Tropospheric O3 from photolysis of O2

Photolytic dissociation of molecular oxygen (O-2) at wavelengths about 205 nm produces ozone (O-3) in the upper tropical troposphere. In tropospheric chemistry models that ignore this process, the O-3 abundance above 14 km in the tropics (a.k.a. Tropopause Transition Layer) is underestimated by 5 to 20 ppb. Even for models including O-2 photolysis, uncertainty in the O-2 cross sections yields similar uncertainty in TTL O-3. The related impact on global atmospheric chemistry is small, i.e., +/- 0.2% in CO and CH4 budgets, but the change in the O-3 column, +/- 1.6 DU in the tropics, may be important in calculating heating rates and climate forcing. Citation: Prather, M. J. ( 2009), Tropospheric O-3 from photolysis of O-2, Geophys. Res. Lett., 36, L03811, doi:10.1029/2008GL036851.