Recent trends and explanation for airborne¹³⁷Cs activity level increases in France

Abstract

Abstract.Airborne 137 Cs level in France is not decreasing significantly anymore (mean yearly value around 0,25 Bq.m −3 ) contrarily to what was noticed in the past decades. This observation points out the role of processes that delay the atmospheric cleaning and participate to the persistence of radionuclide in the air at ground-level after a deposit, in the frame of medium as well as long-dated post-accidental contexts. The current background level also yields to consider 137 Cs in the atmosphere as a tracer of atmospheric processes like resuspension and re-emission from biomass burnings. This allows us to explain 2/3 of the peaks observed over the last six years. The remaining 1/3 is mainly noticed in winter when spreading of pollutants in the atmosphere is often weak due to temperature gradient inversion. On average, continental air masses are responsible for increases by a factor of 3 while oceanic air masses are characterised by levels 3 times lower, compared to the mean value. Feeding of 137 Cs in air at ground-level is the result of both local resuspension that signs 137 Cs activity levels in soils to which is added a remote contribution from time to time (resuspension of Saharan dust or re-emission from fires occurring in eastern territories with high 137 Cs deposition level). Finally, 137 Cs activity levels in air masses crossing over France can be described on average by a longitudinal gradient.

Impact of Saharan dust events on radionuclide levels in Monaco air and in the water column of the northwest Mediterranean Sea

“…(i) Local re-suspension of 137 Cs from soil (Pham et al, 2011;Sýkora et al, 2012); (ii) 137 Cs input from Saharan dust events (Masson et al, 2010;Pham et al, 2005Pham et al, , 2011; (iii) Contributions from field/forest fires burning biota containing 137 Cs of the Chernobyl and global fallout origin (Wotawa et al, 2006;Masson et al, 2009;Hirose and Povinec, 2015). Menut et al (2009) showed that in the case of the 21e22 February 2004 Saharan dust event, the main part (80%) of the dust found in southern France was from the eastern Maghreb region.…”

“…Povinec, 2000, 2002). Radionuclides in the atmosphere rapidly attach on submicron-sized aerosols, and their variability in ground-level air is driven by the behavior of aerosols (Masson et al, 2009;Sýkora et al, 2012;Povinec et al, 2012;Hirose and Povinec, 2015).…”

Aerosol radioactivity record in Bratislava/Slovakia following the Fukushima accident – A comparison with global fallout and the Chernobyl accident

“…The 137 Cs in the terrestrial environment is present in atmospheric aerosols, soil and vegetation. It has been used worldwide as a tracer of environmental processes, specifically for studying transport processes in atmospheric, aquatic and terrestrial ecosystems (Lee et al, 2002;Igarashi et al, 2005;Pham et al, 2005Pham et al, , 2011Lujaniené et al, 2006Lujaniené et al, , 2009Masson et al, 2009). Because of relatively easy analytical methodologies, it has been monitored in the atmosphere since the beginning of the 1960's.…”

Forest Fires and Resuspension of Radionuclides into the Atmosphere

“…Periodic atmospheric radioactivity monitoring performed at several western European countries detected 137 Cs peaks in surface air in the summer of 2002 and afterwards (Masson et al, 2008). In the absence of known accidental radioactivity releases, it was interpreted as re-suspension by summer fires of the 137 Cs from Chernobyl accident deposited in Ukraine and Belorussia forests and soils (Amiro et al, 1996;Paatero et al, 2009).…”