Seasonal and spatial variation of atmospheric 210Pb and 7Be deposition: features of the Japan Sea side of Japan

Monthly depositional fluxes of (210)Pb and (7)Be at Tatsunokuchi, Japan which faces the Japan Sea were studied over a 12-year period from 1991 to 2002. The data were compared with the spatial variability of these fluxes at Taejon in Korea and at 11 other sites in Japan from Ishigaki of the southern islands of Okinawa to Wakkanai of the northern end of Hokkaido over a 2-year period from 2000 to 2001. The monthly depositions of both (210)Pb and (7)Be at Tatsunokuchi revealed very similar seasonal variations with a single peak; both depositions were high in winter and low in summer. This phenomenon was found to be not transient but stationary. The deposition of these nuclides was much greater on the Japan Sea side of Japan than on the Pacific Ocean side. The cause for high deposition of (210)Pb and (7)Be in winter might be explained by a combination of a series of the following processes: blowing out of air masses with a high (210)Pb concentration near the surface layer over the continent by strong winter monsoons, additional flow of cold air masses with high (7)Be concentration at high latitude, well-mixing with generation of ascending current and convection clouds over the Japan Sea, and heavy snowfalls accompanying them.     

Beryllium-7 in near-surface air and deposition at Brisbane, Australia

Measurements of 7Be concentrations in near-surface air and 7Be deposition were carried out at Brisbane, Australia. Concentrations of 7Be in near-surface air measured over 4 years show seasonal variations with values above the annual mean occurring mainly in the spring and summer months of each year. These higher concentrations coincide with the expected influx of stratospheric air to the planetary boundary layer in early spring and higher rates of convective circulation within the troposphere during summer. 7Be deposition measurements over 3 years show seasonal variations similar to the seasonal rainfall pattern. There is a statistically significant (p<0.001) linear relationship between monthly (7)Be deposition and rainfall amount. This relationship is used to calculate the net cumulative (7)Be areal activity density.     

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.     

The temporal variations of (7)Be, (210)Pb and (210)Po in air in England

We have conducted measurements of naturally occurring radionuclides (7)Be, (210)Pb and (210)Po in air at ground level at Chilton, Oxfordshire, England. The sampling and analysis regime for the latter two isotopes has been optimised to minimise uncertainties in measurement due to decay of (210)Po and in-growth of (210)Pb during the sampling and analysis period. Analysis times were reduced by using Cerenkov counting to assay the (210)Bi daughter of (210)Pb. Monthly data collected over a four-year period are presented and discussed. (7)Be activity concentrations appear to peak in spring. (210)Pb activity concentrations also follow a seasonal trend reflecting different (222)Rn emanation rates from soil during winter and summer. Data for (210)Po show no such trend.     

7Be to 210Pb concentration ratio in ground level air in Belgrade area

7Be to 210Pb concentration ratios in ground level air on two monitoring stations (MS1 and MS2) in Belgrade area were determined from 1996 to 2001. The average monthly concentrations of 7Be in ground level air were in the range of 0.6-18.3 mBq/m3 and exhibited one or two summer/early fall maxims and one minimum in winter. The maximum concentrations for 210Pb were generally observed in the fall, with the average concentrations in the range of 1.09 x 10(-4) to 30.9 x 10(-4) Bq/m3. The 7Be/210Pb ratios were in the range of 1.7-12.7 (MS1) and 1.8-11.3 (MS2), with summer maxims and late fall/winter minimums. The mean Radionuclides Loading Indices values approach zero except for 1996/1997 (MS1) and 2001 (MS2) due to higher concentrations of 7Be and 210Pb. The mean monthly concentrations of both radionuclides exhibited lognormal distributions. There is significant correlation between the 7Be/210Pb activities ratio and the air stability classes A + B + C for both monitoring stations (correlation coefficients 0.61-0.65), and no correlation with D class and E + F classes. Correlation was found between the activity of 7Be and air stability classes A + B + C (0.46-0.68), and E + F (0.38 for MS1), while for 210Pb, a moderate correlation (0.38-0.40) was found with the E + F air stability classes.     

