Depositional Fluxes Of 7Be Research Articles

Simulations of 7Be and 10Be with the GEOS-Chem global model v14.0.2 using state-of-the-art production rates

Abstract. The cosmogenic radionuclides 7Be and 10Be are useful tracers for atmospheric transport studies. Combining 7Be and 10Be measurements with an atmospheric transport model can not only improve our understanding of the radionuclide transport and deposition processes but also provide an evaluation of the transport process in the model. To simulate these aerosol tracers, it is critical to evaluate the influence of radionuclide production uncertainties on simulations. Here we use the GEOS-Chem chemical transport model driven by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis to simulate 7Be and 10Be with the state-of-the-art production rate from the CRAC:Be (Cosmic Ray Atmospheric Cascade: Beryllium) model considering realistic spatial geomagnetic cutoff rigidities (denoted as P16spa). We also perform two sensitivity simulations: one with the default production rate in GEOS-Chem based on an empirical approach (denoted as LP67) and the other with the production rate from the CRAC:Be but considering only geomagnetic cutoff rigidities for a geocentric axial dipole (denoted as P16). The model results are comprehensively evaluated with a large number of measurements including surface air concentrations and deposition fluxes. The simulation with the P16spa production can reproduce the absolute values and temporal variability of 7Be and 10Be surface concentrations and deposition fluxes on annual and sub-annual scales, as well as the vertical profiles of air concentrations. The simulation with the LP67 production tends to overestimate the absolute values of 7Be and 10Be concentrations. The P16 simulation suggests less than 10 % differences compared to P16spa but a significant positive bias (∼18 %) in the 7Be deposition fluxes over East Asia. We find that the deposition fluxes are more sensitive to the production in the troposphere and downward transport from the stratosphere. Independent of the production models, surface air concentrations and deposition fluxes from all simulations show similar seasonal variations, suggesting a dominant meteorological influence. The model can also reasonably simulate the stratosphere–troposphere exchange process of 7Be and 10Be by producing stratospheric contribution and 10Be/7Be ratio values that agree with measurements. Finally, we illustrate the importance of including the time-varying solar modulations in the production calculation, which significantly improve the agreement between model results and measurements, especially at mid-latitudes and high latitudes. Reduced uncertainties in the production rates, as demonstrated in this study, improve the utility of 7Be and 10Be as aerosol tracers for evaluating and testing transport and scavenging processes in global models. For future GEOS-Chem simulations of 7Be and 10Be, we recommend using the P16spa (versus default LP67) production rate.

Testing machine learning algorithms for the prediction of depositional fluxes of the radionuclides 7Be, 210Pb and 40K

The monthly depositional fluxes of 7Be, 210Pb and 40K were measured at Malaga, (Southern Spain) from 2005 to 2018. In this work, the depositional fluxes of these radionuclides are investigated and their relations with several atmospheric variables have been studied by applying two popular machine learning methods: Random Forest and Neural Network algorithms. We extensively test different configurations of these algorithms and demonstrate their predictive ability for reproducing depositional fluxes. The models derived with Neural Networks achieve slightly better results, in average, although similar, having into account the uncertainties. The mean Pearson-R coefficients, evaluated with a k-fold cross-validation method, are around 0.85 for the three radionuclides using Neural Network models, while they go down to 0.83, 0.79 and 0.8 for 7Be, 210Pb and 40K, respectively, for the Random Forest models. Additionally, applying the Recursive Feature Elimination technique we determine the variables more correlated with the depositional fluxes of these radionuclides, which elucidates the main dependences of their temporal variability.

