4.3. LNOx estimation for climate and air quality studies
Lightning produces nitrogen oxides (NOx = NO + NO2) that affects the concentration of greenhouse gases such as ozone [Huntrieser et al. , 1998; Pickering et al. , 2016]. Accurately characterizing trends in NOxproduction is crucial for monitoring the composition of the atmosphere, as well as monitoring climate variability and change. Since climate is most sensitive to ozone in the upper troposphere, and since lightning is the most important source of NOx in the upper troposphere at tropical and subtropical latitudes, lightning is a particularly useful parameter to monitor for climate assessments. Satellite-based optical lightning mappers have been used to make preliminary estimates of lightning NOx(LNOx) and used to examine long-term trends in annual production, as well as short-term interannual variability [Koshak , 2017]. Continuing these data records using ISS LIS observations is planned, and is particularly important for supporting the NCA program.
LNOx also impacts ozone estimates made by regional air quality models [e.g., Koshak et al., 2014a]. Hence a better understanding of the contribution of LNOx to greenhouse gas pollution in the lower troposphere is needed. Also onboard the ISS is the Stratospheric Aerosol and Gas Experiment (SAGE) III [Flittner et al. , 2018], which provides observations of nitrogen dioxide (NO2) that will provide ideal comparisons with ISS LIS retrievals of LNOx. New geostationary instruments - Tropospheric Emissions: Monitoring of Pollution (TEMPO), Sentinel-4, and Geostationary Environment Monitoring Spectrometer (GEMS) - will provide unique NO2measurements [Zoogman et al. , 2017; Courrèges-Lacoste et al. , 2017; Kim et al. , 2020] for comparison with ISS LIS. This combination of satellite-based chemistry measurements together with ISS LIS offer an unprecedented opportunity to fully probe LNOx production that is so vital to climate and air quality studies.