GEMS L2 data validation during ASIA-AQ campaign

To understand the dominant chemical mechanisms driving wintertime secondary PM2.5 formation and to validate GEMS L2 data, the National Institute of Environmental Research and the National Aeronautics and Space Administration (NASA) conducted the Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign across four Asian countries (Korea, the Philippines, Malaysia, and Thailand) from February to March 2024. During this campaign, we deployed six Pandora instruments, two AQProfilers, and five AERONET systems around the Seoul metropolitan region. Using these ground-based instruments, we retrieved nitrogen dioxide, ozone and formaldehyde vertical column densities, as well as aerosol properties, and compared the results with GEMS L2 products. A comparison of NO₂ observed by GEMS with that from ground-based remote sensing instruments revealed a correlation coefficient of over 0.6 across all regions. Additionally, a performance comparison of GEMS NO₂ across different versions showed that the overestimation observed in GEMS v2 results was improved in the v4 results. Furthermore, we also compared results from NASA GeoTASO with those from GEMS during this period.