Atmospheric Concentrations Of 7Be Research Articles

Influence of Meteorological Parameters on the Variations of Atmospheric Radionuclides Concentration in Dar es Salaam, Tanzania

Atmospheric concentrations of 7Be and 212Pb were measured for 11 years (2008 – 2018) in Dar es Salaam, Tanzania. The mean activity concentrations of 7Be and 212Pb were found to be within the range of 1.29 – 5.71 mBq/m3 and 10.85 – 50.06 mBq/m3, respectively. The annual mean activity concentrations of 7Be and 212Pb were 4.72 ± 1.18 mBq/m3 and 29.76 ± 13.63 mBq/m3, respectively. Distinct annual trends were depicted on 7Be and 212Pb, suggesting that the two radionuclides were affected differently with atmospheric conditions. Monthly atmospheric concentrations of 7Be showed a strong seasonal variation trend with the highest in January and February and lowest in April. 212Pb depicted the highest concentration during June and July and lowest in January and December. The regression analysis for 7Be and 212Pb activity concentrations together with number of meteorological parameters revealed that the relative humidity, rainfall, air temperature, absolute humidity and wind speed are the most significant parameters affecting radionuclides activity concentrations in the atmosphere. The sunspot numbers show 66.7% of its variability with 7Be activity concentration which further suggesting that other parameters may influence its variation. 212Pb, on the other hand, shows only 27.3% of its variability which clearly indicates that the existence of cosmic rays does not affect its activity concentration in the atmosphere.

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.

Temporal variation of atmospheric 7Be and 210Pb concentrations and their activity size distributions at Astana, Kazakhstan in Central Asia

Atmospheric concentrations of 7Be and 210Pb obtained by a high-volume air sampler with a cascade impactor were measured from September 2016 to November 2017 in Astana, Kazakhstan. The levels and seasonal variations of atmospheric 7Be and 210Pb concentrations were investigated together with their activity size distributions. Typical seasonal variability was observed with higher concentrations of 7Be occurring in the warm summer and that of 210Pb towards the cold winter. These trends may be attributed to the increased vertical mixing within the troposphere during the warm summer season and the frequent inversion conditions of the surface layers during the cold winter season.

Decadal variations of atmospheric 7Be and 10Be concentrations between 1998 and 2014 in Japan

Atmospheric concentrations of 7Be and 10Be were investigated in Dazaifu, Fukuoka (1998–2001) and Tokyo (2002–2014) from 1998 to 2014. The seasonal variations were roughly the same for each year, with high 7Be and 10Be concentrations and high 10Be/7Be isotopic ratios caused by strong stratosphere-troposphere exchange (STE) from February to June, and fluctuating 7Be and 10Be concentrations and constant 10Be/7Be ratios caused by vertical convection in the troposphere from July to December. Using a three-box model, the residence time of the stratosphere, the troposphere, and the boundary layer were estimated to be 2 years, 55 days, and 3 days, respectively, and the mass flux observed during the STE season was estimated to be six times higher than the mass flux observed during the vertical convection season. The amplitude of solar modulation was also found to be three times larger than the amplitude of relative cosmic ray intensity at the Earth’s surface.

Determination of atmospheric concentration of beryllium-7 at ground level

Atmospheric concentration of beryllium-7 (7Be) at ground level was measured from September 2012 to October 2013 in San Carlos de Bariloche, Argentina, using a HPV-5300AFC brushless, automatic flow control outdoor high volume air sampler for continuous use, and 8”×10” 0.8 microns fiberglass filters. The activity of 7Be was determined on a high-purity germanium (HPGe) detector (relative efficiency 12.3%) by standard gamma spectrometry. The average value found was 4.1 ± 0.1 mBq/m3. Seasonal changes in the atmospheric concentration of 7Be were compared with other environmental variables (temperature, humidity, precipitations, and air kerma rate), and correlation, both positive and negative, was observed as expected. Measurements were carried out following the Radiological Environmental Monitoring Programme at Bariloche Atomic Centre. The aim of the study was to determine atmospheric concentration of 7Be at ground level and to correlate its seasonal changes with environmental variables. Air samplers and environmental dosemeter locations were far away from buildings and any other thing that could influence or alter the measurements. Pearson's correlation coefficient was calculated to evaluate the relation between atmospheric 7Be concentration and environmental variables of interest. These changes in 7Be concentration can be attributed to the variations and dynamic of air exchange between the stratosphere and the troposphere and to the variations of the tropopause height. To fully understand and correctly interpret the meaning of these seasonal variations in the concentrations of atmospheric 7Be, active atmospheric processes must be taken into account. According to the measurements carried out, contribution of 7Be concentration to the natural background radiation dose is negligible.

