The seasonal variations of atmospheric 134,137Cs activity and possible host particles for their resuspension in the contaminated areas of Tsushima and Yamakiya, Fukushima, Japan

Abstract

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 ( 134,137 Cs) 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 (Continued on next page)

Characterization of hydrocarbons in aerosols and investigation of biogenic sources as a carrier of radiocesium isotopes

“…The 134 Cs and 137 Cs concentrations around the Tsushima area in Namie town over the sample period were reported by Kinase et al (2017) (Fig. 2).…”

“…Sampling were collected from 8th-26th March 2013 (winter 2013), 10th-30th August 2013 (summer 2013), 24th January-9th February 2014 (winter 2014), 11th April-4th May 2014 (spring 2014), and 26th August-16th September 2014 (summer 2014). The seasons were defined as in Kajino et al (2016) and Kinase et al (2017). Size-resolved aerosol samples were also collected during several periods in 2014.…”

“…Kaneyasu et al (2017) discussed that the shift in size distribution may reflect a source shift from direct emission transported as a sulfate aerosol (approximately 0.54 mm), to secondary emission from the surface area of soil particles (>2.1 mm). Kinase et al (2017) found that the back-up stage (Q7) sometimes contained coarse particles, such as pollen and soil particles, that should have been trapped in the Q1 stage. The collection efficiency would as a result then underestimate the concentrations at the Q1 stage and overestimate them at the Q7 stage.…”

“…Yoschenko et al (2017) estimated that, in the four years since the Fukushima accident, 74% of the radiocesium deposits were distributed in the soil and approximately 20% were distributed in the litter compartment. Kinase et al (2017) found bioaerosols on filters in the summer and autumn seasons via scanning electron microscopy (SEM), when radiocesium concentrations were high. Concentrations of water soluble organic carbon and levoglucosan were compared to the 137 Cs concentrations, but there was little correlation.…”

“…In the case of ferns, moss, fungi, and mold, it migrates to the spores. Subsequently, these become possible sources of secondary emissions (Kinase et al, 2017).…”