No observed data have been found in the Fukushima Prefecture (FP) for the time-series of atmospheric radionuclides concentrations just after the Fukushima Daiichi Nuclear Power Plant (FD1NPP) ...accident. Accordingly, current estimates of internal radiation doses from inhalation, and atmospheric radionuclide concentrations by atmospheric transport models are highly uncertain. Here, we present a new method for retrieving the hourly atmospheric (137)Cs concentrations by measuring the radioactivity of suspended particulate matter (SPM) collected on filter tapes in SPM monitors which were operated even after the accident. This new dataset focused on the period of March 12-23, 2011 just after the accident, when massive radioactive materials were released from the FD1NPP to the atmosphere. Overall, 40 sites of the more than 400 sites in the air quality monitoring stations in eastern Japan were studied. For the first time, we show the spatio-temporal variation of atmospheric (137)Cs concentrations in the FP and the Tokyo Metropolitan Area (TMA) located more than 170 km southwest of the FD1NPP. The comprehensive dataset revealed how the polluted air masses were transported to the FP and TMA, and can be used to re-evaluate internal exposure, time-series radionuclides release rates, and atmospheric transport models.
Using an hourly-resolution time series of the Fukushima radionuclides collected on used filter-tapes installed in suspended particulate matter (SPM) monitors, we measured the hourly radiocesium ...values at the SPM monitoring sites of Futaba and Naraha located within 20 km of the Fukushima Daiichi Nuclear Power Plant (FD1NPP) during March 12–25, 2011. The time-series of the 137Cs concentrations at the sites were analyzed and compared with radiation dose rates at the many monitoring posts/points of Fukushima Prefecture and the Tokyo Electric Power Company. At Futaba, nine plumes of high 137Cs concentrations were found on March 12–13, 15–16, 18–20, and 24–25, 2011, when southeasterly winds prevailed. On March 12, the first peak of the 137Cs concentrations was detected at Futaba at 9:00 Japanese Standard Time (JST) due to the first release from reactor Unit 1 (U1) in the early morning. Furthermore, the highest 137Cs concentration, i.e., 13,600 Bq m–3 was observed at 15:00 JST after a vent operation at U1, just before the hydrogen explosion of U1 at 15:36 JST. On the afternoon of March 15, plumes from the FD1NPP were observed at Futaba due to a constant southeasterly wind and were then transported to downwind, resulting in the formation of a highly deposited zone of radionuclides spanning more than 30 km from near the FD1NPP to the northwest. In contrast, seven plumes of high 137Cs concentrations were found at Naraha on March 15–16, 18, 20–21, 2011, when northerly winds prevailed. On March 15, a plume caused by the first release from Unit 2 was observed at Naraha at 1:00 JST, and the highest concentration, i.e., 8,300 Bq m–3, was observed at 3:00 JST, and then were transported southward to the Kantou area. The activity ratios of 134Cs/137Cs in the plumes were divided into two groups. The plumes at Futaba on March 12–13, which had ratios of 0.92–0.94, are identified to be released from U1, compared to its ratio of 0.94, as derived from the inventory data. All other plumes with the ratios of 1.02–1.04 at Futaba and Naraha during March 15–21 have not been determined to be released from U2 and/or Unit 3.
On March 11, 2011, the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident occurred and large amounts of radionuclides were discharged into the atmosphere. We have operated continuous aerosol ...samplings at four locations in Japan from the accident until the end of 2011. The activities of 90Sr and 137Cs in the aerosol samples were measured using low background liquid scintillation counters and high-purity germanium detectors, respectively. The atmospheric 90Sr and 137Cs concentrations decreased exponentially during 2011. The time variation of the 90Sr/137Cs ratio was obtained, and we found that the ratio rose from 1.2 × 10–3 in March to 1.3 × 10–1 in August 2011. One reason for the increase in the 90Sr/137Cs ratio could be the change in the primary emission source of activity at the FDNPP, which occurred near June 2011.
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011 emitted a considerable amount of radioactive materials. This study isolated radiocesium-bearing microparticles (CsMPs), a form ...of radioactive materials emitted from the FDNPP at the early stage of the accident, from aerosols collected hourly on filter tapes at seven monitoring stations at the greater Kanto Region, including the Tokyo metropolitan area, on 15 March 2011. The aerosols had a spherical shape ~ 1 μm in diameter with activity of less than 1 Bq of
137
Cs per particle. Their physical and chemical characteristics, including radioactivity ratio
134
Cs/
137
Cs as well as chemical composition and state, are essentially the same as previously reported CsMPs. This study demonstrated that air parcels containing CsMPs emitted from the FDNPP were widespread over the greater Kanto Region, more than 250 km away from the FDNPP, during the daytime of 15 March. Trajectory analysis indicated that these particles were emitted from the reactor No. 2 of FDNPP between 14 March evening and 15 March early morning. The information obtained on the widespread distribution of CsMPs can be useful for assessing the actual impacts of radioactive contamination from the FDNPP accident on the environment and human health.
