Application of Emissions Estimates from Geostationary Lightning Mapper (GLM) Observations in Air Quality Simulations

Lightning-generated nitrogen oxide (LNO) is the dominant NOx emission source in the free troposphere, having a significant impact on tropospheric ozone chemistry. LNO significantly influences ozone formation and enhances HNO3 and PAN concentrations in the free troposphere and can be crucial in establishing the natural background ozone. The newly deployed Geostationary Lightning Mappers (GLM) onboard GOES-16 (east) and GOES-18 (west, previously GOES-17) have created the opportunity for an alternate approach for estimating and incorporating LNO in air quality models. We have developed a Geostationary Lightning Mapper Nitrogen Oxides (GLM-NOx) Emissions Processor for creating model-ready LNO emissions for use in air quality simulations. The tool employs a new technique to derive LNO estimates from the GLM observations. The estimates are subsequently used in air quality simulations for the summer of 2019 and the impact on tropospheric ozone is examined.

In this talk, the LNO emissions model, which derives LNO emission estimates from GLM-observed lightning optical energy, and the impact on atmospheric chemistry will be presented. In this study, we first evaluated GLM observations with respect to their lightning detection efficiency over North America. Since the detection efficiency degrades with increasing satellite view angle, it was necessary to merge GLM-16 and GLM-17 observations over the contiguous United States (CONUS) to create a reliable dataset. Based on the theoretical and laboratory estimates of NO production per unit of energy, the GLM-observed optical energy is used to calculate the total column LNO. Using multiyear GLM observations and assuming an average 250 mol/flash global production rate, a calibration scaling factor is defined for the estimates. Observed optical energy from the individual flashes is used to calculate LNO from each flash. Subsequently, NASA Lightning Nitrogen Oxides Model (LNOM) monthly derived vertical profiles, which are based on uniquely fused theoretical and laboratory results with multiyear North Alabama Lightning Mapping Array (LMA) and National Lightning Detection Network (NLDN) observations, are used to vertically distribute the total column estimates. A software package is developed to perform these steps and produce the final CMAQ-ready hourly emissions.

Lightning produced 0.174 Tg N of nitrogen oxides (NOx = NO + NO2) over the contiguous U.S. (CONUS) domain between June and September 2019, which accounts for 11.4% of the total NOx emission. On average, LNO emission increased tropospheric ozone concentration by 1–2% (or 0.3–1.5 ppbv) in the column; the maximum enhancement was at ~4 km above ground level, with a minimum near the surface. The southeast U.S. has the most significant ground-level ozone increase, with up to 1 ppbv (or 2% of the mean observed value) increase in the maximum daily 8-hour average (MDA8) ozone. Our analysis indicated that the current LNO production rate used in the LNO emissions model should be increased. Moreover, the backward trajectory analyses revealed two main reasons for significant ozone increases: long-distance chemical transport and lightning activity in the upwind direction shortly before the event.