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.

Deposition of7Be to Bermuda and the regional ocean: Environmental factors affecting estimates of atmospheric flux to the ocean

[1] The distribution of 7Be in ocean surface waters is used as tracer of upper ocean transport and atmospheric deposition processes. However, there is very little ocean deposition data available to characterize the temporal and spatial input of 7Be to the oceans and test model results. Here we measure the deposition of 7Be in bulk collectors at two sites at Bermuda over a span of nearly 2 years (April 2007 to January 2009) and compare these rates to the flux required to sustain the inventory of 7Be measured in the nearby Sargasso Sea. The Tudor Hill collector site undersampled (by ∼40%) both the rainfall compared to other Bermuda sites and the 7Be flux required for the ocean inventory. On the other hand, the 7Be flux captured at the Bermuda Institute of Ocean Sciences station site (0.048 dpm cm−2 d−1) matched that expected from the ocean observations. Previously measured long-term atmospheric concentration of 7Be in surface air at Bermuda was used to estimate deposition velocities and scavenging ratios, and our estimates in this marine environment were found to be similar to those measured in continental regions. The deposition of 7Be to the oceans is overwhelmingly determined by wet processes; dry deposition to the ocean surface accounts for only a few percent, at most, of the total deposition to the ocean. We place these measurements in a longer-term and large-scale spatial context by using climatological rainfall data on Bermuda and ocean rainfall estimates from the Global Precipitation Climatology Program and Tropical Rainfall Measuring Mission.

Study of 7Be activity concentration in the air of northern Spain

Time series analysis techniques have been applied to the study of the 7Be activity concentration in air, which was obtained by weekly collecting aerosols in filters in the north of Spain, and measuring them by gamma ray spectrometry. Between 2001 and 2009, a trend pattern is found. The cyclical component of this series is clearly influenced by the solar cycle (11 years period). Two kinds of seasonality were found in the time series: annual periodicity and variations with seasons of the year. The irregular component has also been studied but its contribution has been insignificant; one of its possible causes, rainfall, has been analysed and the conclusion is that the atmospheric concentration of 7Be is unaffected by rainfall. The contribution of 7Be presence in air to the total effective dose rate in air has also been studied, resulting negligible.

大気中7Be, 10Be濃度を用いた成層圏-対流圏交換速度の評価

大気中7Be, 10Be濃度を用いた成層圏-対流圏交換速度の評価

Total deposition velocities and scavenging ratios of 7Be and 210Pb at Rokkasho, Japan

The atmospheric concentrations and deposition fluxes of 7Be and 210Pb were observed biweekly in Rokkasho, Japan on the Pacific Ocean coast at the northern end of Honshu Island, from March 2000 to March 2006, to clarify their regional features. Seasonal variation pattern of atmospheric 7Be concentrations had double peaks, and that of 210Pb had a single peak. Deposition fluxes of 7Be and 210Pb showed the same patterns. The total deposition pattern of 7Be was similar to that commonly seen on the Pacific Ocean side of northern Honshu Island, while the pattern of 210Pb was similar to that commonly seen on the Japan Sea side. The lack of high spine mountains windward in Rokkasho may be the cause of this ambiguity in the winter monsoon season. Total deposition velocities and scavenging ratios of 210Pb were similar to those of 7Be from spring to fall, and showed that both nuclides had a similar removal process from the atmosphere. However, the scavenging ratios of 210Pb were slightly larger than those of 7Be in winter, indicating different behaviors for both nuclides in the scavenging process. The scavenging ratios of both nuclides inversely correlated with precipitation rate, and the ratios in winter were larger than in the other seasons.