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.     

Natural and anthropogenic radionuclides in airborne particulate samples collected in Barcelona (Spain)

Results for naturally occurring ⁷Be, ²¹⁰Pb, ⁴⁰K, ²¹⁴Bi, ²¹⁴Pb, ²¹²Pb, ²²⁸Ac and ²⁰⁸Tl and anthropogenic ¹³⁷Cs in airborne particulate matter in the Barcelona area during the period from January 2001 to December 2005 are presented and discussed. The ²¹²Pb and ²⁰⁸Tl, ²¹⁴Bi and ²¹⁴Pb, ⁷Be and ²¹⁰Pb radionuclide levels showed a significant correlation with each other, with correlation coefficients of 0.99, 0.78 and 0.69, respectively, suggesting similar origin/behaviour of these radionuclides in the air. Caessium-137 and Potassium-40 were transported to the air as resuspended particle from the soil. The ⁷Be and ²¹⁰Pb concentrations showed similar seasonal variations, with a tendency for maximum concentrations during the summer months. An inverse relationship was observed between the ⁷Be, ²¹⁰Pb, ⁴⁰K and ¹³⁷Cs concentrations and weekly rainfall, indicating washout of atmospheric aerosols carrying these radionuclides.     

Factors influencing ambient concentrations of (210)Pb and (7)Be over the city of Edinburgh (55.9 degrees N, 03.2 degrees W)

Concentrations of (210)Pb and (7)Be in air were continuously monitored, using a high-volume air sampler and a high-resolution gamma-ray spectrometer, during the period of July 2002 to June 2003 at the University of Edinburgh 55.9 degrees N, 03.2 degrees W. The time series of both radio-isotopes show seasonality, dependence on air-mass origin, residence time and precipitation. Surface air concentrations of (210)Pb and (7)Be ranged from 0.01 to 0.74 mBq m(-3) and 0.63-6.54 mBq m(-3), respectively. The measurements indicate that the average concentrations of both (210)Pb and (7)Be in surface air were 0.21+/-0.01 and 2.50+/-0.04 mBq m(-3), respectively; which agrees closely with the corresponding values reported for coastal air measurements in Europe.     

Possible use of terrestrial mosses in detection of atmospheric deposition of 7Be over large areas

The activities of naturally occurring radionuclides (7)Be, (214)Bi and (210)Pb were measured in samples of terrestrial mosses collected in Serbia (42 degrees 26'19'N-45 degrees 23'12'N). The objective of this work was to establish if detectable amounts of (7)Be and (210)Pb can be found in mosses and investigate their possible variabilities over some area. These are the first steps in introducing mosses as a medium in possible monitoring of spatial distribution of (7)Be atmospheric deposition. The mean value of 360 Bq/kg of (7)Be activity was found in collected moss samples and some nonuniformity in spatial distribution (a 2.8-fold range in measured values) was observed.     

Vertical distributions of 210Pb excess, 7Be and 137Cs in selected grass covered soils in Southeast Queensland, Australia

Net accumulated areal activity densities and profiles of (210)Pb(ex), (7)Be and (137)Cs in the surface 10 cm of the soil are reported for eight sites in Southeast Queensland, Australia. Areal activity densities of (210)Pb(ex) and (7)Be varied from 1,080 to 4,100 Bqm(-2) and from 176 to 778 Bqm(-2), respectively. A significant (p < 0.001) portion of the variance (R(2) > 0.99) in their vertical distributions was explained by depth in the profile using an exponential function. Around 85% of accumulated (210)Pb(ex) was present in the surface 10 cm of the soil. Beryllium-7 was mainly confined to the grass and surface 2 cm of the soil. Average penetration half-depths of 3.6 +/- 0.2 and 0.3 +/- 0.1cm were determined for (210)Pb(ex) and (7)Be, respectively. Areal activity densities of global fallout (137)Cs varied from 10 to 361 Bqm(-2). Its signal was well mixed within the surface 10 cm. Comparison of the measured (137)Cs values to the estimated input value for the region ( approximately 490 Bqm(-2)) and profiling of a 1m deep soil core suggests a vertical migration of (137)Cs over the past decades. The paleo-radon activity flux determined from the (210)Pb(ex) areal activity density (5.1 +/- 0.9 mBqm(-2) s(-1)) was not statistically different to that measured using activated charcoal cups (5.5 +/- 0.4 mBqm(-2) s(-1)), tending to suggest that Southeast Queensland is neither a net source nor a net sink of (210)Pb-bearing aerosols.     

