27ATCHEM Long Term Trends of GOCI-II Aerosol Optical Properties: Continuation of GOCI Data Over 13 Years

Since 2020, the GOCI-II (Geostationary Ocean Color Imager-II) onboard the GEO-KOMPSAT-2B (GK-2B) satellite has been providing aerosol products, continuing the work of its predecessor, GOCI (Lee et al., 2023). The aerosol optical depth (AOD) at 550 nm is retrieved using the Yonsei aerosol retrieval (YAER) inversion algorithm, which utilizes a precomputed look-up table (LUT) spanning UV to near-IR wavelengths. In addition to AOD at 550 nm, GOCI-II also provides fine mode fraction at 550 nm, single scattering albedo at 440 nm, the Angstrom exponent between 440 nm and 870 nm, and aerosol type. The high spatial resolution of 2.5 km² and the hourly temporal resolution during daylight hours make GOCI-II aerosol products particularly valuable for monitoring aerosol distribution over Northeast Asia, a region characterized by frequent aerosol formation and transport. This study presents the details of the GOCI-II YAER algorithm, including its validation, case studies, and secondary uses of the products. Validation against AErosol RObotic NETwork (AERONET) AOD data across land, ocean, and all surface types shows strong agreement in terms of the percentage within the expected error (EE), correlation coefficient, and root mean squared error (RMSE). Additionally, the long-term continuity between GOCI and GOCI-II products is analyzed. Although there are areas for improvement, such as enhanced cloud screening and an updated surface reflectance database, the GOCI-II aerosol products offer critical insights for air quality policymaking and deepen our understanding of aerosol distribution over Northeast Asia. The combined use of GOCI and GOCI-II products enables comprehensive analysis of aerosol climatology and trends in Northeast Asia, facilitating further research on environmental and climate impacts.