Estimating the Influence of Lightning on Upper Tropospheric Ozone Using NLDN Lightning Data and CMAQ model

Lightning is a particularly significant NOx source in the middle and upper troposphere where it affects tropospheric chemistry and ozone. Because the version-4 Community Multiscale Air Quality Modeling System (CMAQ) does not account for NOx emission from lightning, it underpredicts NOx above the mixed layer. In this study, the National Lightning Detection NetworkTM (NLDN) lightning data are applied to the CMAQ model to simulate the influence of lightning-produced NOx (LNOx) on upper tropospheric NOx and subsequent ozone concentration. Using reasonable values for salient parameters (detection efficiency ~ 95%, cloud flash to ground flash ratio ~ 3, LNOx production rate ~ 500 moles N per flash), the NLDN ground flashes are converted into total lightning NOx amount and then vertically distributed on 39 CMAQ model layers according to a vertical-distribution profile of lightning N mass. This LNOx contributes 27% of the total NOx emission during 15 July ~7 September 2006. Although the model prediction of ozone in upper troposphere improves by ~20 ppbv due to lightning-produced NOx above the southeastern and eastern U.S.A., the improved ozone prediction is still ~20-25 ppbv lower than ozonesonde measurements.