Mechanism of 7Be scavenging from the atmosphere through precipitation in relation to seasonal variations in Rokkasho Village, Aomori Prefecture, Japan

7Be deposition fluxes and atmospheric concentrations were measured at Rokkasho Village, Aomori Prefecture, Japan, from 2000 to 2005. It was confirmed that the 7Be deposition fluxes were minimum in summer, and the fallout maximizes in winter. The atmospheric concentration of 7Be was especially low in summer, and high in the other three seasons. A positive correlation was observed between the amount of precipitation and 7Be deposition. Clear seasonal differences were evident among the ratios of 7Be deposition flux to precipitation amounts in the four seasons. The ratios were especially high in winter, higher than those in the other three seasons. 7Be deposition flux was estimated by a simple simulation model using atmospheric 7Be concentrations and local meteorological data. As a result, the estimated deposition value was relatively lower than the measured value in winter.

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°38′N, 22°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.

Temporal changes of 7Be and 210Pb concentrations in surface air at temperate latitudes (40°N)

Atmospheric concentrations of 7Be and 210Pb were measured for 15 years (1987–2001) in ground-level air at Thessaloniki, Northern Greece (40°38′N, 22°58′E). Mean activity concentrations of 7Be and 210Pb were 5.02 mBq m −3 and 664 μBq m −3, respectively, characteristic of the latitude of 40°N. Monthly atmospheric concentrations of 7Be showed a strong seasonal trend with the highest values being observed in the summer and the lowest in the winter period. Multiple regression analysis of the data of 7Be concentrations and a number of meteorological parameters revealed that the sunspot number and temperature are the most significant parameters affecting the concentrations of 7Be in surface air. The observed strong positive correlation between the mean monthly concentrations of 7Be and the temperature confirms that the increased rate of vertical transport within the troposphere, especially during the warm months, has as a result to carry down to the surface layer air masses enriched in 7Be. Highest values of the mean monthly atmospheric concentrations of 210Pb were observed in the autumn and lowest in the spring period. The positive correlation that was observed between 210Pb and 7Be concentrations during the summer months suggests that these two radionuclides could be used together as tracers of environmental processes.

Observation of 7Be on the surface of LDEF spacecraft

THELong Duration Exposure Facility (LDEF), an orbiting unmanned satellite, was recently returned to Earth after almost six years in space. From radioactivity measurements, we have found significant quantities of the isotope7Be on the leading edge (but only on the leading edge) of LDEF. Although the absolute atmospheric concentration of 7Be needed to explain this detection is extremely small (10–7atoms cm–3), its concentration at LDEF's altitude (310 km) must be several orders of magnitude higher than in the stratosphere below, where it is produced by cosmic-ray reactions with atmospheric nitrogen and oxygen nuclei. To explain the presence of 7Be on the surface of LDEF, it must first be rapidly and efficiently transported to high altitudes, and then adsorbed onto the surface of the spacecraft. Neither process had been expected. Our detection may therefore lead to the use of 7Be as an exo-atmospheric tracer, as well as to studies of surface interactions in space.

Aerosol deposition velocities on the Pacific and Atlantic oceans calculated from 7Be measurements

The concentrations of 7Be have been measured in Pacific and Atlantic ocean water for the past several years to determine the deposition velocity of aerosol particles on the ocean surface. 7Be is produced at a relatively constant rate in the atmosphere by spallation reactions of cosmic rays with atmospheric nitrogen and oxygen. Immediately after its formation 7Be becomes attached to aerosol particles, and therefore can serve as tracers of the subsequent behavior of these particles. Isopleths of 7Be surface water concentrations, 7Be inventory in the ocean, and deposition velocity have been prepared for the Pacific Ocean from 30°S to 60°N and for the Atlantic Ocean from 10°N to 55°N. The concentrations, inventories and deposition velocities tended to be higher in regions where precipitation was high, and generally increased with latitude. The average flux of 7Be across the ocean surface was calculated to be 0.027 atoms cm −2 s −1 which is probably not significantly greater than the worldwide average 7Be flux across land and ocean surfaces of 0.022 atoms cm −2 s −1 calculated by Lal and Peters. The average deposition velocity was calculated to be 0.80 cm s −1. This value may be 10–50% too low, since it was calculated using atmospheric 7Be concentrations which were measured at continental stations. Measurements of atmospheric 7Be concentrations at ocean stations suggest that the concentrations at the continental stations averaged 10–50% higher than the concentrations over the ocean.