Assessing the Impact of Lightning NO _x Emissions in CMAQ Using Lightning Flash Data from WWLLN over the Contiguous United States

Abstract

Comparison of lightning flash data from the National Lightning Detection Network (NLDN) and from the World Wide Lightning Location Network (WWLLN) over the contiguous United States (CONUS) for the 2016–2018 period reveals temporally and spatially varying flash rates that would influence lightning NO _x (LNO _x) production due to known detection efficiency differences especially during summer months over land (versus over ocean). However, the lightning flash density differences between the two networks show persistent seasonal patterns over geographical regions (e.g., land versus ocean). Since the NLDN data are considered to have higher accuracy (lightning detection with >95% efficiency), we developed scaling factors for the WWLLN flash data based on the ratios of WWLLN to NLDN flash data over time (months of year) and space. In this study, sensitivity simulations using the Community Multiscale Air Quality (CMAQ) model are performed utilizing the original data sets (both NLDN and WWLLN) and the scaled WWLLN flash data for LNO _x production over the CONUS. The model performance of using the different lightning flash datasets for ambient O ₃ and NO _x mixing ratios that are directly impacted by LNO _x emissions and the wet and dry deposition of oxidized nitrogen species that are indirectly impacted by LNO _x emissions is assessed based on comparisons with ground-based observations, vertical profile measurements, and satellite products. During summer months, the original WWLLN data produced less LNO _x emissions (due to its lower lightning detection efficiency) compared to the NLDN data, which resulted in less improvement in model performance than the simulation using NLDN data as compared to the simulation without any LNO _x emissions. However, the scaled WWLLN data produced LNO _x estimates and model performance comparable with the NLDN data, suggesting that scaled WWLLN may be used as a substitute for the NLDN data to provide LNO _x estimates in air quality models when the NLDN data are not available (e.g., due to prohibitive cost or lack of spatial coverage).