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

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

Author: Kulan, A.

Reference: Journal of Environmental Radioactivity, 90 (2), p.140-150, Jan 2006

DOI: 10.1016/j.jenvrad.2006.06.010

Keywords: ⁷Be; ¹³⁷Cs; Atmosphere; Aerosols; Chernobyl fallout; Nuclear weapons fallout; Sweden; Europe

Abstract: Seasonal fluctuations of cosmogenic ⁷Be (T_1/2 = 53.4 days) and anthropogenic ¹³⁷Cs (T_1/2 = 30 years) activities in surface air (aerosols) have been extracted from a long data record (1972–2000) at high latitude (56°N–68°N, Sweden). Normalization to weekly average values was used to control long-term trends so that cyclical trends could be investigated. Enhanced ⁷Be activity was observed in spring and summer seasons and likely relates to the seasonal thinning of the tropopause. Variations in the ¹³⁷Cs 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 ¹³⁷Cs activity was strongly related to nuclear weapons test fallout and exhibits temporal fluctuations resembling the ⁷Be. Conversely, since 1986 the Chernobyl-produced ¹³⁷Cs 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 ¹³⁷Cs 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.

URL: http://www.sciencedirect.com/science/article/pii/S0265931X06001032