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Quantification of Lightning-induced Nitrogen Oxides in CMAQ and the Assessment of its impact on Ground-level Air Quality
Citation:
Kang, D., R. Mathur, R. Gilliam, G. Pouliot, AND David-C Wong. Quantification of Lightning-induced Nitrogen Oxides in CMAQ and the Assessment of its impact on Ground-level Air Quality. 5th International Symposium on Regional Air Quality Management, Guangzhou, CHINA, November 16 - 19, 2017.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Computational Exposure Division (CED) develops and evaluates data, decision-support tools, and models to be applied to media-specific or receptor-specific problem areas. CED uses modeling-based approaches to characterize exposures, evaluate fate and transport, and support environmental diagnostics/forensics with input from multiple data sources. It also develops media- and receptor-specific models, process models, and decision support tools for use both within and outside of EPA.
Description:
Lightning-induced nitrogen oxides (LNOX), in the presence of sunlight, volatile organic compounds and water, can be a relatively large but uncertain source for ozone (O3) and hydroxyl radical (OH) in the atmosphere. Using lightning flash data from the National Lightning Detection Network (NLDN) with an updated LNOX emission estimation algorithm in the Community Multiscale Air Quality (CMAQ) model, we estimate the hourly variations in LNOX emissions for the summer of 2011, compare with anthropogenic and soil sources, and simulate its impact on distributions of tropospheric O3 across the continental United States. We find that typical summer-time lightning activity across the Western U.S. injects NOx emissions comparable to that from anthropogenic sources into the troposphere over the region. Comparison of two model simulation cases with and without LNOX emissions show that significant amount of ground-level O3 in the Western U.S. during the summer can be attributed to the lightning NOX emissions. The model simulated surface-level O3 in the case with lightning NOX emissions matched the observed values much closer than the model case without lightning NOX emissions. Periods of significant reduction in bias in simulated O3 between these two cases strongly correlates with the periods when lightning activity occurred in the region. The inclusion of LNOX increased daily maximum 8-hour O3 by up to 17 ppb and improved model performance relative to measured surface O3 mixing ratios in the Western U.S. region. The magnitude of LNOX emissions estimated for other summers is comparable to the 2011 estimates suggesting that summertime surface-level O3 levels in the Western U.S. region could be significantly influenced by lightning NOx and needs to be accurately characterized in assessments of O3 background values in the region.
