Wet Deposition Velocity Research Articles

Site-specific transfer parameters for the tritium transport model at a tropical site, Tarapur, west coast of India

The study of the fate of atmospheric release and transport of Tritium requires an understanding of the exchange/transfer of Tritium (HTO) from within the compartments; air, soil, and plant systems. The Tritium transfer parameters within these compartments are used in specific activity models to compute TFWT and OBT in terrestrial plants and are highly dependent on the site-specific conditions. Hence a study was carried out to generate site-specific Tritium transport model parameters in the tropical environment of Tarapur which receives the atmospheric releases of Tritium from nuclear facilities operating at this site, on the West coast of India. The paper presents the details of the study carried out in Tarapur, India. The transfer parameters generated through this study are soil water to air moisture HTO transfer ratio: CRs, plant water to air moisture HTO transfer ratio: Rpa, and plant water to soil water HTO transfer ratio: Rpw. The geometric mean and geometric standard deviation (GSD) of the transfer ratios, CRs, Rpa and Rpw determined were found to be 0.50 (GSD: 3.52), 0.53 (GSD: 2.51) and 1.12 (GSD: 2.58), respectively. In addition, the Tritium scavenging ratio, surface loading, and wet deposition velocity were also derived and were found to be 1.59 ± 1.32, 1.21 × 10−2 Bq m−2 s−1, and 7.91 × 10−2 m s−1, respectively. The study has generated a set of site-specific model input parameters for a tropical coastal site of Tarapur, India, and details are discussed in the manuscript.

SITE-SPECIFIC DRY AND WET DEPOSITION VELOCITIES USING 7BE AND MASS INTERCEPTION FACTOR FOR VARIOUS TYPES OF PLANT LEAVES AT NARORA SITE, INDIA.

Comprehensive studies were carried out during the period 2016-19 on the estimation of site-specific wet and dry deposition velocities and the mass interception factor for Narora site based on the concentrations of 7Be in air, air deposits, rain water and vegetation samples. Mean wet and dry deposition velocities for Narora site were found to be 1.64E-2 and 1.58E-3ms-1, respectively. Mass interception factors for vegetation found to be 0.34-2.51m2kg-1 dry weight with a mean of 0.97m2kg-1 dry weight. The obtained parameters shall be used for estimation of impact due to radionuclide related to Narora Atomic Power station.

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.

Atmospheric chemistry of hydrogen fluoride

Although a large volume of monitoring and computer simulation data exist for global coverage of HF, study of HF in the troposphere is still limited to industry whose primary interest is the safety and risk assessment of HF release because it is a toxic gas. There is very limited information on atmospheric chemistry, emission sources, and the behavior of HF in the environment. We provide a comprehensive review on the atmospheric chemistry of HF, modeling the reactions and transport of HF in the atmosphere, the removal processes in the vertical layer immediately adjacent to the surface (up to approximately 500 m) and recommend research needed to improve our understanding of atmospheric chemistry of HF in the troposphere. The atmospheric chemistry, emissions, and surface boundary layer transport of hydrogen fluoride (HF) are summarized. Although HF is known to be chemically reactive and highly soluble, both factors affect transport and removal in the atmosphere, the chemistry can be ignored when the HF concentration is at a sufficiently low level (e.g., 10 ppmv). At a low concentration, the capability for HF to react in the atmosphere is diminished and therefore the species can be mathematically treated as inert during the transport. At a sufficiently high concentration of HF (e.g., kg/s release rate and thousands of ppm), however, HF can go through a series of rigorous chemical reactions including polymerization, depolymerization, and reaction with water to form molecular complex. As such, the HF species cannot be considered as inert because the reactions could intimately influence the plume’s thermodynamic properties affecting the changes in plume temperature and density. The atmospheric residence time of HF was found to be less than four (4) days, and deposition (i.e., atmosphere to surface transport) is the dominant mechanism that controls the removal of HF and its oligomers from the atmosphere. The literature data on HF dry deposition velocity was relatively high compared to many commonly found atmospheric species such as ozone, sulfur dioxide, nitrogen oxides, etc. The global average of wet deposition velocity of HF was found to be zero based on one literature source. Uptake of HF by rain drops is limited by the acidity of the rain drops, and atmospheric particulate matter contributes negligibly to HF uptake. Finally, given that the reactivity of HF at a high release rate and elevated mole concentration cannot be ignored, it is important to incorporate the reaction chemistry in the near-field dispersion close to the proximity of the release source, and to incorporate the deposition mechanism in the far-field dispersion away from the release source. In other words, a hybrid computational scheme may be needed to address transport and atmospheric chemistry of HF in a range of applications. The model uncertainty will be limited by the precision of boundary layer parameterization and ability to accurately model the atmospheric turbulence.

