Impact of prescribed global and geostationary lightning observations on surface air quality in a chemical transport model

Abstract:

Production of reactive oxides of nitrogen (NO_x) by lightning has small but non-negligible impacts on background surface air quality. Accurate spatiotemporal reproduction of lightning occurrence has long remained a first-order problem in the representation of this source in global and regional air quality models. Here, we explore the impact of prescribing lightning occurrence from space-based and ground-based observing systems in the GEOS-Chem chemical transport model. First, lightning flashes are aggregated from the ground-based global Earth Networks Total Lightning Network (ENTLN) at 0.25^o latitude by 0.3125^o longitude and hourly resolution for 2012-2020. Local detection efficiency correction factors are determined by comparing ENTLN to contemporaneous overpasses of the Lightning Imaging Sensor on the International Space Station (ISS-LIS); recent global lightning detection efficiency is 40 %, with near-perfect detection over North America. Second, we aggregate lightning flash counts from the novel Geostationary Lightning Mapper (GLM) instruments on GOES-16 and GOES-17 over the Americas at the same spatial and temporal resolution beginning in December 2017. We use these gridded lightning products to drive a series of global and high-resolution North American sensitivity simulations for January 2018 through August 2019 that evaluate the air quality implications of (1) prescribing lightning flash occurrence versus (2) traditional online parameterization as a function of convective cloud-top height versus (3) no lightning. We further isolate the impact of uncertainties in lightning occurrence versus those in the vertical altitude of the emission release. The simulations are evaluated against surface air quality measurements of ozone, CO, NO₂ and PM_2.5 from each continent, global ozonesonde (WOUDC, SHADOZ) and aircraft observation programs (IAGOS, ATom), and TROPOMI tropospheric NO₂, CO, HCHO and methane columns. Prescribing lightning has the greatest improvement in representing air quality variability in the major subtropical subsidence zones of the world, including Mexico, the southwestern United States and western China.