Chemistry question pertaining to atm?

The ozone layer is about 20 Km thick, has an average total pressureof 10 mm Hg (1.3*10^-2), and has an average temperature of 230 K. The partial pressure of ozone in the layer is only about 1.2*10^-6 mm Hg (1.6*10^-9 mm Hg) .