Nitrogen oxides (NOx ≡ NO + NO2) in the upper troposphere (UT) have a large impact on global tropospheric ozone and OH (the main atmospheric oxidant). New cloud-sliced observations of UT NO2 at 450–280 hPa (~ 6–9 km) from the OMI satellite instrument produced by NASA and KNMI provide global coverage to test our understanding of the factors controlling UT NOx. We find that these products offer useful information when averaged over coarse scales (20° × 32°, seasonal), and that the NASA product is more consistent with aircraft observations of UT NO2. Correlation with LIS/OTD satellite observations of lightning flash frequencies shows that lightning is the dominant source of NOx to the upper troposphere except for extratropical latitudes in winter. We infer a global mean NOx yield of 280 moles per lightning flash, with no significant difference between the tropics and mid-latitudes, and a global lightning NOx source of 5.6 Tg N a−1. There is indication that the NOx yield per flash increases with lightning flash footprint and with flash energy.
