Significant ground-level ozone attributed to lightning-induced nitrogen oxides during summertime over the Mountain West States
Kang, D., R. Mathur, G. Pouliot, R. Gilliam, AND David-C Wong. Significant ground-level ozone attributed to lightning-induced nitrogen oxides during summertime over the Mountain West States. npj Climate and Atmospheric Science. Springer Nature Group, New York, NY, 3:6, (2020). https://doi.org/10.1038/s41612-020-0108-2
The contribution of lightning NOx to atmospheric chemistry has long been recognized. However, due to the lack of observations and robust algorithms, large uncertainties are associated with lightning strikes and lightning generated NOx (quantity and distribution) in air quality models. With the available high-quality lightning strike data from the lightning national detection network (NLDN) and the advancement of model algorithms to generate and distribute lightning NOx based on lightning strikes, we implemented the lightning NOx (LNOx) production and distribution scheme in CMAQ based on hourly NLDN data in time and space. More importantly, as technological advances and regulatory measures reduce anthropogenic NOx emissions in the region, the relative contributions of LNOx to O3 levels in the region will increase. Consequently, accurate quantification of LNOx emissions, their contribution to background O3 levels, and their role in modulating air quality in the region will become increasingly important.
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 NOx 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 NOx emissions comparable to those from anthropogenic sources into the troposphere over the region. Comparison of two model simulation cases with and without lightning NOx emissions show that significant amount of ground-level O3 in the MWS during the summer can be attributed to the lightning NOX emissions. The simulated surface-level O3 from a model configuration incorporating lightning NOx emissions showed better agreement with the observed values than the model configuration without lightning NOx 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 NOx 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 NOx emissions on O3 air quality. The magnitude of lightning NOx emissions estimated for other summers is comparable to the 2011 estimates suggesting that summertime surface-level O3 levels in the MWS region could be significantly influenced by lightning NOx.