Long term 7Be deposition in Romania

This study is based on monthly 7Be deposition data at 29 of the stations of Romania's National Environmental Radioactivity Surveillance Network (NERSN), with different geographical and climatological conditions, extending over periods up to 17 years (1979–1995). The 7Be activity in each monthly sample from each station was determined using high-resolution gamma-ray spectrometry performed at the Environmental Radioactivity Laboratory, Bucharest-Afumati.The annual dynamics of atmospheric deposition of 7Be at each NERSN station showed a strong seasonal trend, very similar to the precipitation regime, with the highest values being observed in spring/summer and the lowest in winter. But the annual 7Be deposition fluxes varied broadly from station to station and year to year, from a minimum of 164 Bq/m2/y (Bechet, 1989) to a maximum of 1388 Bq/m2/y (Baia Mare, 1988). This large space-time variability of deposition was mainly due to the variability of the precipitation regime.The analysis of experimental data confirms the strong correlation of 7Be deposition data with precipitation, air temperature and the number of sunspots.Wet and dry deposition data are presented and discussed for four stations where separate dry and wet 7Be deposition measurements were performed.

Atmospheric deposition of 7Be, 210Pb and 210Po during typhoons and thunderstorm in Shanghai, China and global data synthesis

Atmospherically-delivered 7Be, 210Po and 210Pb in bulk precipitation and air samples collected around the globe have provided valuable quantification on the rates of removal, as well as proportional mixing of attendant air masses; however, such studies during thunderstorm and typhoon events are limited. We report the first continuous time-series rainwater sampling and analysis of 7Be, 210Pb and 210Po from two typhoons and one thunderstorm during 2015 summer in Shanghai. The depositional fluxes within individual rain events of typhoons and thunderstorms varied by a factor of 10 for 7Be, 5.7 for 210Pb, 7.4 for 210Po, and 7.0 for 7Be/210Pb activity ratios (AR). Such large observed variations in the depositional fluxes of 7Be, 210Pb, 210Po and 7Be/210Pb activity ratios were attributed to air masses injected from surrounding high pressure system adjoining the typhoon to low pressure system within the typhoon. Based on 7Be/210Pb activity ratios, we estimated the variations in the fraction of maritime and continental air masses into the typhoon. Observed constancy in the 210Po/210Pb AR indicates that the residence times of air masses contributing to the typhoon during heavy rain are similar. From a synthesis of global fallout of 7Be and 210Pb during pulse events (precipitation≥50 mm from single rainout event), we quantify the importance of pulse events in the atmospheric fallout of these radionuclides.

Influence of rainfall on atmospheric deposition fluxes of 7Be and 210Pb in Mangaluru (Mangalore) at the Southwest Coast of India

The depositional fluxes of 7Be and 210Pb were measured at Mangalore (12.82° N, 74.92° E) on the South West Coast region, which is one of the highest rainfall regions in India. This region receives pristine air masses from the Southern Indian Ocean (oceanic) and polluted air from Asia (continental). The activity concentration for individual rain events collected during the monsoon season varied between 0.15 and 4.3 Bq L−1 (with geometric mean, GM = 1.1 Bq L−1, geometric standard deviation, GSD = 2.6) and 0.01–0.71 Bq L−1 (GM = 0.12 Bq L−1, GSD = 2.8) for 7Be and 210Pb, respectively. The GM value for monthly (dry period) 7Be and 210Pb concentrations in air were 6.9 mBq m−3 (GSD = 1.3) and 1.2 mBq m−3 (GSD = 2.1), respectively. The dry deposition flux of 7Be varied in the range of 0.081–0.184 Bq m−2 d−1 (GM = 0.12 Bq m−2 d−1, GSD = 1.3) and that of 210Pb varied in the range of 0.026–0.293 Bq m−2 d−1 (GM = 0.11 Bq m−2 d−1, GSD = 1.8). The GM value of the wet deposition flux of 7Be was higher by two orders of magnitude when compared with that of the dry deposition flux, whereas, that in the case of 210Pb it was higher by an order of magnitude. The mean annual deposition fluxes of 7Be and 210Pb were 2026 Bq m−2 y−1 and 221 Bq m−2 y−1, respectively. The large variability observed in the wet deposition fluxes was attributed to the large variations in the intensity of the rainfall. The wet deposition velocities of the aerosols, estimated based on the concentrations of these radionuclides in air and their corresponding deposition fluxes, were found to be 6.8 cm s−1 for 7Be and 6.5 cm s−1 for 210Pb. Although the two radionuclides originate from distinct sources, a strong positive correlation was observed between the temporal variability of their deposition fluxes. In addition to this, a high degree of correlation was observed between the deposition fluxes of both 7Be and 210Pb and rainfall. This points at the dominating effect of scavenging by rainfall in controlling their fluxes.

