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| Titel |
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 |
| VerfasserIn |
N. I. Kristiansen, A. Stohl, G. Wotawa |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 22 ; Nr. 12, no. 22 (2012-11-16), S.10759-10769 |
| Datensatznummer |
250011596
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| Publikation (Nr.) |
 copernicus.org/acp-12-10759-2012.pdf |
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| Zusammenfassung |
| Caesium-137 (137Cs) and iodine-131 (131I) are radionuclides of
particular concern during nuclear accidents, because they are emitted in
large amounts and are of significant health impact. 137Cs and 131I
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 (133Xe), also
released during the accident, served as a passive tracer of air mass
transport for determining the removal times of 137Cs and 131I via
the decrease in the measured ratios 137Cs/133Xe and
131I/133Xe over time. After correction for radioactive decay, the
137Cs/133Xe ratios reflect the removal of aerosols by wet and dry
deposition, whereas the 131I/133Xe ratios are also influenced by
aerosol production from gaseous 131I. We find removal times for
137Cs of 10.0–13.9 days and for 131I of 17.1–24.2 days during
April and May 2011. The removal time of 131I is longer due to the
aerosol production from gaseous 131I, thus the removal time for
137Cs serves as a better estimate for aerosol lifetime. The removal time
of 131I is of interest for semi-volatile species. We discuss possible
caveats (e.g. late emissions, resuspension) that can affect the results, and
compare the 137Cs removal times with observation-based and modeled
aerosol lifetimes. Our 137Cs 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. |
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