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

Using lightning flash data from the National Lightning Detection Network with an updated lightning nitrogen oxides (NOx) emission estimation algorithm in the Community Multiscale Air Quality (CMAQ) model, we estimate the hourly variations in lightning NOxemissions 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 NOxemissions comparable to those from anthropogenic sources into the troposphere over the region. Comparison of two model simulation cases with and without lightning NOxemissions show that significant amount of ground-level O3in the MWS during the summer can be attributed to the lightning NOXemissions. The simulated surface-level O3from a model configuration incorporating lightning NOxemissions showed better agreement with the observed values than the model configuration without lightning NOxemissions. The time periods of significant reduction in bias in simulated O3between these two cases strongly correlate with the time periods when lightning activity occurred in the region. The inclusion of lightning NOxincreased daily maximum 8 h O3by up to 17 ppb and improved model performance relative to measured surface O3mixing 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 NOxemissions on O3air quality. The magnitude of lightning NOxemissions estimated for other summers is comparable to the 2011 estimates suggesting that summertime surface-level O3levels in the MWS region could be significantly influenced by lightning NOx.