Lightning NOx Emissions and the Implications for Surface Air Quality over the Contiguous United States
Kang, D. AND K. Pickering. Lightning NOx Emissions and the Implications for Surface Air Quality over the Contiguous United States. EM: AIR AND WASTE MANAGEMENT ASSOCIATION'S MAGAZINE FOR ENVIRONMENTAL MANAGERS. Air & Waste Management Association, Pittsburgh, PA, , 1-6, (2018).
Ground-level ozone (O3), predominantly formed from chemical reactions in the atmosphere, responds to varying precursor emissions, meteorology, and climate change (Lin et. al, 2017). To protect human health and welfare from its detrimental effects (EPA Report, 2013), the National Ambient Air Quality Standards (NAAQS) for O3 has been tightened through the years (http://www.epa.giv/ttn/naaqs/standards/ozone/s_o3_history.html). In response to the lowered O3 standards, extensive control measures for regional nitrogen oxides (NOx), one of the crucial precursors in O3 formation, have been implemented across the United States (US), and they have led to significant reduction in anthropogenic NOx emissions in the past two decades (Cooper et al., 2012; Simon et al., 2015).
As one of the largest sources of natural NOX, it is estimated that lightning-induced NOX (LNOX) contributes 10-15% of the total global NOX emissions budget. Lightning activity exhibits strong spatial and temporal variations, and consequently so does the tropospheric distribution of NOX from lightning flashes. To assess the impact of LNOX on ground-level air quality, the Community Multiscale Air Quality (CMAQ) modeling system quantifies LNOX based on hourly gridded lightning strikes. The relative impact of LNOX on near-surface O3 depends not only on the extent and magnitude of lightning activity, but on NOX emissions from other sources, such as anthropogenic NOX and soil NO emissions. In this study, simulations for the April-September, 2011 period are performed using the WRF-CMAQ offline modeling system with and without LNOX. Total column lightning NOX and its relative contributions to total NOX emissions are quantified by region and time of year. The impact of LNOX on ground-level air quality is assessed by region and season based on evaluation against gas phase, accounting for spatial differences in the relative importance of LNOX relative to other sources of NOX emissions.