Distribution of fallout radionuclides (7Be, 137Cs, 210Pb and 239,240Pu) in soils of Taiwan

Depth profiles and cumulative deposition of four fallout radionuclides (7Be, 137Cs, 210Pb and 239,240Pu) were determined in presumably undisturbed soils in Taiwan. Inventories of these radionuclides in different areas correlate significantly with each other (except 7Be) and with mean annual rainfall, providing a necessary condition for the development of soil erosion studies in Taiwan. However, the data show very large spatial variability between and within landscape units, reflecting the steep topographic and meteorological gradients in the island. Thus, the application of fallout radionuclides to study soil conservation in Taiwan is expected to be a demanding task; it will call for dense sampling even at undisturbed reference sites.     

The effect of air mass origin on the ambient concentrations of Be and Pb in Islamabad, Pakistan

Concentration of radionuclides ²¹⁰Pb and ⁷Be, having half lives of 22.3 years and 53.29 days, respectively, in the surface air samples of Islamabad (33.38° N, 73.10° E and Altitude ∼536 m asl.) are measured. The non-destructive technique of gamma-spectrometry, with a high purity germanium HPGe detector, was employed for the analysis of all samples. The annual average concentrations of ²¹⁰Pb and ⁷Be in the surface air samples were determined as 0.284 ± 0.15 and 3.171 ± 1.14 mBq m⁻³, respectively. Our results have shown a seasonal variation of the concentration of ⁷Be in air samples with high values for the spring season. High concentrations for ²¹⁰Pb are obtained when air masses originate from plain areas of Pothohar region, located in the South-West, West and North West of Islamabad. Our values of concentrations show a nice agreement with the relevant reported results.     

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

Results of analysis of ⁷Be, ¹³⁷Cs and ²¹⁰Pb 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 ⁷Be and temperature (r = 0.50), ²¹⁰Pb and temperature and humidity (r = 0.43 and 0.41, respectively), and ¹³⁷Cs and precipitation (r = 0.51). The minimum and maximum ⁷Be activity concentrations were observed during 2000 and 2009, corresponding with the maximum and minimum solar activity, respectively. The maximum ¹³⁷Cs activity concentration found in May-June 1998 was due to the accident at Algeciras in Spain. The deposition velocities of ⁷Be, ¹³⁷Cs and ²¹⁰Pb 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.     

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

Activity concentrations of the long-lived natural radionuclides ²²⁶Ra, ²²⁸Ra, ²¹⁰Pb, ⁴⁰K and of ⁷Be in surface air were measured twice monthly at a semi-rural location 10 km north of Munich (FRG) for at least three years. For the time interval 1983–1985, all values were found to be distributed log-normally, with geometric means (in μBq m⁻³) of 1·2 for ²²⁶Ra, 0·5 for ²²⁸Ra, 580 for ²¹⁰Pb, 12 for ⁴⁰K and 3500 for ⁷Be. Reflecting their common origin, the activity concentrations of ²²⁶Ra and ⁴⁰K are correlated with surface air dust concentrations (geometric mean 59 μg m⁻³). Seasonal variations of ²¹⁰Pb and ⁷Be air activity concentrations are established for the time interval 1978–1985.The contribution of local soil activity to the air activity concentrations of these radionuclides and of natural uranium is discussed. Resuspension factors are found to be of the order of 10⁻⁹m⁻¹.     

