Long-term variations of 14C and 137Cs in the Bratislava air – implications of different atmospheric transport processes

This study summarizes measurements of atmospheric 14C and 137Cs in the Bratislava air since 1976. Higher 14C levels observed in spring and early summer months until the 1980’s confirm injection of the stratospheric air into the troposphere. Later, deep winter minima were observed in 14C concentrations, probably due to the depletion of the atmospheric 14C levels in winter months by the injection of large quantities of fossil CO2. Presently observed 14C maxima in summer and minima in winter were caused by the depletion of the atmospheric 14C in winter months, amplified by temperature inversions during winter, rather than by the injection of the stratospheric air into the troposphere. The observed 137Cs activity concentrations also showed an impact of the stratospheric air on the 137Cs levels until the early 1980’s, documented by typical spring/early summer maxima and winter minima. The global fallout 137Cs record was then disturbed by the Chernobyl accident (1986) when large quantities of 137Cs were released to the atmosphere. The recent 137Cs variations observed in the atmosphere, characterised by winter maxima and summer minima, are assumed to be mainly due to the resuspension of 137Cs from the soil. A correlation was found between the 137Cs activity concentration and the dust level in the air (the correlation coefficient r = 0.74), as well as an anticorrelation with the temperature (r = −0.56).

► The recent 14C variations in the Bratislava air were caused by the depletion of the atmospheric 14C levels in winter months due to inputs of fossil CO2 into the atmosphere.
► The recent 137Cs variations observed in the Bratislava air were mainly due to the resuspension of 137Cs from the soil.
►  The 137Cs activity concentration correlated with the dust level in the air (the correlation coefficient r = 0.74), and anticorrelated with the temperature (r = −0.56).