7Be, 210Pb and 40K depositions over 11 years in Málaga

The monthly bulk depositional fluxes of three natural radionuclides (7Be, 210Pb and 40K) were measured at a Mediterranean coastal station (Málaga) over an 11-year period from 2005 to 2015. The mean annual depositional fluxes of 7Be, 210Pb and 40K were 1215, 144 and 67 Bq m−2 year−1 respectively, showing a clear seasonal trend with minimum values recorded during summer and maximum values in winter. The rainfall regime with dry summers allows estimating the dry deposition. Assuming constant dry deposition through each year, 7Be, 210Pb and 40K would account for 12.5, 26.5 and 33% of the bulk fallout respectively which indicates that deposition for 210Pb and 40K are significantly higher than 7Be. The precipitation-normalized enrichment factor alpha used to explain seasonal variations in the depositional fluxes of radionuclides with respect the rainfall, indicates higher depositional fluxes during spring and summer than expected from the amount of rainfall. Despite their different origin, 210Pb and 7Be monthly depositional fluxes have strong correlation. The atmospheric deposition fluxes of 7Be, 210Pb and 40K were controlled mainly by the amount of rainfall (r = 0.89, 0.91 and 0.66 respectively). Moreover, principal component analysis was applied to the datasets and deposition of radionuclides and rainfall in the same component highlighting the importance of the washout mechanism. The mean depositional velocity of aerosols evaluated using 7Be and 210Pb are similar and are compared to other published values.

Using beryllium-7 to assess cross-tropopause transport in global models

Abstract. We use the Global Modeling Initiative (GMI) modeling framework to assess the utility of cosmogenic beryllium-7 (7Be), a natural aerosol tracer, for evaluating cross-tropopause transport in global models. The GMI chemical transport model (CTM) was used to simulate atmospheric 7Be distributions using four different meteorological data sets (GEOS1-STRAT DAS, GISS II′ GCM, fvGCM, and GEOS4-DAS), featuring significantly different stratosphere–troposphere exchange (STE) characteristics. The simulations were compared with the upper troposphere and/or lower stratosphere (UT/LS) 7Be climatology constructed from ∼ 25 years of aircraft and balloon data, as well as climatological records of surface concentrations and deposition fluxes. Comparison of the fraction of surface air of stratospheric origin estimated from the 7Be simulations with observationally derived estimates indicates excessive cross-tropopause transport at mid-latitudes in simulations using GEOS1-STRAT and at high latitudes using GISS II′ meteorological data. These simulations also overestimate 7Be deposition fluxes at mid-latitudes (GEOS1-STRAT) and at high latitudes (GISS II′), respectively. We show that excessive cross-tropopause transport of 7Be corresponds to overestimated stratospheric contribution to tropospheric ozone. Our perspectives on STE in these meteorological fields based on 7Be simulations are consistent with previous modeling studies of tropospheric ozone using the same meteorological fields. We conclude that the observational constraints for 7Be and observed 7Be total deposition fluxes can be used routinely as a first-order assessment of cross-tropopause transport in global models.

Atmospheric deposition patterns of 210Pb and 7Be in Cienfuegos, Cuba

The radiometric composition of bulk deposition samples, collected monthly for one year, February 2010 until January 2011, at a site located in Cienfuegos (22° 03′ N, 80° 29′ W) (Cuba), are analysed in this paper. Measurement of 7Be and 210Pb activity concentrations were carried out in 12 bulk deposition samples. The atmospheric deposition fluxes of 7Be and 210Pb are in the range of 13.2–132 and 1.24–8.29 Bq m−2, and their mean values are: 56.6 and 3.97 Bq m−2, respectively. The time variations of the different radionuclide have been discussed in relation with meteorological factors and the mean values have been compared to those published in recent literature from other sites located at different latitudes. The annual average flux of 210Pb and 7Be were 47 and 700 Bq m−2 y−1, respectively. Observed seasonal variations of deposition data are explained in terms of different environmental features. The atmospheric deposition fluxes of 7Be and 210Pb were moderately well correlated with precipitation and well correlated with one another. The 210Pb/7Be ratios in the monthly depositions samples varied in the range of 0.05–0.10 and showed a strong correlation with the number of rainy days.

