ROLE OF DEEP CLOUD CONVECTION IN THE OZONE BUDGET OF THE TROPOSPHERE

Convective updrafts in thunderstorms prolong the lifetime of ozone (O- 3,) and its anthropogenic precursor NOx [nitric oxide (NO) + nitrogen dioxide (NO2)] by carrying these gases rapidly upward from the boundar y layer into a regime where the O-3 production efficiency is higher, c hemical destruction is slower, and surface deposition is absent. On th e other hand, the upper troposphere is relatively rich in O-3 and NOx from natural sources such as downward transport from the stratosphere and lightning; convective overturning conveys the O-3 and NOx toward t he Earth's surface where these components are more efficiently removed from the atmosphere. Simulations with a three-dimensional global mode l suggest that the net result of these counteractive processes is a 20 percent overall reduction in total tropospheric O-3. However, the net atmospheric oxidation efficiency is enhanced by 10 to 20 percent.