On concentration of 42Ar in the Earth's atmosphere

Data from the DBA liquid argon ionization chamber experiment have been used to obtain an estimate on the concentration of 42Ar in the Earth's atmosphere, 6.8−3.2+1.7·10−21 atoms of 42Ar per atom of 40Ar corresponding to the 42Ar activity of 1.2−0.5+0.3μBq per cubic meter of air.