Beryllium-7 atmospheric deposition and soil inventory on the northern Loess Plateau of China

Beryllium-7 is a potentially powerful tracer of soil erosion, but information on 7Be atmospheric deposition and associated soil inventories on the Loess Plateau of China is not readily available. In the study reported in this paper, we measured the 7Be inventories in undisturbed soil at different sampling times on the northern Loess Plateau of China for three years, between 2010 and 2012, and estimated the 7Be deposition fluxes and the daily 7Be inventories in undisturbed soil. The annual 7Be deposition fluxes during this period varied between 1303 ± 119 and 2222 ± 147 Bq m−2, with a mean of 1759 ± 416 Bq m−2. There is a marked seasonality for the 7Be deposition fluxes with the maximum in summer, approximately 50% to the annual deposition flux, and the minimum in winter, approximately 5% to the annual deposition flux. Precipitation amounts can explain more than 70% of the variation in 7Be deposition flux. 7Be deposition in the form of dustfall, dew and frost make a significant contribution to the 7Be deposition flux in the study region. The daily 7Be inventories in undisturbed soil varied markedly through time and ranged between 89.2 and 941.8 Bq m−2 with a mean of 392 ± 210 Bq m−2. They demonstrated a unimodal distribution over the year, with the highest values in August or September and the lowest in late winter or early spring.

Short-term variability of 7Be atmospheric deposition and watershed response in a Pacific coastal stream, Monterey Bay, California, USA

Beryllium-7 is a powerful and commonly used tracer for environmental processes such as watershed sediment provenance, soil erosion, fluvial and nearshore sediment cycling, and atmospheric fallout. However, few studies have quantified temporal or spatial variability of 7Be accumulation from atmospheric fallout, and parameters that would better define the uses and limitations of this geochemical tracer. We investigated the abundance and variability of 7Be in atmospheric deposition in both rain events and dry periods, and in stream surface-water samples collected over a ten-month interval at sites near northern Monterey Bay (37°N, 122°W) on the central California coast, a region characterized by a rainy winters, dry summers, and small mountainous streams with flashy hydrology. The range of 7Be activity in rainwater samples from the main sampling site was 1.3–4.4 Bq L−1, with a mean (±standard deviation) of 2.2 ± 0.9 Bq L−1, and a volume-weighted average of 2.0 Bq L−1. The range of wet atmospheric deposition was 18–188 Bq m−2 per rain event, with a mean of 72 ± 53 Bq m−2. Dry deposition fluxes of 7Be ranged from less than 0.01 up to 0.45 Bq m−2 d−1, with an estimated dry season deposition of 7 Bq m−2 month−1. Annualized 7Be atmospheric deposition was approximately 1900 Bq m−2 yr−1, with most deposition via rainwater (>95%) and little via dry deposition. Overall, these activities and deposition fluxes are similar to values found in other coastal locations with comparable latitude and Mediterranean-type climate. Particulate 7Be values in the surface water of the San Lorenzo River in Santa Cruz, California, ranged from <0.01 Bq g−1 to 0.6 Bq g−1, with a median activity of 0.26 Bq g−1. A large storm event in January 2010 characterized by prolonged flooding resulted in the entrainment of 7Be-depleted sediment, presumably from substantial erosion in the watershed. There were too few particulate 7Be data over the storm to accurately model a 7Be load, but the results suggest enhanced watershed export of 7Be from small, mountainous river systems compared to other watershed types.

