TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 52, 2018

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

Mayuko Nakagawa,1* Keita Yamada,2 Sakae Toyoda,2 Kazuyuki Kita,3 Yasuhito Igarashi,4 Shingo Komatsu,2 Kentaro Yamada,2 and Naohiro Yoshida1, 2

1Earth Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551, Japan
2Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, Kanagawa, 226-8502, Japan
3College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki, 310-8512, Japan
4Atmospheric Environment and Applied Meteorology Research Department, Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki, 305-0052, Japan

(Received May 2, 2017; Accepted December 2, 2017)

Abstract: In this study, the potential natural sources of secondary radiocesium isotope (134Cs and 137Cs) emissions were investigated, with a focus on n-alkanes, a characteristic bioaerosol compound. Monitoring was performed to obtain a time series of aerosol, samples, from winter 2013 to summer 2014, and size-resolved aerosol samples in 2012 and 2014. Samples were collected from the area heavily contaminated after the Fukushima Daiichi Nuclear Power Plant accident in March 2011. A correlation analysis of radiocesium, n-alkanes, and black carbon concentrations was performed to identify the contributions of aerosols from biogenic and anthropogenic sources. Biogenic n-alkanes exhibited similar concentration ranges except for spring 2014. The continuous input of biogenic n-alkanes is characteristic of a sampling site surrounded by forest, where pollen dispersion increased the concentration of biogenic n-alkanes in spring 2014. On the other hand, anthropogenic n-alkane concentrations were significantly increased in spring and summer 2014 (>50 ng/m3), compared with those prior to winter 2014 (<20 ng/m3). This anthropogenic n-alkane increase represents the beginning of reconstruction near the area. The carbon preference index (CPI) clearly showed biogenic n-alkanes with coarse-sized particles (CPI > 3), and more anthropogenic n-alkanes were contained in fine particle aerosols. Our results showed that radiocesium and biogenic n-alkane concentrations in seasonal and size-resolved aerosol samples have a partially positive correlation, which supports the hypothesis that the secondary emissions of radionuclides occurred in the forested areas.
Key words: secondary radioactive emission, radiocesium, n-alkane, biogenic sources, aerosols

*Corresponding author E-mail: nakagawa.m.ae@m.titech.ac.jp

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