To assess the uncertainty of meteorological simulations in the transport and deposition of radio‐Cs release associated with the Fukushima Daiichi Nuclear Power Station accident in Japan, a multiple ...meteorological model and module ensemble analysis with a single chemical transport model (CTM) was conducted. Although several multimodel ensemble studies have previously been performed, the current type (i.e., one CTM with several meteorological fields) was applied for the first time and represents a useful way to evaluate the uncertainty of each component of CTM. The current analysis concluded that the underestimation of the deposition efficiency of CTM was the reason for the underestimation of simulated radio‐Cs deposition, whereas the simulated dispersion and precipitation and estimated source term were all reasonable: all of the simulations underestimated the deposition amount, whereas some underestimated but others overestimated the simulated precipitation and radio‐Cs concentrations. The CTM simulation performed using the meteorological ensemble mean field was successful in reducing variance, and they gave reasonable results. The simulated deposition using the meteorological ensemble was better than others because the ensemble mean enlarged the light precipitation areas and because the land contamination was mainly caused by light precipitation. The current ensemble study indicated that in‐cloud scavenging was the most dominant mechanism of radio‐Cs deposition, followed by dry deposition and fog deposition over the entire land area. In some deposition regions, fog deposition was dominant, exceeding 80%, depending on the simulations. The simulated concentrations and depositions varied by more than twofold, depending on the selection of the meteorological field.
Key Points
Sensitivity to meteorological models was assessed for the first time for the Fukushima nuclear accident study
Modeled deposition rates were underestimated, while precipitation values and source term were reasonable
In‐cloud scavenging was the most dominant mechanism for radio‐Cs deposition, followed by dry and fog depositions
To understand the dissolutive behaviour of radio Cs discharged to the ocean environment as a result of the Fukushima Dai-ichi Nuclear Power Plant accident, an aerosol sample collected on the 15th of ...March 2011 at Kawasaki City (Kanagawa) was sequentially leached with seawater for 30 days. In addition, a surface soil sample collected from Kawamata Town (Fukushima) two months after the accident, was leached for three days with natural seawater, diluted seawaters and ultrapure water to observe the effect of the ionic strength of the waters on the respective leaching ratios and apparent distribution coefficient (Kd) values. Furthermore, the soil sample was subjected to a 223-day continuous sequential leaching with a natural seawater and with a 1:1 mixture of ultrapure water and seawater. When leaching the aerosol sample in seawater, about 40% of the total 137Cs was extracted in the first three days, and a further 20% of the total 137Cs was extracted within 30 days. Lower Kd values for 137Cs between the soil and leachates were obtained with seawater and diluted seawater compared to ultrapure water. For the long-term experiment (223 days) using the three leaching solutions, approximately 0.1–2% of the total 137Cs was leached in the first three days. Eventually, more than 15% of total 137Cs in the surface soil sample was efficiently desorbed by seawater leaching. In comparison, about 9% of the total 137Cs was leached with 1:1 diluted seawater and less than 1% of the total 137Cs was leached with ultrapure water over the 223 days. In general, there were some similarities between the leaching behaviour for natural 133Cs and radio Cs. In the surface soil, radio Cs species was eventually incorporated into the clays after undergoing solubilisation as fallout aerosols in natural waters. Thereafter, the insoluble or less soluble forms of radio Cs in the soil would be partially extracted by seawater after the transport of contaminated surface soils to the ocean via rivers.
This article introduces an international regional experiment, East Asian Regional Experiment 2005 (EAREX 2005), carried out in March–April 2005 in the east Asian region, as one of the first phase ...regional experiments under the UNEP Atmospheric Brown Cloud (ABC) project, and discusses some outstanding features of aerosol characteristics and its direct radiative forcing in the east Asian region, with some comparison with the results obtained in another ABC early phase regional experiment, ABC Maldives Monsoon Experiment (APMEX) conducted in the south Asian region. Time series of aerosol optical thickness (AOT), single scattering albedo (SSA), aerosol extinction cross section profile and CO concentration shows that air pollutants and mineral dust were transported every 5 to 7 days in the EAREX region to produce SSA values at wavelength of 700 nm from 0.86 to 0.96 and large clear‐sky shortwave forcing efficiency at 500 nm from 60 W m−2 to 90 W m−2, though there are some unexplained inconsistencies depending on the evaluation method. The simulated whole‐sky total forcing in the EAREX region is −1 to −2 W m−2 at TOA and −2 to −10 W m−2 at surface in March 2005 which is smaller in magnitude than in the APMEX region, mainly because of large cloud fraction in this region (0.70 at Gosan versus 0.51 at Hanimadhoo in the ISCCP total cloud fraction). We suggest there may be an underestimation of the forcing due to overestimation of the simulated cloudiness and aerosol scale height. On the other hand, the possible error in the simulated surface albedo may cause an overestimation of the magnitude of the forcing over the land area. We also propose simple formulae for shortwave radiative forcing to understand the role of aerosol parameters and surface condition to determine the aerosol forcing. Such simple formulae are useful to check the consistency among the observed quantities.
