Two decades of regular observations of 14CO2 and 13CO2 content in atmospheric carbon dioxide in central Europe:: Long-term changes of regional anthropogenic fossil CO2 emissions

Time series are presented of radiocarbon and C-13 contents in atmospheric carbon dioxide over eastern Europe (southern Poland), covering the periods 1983-1994 and 2000-2004. The carbon isotope composition was measured in biweekly composite samples of atmospheric CO2, Collected about 20 m above the local ground level. The data for 2 observational sites are presented: i) city of Krakow (50 degrees 04'N, 19 degrees 55'E; 220 m asl; for 1983-1994 and 2000-2004); and ii) Kasprowy Wierch, Tatra Mountains (49 degrees 14'N, 19 degrees 56'E; 1989 m asl; for 2000-2004). The latter site is considered a regional reference station, relatively free of anthropogenic influences. During the period 1983-1994, observations in the Krak6w area revealed a gradual decrease of C-14 content with a broad minimum around 1991 and a small increase by about 10 parts per thousand in the subsequent years. delta C-13 also changes with time, showing a decreasing trend from approximately -9.6 parts per thousand in 1983, with a slope of -0.02 parts per thousand/ yr. The observed trends for both isotopes coincide well with a substantial reduction of coal consumption in Poland and partial replacement of coal by natural gas, especially in urban regions. After 2000, the delta C-13 slightly increases, reaching a mean value of -10 parts per thousand in 2004, while Delta C-14 is below the reference level by similar to 3.5 parts per thousand. Observations at Kasprowy Wierch (regional reference station) also reflect a diminishing input of fossil carbon into the regional atmosphere. The fossil component in atmospheric CO2, calculated with the aid of C-14 data available for the 2 study periods, shows a reduction of anthropogenic input by a factor of 2, which is confirmed by annual statistics of coal consumption.