No abstract available

[en] Radio-Cs concentrations in fresh leaves/needles, litter, surface soil, and stream sand were continuously investigated in a deciduous broadleaf forest and cedar forest in Namie-town, Fukushima prefecture from June 2012 to June 2016, except for snow-cover periods. The result of a car-borne survey from Fukushima city to Minamitsushima showed that the air dose rate declined faster than the physical attenuation due to decontamination, outside of forests. Radio-Cs concentrations ("1"3"7Cs + "1"3"4Cs) in litter and surface soil in broadleaf forest were constant at 52.0, 102 kBq kg-dry"-"1, respectively from 2014. In a cedar forest, however, the radio-Cs concentrations in fresh needles and litter declined from 2012 to 2015, probably because of washing and leaching by throughfall, and radio-Cs was accumulated in surface soil. In broadleaf forest, the buffer depth of radio-Cs in soil (1.26 cm) which indicates the extent of infiltration into deeper layers was greater than in the cedar forest (1.14 cm) in April 2013. However, the buffer depth in the cedar forest overtook that in the broadleaf forest in December, 2015 (1.5 cm in broadleaf forest and 2.6 cm in cedar forest). The radio-Cs values in the stream bottom sand were concentrated in smaller sand (over 2 mm, 3.04; 0.21-2.0 mm, 10.2; under 0.21 mm, 54.5 kBq kg-dry"-"1 in downstream near the broadleaf forest and over 2.0 mm, 2.67, 0.21-2.0 mm, 7.95; under 0.21 mm, 41.3 kBq kg-dry"-"1 in the upstream area near the cedar forest). It is concerned that a part of them causes the outflow of radio-Cs as suspended sand. The relative radio-Cs concentration ratio between smaller bottom sand and surface soil, which indicates the outflow of radio-Cs from forest via stream declined (2013: 0.54, 2016: 0.29 in downstream and 2013: 1.4, 2016: 0.31 in the upstream region). However, we found that floating male flowers of cedar containing high radio-Cs (23.8 kBq kg-dry"-"1) could be another transport media in the spring. (author)

No abstract available

[en] The abundance of humic-like substances in the atmosphere has received considerable attention since these substances play an important role in various atmospheric processes. The wide variety of quantitative techniques used to study humic-like substances produce dissimilar results, making data comparison difficult. Also, global background concentrations and the transfer of atmospheric humic-like substances are poorly known. Here, we compared resins to extract humic-like substances in aerosols, and we measured contents in aerosols from Mt. Fuji. Results show that diethylaminoethyl cellulose resins extracted more humic-like substances than the diethylaminoethyl resin (hydroxylated methacrylic polymer). The mean humic-like substances concentrations in the free troposphere in East Asia is similar to that in Europe, suggesting that the global background level of humic-like substances is 0.05 μg C m⁻³, based on the humic-like substances concentrations on Mt. Fuji and Mt. Sonnblick. Humic-like substances concentrations, especially fulvic acids concentration, at the summit of Mt. Fuji increased when air masses came from the continent along with the carbon monoxide and ozone.

[en] A large quantity of radionuclides was released by the Fukushima Daiichi Nuclear Power Plant accident in March 2011, and those deposited on ground and vegetation could return to the atmosphere through resuspension processes. Although the resuspension has been proposed to occur with wind blow, biomass burning, ecosystem activities, etc., the dominant process in contaminated areas of Fukushima is not fully understood. We have examined the resuspension process of radiocesium (^134,137Cs) based on long-term measurements of the atmospheric concentration of radiocesium activity (the radiocesium concentration) at four sites in the contaminated areas of Fukushima as well as the aerosol characteristic observations by scanning electron microscopy (SEM) and the measurement of the biomass burning tracer, levoglucosan.

The radiocesium concentrations at all sites showed a similar seasonal variation: low from winter to early spring and high from late spring to early autumn. In late spring, they showed positive peaks that coincided with the wind speed peaks. However, in summer and autumn, they were correlated positively with atmospheric temperature but negatively with wind speed. These results differed from previous studies based on data at urban sites. The difference of radiocesium concentrations at two sites, which are located within a 1 km range but have different degrees of surface contamination, was large from winter to late spring and small in summer and autumn, indicating that resuspension occurs locally and/or that atmospheric radiocesium was not well mixed in winter/spring, and it was opposite in summer/autumn. These results suggest that the resuspension processes and the host particles of the radiocesium resuspension changed seasonally. The SEM analyses showed that the dominant coarse particles in summer and autumn were organic ones, such as pollen, spores, and microorganisms. Biological activities in forest ecosystems can contribute considerably to the radiocesium resuspension in these seasons. During winter and spring, soil, mineral, and vegetation debris were predominant coarse particles in the atmosphere, and the radiocesium resuspension in these seasons can be attributed to the wind blow of these particles. Any proofs that biomass burning had a significant impact on atmospheric radiocesium were not found in the present study.

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