Evaluating top-down NMVOCs emissions in Northeast Asia and their impacts on simulated O3 concentrations in South Korea using OMI retrievals and aircraft observations during the KORUS-AQ campaign

Simulated CH₂O concentrations have been underestimated in recent years in Northeast Asia by a factor of two compared to satellite retrievals and aircraft observations. Here, we constrained formaldehyde sources, i.e., NMVOCs emissions, using OMI CH₂O retrievals and aircraft observations of CH₂O and NMVOCs during the international KORea-US cooperative Air Quality field study in Korea (KORUS-AQ) in May-June 2016. For the analysis, we first updated a 3-D chemical transport model, GEOS-Chem and its adjoint with the latest anthropogenic emissions, i.e., KORUS v4.5, with the optimized background CH₄ field, and with the latest chemistry for aromatic species and C₂H₄. We conducted Iterative Finite Difference Mass Balance (IFDMB) and 4D-VAR inversions to calculate optimized NMVOCs emissions in Northeast Asia. Comparisons of different inversion methods will be provided: IFDMB, IFDMB with simple averaging kernels to account for transport, and 4D-VAR. The total VOCs emissions throughout the domain were increased by a few percent. At some grid points, where emissions are high, the total VOCs emissions were increased by a factor of two to four, whereas a few grid points showed decreased emissions by a factor of two. With the a priori emissions, the simulated O₃ concentrations below 2 km were underestimated with a slope of 0.7 and correlation coefficient of 0.6 compared to the aircraft observations during the KORUS-AQ campaign. Evaluation of the model simulations using the optimized emissions in comparison to observed O₃ and PM_2.5 concentrations will be presented. Lastly, we will quantify the contributions of anthropogenic and biogenic NMVOCs emissions from different source regions to simulated O₃ concentrations in South Korea.