Estimates of Lightning-Generated NOx from Geostationary Satellite (GOES-16) GLM Observations for use in Air Quality Models

Nitrogen oxides (NOx=NO+NO2) play a critical role in tropospheric chemistry. Soil and lightning are the main natural emission sources for tropospheric NOx. Lightning-generated nitrogen oxide (NO) is the dominant NOx emission source in the free troposphere and greatly impacts tropospheric ozone chemistry. Previous studies have indicated that lightning NOx (LNOx) significantly influences ozone formation and enhances HNO3 and PAN concentrations in the free troposphere. Traditionally, due to the large uncertainty in the magnitude of LNOx production per flash, limited availability of data, and the view that the impact of LNOx on surface ozone is negligible, regional air quality models generally discounted this NOx emissions source. However, over the past decade, there have been many attempts to reduce the uncertainties in the LNOx production rate and several techniques have been introduced for inclusion of LNOx in air quality models.

In the current study, we use the lightning observations from the Geostationary Lightning Mapper (GLM) onboard GOES-16 to produce hourly LNOx emission estimates for use in the air quality models over contiguous United States. GLM provides the location and optical energy of lightning flashes. Based on Koshak 2017, a procedure was devised to convert optical energy into LNOx. The conversion relies on a conversion factor that encapsulates the correction needed for all the uncertainties in the formulation. This correction factor was determined based on compiling all the available GLM data and ensuring that the average LNO production per flash remains in the range of 100-500 mole/flash, and the total nitrogen production over U.S. remains reasonable. The preliminary results from this study, including the monthly and seasonal variation of LNOx and impact on air quality simulations will be presented.