  $^{222}$Rn is a noble radioactive gas produced along the $^{238}$U decay
chain, which is present in the majority of soils and rocks. As $^{222}$Rn is
the most relevant source of natural background radiation, understanding its
distribution in the environment is of great concern for investigating the
health impacts of low-level radioactivity and for supporting regulation of
human exposure to ionizing radiation in modern society. At the same time,
$^{222}$Rn is a widespread atmospheric tracer whose spatial distribution is
generally used as a proxy for climate and pollution studies. Airborne gamma-ray
spectroscopy (AGRS) always treated $^{222}$Rn as a source of background since
it affects the indirect estimate of equivalent $^{238}$U concentration. In this
work the AGRS method is used for the first time for quantifying the presence of
$^{222}$Rn in the atmosphere and assessing its vertical profile. High
statistics radiometric data acquired during an offshore survey are fitted as a
superposition of a constant component due to the experimental setup background
radioactivity plus a height dependent contribution due to cosmic radiation and
atmospheric $^{222}$Rn. The refined statistical analysis provides not only a
conclusive evidence of AGRS $^{222}$Rn detection but also a (0.96 $\pm$ 0.07)
Bq/m$^{3}$ $^{222}$Rn concentration and a (1318 $\pm$ 22) m atmospheric layer
depth fully compatible with literature data.
