Emerging investigator series: spatially and temporally resolved lightning NOx production rates obtained with space-based lightning detectors.

Lightning is a dominant free tropospheric source of nitrogen oxides (NOx), impacting climate by affecting global tropospheric ozone (O3) and other key oxidants. We calculate temporally and spatially resolved lightning NOx (LNOx) production rates using lightning flash energies from space-based Lightning Imaging Sensors (LIS). Our production rates average ∼309 moles per flash (mol fl-1) over oceans, peaking at midday, and ∼172 mol fl-1 over land, peaking in the early morning. Replacing static values in the original GEOS-Chem model inventory with our spatially and hourly varying production rates yields global annual LNOx emissions of 4.4 Tg nitrogen (N) for 2015-2019; almost 2 Tg N less than the original inventory. Annual terrestrial LNOx emissions still exceed those over the ocean, due to more frequent lightning over land, but the relative proportion of maritime emissions increases. The largest decline in LNOx emissions is north of 35°N in summer, as static 500 mol fl-1 is replaced with 150-250 mol fl-1. Global decline in LNOx emissions decreases abundances of free tropospheric NOx, O3, the hydroxyl radical (OH) and peroxyacetyl nitrate (PAN). Hourly variability in LIS flash radiances is broadly consistent with high-frequency Geostationary Lightning Mapper (GLM) flash energies, though the comparison is limited to tropical America. Introducing hourly variability in LNOx production rates leads to a greater than 10% localised decline in equatorial lower tropospheric O3. Independent validation is critically needed, given our updated LNOx emissions offer a viable solution to model overestimates in O3 and OH and underestimates in the lifetime of the greenhouse gas methane.