Issues with HCHO retrieval for GEMS instruments on GEO-KOMPSAT

GEOstationary-KOrean MultiPurpose SATellite (GEO-KOMPSAT) will be launched by the Korean Ministry of Environment in 2018 to monitor the changes of air quality and climate in East Asia. This mission will be the first geostationary observations of trace gases. The target measurements of GEMS instrument on the GEO-KOMPSAT include SO2, NO2, O3, HCHO, and aerosols. We here examine several issues with retrieval methods primarily focusing on HCHO that is an important oxidation product of hydrocarbons using a unified retrieval system. The system comprises an atmospheric chemistry transport model (CTM), a radiative transfer model (RTM), and a HCHO retrieval algorithm. We test sensitivity of retrieved HCHO concentrations with respect to fitting wavelength band, O3 vertical column concentration, and the ring effect. Best optimization of those factors in the algorithm can be suggested by minimizing the error between a priori HCHO concentrations from the CTM and retrieved HCHO concentrations.