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

Daiwen Kang,George A Pouliot,Robert C Gilliam,Rohit Mathur,David C Wong

doi:10.1038/s41612-020-0108-2

Daiwen Kang, George A Pouliot + Show 3 more

Open Access

https://doi.org/10.1038/s41612-020-0108-2

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Abstract

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.

Highlights

Due to its adverse impact on human health[1] and ecosystem well being,[2] tropospheric ozone (O3) has been at the center of air quality research during the past decades.[3,4,5] Ground-level O3 is either produced through complex photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs),[6] with both anthropogenic and natural origins, or transported from other locations.[7]
The addition of lightning NOx emissions can result in further deterioration of model performance for predicted O3 at many locations such as in the eastern U.S as illustrated in Fig. 1a, which presents the change in bias in simulated surface daily maximum
Significant impacts of lightning NOx on day to day variations in domain-mean surface DM8HR O3 over the Mountain West States (MWS) region is noted in Fig. 1d, which illustrates that lightning NOx emissions increase region-average DM8HR O3 by up to 6 ppb and helps reduce the model low-bias

Summary

Introduction

Due to its adverse impact on human health[1] and ecosystem well being,[2] tropospheric ozone (O3) has been at the center of air quality research during the past decades.[3,4,5] Ground-level O3 is either produced through complex photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs),[6] with both anthropogenic and natural origins, or transported from other locations.[7]. Lightning generates relatively large but uncertain quantities of NOx and strongly impacts the composition of trace gases in the troposphere.[13,14,15] Globally, lightning is estimated to generate 2–8 Tg N per year[16] which is considerably smaller than presentday global contributions from anthropogenic (~20.5 Tg N per year) and biomass burning (~5.5 Tg N per year) sources.[17] Despite the strong influence on troposphere burdens of O3 and OH, impacts of lightning NOx emissions on the surface-level air composition and chemistry have been suggested by past studies to be generally small, and except for some applications with global models, regional air quality assessments have historically not included lightning NOx emissions.[16] Uncertainties in lightning NOx emissions are influenced by limitations in the description of space and time variability in lightning frequency and intensity, NOx production rates from lightning flashes, and the vertical distribution and transport of lightning NOx after its production. Since lightning activity is often associated with deep convection in the atmosphere, the lightning flash rate can be parameterized using convection schemes.[18,19] convection schemes in meteorological models generally show low skill in producing the convective precipitation and the lightning distribution.[20,21] Though many studies report enhancement in surface-level NOx levels following thunderstorm activity, the impacts on surfacelevel O3 are ambiguous and typically complicated by the local photochemical conditions such as the availability of other precursors and sunlight.[22,23,24,25] Regional modeling calculations have shown up to 10 ppb enhancements in simulated instantaneous O3 mixing ratios[8,13,23,25] due to addition of lightning NOx

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