Atmospheric transport and deposition of radionuclides released after the Fukushima Dai-chi accident and resulting effective dose

On 11 March 2011 an earthquake off the Pacific coast of the Fukushima prefecture generated a tsunami that hit Fukushima Dai-ichi and Fukushima Da-ini Nuclear Power Plants. From 12 March a significant amount of radioactive material was released into the atmosphere and dispersed worldwide. Among the most abundant radioactive species released were iodine and cesium isotopes. By means of an atmospheric dispersion Lagrangian code and publicly available meteorological data, the atmospheric dispersion of 131I, 134Cs, and 137Cs have been simulated for three months after the event with a spatial resolution of 0.5° × 0.5° globally. The simulation has been validated by comparison to publicly available measurements collected in 206 locations worldwide. Sensitivity analysis shows that release height of the radionuclides, wet deposition velocity, and source term are the parameters with the most impact on the simulation results.The simulation shows that the radioactive plume, consisting of about 200 PBq by adding contributions from 131I, 134Cs, and 137Cs, has been transported over the entire northern hemisphere depositing up to 1.2 MBq m−2 nearby the NPPs to less than 20 Bq m−2 in Europe. The consequent effective dose to the population over a 50-year period, calculated by considering both external and internal pathways of exposure, is found to be about 40 mSv in the surroundings of Fukushima Dai-ichi, while other countries in the northern hemisphere experienced doses several orders of magnitude lower suggesting a small impact on the population health elsewhere.

Studies on the Rain Scavenging Process of Tritium in a Tropical Site at Narora in India

This study presents the results of systematic experiments on tritium (3H) concentrations in ground level air against those in rainwater near a pressurized heavy water reactor in a tropical region. The samples were collected over the rainy season of year 2011 from eight locations in the environment around Narora Atomic Power Station. The specific activity ratio of 3H between rainwater and air moisture at ground level was calculated for each data set. The average specific activity ratio was found to be ranged from 0.12 to 1.1. A correlation ( to 0.76, ) was observed between the total rain hours in a day and the rainwater 3H activity. Higher rain duration with slower rain rate yielded higher 3H concentrations as more time was available for the scavenging/wash-out process to take effect together with lower dilution. Annual tritium (HTO) wet deposition has been measured and calculated for the year 2011 within 0.8 km distance from 145 m high stack of Narora Atomic Power Station (NAPS) at nine locations in different directions. The range of deposition velocity, (m·s−1), at nine locations for the years 2011 is found to be from 4.43E − 04 to 6.42E − 03. The average value for wet deposition velocity for NAPS site is estimated as 3.17E − 03 m·s−1.

Environmental transportation of tritium and estimation of site-specific model parameters for Kaiga site, India

Tritium content in air moisture, soil water, rain water and plant water samples collected around the Kaiga site, India was estimated and the scavenging ratio, wet deposition velocity and ratio of specific activities of tritium between soil water and air moisture were calculated and the results are interpreted. Scavenging ratio was found to vary from 0.06 to 1.04 with a mean of 0.46. The wet deposition velocity of tritium observed in the present study was in the range of 3.3E-03 to 1.1E-02 m s(-1) with a mean of 6.6E-03 m s(-1). The ratio of specific activity of tritium in soil moisture to that in air moisture ranged from 0.17 to 0.95 with a mean of 0.49. The specific activity of tritium in plant water in this study varied from 73 to 310 Bq l(-1). The present study is very useful for understanding the process and modelling of transfer of tritium through air/soil/plant system at the Kaiga site.

Total particulate and reactive gaseous mercury in ambient air on the eastern slope of the Mt. Gongga area, China

Total particulate mercury (TPM) and reactive gaseous mercury (RGM) concentrations in ambient air on the eastern slope of the Mt. Gongga area, Sichuan Province, Southwestern China were monitored from 25 May, 2005 to 29 April, 2006. Simultaneously, Hg concentrations in rain samples were measured from January to December, 2006. The average TPM and RGM concentrations in the study site were 30.7 and 6.2 pg m(-3), which are comparable to values observed in remote areas in Northern America and Europe, but much lower than those reported in some urban areas in China. The mean seasonal RGM concentration was slightly higher in spring (8.0 pg m(-3)) while the minimum mean concentration was observed in winter (4.0 pg m(-3)). TPM concentrations ranged across two orders of magnitude from 5.2 to 135.7 Pg m(-3) and had a clear seasonal variation: winter (74.1 pg m(-3)), autumn (22.5 Pg m(-3)), spring (15.3 Pg m(-3)) and summer (10.8 Pg m(-3)), listed in decreasing order. The annual wet deposition was 9.1 mu g m(-2) and wet deposition in the rainy season (May-October) represented over 80% of the annual total. The temporal distribution of TPM and RGM suggested distinguishable dispersion characteristics of these Hg species on a regional scale. Elevated TPM concentration in winter was probably due to regional and local enhanced coal burning and low wet deposition velocity. The RGM distribution pattern is closely related to daily variation in UV radiation observed during the winter sampling period indicating that photo-oxidation processes and diurnal changes in meteorology play an important role in RGM generation. (c) 2007 Elsevier Ltd. All rights reserved.