Dry and wet deposition of 7Be, 210Pb and 137Cs in Monaco air during 1998–2010: Seasonal variations of deposition fluxes

Temporal variations of 7Be, 210Pb and 137Cs activity concentrations in precipitation in Monaco from 1998 to 2010 showed that maxima of 7Be and 210Pb deposition fluxes coincide with the peaks of precipitation amounts observed in different months of a year, and most of 7Be and 210Pb was washout from the atmosphere by precipitation. The seasonal variations were not uniform from year to year, and the amount of precipitation controlled the deposition fluxes of 7Be and 210Pb, which was not the case for 137Cs. The fractional deposition fluxes of 7Be and 210Pb in different seasons were in the order fall > spring > winter > summer, while the fractional amount of precipitation followed the order fall > winter > spring > summer. The fractional deposition fluxes of 137Cs were found in the order spring > fall > summer > winter. The precipitation-normalized deposition fluxes of 7Be, 210Pb and 137Cs were generally higher during summer. The highest 7Be/210Pb activity ratio was observed in 2010, and the smallest one in 2001, following the influence of the modulation of cosmic rays on the production rates of 7Be in the atmosphere by solar activity. Activity ratios of 7Be/210Pb observed in winter and fall were generally higher than during summer and spring.

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

Abstract The radiometric composition of bulk deposition samples, collected monthly in a 5 year period (1 January 2005 until 31 December 2009) at a site located 30 m a.s.l in Malaga (4°28′ 8″W; 36° 43′40″N), are analysed in this paper. Measurement of gross alpha, gross beta, artificial and natural radionuclide activity concentrations were carried out in 60 bulk deposition samples. We analysed the time series of gross alpha, gross beta 7Be, 210Pb and 40K. The specific activities of gross alpha and gross beta measured in bulk deposition material are in the range from 0.012–0.32 and 0.045–1.81 Bq l−1 and theirs mean values are: 0.11 and 0.59 Bq l−1 respectively. The activity values of 7Be and 210Pb are in the range from 0.65–8.3 and 0.05–1.32 Bq l−1 with mean values of 2.5 and 0.41 Bq l−1 respectively. The highest specific activities of 40K in bulk deposition material were recorded in connection with high altitude Saharan dust intrusion. The time variations of the different radionuclide concentrations have been discussed in relation with various meteorological factors and the mean values have been compared to those published in recent literature for other sites located at different latitudes. To study the deposition, monthly deposition data from a funnel collector were compared from 2005 to 2009.The monthly range in deposition fluxes for gross alpha varied widely (0.40–11 Bq m−2 month−1) and the average annual deposition is 21 Bq m−2 y−1. The monthly fluxes for gross beta varied (1.3–33.8 Bq m−2 month−1) and the average annual deposition is approximately 120 Bq m−2 y−1. The total annual deposition fluxes of 210Pb varied between 64.9 and 160.8 Bq m−2 y−1 with a mean of 120 Bq m−2 y−1. The annual 7Be depositional flux varied between 432 and 1204 Bq m−2 y−1 with a mean of 676 Bq m−2 y−1. Observed seasonal variations of deposition data are explained in terms of different environmental features. The atmospheric deposition fluxes of 7Be and 210Pb were moderately well correlated with rainfall (r2 of 0.72 and 0.76 respectively) and well correlated one with the other (r2 of 0.79).

Beryllium‐10 and beryllium‐7 in precipitation in Dübendorf (440 m) and at Jungfraujoch (3580 m), Switzerland (1998–2005)

