nucleus activity ratio was also noticed for ²²Na and ⁷Be. Cosmogenic radionuclides being mainly of stratospheric origin, are subsequently attached to fine aerosols, via which they are transported to the ground level air. The mean aerosol transport time within the troposphere was estimated as equal to 7.5 days on average, reaching even 50 days in warm seasons. Limitations of the applied model were identified.

Exploratory data analysis in the study of 7Be present in atmospheric aerosols

PURPOSE

Exploratory data analysis (EDA) is applied in this research to study the behavior of radioactive aerosols present in the surface atmosphere of Granada, using (7)Be as radiotracer. The reason for this study is to reduce the large number of parameters involved in understanding their behavior, given the complexity of the atmosphere.

METHODS

Aerosol particles were collected weekly in Granada (Spain) over a 5-year period. Low-background gamma spectrometry was used to determine concentrations of (7)Be-aerosol activity. The variables studied were: (7)Be concentration, cosmic ray intensity, temperature, temperature interval, rainfall, relative humidity, and Saharan intrusions. Least significant difference test (LSD), hierarchical cluster analysis (HCA), and principal component analysis (PCA) with varimax rotation have been applied to study the datasets.

RESULTS AND DISCUSSION

The results of our study reveal that aerosol behavior is represented by two principal components which explain 86.23 % of total variance. Components PC1 and PC2 respectively explain 74.61 and 11.62 % of total variance. PC1 explains the cyclical and seasonal pattern of the samples, while PC2 is related to the production of (7)Be. In addition, PCA and HCA show good distribution of the samples by families with two groups, summer and winter, at the extremes and spring-autumn in the middle. This result corroborates that there are no differences between spring and autumn in the climate of Granada.

CONCLUSIONS

EDA has been found to be quite useful in studying the behavior of radioactive aerosols in the surface atmosphere of a city with the climate and geographical characteristics of Granada.

Lead-210 and Beryllium-7 fallout rates on the southeastern coast of Brazil

Total ²¹⁰Pb and ⁷Be fallout rates were measured on the coastal region of Niteroi, Brazil. The monthly depositional flux of ²¹⁰Pb and ⁷Be varied by a factor of 26, from 1.7 to 43.3 mBq cm⁻² year⁻¹ and ∼27, from 7.5 to 203.5 mBq cm⁻² year⁻¹, respectively. The relatively large oscillations in the depositional flux of ²¹⁰Pb at this study site were likely due to variations in air mass sources, while the ⁷Be fluctuations may be driven by a combination of weather conditions. Local geology could support the periodic high fluxes of ²¹⁰Pb from continental air masses, as shifting oceanic wind sources were affirmed by the uncorrelated ²¹⁰Pb and ⁷Be fallout activities and ⁷Be/²¹⁰Pb ratios. The ²¹⁰Pb atmospheric deposition was found to be in agreement with local sediment inventories, an important consideration in geochemical studies that estimate sedimentation processes.

Temporal changes of 7Be, 137Cs and 210Pb activity concentrations in surface air at Monaco and their correlation with meteorological parameters

Results of analysis of (7)Be, (137)Cs and (210)Pb on aerosol filters carried out from 1998 to 2010 in Monaco show that a weak correlation between activity concentrations of these radionuclides in the atmosphere and meteorological parameters has been found for (7)Be and temperature (r = 0.50), (210)Pb and temperature and humidity (r = 0.43 and 0.41, respectively), and (137)Cs and precipitation (r = 0.51). The minimum and maximum (7)Be activity concentrations were observed during 2000 and 2009, corresponding with the maximum and minimum solar activity, respectively. The maximum (137)Cs activity concentration found in May-June 1998 was due to the accident at Algeciras in Spain. The deposition velocities of (7)Be, (137)Cs and (210)Pb depended on the precipitation rate, and attained maximum values during dry seasons. The investigated radionuclides may be used as atmospheric tracers, especially in long-term periods.

7Be in ground level air in Daejeon, Korea

(7)Be concentrations in the ground level air in Daejeon, Korea were determined during the period of January 1998 to December 2009 by gamma-ray spectrometric analysis of particulate samples collected on filter paper with a high-volume air sampler. The monthly concentrations of (7)Be in the ground level air were in the range of 1.3-7.7 mBq m(-3) with strong seasonal trends of low values in the summer and high values in the spring and autumn. The annual mean values of (7)Be concentrations showed weak reverse correlation with the annual average sunspot number.

