Abstract
Abstract. 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 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 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 Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) satellite observations of lightning flash frequencies suggests that lightning is the dominant source of NOx to the upper troposphere except for extratropical latitudes in winter. The NO2 background in the absence of lightning is 10–20 pptv. We infer a global mean NOx yield of 280±80 moles per lightning flash, with no significant difference between the tropics and midlatitudes, and a global lightning NOx source of 5.9±1.7 Tg N a−1. There is indication that the NOx yield per flash increases with lightning flash footprint and with flash energy.
Highlights
Nitrogen oxides (NOx ≡ NO + NO2) in the upper troposphere (UT) have profound effects on the oxidizing capacity of the atmosphere and on climate, but the factors controlling their concentrations are poorly understood
INTEX-B is in the same year as the Ozone Monitoring Instrument (OMI) products but we consider interannual variability to be a small source of error
Measurements of NOx in the UT have mainly been from aircraft campaigns that are limited in space and time
Summary
Nitrogen oxides (NOx ≡ NO + NO2) in the upper troposphere (UT) have profound effects on the oxidizing capacity of the atmosphere and on climate, but the factors controlling their concentrations are poorly understood. Global CTMs typically use 100–500 mol N fl−1, sometimes assuming higher production rates at midlatitudes than in the tropics (Hudman et al, 2007; Ott et al, 2010), and a global lightning NOx source of 3–7 Tg N a−1 to match observations of tropospheric ozone and NOy species (Sauvage et al, 2007). A number of studies have used satellite observations of tropospheric NO2 columns from solar backscatter to infer lightning NOx emissions (Beirle et al, 2010; Pickering et al, 2016; Bucsela et al, 2010), including in combination with global models (Boersma et al, 2005; Martin et al, 2007; Miyazaki et al, 2014).
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