Stable isotope compositions of CO2 in background air and at polluted sites in Hungary

CO2 samples were collected from air at three sites in Hungary for comparison of polluted and background areas. In order to reduce the uncertainties caused by the varying amount of N2O, a gas chromatography (GC)-based vacuum separation was applied. The reliability of the procedure was demonstrated by careful standardization and comparison with global network data. The stable isotope data show complex diurnal and seasonal variations that can be explained by fractionations during photosynthesis and respiration. The isotopic characteristics of pollution-derived (anthropogenic) and biogenic CO2 appear to be indistinguishable at the study sites. However, the sites at unpolluted areas reveal a seasonal variation in the carbon isotope composition of biogenic CO2 that may be related to changes in soil biogenic activities. The atmospheric background CO2 shows constant delta(13)C in the region. Finally, the study demonstrates the need for careful standardization of sampling in order to make the data obtained from different sampling systems comparable. Copyright (C) 2002 John Wiley Sons, Ltd.