Comparative trends and seasonal variation of ⁷Be, ²¹⁰Pb and ¹³⁷Cs at two altitude sites in the central part of France

The atmospheric concentrations of ¹³⁷Cs, ²¹⁰Pb, and ⁷Be were measured over a three-year period at two research stations located less than 12 km apart and at different altitudes (puy de Dôme, 1465 m a.s.l. and Opme, 660 m a.s.l., France). Seasonal trends in all radionuclides were observed at both stations, with high concentration measured during the summer and low concentrations during the winter. The ²¹⁰Pb concentrations at both stations were similar to each other. Higher concentrations of both ⁷Be and ¹³⁷Cs were measured at puy de Dôme than at Opme. These observations can be explained by the stratospheric and upper tropospheric sources of ⁷Be and the long-range transportation of ¹³⁷Cs at high altitudes. Air mass origins during sampling periods were classified into several groups by their route to the stations (marine, marine modified, continental and mediterranean). We observed that ⁷Be concentrations were constant regardless of the air mass origins, unlike ¹³⁷Cs and ²¹⁰Pb concentrations that increased when influenced by continental air masses. Higher ⁷Be concentrations were observed when air masses were arriving from the upper troposphere than from the boundary layer, the opposite was observed for ¹³⁷Cs. The temporal trend in concentrations of ⁷Be shows good agreement with previous modelling studies suggesting that there is a good understanding of its sources and the atmospheric vertical mixing of this radionuclide. The sources and mixing of ²¹⁰Pb, however, seem to be more complex than it appeared to be in previous modelling studies.

Seasonal and inter-annual variation of Beryllium-7 deposition in birch-tree leaves and grass in the northeast upland area of the Czech Republic

The activity concentrations of Beryllium-7 ((7)Be), a naturally occurring radioisotope produced in the atmosphere, were measured in leaves of birch-trees, above-ground parts of grass, soil and rainwater in the mountain massive Kralicky Sneznik (the northeast of the Czech Republic, altitude about 750 m) in the years of 2005, 2006 and 2007. Dried and ground samples of the plants and soils, and water samples from wet deposition were used to determine the (7)Be content using a semiconductor gamma spectrometer. The (7)Be values ranged from 147.0 to 279.6 Bq kg(-1), from 48.7 to 740.8 Bq kg(-1), from 2.1 to 8.7 Bq kg(-1), and from 0.6 to 1.9 Bq kg(-1) in birch-tree leaves, grass samples, soils, and rainwater, respectively. Insignificant inter-annual variations but significant increase in the (7)Be activity concentrations during the spring and summer months were observed in birch-tree leaves and grass samples. The seasonal variation of the (7)Be concentrations in grass samples correlated (R(2) = 0.4663 and 0.6489) with precipitation. No similar correlation was found for (7)Be in birch-tree leaves. Beryllium-7 content in birch-tree leaves and in aerial parts of grass was mainly caused by direct transport of (7)Be from wet deposition into aerial parts of the observed plants.

Distribution of radiocesium and natural gamma emitters in pine needles in coniferious forest sites of Izmir

Using a high-resolution gamma-spectrometer system, the activity concentrations of 7Be, 137Cs, 40K and 226Ra were determined in the pine needles. Activity concentrations of the concerned radionuclides in the needle samples were as follows: 7Be, 24.6+/-2.40 to 210+/-7.21 Bq kg(-1), 40K, 23.5+/-12.4 to 287+/-15.6 Bq kg(-1), 226Ra, 0.44+/-0.12 to 12.3+/-2.18 Bq kg(-1), and 137Cs, 0.61+/-0.30 to 2.29+/-0.38 Bq kg(-1). It is found that the frequency distributions obtained for 7Be and 137Cs can be fitted to a normal distribution, and for 40K and 226Ra can be fitted to a log-normal distribution.

Use of beryllium-7 to document soil redistribution following forest harvest operations

Rapid and reliable methods for documenting soil erosion associated with forest harvest operations are needed to support the development of best management practices for soil and water conservation. To address this need, the potential for using 7Be measurements to estimate patterns and amounts of soil redistribution associated with individual post-harvest events was explored. The 7Be technique, which was originally developed for use on agricultural land, was employed to estimate soil redistribution associated with a period of heavy rainfall within a harvested forest area located in the Lake Region of Chile (39 degrees 44'7'' S, 73 degrees 10'39'' W; 22% slope; and mean annual rainfall 2300 mm yr(-1)). The results provided by the 7Be technique were validated against direct measurements of soil gain or loss during the same period obtained using erosion pins. The information produced by the two approaches was similar. The results of this study demonstrate the potential for using 7Be measurements to document event-based erosion in recently harvested forest areas.

