Significant ground-level ozone attributed to lightning-induced nitrogen oxides during summertime over the Mountain...

Using lightning flash data from the National Lightning Detection Network with an updated lightning nitrogen oxides (NO_x) emission estimation algorithm in the Community Multiscale Air Quality (CMAQ) model, we estimate the hourly variations in lightning NO_x emissions for the summer of 2011 and simulate its impact on distributions of tropospheric ozone (O₃) across the continental United States. We find that typical summer-time lightning activity across the U.S. Mountain West States (MWS) injects NO_x emissions comparable to those from anthropogenic sources into the troposphere over the region. Comparison of two model simulation cases with and without lightning NO_x emissions show that significant amount of ground-level O₃ in the MWS during the summer can be attributed to the lightning NO_X emissions. The simulated surface-level O₃ from a model configuration incorporating lightning NO_x emissions showed better agreement with the observed values than the model configuration without lightning NO_x emissions. The time periods of significant reduction in bias in simulated O₃ between these two cases strongly correlate with the time periods when lightning activity occurred in the region. The inclusion of lightning NO_x increased daily maximum 8 h O₃ by up to 17 ppb and improved model performance relative to measured surface O₃ mixing ratios in the MWS region. Analysis of model results in conjunction with lidar measurements at Boulder, Colorado during July 2014 corroborated similar impacts of lightning NO_x emissions on O₃ emissions estimated for other summers is comparable to the 2011 air quality. The magnitude of lightning NO_x estimates suggesting that summertime surface-level O₃ levels in the MWS region could be significantly influenced by lightning NO_x.