Representing improved tropospheric ozone distribution by including lightning NOx emissions in CHIMERE

Abstract. Estimating nitrogen oxide emissions from lightning (LNOx) in models is highly uncertain, affecting the accuracy of atmospheric composition and air quality assessments. Still, it is essential to include the emissions in model to increase the realism in representing the model outcomes. LNOx emissions have recently been incorporated into the updated version of the CHIMERE model (v2023r2). In the present study, we evaluate the present state of modelling the lightning flashes and the LNOx emissions, using a classical scheme based on cloud top height (CTH) and the model CHIMERE. We asses the impact of LNOx on tropospheric ozone (O₃) concentration over the northern hemisphere (NH) through a detailed evaluation of simulated tropospheric O₃. The total NO emission from lightning is estimated as 8.82 Tg N yr⁻¹ over the NH. There is an overall increase in O₃ concentration due to inclusion of LNOx. The increase is highest in the mid to upper troposphere, specifically over the tropics. The comparison of the simulated O₃ to measurements shows that the inclusion of LNOx emissions substantially improves the tropospheric O₃ distribution, reducing bias significantly. This is particularly true for the free troposphere over the tropical region. The LNOx emissions hence critically influence the O₃ concentration as well as the concentration of hydroxyl radicals (OH). There are 15 % and 40 % increases, respectively, in O₃ and OH burden as observed due to the inclusion of LNOx in model, which further impact the atmospheric lifetime of trace gas methane (CH₄) by reducing it by 24 %.