This study presents the first Pandora-based validation of Geostationary Environment Monitoring Spectrometer (GEMS) tropospheric nitrogen dioxide (NO₂) measurements in the Philippines, focusing on observations over Quezon City during April 2025. Ground-based Pandora NO₂ data were compared with GEMS Level 2 tropospheric NO₂ products using time matching, cloud fraction filtering, and distance-weighted horizontal representativeness correction. Results show that GEMS consistently underestimated Pandora NO₂ columns, with correlations up to 0.535 for the full month and improving to as high as 0.752 during the elevated pollution episode from April 25–30 under low-cloud conditions. While representativeness of correction slightly improved agreement, systematic underestimation persisted, indicating that retrieval biases are influenced by factors beyond spatial mismatch. The findings highlight the importance of continuous ground-based validation and refinement of satellite NO₂ retrievals, particularly in tropical urban environments. The poster generated interest among conference participants due to its relevance to air quality monitoring in Southeast Asia and its contribution to expanding GEMS validation studies beyond East Asia.

This study is part of the 46th Asian Conference on Remote Sensing (ACRS) on 27-31 October 2025 in Makassar, Indonesia.

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