Space-based constraints on the production of nitric oxide by lightning

We interpret observations of trace-gases from three satellite platforms to provide top-down constraints on the production of NO by lightning. The space-based observations are tropospheric NO₂ columns from SCIAMACHY, tropospheric O₃ columns from OMI and MLS, and upper tropospheric HNO₃ from ACE-FTS. A global chemical transport model (GEOS-Chem) is used to identify locations and time periods in which lightning would be expected to dominate the trace gas observations. The satellite observations are sampled at those locations and time periods. All three observations exhibit a maximum in the tropical Atlantic region and a minimum in the tropical Pacific. This wave-1 pattern is driven by injection of lightning NO into the upper troposphere over the tropical continents, followed by photochemical production of NO₂, HNO₃, and O₃ during transport. Lightning produces a broad enhancement over the tropical Atlantic and Africa of 2-6 × 10¹⁴ molecules NO₂ cm^-2, 4 × 10¹⁷ molecules O₃ cm^-2 (15 Dobson Units), and 125 pptv of upper tropospheric HNO₃. The lightning background is 25-50% weaker over the tropical Pacific. A global source of 6 ± 2 Tg N yr^-1 from lightning in the model best represents the satellite observations of tropospheric NO₂, O₃, and HNO₃.