A long range transport of SO 2 and Sulfate between Korea and East China

The STEM II (Sulfur Transport Eulerian Model II) was adapted to simulate transport/chemistry/deposition of air pollutants in Korea and East China. A 72 h model simulation starting from 9 a.m. 25 November LST, 1989 was performed, during which a light precipitation occurred for the last 36 h. The model predictions for NO and SO 2 agree reasonably well with measurements but O 3 is underpredicted due to inaccurate VOC related input data. In addition, water soluble species such as H 2O 2 and HNO 3 were washed out rapidly and the fastest wet deposition velocity was found in the region where the rain fall velocity is the highest. The movement of the high concentration region was clearly identified for the sulfate but was not visible for SO 2. The Air Pollutant Transport Index was developed to quantify the importance of transport of air pollutants in determining the air quality.

Atmospheric nitrogen deposition to the North Sea

The groups of nitrogen components that contribute most to the eutrophication of the sea are ammonia, nitrogen oxides and their respective reaction products. The emission of ammonia is mainly from animal husbandry, whereas the emission of nitrogen oxides is mainly from combustion processes. Ammonia reacts in the atmosphere to form particulate ammonium. Nitrogen oxides react to form nitric acid, nitrous acid, particulate nitrate and peroxyacetyl nitrate. The various nitrogen components have different physical and chemical properties. Therefore, their dry and wet deposition velocities differ. The dry deposition velocity of gas to the sea depends on its solubility, reactivity, concentration in seawater and the wind speed. The dry deposition velocity of a particle depends on its size and the wind speed. The wet removal rate is a function of meteorological conditions. For a gas it further depends on the solubility and reactivity of the gas. For a particle, it further depends on the particle's ability to act as a condensation nucleus for particles. The total deposition of ammonia and its reaction products to the North Sea is about 140 kt N a −1. The total deposition of nitrogen oxides and their reaction products is about 200 kt N a −1.

Wet deposition of radionuclides derived from the Chernobyl accident

Chernobyl radioactivity in precipitation was measured at Tsukuba, Japan, as were both surface-air concentrations and particle-size distributions of Chernobyl-released radionuclides. To understand the wet removal processes of the Chernobyl radionuclides, i.e.137Cs,103Ru, and90Sr, wet deposition velocities were calculated. The wet deposition velocities of the Chernobyl radioactivity for individual rainfall events varied largely. The wet deposition velocity is given as the product of washout ratio and rainfall rate. Typically, it was found that the washout ratios of90Sr are systematically larger than those of137Cs. In order to explain this fact, we examined the relationship between the washout ratios and particle sizes of radionuclide-bearing aerosols. A positive correlation between corrected washout ratios and particle size was found with a particle diameter range from 0.35 to 1.2 µm. The result strongly suggests that the factors controlling the wet removal of the Chernobyl radioactivity for individual rainfall events are surface air concentration, particle size, and rainfall rate, rather than precipitation amount, which is in agreement with previous understandings. This suggests that high contamination areas of radioactivity are formed during heavy rainfall events with high rainfall rates in the case of tropospheric injection such as the Chernobyl accident.

Atmospheric transport and deposition of trace elements onto the Greenland Ice Sheet

Airborne particles of diameter > 0.4 μm reaching Dye 3, Greenland during April–May 1983 were highly variable in size and concentration from day to day. Five-day backward air mass trajectories suggest the importance of long-range transport from more northerly latitudes on days with high concentrations; particle sizes were larger on these days. Lower concentrations and smaller particle sizes were associated with transport from the south. It is inferred that Dye 3 may receive material emitted from Eurasian sources and transported over the Pole, similar to inferences for more northern Arctic sites. Elemental analysis of individual particles showed an abundance of crustal material, with many particles also containing sulfur. Bulk chemical analyses of airborne particles and fresh snow, collected during three snowstorms where ice nucleation dominated, provided data which were used to estimate mass-basis scavenging ratios. Average scavenging ratios were in the range ~1000–2000 for the crustal elements Al, Fe, K, Mg, Mn, and Na. Similar values were observed for Cd, Cu and NO 3 −. The corresponding ratios for Pb and SO 4 2− averaged less than 200. These ratios were used with precipitation rate data to estimate wet deposition velocities in the order of ~2 cm s −1 for the first nine species, and ~0.2 cm s −1 for Pb and SO 4 2−. Comparing fresh and older surface snow concentrations gave an average dry deposition velocity of roughly 0.2 cm s −1 for the crustal elements, with the small fraction of large particles (~5–10 μm) dominating deposition; much smaller values were associated with the remaining species. When used with other data in the literature, the results of this study suggest that total deposition velocities of Pb and SO 4 2− may be as small as 0.05 cm s −1 in relatively dry regions of the Arctic.