Spatiotemporal Assessment of the TEMPO Formaldehyde Column Retrieval Using the Pandonia Global Network

Launched in April 2023, the Tropospheric Emissions: Monitoring of Pollution (TEMPO), instrument provides for the first time hourly measurements of atmospheric pollutants over most of North America at high spatial resolution (~2 × 4.75 km²). This evaluation of TEMPO's first year demonstrates the capability of total formaldehyde column retrievals (ΩHCHO, version 3) at different locations, seasons, and meteorological conditions. The ΩHCHO product is assessed using 36 ground-based Pandora direct-sun measurements from Pandonia Global Network (PGN) as a reference data set. The 36 PGN sites were chosen for consistency in direct-sun and sky-scan measurement modes. In the first year of operation (Aug 2023-Sep 2024), TEMPO ΩHCHO exhibits moderate to strong agreement at PGN sites in both measurement modes (R ² = 0.63 to 0.85). TEMPO shows a negligible bias of -2 ± 20% at lower ΩHCHO (<1.0 × 10¹⁶ molecule cm^-2) and a larger underestimation of -22 ± 5% at higher ΩHCHO (>1.5 × 10¹⁶ molecule cm^-2). TEMPO clearly captures the seasonal variability of ΩHCHO, with summer values being greatest and winter, spring, and fall values being lower by - 62%, - 45%, and - 29%, respectively. TEMPO shows no consistent bias at any time of day with excellent agreement with Pandora for different meteorological conditions. For all hourly differences between TEMPO and Pandora, 96% fall within 1 × 10¹⁶ molecules cm^-2. TEMPO provides almost 50% more days with at least one observation compared to observations taken only at 1 p.m., from typical polar-orbiting satellites. These findings confirm the high quality of TEMPO's ΩHCHO measurements under a wide variety of conditions and show great promise for future scientific applications.