A numerical study of lightning-induced NOx and formation of NOy observed at the summit of Mt. Fuji using an explicit bulk lightning and photochemistry model

This study coupled a meteorological model with explicit bulk lightning and chemical transport models to investigate the impacts of lightning-induced nitrogen oxides (LNO_x) on nitrogen monoxide (NO), nitrogen dioxide (NO₂), and total reactive nitrogen oxide (NO_y) measured on August 22, 2017, at the top of Mt. Fuji, Japan. Our simulation results indicated that the LNO_x emitted around Wakasa Bay in the windward area of Mt. Fuji largely contributed to the NO_y content measured at the top of Mt. Fuji. Furthermore, sensitivity experiments regarding the height of LNO_x emissions indicated that the NO_y content measured atop Mt. Fuji originated from LNO_x emitted below 6 km. Our simulation assumed that a two-mode vertical distribution of LNO_x emissions was more consistent with measured NO_y at Mt. Fuji than a single-mode structure assumption in this case. A comparison of simulated NO_x (= NO + NO₂) and measured NO_x at Mt. Fuji indicated that the reaction rates of the NO and NO₂ cycles were well reproduced in our model; however, the ratio of NO_z (NO_y species other than NO_x) to NO_y estimated by the model were lower than the observed value, implying that the model either underestimated the reaction rate of LNO_x or overestimated the wet removal of lightning-induced NO_z. Finally, our results also suggest that the simultaneous observation of NO_y and NO_x is important for understanding LNO_x emissions, subsequent atmospheric chemical reactions, and removal processes, as well as validating chemical transport models.