Lightning NO x emissions over the USA investigated using TES, NLDN, LRLDN, IONS data and the GEOS-Chem model

Abstract

Knowledge of the lightning source of NOx is required to better understand NOx and ozone distributions and changes in the troposphere, the oxidising capacity of the troposphere as well as some of the feedbacks between chemistry and climate change. In this paper, we use the National Lightning Detection (NLDN) and the Long Range Lightning Detection Network (LRLDN) data as well as the HYPSLIT transport and dispersion model to show the presence of ozone enhanced layers downwind of convective events in the ozone vertical profiles from the Tropospheric Emission Spectrometer (TES) instrument over the USA in July 2006. We use the TES dataset in conjunction with ozonesonde measurements from the Intercontinental Chemical Transport Experiment (INTEX) Ozonesonde Network Study (IONS) 2006 to test the parameterization of the lightning source of NOx in a global chemistry transport model. We find that the global 3-D chemistry transport model GEOS-Chem with a lightning activity calculated with a parameterization based on cloud top height, scaled regionally and monthly to OTD/LIS (Optical Transient Detector/Lightning Imaging Sensor) climatology, and with a production of 260 mol NO/Flash captures the ozone enhancements seen by TES, but underestimates their intensities. We show that the model's ability to reproduce the location of the enhancements is due to the fact that this model reproduces the pattern of the convective events occurrence on a daily basis during the summer of 2006, even though it does not well represent the relative distribution of lightning intensities. By imposing an updated lightning NO production value of 520 mol NO/Flash, we decrease the bias between TES and GEOS-Chem over the US in July 2006 by 40%.