Beryllium‐10 and beryllium‐7 have been measured in monthly precipitation samples at a high (Jungfraujoch, 46.32°N 7.59°E, 3580 m) and a low (Dübendorf, 47.25°N 8.27°E, 440 m) altitude station in Switzerland from 1998 till today. The average deposition fluxes of 7Be are 380 ± 30 atoms m−2 s−1 in Dübendorf and 320 ± 20 atoms m−2 s−1 at Jungfraujoch, and the fluxes of 10Be are 810 ± 70 atoms m−2 s−1 in Dübendorf and 810 ± 60 atoms m−2 s−1 at Jungfraujoch. The 10Be/7Be ratio measured at Jungfraujoch (2.4 ± 0.1) is higher than in Dübendorf (2.1 ± 0.1), which is probably caused by a greater share of stratospheric air at Jungfraujoch in which the 7Be content is reduced because of radioactive decay. The ratios correspond to a mean atmospheric residence time of ∼110–120 d. The deposition fluxes show a seasonal change with a summer maximum and a winter minimum. The 10Be/7Be ratio exhibits a maximum in the first half of the year at Jungfraujoch in accordance with seasonal stratosphere‐troposphere exchange (STE) variations. In Dübendorf the maximum occurs 1 month later. An analysis with a two‐box model shows that the calculated variability due to seasonally varying STE explains only one third of the observed variability in the 10Be/7Be ratio. The rest of the variability is caused by local effects, such as the precipitation rate and the larger than average STE variability at the midlatitudes. According to the model calculations, the global mean 10Be/7Be ratio only varies between 1.1 and 1.5 with a seasonally varying STE. The larger measured values in the midlatitudes point to a latitudinal dependence of the 10Be/7Be ratio.

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.

Deposition patterns of atmospheric 7Be and 210Pb in coast of East China Sea, Shanghai, China

In complied data of atmospheric deposition of 210Pb and 7Be in the world, the data from China is of lack. In the present paper, atmospheric depositional fluxes of 7Be and 210Pb were simultaneously measured in semimonthly interval for 1 year (from November 2005 to October 2006) at Shanghai (31°13′39″N, 121°23′56″E), China, 50 km from the coastal of East China Sea. The annual average flux of 210Pb and 7Be in 2006 is 4.79×10 2 and 2.07×10 3 Bq m −2 year −1, respectively. Compared with the published data, the highest flux of 210Pb in 2006 at Shanghai was clearly observed during studying periods. The possible reason for such high flux of 210Pb is discussed. Furthermore, deposition fluxes of both 210Pb and 7Be show varieties in seasons: highest flux of 210Pb in winter (November–August) and that of 7Be in spring (March–May). Moreover, the correlation between activity fluxes and precipitation are weak both for 7Be and 210Pb in whole of 2006; however, the high correlation are observed in autumn and spring for 7Be and that only in autumn for 210Pb.

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.

Atmospheric deposition fluxes of 7Be, 210Pb and 210Po at Xiamen, China

The atmospheric deposition fluxes of 7Be, 210Pb and 210Po at Xiamen were measured. The samples were collected from March 2004 to April 2005 and the sampling period was one month. The 7Be and 210Pb activity were measured using HPGe γ-spectrometer after concentration using Fe(OH)3 co-precipitation method. The 210Po was counted with an α-spectrometer after the sample was digested and spontaneous plated onto a silver planchet. At Xiamen, the atmospheric deposition fluxes of 7Be varied between 0.11 and 2.93 Bq·m−2·d−1 and the average was 1.64 Bq·m−2·d−1; 210Pb fluxes varied between 0.04 and 0.85 Bq·m−2·d−1, and the average was 0.51 Bq·m−2·d−1; 210Po fluxes varied between 0.002 and 0.133 Bq·m−2·d−1, and the average was 0.061 Bq·m−2·d−1. There were positive correlations between the deposition fluxes of 7Be, 210Pb or 210Po and the amount of precipitation. The residence time of aerosols varied between 6.0 and 54.0 days with a mean of 27.1 days, which were calculated by 210Po/210Pb fluxes ratios.

Radionuclides in deposition in the Ignalina NPP region in 2005

Abstract Results of radionuclide activity concentration measurements in deposition and ground-level air conducted at the station of the Institute of Physics situated 3.5 km from the Ignalina Nuclear Power Plant (Ignalina NPP) in 2005 are analyzed. Atmospheric depositional fluxes of 7Be, 60Co and 137Cs are estimated. Radionuclide particle deposition rates are calculated. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model of the global dispersion and deposition is used to explain variations in the 137Cs activity concentration in the ground-level air in the Ignalina NPP region in 2005. An increase in the 137Cs activity concentration of up to 17.4 µBq m−3 on 30 October-5 November is studied. Modelling results show that the Chernobyl NPP Unit 4 Sarcophagus and the radiocaesium resuspension from the Chernobyl NPP accident polluted regions are sources of 137Cs to the environment of the Ignalina NPP. Results on solubility in water of aerosols — carriers of 137Cs — are discussed.

