Estimating Hourly Nitrogen Oxide Emissions Across Asia Using Data from the GEMS Geostationary Satellite

Conventional bottom-up emission inventories for atmospheric pollutants suffer from infrequent updates and substantial uncertainties. The Geostationary Environment Monitoring Spectrometer (GEMS) now provides columnar measurements for key atmospheric pollutants, including tropospheric O3, aerosols, and their precursors (NO2, SO2, HCHO, and glyoxal), on an hourly basis throughout the sunlit day, with a nominal spatial resolution of a few kilometres. These satellite data represent new constraints to determine top-down estimates of air pollutant emissions, providing complementary information to the bottom-up inventories. Collectively, bottom-up and top-down information provide better actionable information to develop more effective air pollution mitigation strategies. To demonstrate this, we infer emissions of nitrogen oxides (NOx=NO+NO2) across Asia from GEMS column observations of NO2 by using the adjoint of GEOS-Chem atmospheric chemical transport model. We explore diurnal variations in NOx emissions across diverse Asian cities, assessing their implications for emission policy formulation. Additionally, we conduct a critical evaluation of our top-down estimates of NOx emissions by comparing model simulations of NO2, driven by these estimates, with independent observations of NO2 throughout the region.