Kinetics of NOx in the upper troposphere: new constraints on satellite remote sensing of lightning NOx

Abstract:

Satellite retrievals of NO₂, O₃, and HNO₃ have been used in conjunction with chemical transport models, such as GEOS-Chem, to constrain the amount of NO_x emitted annually from lightning by comparing the model to both observed NO₂ column densities and to upper tropospheric (UT) concentrations of O₃ and HNO₃. Recent experiments have provided evidence for two changes to the kinetics of NO_x in the UT. First, CH₃O₂NO₂ has been shown to be an important temporary sink for NO_x, suppressing NO_x in the UT. Second, the rate coefficient for the reaction of OH with NO₂ at the temperatures and pressures of the UT is slower than in current recommendations. We investigate the impact of updated kinetics that are consistent with in situ observations on model predictions of NO₂, O₃, and HNO₃ concentrations and columns and on the inferred constraints on lightning NO_x emissions. Changes to NO₂, O₃, and HNO₃ concentrations resulting from the new kinetics are above the level of uncertainty in daily satellite observations. We hypothesize that the new kinetics will require an increase in lightning NO_x emissions to match models to observations, and are working to confirm and quantify this increase.