Atmospheric removal times of the aerosol-bound radionuclides 137Cs and 131I measured after the Fukushima Dai-ichi nuclear accident – a constraint for air quality and climate models
Item
Title (Dublin Core)
Atmospheric removal times of the aerosol-bound radionuclides 137Cs and 131I measured after the Fukushima Dai-ichi nuclear accident – a constraint for air quality and climate models
Description (Dublin Core)
Caesium-137 (<sup>137</sup>Cs) and iodine-131 (<sup>131</sup>I) are radionuclides of particular concern during nuclear accidents, because they are emitted in large amounts and are of significant health impact. <sup>137</sup>Cs and <sup>131</sup>I attach to the ambient accumulation-mode (AM) aerosols and share their fate as the aerosols are removed from the atmosphere by scavenging within clouds, precipitation and dry deposition. Here, we estimate their removal times from the atmosphere using a unique high-precision global measurement data set collected over several months after the accident at the Fukushima Dai-ichi nuclear power plant in March 2011. The noble gas xenon-133 (<sup>133</sup>Xe), also released during the accident, served as a passive tracer of air mass transport for determining the removal times of <sup>137</sup>Cs and <sup>131</sup>I via the decrease in the measured ratios <sup>137</sup>Cs/<sup>133</sup>Xe and <sup>131</sup>I/<sup>133</sup>Xe over time. After correction for radioactive decay, the <sup>137</sup>Cs/<sup>133</sup>Xe ratios reflect the removal of aerosols by wet and dry deposition, whereas the <sup>131</sup>I/<sup>133</sup>Xe ratios are also influenced by aerosol production from gaseous <sup>131</sup>I. We find removal times for <sup>137</sup>Cs of 10.0–13.9 days and for <sup>131</sup>I of 17.1–24.2 days during April and May 2011. The removal time of <sup>131</sup>I is longer due to the aerosol production from gaseous <sup>131</sup>I, thus the removal time for <sup>137</sup>Cs serves as a better estimate for aerosol lifetime. The removal time of <sup>131</sup>I is of interest for semi-volatile species. We discuss possible caveats (e.g. late emissions, resuspension) that can affect the results, and compare the <sup>137</sup>Cs removal times with observation-based and modeled aerosol lifetimes. Our <sup>137</sup>Cs removal time of 10.0–13.9 days should be representative of a "background" AM aerosol well mixed in the extratropical Northern Hemisphere troposphere. It is expected that the lifetime of this vertically mixed background aerosol is longer than the lifetime of fresh AM aerosols directly emitted from surface sources. However, the substantial difference to the mean lifetimes of AM aerosols obtained from aerosol models, typically in the range of 3–7 days, warrants further research on the cause of this discrepancy. Too short modeled AM aerosol lifetimes would have serious implications for air quality and climate model predictions.
Creator (Dublin Core)
Kristiansen, N. I.
Stohl, A.
Wotawa, G.
Date (Dublin Core)
2018-01-15
Type (Dublin Core)
info:eu-repo/semantics/Text
Format (Dublin Core)
info:eu-repo/semantics/application/pdf
Identifier (Dublin Core)
10.5194/acp-12-10759-2012
https://acp.copernicus.org/articles/12/10759/2012/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
Relation (Dublin Core)
info:eu-repo/grantAgreement/EC/FP7/282688
Rights (Dublin Core)
info:eu-repo/semantics/openAccess
