Radioactivity in the Atmosphere

A short review is made on atmospheric radionuclides with emphasis on their activity concentrations in the troposphere, mostly for surface air over Europe. Discussed are those species which have activity concentrations above about 1 mBq/m3. For this atmospheric layer highest average activity concentrations (> 1 Bq/m3) have i) 222Rn ("radon") and its short-lived decay products, (ii) 220Rn ("thoron"), however, only for the lowest meter above ground, and iii) 85Kr. In the range 1 mBq/m3 to 1 Bq/m3 are Τ(3H), 14C, 37Ar and 7Be as well as the "thoron" decay product 212Pb. Average activity concentrations slightly below 1 mBq/m3 has 210Pb, the only long-lived decay product of "radon". The sources of these radionuclides are discussed. Not included in this review are radionuclides contained in the atmosphere at very low activity concentrations or from single emissions such as e.g. from the Tschernobyl accident in 1986.