Lightning NOx Emissions: Reconciling Measured and Modeled Estimates With Updated NOx Chemistry

Lightning is one of the most important sources of upper tropospheric NOx; however, there is a large spread in estimates of the global emission rates (2–8 Tg N yr
1). We combine upper tropospheric in situ observations from the Deep Convective Clouds and Chemistry (DC3) experiment and global satellite-retrieved NO2 tropospheric column densities to constrain mean lightning NOx (LNOx) emissions per flash. Insights from DC3 indicate that the NOx lifetime is ~3 h in the region of outflow of thunderstorms, mainly due to production of methyl peroxy nitrate and alkyl and multifunctional nitrates. The lifetime then increases farther downwind from the region of outflow. Reinterpreting previous analyses using the 3 h lifetime reduces the spread among various methods that have been used to calculate mean LNOx emissions per flash and indicates a global LNOx emission rate of ~9 Tg N yr
1, a flux larger than the high end of recent estimates. Plain Language Summary Lightning is an important source of upper troposphere nitrogen oxides; however, there is high uncertainty in the amount of nitrogen oxides produced from lightning. Using recent updates in upper tropospheric nitrogen oxides chemistry, this study decreases this uncertainty from a factor of 4 to less than a factor of 2 and shows that the amount of nitrogen oxides produced from lightning should be higher.