Nitrogen oxides in the global upper troposphere: interpreting cloud-sliced NO ₂ observations from the OMI satellite instrument

Nitrogen oxides (inline-formula $M2inlinescrollmathmlchem{\mathrm{normal\; NO}}_x\equiv \mathrm{normal\; NO}+{\mathrm{normal\; NO}}_{\mathrm{normal\; 2}}$ 85pt13ptsvg-formulamathimgf610f94fb6c20199e6f641866e657b1f acp-18-17017-2018-ie00001.svg85pt13ptacp-18-17017-2018-ie00001.png ) 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 inline-formulaNO₂ at 450–280 hPa (inline-formula∼6–9 km) from the Ozone Monitoring Instrument (OMI) produced by NASA and the Royal Netherlands Meteorological Institute (KNMI) provide global coverage to test our understanding of the factors controlling UT inline-formulaNO_x. We find that these products offer useful information when averaged over coarse scales (inline-formula $M6inlinescrollmathml\mathrm{normal\; 20}{}^{\circ }\times \mathrm{normal\; 32}{}^{\circ }$ 46pt11ptsvg-formulamathimg55f159cafb79d8ecf49805e6c5c5fba2 acp-18-17017-2018-ie00002.svg46pt11ptacp-18-17017-2018-ie00002.png , seasonal), and that the NASA product is more consistent with aircraft observations of UT inline-formulaNO₂. Correlation with Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) satellite observations of lightning flash frequencies suggests that lightning is the dominant source of inline-formulaNO_x to the upper troposphere except for extratropical latitudes in winter. The inline-formulaNO₂ background in the absence of lightning is 10–20 pptv. We infer a global mean inline-formulaNO_x yield of inline-formula280±80 moles per lightning flash, with no significant difference between the tropics and midlatitudes, and a global lightning inline-formulaNO_x source of inline-formula5.9±1.7 Tg N ainline-formula⁻¹. There is indication that the inline-formulaNO_x yield per flash increases with lightning flash footprint and with flash energy.