Surface air concentration and deposition of lead-210 in French Guiana: two years of continuous monitoring

To make up for the lack of data on (210)Pb aerosol deposition in tropical regions and to use this radionuclide as an aerosol tracer, a monitoring station was run for two years at Petit-Saut, French Guiana. Lead-210 concentration in air at ground level was monitored continuously together with atmospheric total deposition. The air concentration has a mean value of 0.23+/-0.02 mBq m(-3) during both wet and dry seasons, and it is only weakly affected by the precipitation mechanism. This result was unexpected in a wet tropical region, with a high precipitation rate. In contrast, deposition clearly correlates with precipitation for low/moderate rainfall (<15 cm per 15-day), while this correlation is masked by strong fluctuations at high rainfall. The estimated mean annual deposition over the last ten years is 163+/-75 Bq m(-2) y(-1). This provides a procedure for estimating this mean flux at other sites in French Guiana.     

Short-term seasonal variability in Be wet deposition in a semiarid ecosystem of central Argentina

The ⁷Be wet deposition has been intensively investigated in a semiarid region at San Luis Province, Argentina. From November 2006 to May 2008, the ⁷Be content in rainwater was determined in 58 individual rain events, randomly comprising more than 50% of all individual precipitations at the sampling period. ⁷Be activity concentration in rainwater ranged from 0.7 ± 0.3 Bq l⁻¹ to 3.2 ± 0.7 Bq l⁻¹, with a mean value of 1.7 Bq l⁻¹ (sd = 0.53 Bq l⁻¹). No relationship was found between ⁷Be content in rainwater and (a) rainfall amount, (b) precipitation intensity and (c) elapsed time between events. ⁷Be ground deposition was found to be well correlated with rainfall amount (R = 0.92). For the precipitation events considered, the ⁷Be depositional fluxes ranged from 1.1 to 120 Bq m⁻², with a mean value of 32.7 Bq m⁻² (sd = 29.9 Bq m⁻²). The annual depositional flux was estimated at 1140 ± 120 Bq m⁻² y⁻¹. Assuming the same monthly deposition pattern and that the ⁷Be content in soil decreases only through radioactive decay, the seasonal variation of ⁷Be areal activity density in soil was estimated. Results of this investigation may contribute to a valuable characterization of ⁷Be input in the explored semiarid ecosystem and its potential use as tracer of environmental processes.     

Determination of radionuclide levels in rainwater using ion exchange resin and γ-spectrometry

The evaluation of radioactivity accidentally released into the atmosphere involves determining the radioactivity levels of rainwater samples. Rainwater scavenges atmospheric airborne radioactivity in such a way that surface contamination can be deduced from rainfall rate and rainwater radioactivity content. For this purpose, rainwater is usually collected in large surface collectors and then measured by γ-spectrometry after such treatments as evaporation or iron hydroxide precipitation. We found that collectors can be adapted to accept large surface (diameter 47 mm) cartridges containing a strongly acidic resin (Dowex AG 88) which is able to quantitatively extract radioactivity from rainwater, even during heavy rainfall. The resin can then be measured by γ-spectrometry. The detection limit is 0.1 Bq per sample of resin (80 g) for ¹³⁷Cs. Natural ⁷Be and ²¹⁰Pb can also be measured and the activity ratio of both radionuclides is comparable with those obtained through iron hydroxide precipitation and air filter measurements. Occasionally ²²Na has also been measured above the detection limit. A comparison between the evaporation method and the resin method demonstrated that 2/3 of ⁷Be can be lost during the evaporation process. The resin method is simple and highly efficient at extracting radioactivity. Because of these great advantages, we anticipate it could replace former rainwater determination methods. Moreover, it does not necessitate the transportation of large rainwater volumes to the laboratory.     

