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

Abstract

Time series are presented of radiocarbon and 13C contents in atmospheric carbon dioxide over eastern Europe (southern Poland), covering the periods 19831994 and 20002004. 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 Krakw (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 Krakw area revealed a gradual decrease of 14C content with a broad minimum around 1991 and a small increase by about 10 in the subsequent years. d13C also changes with time, showing a decreasing trend from approximately 9.6 in 1983, with a slope of 0.02/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 d13C slightly increases, reaching a mean value of 10 in 2004, while delta-14C is below the reference level by ~3.5. 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 14C 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.