Effects of lightning NO_x production during the 21 July European Lightning Nitrogen Oxides Project storm studied with a three-dimensional cloud-scale chemical transport model

The 21 July 1998 thunderstorm observed during the European Lightning Nitrogen Oxides Project (EULINOX) project was simulated using the three-dimensional Goddard Cumulus Ensemble (GCE) model. The simulation successfully reproduced a number of observed storm features including the splitting of the original cell into a southern cell which developed supercell characteristics and a northern cell which became multicellular. Output from the GCE simulation was used to drive an offline cloud-scale chemical transport model which calculates tracer transport and includes a parameterization of lightning NO_x production which uses observed flash rates as input. Estimates of lightning NO_x production were deduced by assuming various values of production per intracloud and production per cloud-to-ground flash and comparing the results with in-cloud aircraft observations. The assumption that both types of flashes produce 360 moles of NO per flash on average compared most favorably with column mass and probability distribution functions calculated from observations. This assumed production per flash corresponds to a global annual lightning NO_x source of 7 Tg N yr^-1. Chemical reactions were included in the model to evaluate the impact of lightning NO_x on ozone. During the storm, the inclusion of lightning NO_x in the model results in a small loss of ozone (on average less than 4 ppbv) at all model levels. Simulations of the chemical environment in the 24 hours following the storm show on average a small increase in the net production of ozone at most levels resulting from lightning NO_x maximizing at approximately 5 ppbv day^-1 at 5.5 km. Between 8 and 10.5 km, lightning NO_x causes decreased net ozone production.