Seasonal Be-7 and Cs-137 activities in surface air before and after the Chernobyl event

Kulan, AbdulhadiUppsala universitet,Miljö- och landskapsdynamik,exogengeokemi (författare)

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.

Ingår i:Journal of Environmental Radioactivity: Elsevier BV90:2, s. 140-1500265-931X1879-1700

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