Lightning-generated NO_x and its impact on tropospheric ozone production: A three-dimensional modeling study of a Stratosphere-Troposphere Experiment: Radiation, Aerosols and Ozone (STERAO-A) thunderstorm

A three-dimensional cloud-scale chemical transport model has been used to simulate trace gas transport, lightning NO production, and photochemical ozone production in the 12 July 1996 storm observed during the Stratosphere-Troposphere Experiment: Radiation, Aerosols and Ozone (STERAO-A) field experiment. The model is driven by meteorological fields from a nonhydrostatic cloud-resolving model (see Stenchikov et al., 2005). An assumption that both cloud-to-ground and intracloud flashes produce 460 moles NO/flash on average yielded the best comparison with the profile of NO observed in the storm anvil. Scenarios in which the NO production of an intracloud flash was 75 to 100% of the production of a cloud-to-ground flash best matched the column NO_x mass computed from observations. Additional ozone production attributable to lightning NO within the storm cloud during the lifetime of the storm was very small (∼2 ppbv). However, simulations of the photochemistry over the 24 hours following the storm show that an additional 10 ppbv of ozone production can be attributed to lightning NO production in the upper troposphere. Convective transport of HO_x precursors led to the generation of a HO_x plume, which substantially aided the downstream ozone production. Soluble species mixing ratios in the simulated cloud were all within a factor of two of observations.