Correlation between continental air mass and ozone concentrations

High ozone concentrations are observed in late spring and summer during ant icyclonic situations. Much of the ozone is the result of a photochemical pr oduction on a large scale due to the presence of precursors NOx(,) CO and H C, while the air mass is moving over polluted areas. Daily concentration mi nima of radon, a radioactive gas emitted from the ground, can be considered as a good tracer of the continental character of the air mass. Correlation between daily maxima of ozone and daily minima of radon is analysed. Posit ive correlations are observed in summer, strengthening the hypothesis of oz one formation on a large scale (the half-life of radon is 3.8 days). On the other hand, in winter, daily minima of radon and daily maxima of ozone are negatively correlated. During this season, deposition and chemical destruc tion of ozone seem to be more significant than production while the air mas s is moving over the continent.