The Impact of Lightning NOx Production on Ground‐Level Ozone in Tehran

Abstract

AbstractLightning‐generated nitrogen oxides (LNOx) have an impact on the concentration of ground‐level ozone which acts as a toxic air pollutant, thereby negatively influencing human health and the environment. To understand the impact of LNOx on ground‐level ozone, we simulated four thunderstorm events in Tehran using the WRF‐Chem model. As observations of LNOx are not available, we evaluated the temporal distribution of the simulated ground‐level ozone concentration against an air quality monitoring station. We also compared the simulation results against the spatial distribution of the total column ozone from the Ozone Monitoring Instrument. WRF‐Chem performs well in the simulation of ground‐level ozone concentration, with the best performance for an event with the highest lightning activity (correlation coefficient of 0.91). The analysis of the spatial distribution of the observed and simulated total column ozone also indicates the good performance of WRF‐Chem. Hourly variation in the simulated LNOx during lightning activity is compared against both hourly variation in the observed ground‐level ozone and the number of lightning for four thunderstorm events. There is an agreement between the simulated LNOx and the observed ground‐level ozone during lightning for two events, with correlation coefficients of 0.55 and 0.57. LNOx emissions enhance ozone production in the middle to upper troposphere, which can subsequently contribute to an increase in ground‐level ozone by transport, vertical mixing, and chemistry. In addition, the initiation of chemical processes in response to cloud‐to‐ground lightning strikes may contribute to an increase in both LNOx and the concentration of ground‐level ozone.