Seasonal variability in 7Be depositional fluxes at Granada, Spain

Measurement of 7Be depositional fluxes at Granada, Spain (37 degrees 10'50''N-3 degrees 35'44''W, altitude 670 m) in the period 1995 through 1998 indicates substantial variations between the four seasons and also between corresponding seasons in different years, ranging from 23.6 to 242 Bq m(-2) per season. A strongly positive correlation with precipitation is shown, which explains about 70% of the variations in the 7Be depositional fluxes over the 16 seasons studied. The depositional 7Be flux is on the average highest in the fall and lowest in the summer. The study shows that precipitation primarily controls the 7Be depositional flux and plays a dominant role in the removal of 7Be from the troposphere. The average annual 7Be depositional flux at Granada amounts to 469+145 Bq m(-2).

A study of the vertical diffusion of the cosmogenic radionuclides, 7Be and 22Na in the atmosphere

The study of the mean vertical concentration profile of cosmogenic radionuclides provides information on the vertical transport in the troposphere and stratosphere. This paper is based on the results of accurate measurements of the mean monthly activity concentrations of (7)Be and (22)Na in ground-level air, data of the production rate of cosmogenic radionuclides in the atmosphere and a one-dimensional steady-state diffusion equation numerically solving the finite difference approximation.

Concentration measurements of 7Be at ground level air at Palermo, Italy-comparison with solar activity over a period of 21 years

Air activity concentrations of (7)Be in Palermo determined for the period January 1995-December 2002 by gamma-ray spectrometric analysis of particulate samples collected on paper filter by a high-volume sampler (approximately 900 m(3) h(-1)) are reported. The temporal behaviour of (7)Be concentration presents the same characteristics already observed in the measurements carried out over the previous 13-year (1982-1994) investigated period. The mean value of 5.06 mBq m(-3) obtained from the analysis of the 4636 particulate samples collected from 1982 to 2002 can be considered a representative value of (7)Be air concentration at ground level in our geographical zone. The comparison of long-term variation in the (7)Be concentrations with the cyclic solar activity-extended to the whole period of 21 years-confirms the inverse correlation between the two quantities.

Seasonal 7Be concentrations in near-surface air of Granada (Spain) in the period 1993-2001

Near-surface air samples for assessment of seasonal 7Be levels were taken weekly at Granada, Spain, (37 degrees 10'50"N-3 degrees 35'44"W, altitude 670 m) in the period 1993-2001. The 7Be levels measured reflect strong seasonal trends. Concentrations during autumn and/or winter showed a minimum (ca. 1.5 mBq/m3), and in each year a fallout maximum was found in summer (ca. 7.6 mBq/m3). Multiple regression of 7Be concentrations with temperature and rainfall, and with sunspot number explained about 71% of the variance in the 7Be data. The data reveal strong variations in the mean annual 7Be concentrations due to variations in the flux of cosmic galactic primary radiation caused by the 11-year sunspot cycle. A difference of a factor of 2.6 was found between the highest level (5.8 mBq/m3) obtained in 1996 (beginning of the solar cycle 23) and the lowest (2.6 mBq/m3) obtained in 2000 (maximum of the solar cycle 23).

Measurements of atmospheric 7Be properties using high-efficiency gamma spectroscopy

Two 7Be-related properties have been measured using a high-efficiency germanium gamma spectrometer (relative efficiency of 90%), namely, the activity median aerodynamic diameter (AMAD) of 7Be-associated atmospheric aerosols and the airborne 7Be radioactivity. With time resolutions of about 1-3d correlations between these 7Be-related properties and different meteorological parameters were identified. We found that AMAD is anti-correlated to 7Be counts. It is correlated with the relative humidity (RH) and mean cloud cover with high confidence, but not with temperature. We also found that 7Be radioactivity was correlated with the RH with a moderate confidence, but not with the mean cloud cover or temperature. Furthermore, wet precipitation present in the middle of the sampling period decreased the 7Be activity and increased the AMAD, while wet precipitation before or at the beginning of the sampling period decreased both 7Be activity and AMAD. Finally, after a cold front passed by, the AMAD decreased and the 7Be activity increased. Possible explanations are also given.