On concentration of ${}^{42}$Ar 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 ${}^{42}$Ar in the Earth’s atmosphere, $6.8_{-3.2}^{+1.7}\cdot {10}^{-21}$ atoms of ${}^{42}$Ar per atom of ${}^{40}$Ar corresponding to the ${}^{42}$Ar activity of $1.2_{-0.5}^{+0.3}$ $\mu$Bq per cubic meter of air.