Seasonal variations on the residence times and partitioning of short-lived radionuclides ( 234Th, 7Be and 210Pb) and depositional fluxes of 7Be and 210Pb in Tampa Bay, Florida

Historically, Tampa Bay has been impacted heavily by a wide range of anthropogenic perturbations that may include, agricultural-, shipping-, phosphate mining/distribution-related activities, as well as a burgeoning coastal population. Due to the presence of U-rich underlying sediments, elevated activities of U- and Th-series daughter products may be naturally released into this system. This region is also known for summer thunderstorms and corresponding increases in precipitation and surface water runoff. Only limited work has been conducted on the partitioning of particle-reactive radionuclides (such as 7Be, 210Pb, and 234Th) in such a dynamic coastal system. We investigated both the removal residence time and partitioning of these radionuclides between filter-retained particulate matter (≥ 0.5 μm) and the filtrate (< 0.5 μm) phase during late spring (June 2003) and mid summer (August 2003) in the water column of Tampa Bay. Our results indicate that the partitioning of 7Be, 210Pb, and 234Th between filtrate and filter-retained phase is controlled foremost by enhanced bottom resuspension events during summer thunderstorms. As a consequence, no significant relationship exists between the distribution coefficients ( K d values) of these isotopes and the concentration of suspended particulate matter (SPM). Relatively faster recycling rates of atmospheric water vapor derived from the ocean results in lower atmospheric depositional fluxes of 210Pb to the study site than predicted. The relationship between 7Be and 210Pb in bulk (wet + dry) deposition is compared to their respective water column activities. The residence times of particulate and dissolved 234Th, 7Be and 210Pb, as well the distribution coefficients of these radionuclides, are then compared to values reported in other coastal systems.

Factors Influencing the Atmospheric Depositional Fluxes of Stable Pb, 210Pb, and 7Be into Chesapeake Bay

Atmospheric depositional fluxes of 7Be and210Pb (bulk) and stable Pb (wet) were measuredsimultaneously for one year (from September 1995–August 1996) atStillpond, Maryland on the uppereastern shore of the Chesapeake Bay. The annual total(bulk) depositional fluxes of 210Pb and 7Bewere 0.78 and 13 dpm cm-2, respectively, andagree well with other previously reported results atnearby locations such as Norfolk, VA and Lewes, DE. The wet depositional flux of stable Pb (58 ng cm-2 yr-1)was also similar to thatmeasured at other Chesapeake sites during 1990–1991(55 ng cm-2 yr-1, for both Wye and Elms,Maryland). This suggests that a constant Pb flux hasbeen reached since the mandatory use of unleadedgasoline was instituted. The concentrations of7Be, 210Pb, and to a lesser extent stable Pbwere diluted exponentially by precipitation, based onconcentrations versus precipitation plots. Due tohigher enrichment of 210Pb in the lowertroposphere, the dilution effect was largest on210Pb (i.e., controlled mainly by below-cloudscavenging processes), and thus its depositional fluxincrease is negligible as precipitation amountincreases. A good correlation between the amount ofprecipitation and total depositional flux of 7Beand stable Pb, which are more enriched in the uppertroposphere, suggests that precipitation amount isimportant in controlling their fluxes (i.e.,controlled by both below-cloud scavenging and in-cloudcondensation processes). Based on 7Be versus210Pb plots, it appears that 7Be, relativeto 210Pb, is less efficiently scavenged bysnowfall. Our results suggest that in addition toprecipitation amounts, marine air-mass transport orsnowfall may be important factors in controlling theseasonal variability of the fallout fluxes of tracemetals in coastal areas.