Radon 222 and tropospheric vertical transport

Radon 222 is an inert gas whose loss is due only to radioactive decay with a half life of 3.83 days (5.51‐day “exponential” lifetime). It is a very useful tracer of continental air because only ground level continental sources are significant. Thus it is similar in several ways to many air pollutants (e.g., NO x (NO+NO 2 ), SO 2 , and certain hydrocarbons). Previously published measured 222 Rn profiles are analyzed here by averaging for the summer, winter, and spring‐fall seasons. The analysis shows that in summer, about 55% of the 222 Rn is transported above the planetary boundary layer, considerably more than during the other seasons. Similarly, in summer, about 20% rises to over 5.5 km (500 mbar). The average profiles have been used to derive vertical eddy diffusion coefficients with maximum values of 5–7×10 5 cm 2 s −1 in the midtroposphere and 8×10 3 to 5×10 4 cm 2 s −1 near the surface.