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Seasonal Be-7 and Cs-137 activities in surface air before and after the Chernobyl event
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Environment and Landscape Dynamics. (exogengeokemi)
2006 (English)In: Journal of Environmental Radioactivity, ISSN 0265-931X, E-ISSN 1879-1700, Vol. 90, no 2, 140-150 p.Article in journal (Refereed) Published
Abstract [en]

Seasonal fluctuations of cosmogenic Be-7 (T-1/2=53.4 days) and anthropogenic Cs-137 (T-1/2 = 30 years) activities in surface air (aerosols) have been extracted from a long data record (1972-2000) at high latitude (56 degrees N-68 degrees N, Sweden). Normalization to weekly average values was used to control long-term trends so that cyclical trends could be investigated. Enhanced Be-7 activity was observed in spring and summer seasons and likely relates to the seasonal thinning of the tropopause. Variations in the Cs-137 activity record seem to reflect how the isotope was injected in the atmosphere (stratospheric from bomb tests and tropospheric from the Chernobyl accident) and subsequent transport mechanisms. Accordingly, until 1986, the surface air Cs-137 activity was strongly related to nuclear weapons test fallout and exhibits temporal fluctuations resembling the Be-7. Conversely, since 1986 the Chernobyl-produced Cs-137 dominates the long-term record that shows annual cycles that are strongly controlled by atmospheric boundary layer conditions. Additionally, short-term data within the post-Chernobyl period suggest subtle intrusion of air masses rich in (CS)-C-137 that may occur throughout the year, and differences resulting from spatial occurrence at these latitudes. This is an important observation that may have to do with year-to-year variation and calls for caution when interpreting short-term data records.

Place, publisher, year, edition, pages
2006. Vol. 90, no 2, 140-150 p.
Keyword [en]
Be-7, Cs-137, atmosphere; aerosols, Chernobyl fallout, nuclear weapons fallout, Sweden, Europe
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-96041DOI: 10.1016/j.jenvrad.2006.06.010ISI: 000240803500004OAI: oai:DiVA.org:uu-96041DiVA: diva2:170460
Available from: 2007-05-15 Created: 2007-05-15 Last updated: 2011-06-14Bibliographically approved
In thesis
1. Atmospheric Production and Transport of Cosmogenic 7Be and 10Be
Open this publication in new window or tab >>Atmospheric Production and Transport of Cosmogenic 7Be and 10Be
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the atmospheric distribution of the cosmogenic isotopes 7Be (half-life 53 days) and 10Be (half-life 1.51 million years) as well as the anthropogenic isotope 137Cs (half-life 30 years) in aerosols and precipitation. Samples covering continuous or selected parts of the period 1972-2005 in Sweden and Europe are evaluated with respect to production, air mass transport and fallout processes. Such information is valuable in assessing the potential of these isotopes as indicators of air mass mixing and solar modulation factors that affect climate change. The results of 7Be and 10Be show seasonal variability and an 11-year cyclic pattern which is anti-correlated with the solar activity. Variations in seasonal trends of 7Be and 137Cs in aerosols during the post- and pre-Chernobyl period reflect tropospheric influence from 137Cs-heavily contaminated regions. A clear latitude dependence is observed in our beryllium isotope data where highest fallout is found in mid-latitudes compared to high and low latitude regions in the Northern hemisphere. This pattern reflects the general air mass circulation in the troposphere. However, stratospheric air mass influence was also identified in mainly single events and through tropopause folding during spring-summer seasons. The ratio of 10Be/7Be is used to estimate effects of air mass transport on production signal. The results show ratios between 1 and 3, much higher than the theoretically predicted value (0.6) in the atmosphere, which suggests contribution from 7Be-depleted (old) air masses. The relationship between monthly 7Be atmospheric activity and Total Fractional Cloud Cover (TFCC), collected from satellite imagery, over Sweden for the years (1991-2000) indicates a negative seasonal correlation. This observation can be related to depletion of aerosol from the atmosphere due to trapping in clouds.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 55 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 321
Earth sciences, Aerosols, Atmosphere, Cosmogenic Be-7 and Be-10, Cs-137, Clouds, Sweden, Europe, Geovetenskap
urn:nbn:se:uu:diva-7965 (URN)978-91-554-6925-2 (ISBN)
Public defence
2007-06-05, Axel Hambergsalen, Geocentrum, Villav. 16, Uppsala, 10:00
Available from: 2007-05-15 Created: 2007-05-15Bibliographically approved

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