Cosmogenic 7Be deposition in North Wales: 7Be concentrations in sheep faeces in relation to altitude and precipitation

Beryllium-7 (7Be) is a cosmogenic radionuclide with a half-life of 53.3 days produced mostly in the stratosphere by cosmic ray spallation of nitrogen and oxygen and entering the lower troposphere by atmospheric circulation processes. Most of the nuclide is removed by rainout during precipitation, so given that rainfall generally increases with altitude, it was considered probable that 7Be deposition would also be greater at higher altitudes. The aim of this study was to determine if there is any relationship between 7Be concentrations, altitude and precipitation by measuring 7Be activity within sheep faeces. An area of North Wales and Northwest England was selected for study, extending from the Dee Estuary at sea level to Snowdon at 1065 m. The results obtained showed a significant increase in 7Be activity with increasing altitude and precipitation consistent with predictions based on the existing literature.     

Precipitation scavenging of 7Be and 137Cs radionuclides in air

Atmospheric depositional fluxes of the naturally occurring 7Be of cosmogenic origin and 137Cs from fallout of the Chernobyl accident were measured over a 6-year period (January 1987-December 1992) at Thessaloniki, Greece (40 degrees 38'N, 22 degrees 58'E). Total precipitation accumulation during 1987-1992 varied between 33.7 cm and 65.2 cm, reflecting a relatively dry (precipitation-free) climate. The activity concentrations of 7Be and 137Cs in rainwater depended on the precipitation rate, being higher for low precipitation rates and lesser for high precipitation rates. 137Cs was removed by rain and snow more efficiently than 7Be. Snowfall was more efficient than rainfall in removing the radionuclides from the atmosphere. The annual bulk depositional fluxes of 7Be varied between 477 and 1133 Bq m(-2) y(-1) and this variability was attributed to the amount of precipitation and the variations of the atmospheric concentrations of 7Be. The annual bulk depositional fluxes of 137Cs showed a significant decrease over time from 1987 to 1992, resulting in a removal half-life of 1.33 years. The presence of 137Cs in air, and therefore in rainwater and snow, long after the Chernobyl accident (26 April 1986) was mainly due to the resuspension process. The normalized depositional fluxes of both radionuclides showed maximal values during the spring season where the maximum amount of precipitation occurred. The relatively high positive correlation between 7Be and 137Cs normalized depositional fluxes indicates that the scavenging process of local precipitation controlled the fluxes of both radionuclides. The dry depositional flux of 7Be was less than 9.37% of total (wet and dry) depositional flux. The fraction of dry-to-total depositional flux of 137Cs was much higher than that of 7Be, due to the resuspended soil.     

Relationship between variations of Be, Pb and Pb concentrations and sub-regional atmospheric transport: Simultaneous observation at distant locations

In order to investigate the applicability of ²¹²Pb as a tracer for atmospheric transport in the sub-regional scale (few hundred kilometers in horizontal direction and up to ∼1 km by height), we measured the air concentrations of the short-lived radionuclide ²¹²Pb along with the long-lived ⁷Be and ²¹⁰Pb near the ground surface. For this purpose, simultaneous observations were continued for several days at three locations: a reference point representative for standard land surface atmosphere conditions, a second location at an altitude 650 m near the reference point, and on a solitary island ∼180 km from the reference point. Measurements of radioactivity in aerosol particle samples collected at intervals of 2-3 h with a high-volume air sampler were performed by extremely low background gamma-ray spectrometry with the use of Ge detectors located at the Ogoya Underground Laboratory. Concentration of ⁷Be or ²¹⁰Pb and their variation patterns was found to be similar among the three points during the whole observation period except for moment of the passage of a cold front. The results indicate that distributions of concentrations of the long-lived nuclides were uniform in this range. On the other hand, concentration levels and the variation patterns of the short-lived ²¹²Pb differed greatly from one location to another, reflecting differences in geographical location and altitude of the observation points. Additionally, there were certain indications that observed concentration of ²¹²Pb contained two components: an autogenous component from sources nearby and a heterogenous one from faraway sources carried by atmospheric horizontal transport. Results of this study provide experimental proof that ²¹²Pb can be used as a tracer of sub-regional atmospheric transport.