The influence of (CO2)-C-14 releases from regional nuclear facilities at the Heidelberg (CO2)-C-14 sampling site (1986-2014)

摘要

Atmospheric Delta(CO2)-C-14 measurements are a wellestablished tool to estimate the regional fossil-fuel-derived CO2 component. However, emissions from nuclear facilities can significantly alter the regional Delta(CO2)-C-14 level. In order to accurately quantify the signal originating from fossil CO2 emissions, a correction term for anthropogenic (CO2)-C-14 sources has to be determined. In this study, the HYSPLIT atmospheric dispersion model has been applied to calculate this correction for the long-term Delta(CO2)-C-14 monitoring site in Heidelberg. Wind fields with a spatial resolution of 2.5 degrees x 2.5 degrees, 1 degrees x 1 degrees, and 0.5 degrees x 0.5 degrees show systematic deviations, with coarser resolved wind fields leading to higher mean values for the correction. The finally applied mean Delta(CO2)-C-14 correction for the period from 1986-2014 is 2.3% with a standard deviation of 2.1% and maximum values up to 15.2 parts per thousand. These results are based on the 0.5 degrees x 0.5 degrees wind field simulations in years when these fields were available ( 2009, 2011-2014), and for the other years they are based on 2.5 degrees x 2.5 degrees wind field simulations, corrected with a factor of 0.43. After operations at the Philippsburg boiling water reactor ceased in 2011, the monthly nuclear correction terms decreased to less than 2 parts per thousand, with a mean value of 0.44 +/- 0.32 parts per thousand from 2012 to 2014.