Improved lightning NOx emission inventory evaluated with vertical profiles of NO2 and ozone obtained by cloud-slicing TROPOMI

Lightning is the dominant source of nitrogen oxides (NO_x) in the free troposphere. Yet, its representation in models is highly parameterised, limiting our ability to determine past and future changes in lightning NO_x and causing errors in model representation of tropospheric ozone and NO_x. Models such as GEOS-Chem use fixed lightning NO_x production rates constrained with historic satellite instrument observations of ozone. A new approach is to model NO_x production per flash (mol N fl^-1) using lightning energy dependent NO_x yields and lightning flash radiant energy data from the space-based lightning imaging sensor (LIS) aboard both the Tropical Rainfall Measuring Mission (TRMM) satellite and the International Space Station (ISS). This updated approach is then used in GEOS-Chem to compute total lightning NO_x yields through the Harmonized Emissions Component (HEMCO), rather than using fixed values. The updated annual lightning NO_x emissions total 6.5 Tg N, similar to the original parameterised representation (5.8 Tg N), but with much greater variability in NO_x production rates. The original implementation uses 260 mol N fl^-1 everywhere except the northern extratropics that are at 500 mol fl^-1. In the updated implementation, values range from 27 to 632 mol N fl^-1 over the ocean and from 66 to 482 mol N fl^-1 over land. Greater values over the ocean are due to oft-reported much more energetic maritime lightning. To test the effect on tropospheric ozone and NO_x, we are currently comparing seasonal mean GEOS-Chem and TROPOMI-derived vertical profiles of ozone and NO₂. The TROPOMI-derived values, obtained by cloud-slicing partial columns over optically thick clouds, we have previously evaluated to be consistent with NASA DC-8 aircraft measurements in the free troposphere for cloud-sliced NO₂ (differences < 20 pptv) and the global ozonesonde network for cloud-sliced ozone across the whole troposphere (differences < 35 ppbv). This offers the means to assess the representation of lightning NO_x and better understand its influence on tropospheric NO_x and ozone.