Data of the atmospheric activity concentrations (in Bq/m3) of 129I dispersed into the environment as aerosol immediately after the nuclear accident at Fukushima Daiichi Nuclear Power Plant in 2011 ...are presented. The radioactivity of 129I was determined in suspended particulate matter (SPM) collected on filter tapes at 41 SPM monitoring sites in Fukushima and other prefectures in eastern Japan including the metropolitan area. For quantitative determination of 129I in SPM samples by accelerator mass spectrometry (AMS), 129I was chemically separated. Prior to the 129I measurement, the 137Cs activity was determined for the same SPM sample by gamma-ray spectrometry using Ge-semiconductor detectors. Combining activity concentrations of the two nuclides, an activity ratio of 129I/137Cs (in Bq/Bq) was calculated for each SPM sample. In our research project, atmospheric activity concentrations of 129I and 137Cs, and their activity ratios were obtained for 920 SPM samples. Scientific discussion related to those data was described in the research article entitled “Time-series variations of atmospheric 129I concentrations and 129I/137Cs ratios in eastern Japan just after the 2011 nuclear accident in Fukushima, Japan” (Ebihara et al. 2022), where 363 data sets were presented. The remaining 557 data sets are presented in this article, so this data article makes up for the original research article (Ebihara et al. 2022). Blank values were obtained for whole analytical procedure. In addition, those for reagents and filters (both bland-new and used filters) were analyzed for assessing the contribution of the 129I activity from these samples. Those data also are presented in this article.
A biogeochemical model, Denitrification‐Decomposition (DNDC), was modified to enhance its capacity of predicting greenhouse gas (GHG) emissions from paddy rice ecosystems. The major modifications ...focused on simulations of anaerobic biogeochemistry and rice growth as well as parameterization of paddy rice management. The new model was tested for its sensitivities to management alternatives and variations in natural conditions including weather and soil properties. The test results indicated that (1) varying management practices could substantially affect carbon dioxide (CO2), methane (CH4), or nitrous oxide (N2O) emissions from rice paddies; (2) soil properties affected the impacts of management alternatives on GHG emissions; and (3) the most sensitive management practices or soil factors varied for different GHGs. For estimating GHG emissions under certain management conditions at regional scale, the spatial heterogeneity of soil properties (e.g., texture, SOC content, pH) are the major source of uncertainty. An approach, the most sensitive factor (MSF) method, was developed for DNDC to bring the uncertainty under control. According to the approach, DNDC was run twice for each grid cell with the maximum and minimum values of the most sensitive soil factors commonly observed in the grid cell. The simulated two fluxes formed a range, which was wide enough to include the “real” flux from the grid cell with a high probability. This approach was verified against a traditional statistical approach, the Monte Carlo analysis, for three selected counties or provinces in China, Thailand, and United States. Comparison between the results from the two methods indicated that 61‐99% of the Monte Carlo‐produced GHG fluxes were located within the MSA‐produced flux ranges. The result implies that the MSF method is feasible and reliable to quantify the uncertainties produced in the upscaling processes. Equipped with the MSF method, DNDC modeled emissions of CO2, CH4, and N2O from all of the rice paddies in China with two different water management practices, i.e., continuous flooding and midseason drainage, which were the dominant practices before 1980 and in 2000, respectively. The modeled results indicated that total CH4 flux from the simulated 30 million ha of Chinese rice fields ranged from 6.4 to 12.0 Tg CH4‐C per year under the continuous flooding conditions. With the midseason drainage scenario, the national CH4 flux from rice agriculture reduced to 1.7–7.9 Tg CH4‐C. It implied that the water management change in China reduced CH4 fluxes by 4.2–4.7 Tg CH4‐C per year. Shifting the water management from continuous flooding to midseason drainage increased N2O fluxes by 0.13–0.20 Tg N2O‐N/yr, although CO2 fluxes were only slightly altered. Since N2O possesses a radiative forcing more than 10 times higher than CH4, the increase in N2O offset about 65% of the benefit gained by the decrease in CH4 emissions.
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