Variability in Lightning NOx Production Rates due to Regional Differences in Lightning Type and Polarity

Emissions of nitrogen oxides (NOx) influence atmospheric oxidation chemistry and drive ozone production. Lightning is the dominant source of nitrogen oxides (NOx = NO + NO2) in the upper troposphere (UT). NOx is a key driver of chemistry in the UT and accurate and precise estimates of per flash lightning NOx production rates (LNOx) are needed to constrain the oxidative capacity in the UT and the global ozone burden; however, LNOx estimates are highly variable and uncertain. Here, we investigate LNOx variability in the U.S. due to lighting flash type and polarity. We correlate space-based NO2 observations from the Ozone Monitoring Instrument and surface lightning data from the Earth Networks Total Lightning Network separately in three regions of the U.S., Southeast, South Central, and North Central U.S., which exhibit different lightning characteristics. We find that differences in U.S. regional LNOx estimates are generally consistent with regional differences in the prevalence and proportion of inter-cloud (IC) and positive and negative cloud-to-ground (+CG and –CG) lightning flashes in each region. We find CG flashes generally produce at least ten times more NOx than IC flashes. We repeat the analysis, correlating NO2 observations with current data, rather than flash frequency, determining the same IC, +CG, and –CG LNOx patterns but deriving lower NOx yields with reduced variability, suggesting current is a more precise predictor than flash frequency.