First top-down diurnal adjustment to NOx emissions inventory in Asia informed by the Geostationary Environment Monitoring Spectrometer (GEMS) tropospheric NO2 columns

Pioneering the use of the Geostationary Environment Monitoring Spectrometer's (GEMS) observation data in air quality modeling, we adjusted Asia's NO_x emissions inventory by leveraging the instrument's unprecedented sampling frequency. GEMS tropospheric NO₂ columns served as top-down constraints, guiding our Bayesian inversion to constrain NO_x emissions in Asia during spring 2022. This enabled the model to better capture the diurnal variation in NO_x emissions, such as its morning rush hour peak, particularly when more retrievals were available each day, improving the simulation accuracy to a certain extent. The GEMS-informed adjustment reduced the extent of model underestimation of surface NO₂ concentrations from 17.38 to 5.58% in Korea and from 13.05 to 4.54% in China, showing about 9.40% and 5.77% greater improvements, respectively, compared to the adjustment based on the sun-synchronous low earth orbit observation proxy. Our findings highlight the potential of geostationary observation data in refining the diurnal cycle of inventoried NO_x emissions, thereby more effectively improving the accuracy of air quality simulations.