Abstract
It is the conventional understanding that rain removes aerosols from the atmosphere. However, the question of whether rain plays a role in releasing aerosols to the atmosphere has recently been posed by several researchers. In the present study, we show additional evidence for rain-induced aerosol emissions in a forest environment: the occurrence of radiocaesium-bearing aerosols in a Japanese forest due to rain. We carried out general radioactive aerosol observations in a typical mountainous village area within the exclusion zone in Fukushima Prefecture to determine the impacts and major drivers of the resuspension of radiocaesium originating from the nuclear accident in March 2011. We also conducted sampling according to the weather (with and without rain conditions) in a forest to clarify the sources of atmospheric radiocaesium in the polluted forest. We found that rain induces an increase in radiocaesium in the air in forests. With further investigations, we confirmed that the fungal spore sources of resuspended radiocaesium seemed to differ between rainy weather and nonrainy weather. Larger fungal particles (possibly macroconidia) are emitted during rainy conditions than during nonrainy weather, suggesting that splash generation by rain droplets is the major mechanism of the suspension of radiocaesium-bearing mould-like fungi. The present findings indicate that radiocaesium could be used as a tracer in such research fields as forest ecology, meteorology, climatology, public health and agriculture, in which fungal spores have significance.
Highlights
It is the conventional understanding that rain removes aerosols from the atmosphere
We carried out atmospheric observations of radiocaesium (134Cs and 137Cs) initially originating from the Fukushima Dai-ichi Nuclear Power Plant (F1NPP or FDNPP) accident in March 2 01115 to determine its concentrations, the processes involved in its aerosolization and the corresponding carrier[13,14,16]
We conducted atmospheric sampling under both rainy and nonrainy conditions at two heavily contaminated forest sites, the Namie site and the Kawamata site (Fig. 1 and Supplementary Photographs 1 and 2), which are dominated by deciduous trees and coniferous trees, respectively
Summary
It is the conventional understanding that rain removes aerosols from the atmosphere. the question of whether rain plays a role in releasing aerosols to the atmosphere has recently been posed by several researchers. The existence of odours known as petricor[9] and geosmin[10], which occur with the start of rain or with light rain, has been acknowledged for a long time, but their formation mechanism was revealed very recently[3,7,8] In these cases, the suspension flux from the surface overwhelms the deposition flux of the aerosols in question in the near-surface air layer. The underlying mechanisms include (1) microbubbles bursting inside raindrops upon contact with the Earth’s dried porous s urface[3,7], (2) active fungal spore dispersion due to high humidity (e.g., ref.2,4), and (3) aerosol bursts caused by the splashing of raindrops (e.g. ref.[11]) Details of these phenomena are given in the Discussion section. We refer to these biologically/ecologically mediated atmospheric phenomena as bioecological resuspension of radiocaesium
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
