Cross-Satellite Evaluation of TEMPO Version 04 NO2 and HCHO Products with TROPOMI and OMI for Air Quality Applications

Tropospheric Emissions: Monitoring of Pollution (TEMPO) provides near-hourly daytime retrievals of air-quality-relevant trace gases over North America from geostationary orbit. We compare TEMPO Version 04 (V04) Level 2 (L2) tropospheric nitrogen dioxide (NO 2 ) and total formaldehyde (HCHO) vertical column densities (VCDs) against low-Earth-orbit (LEO) products from the TROPOspheric Monitoring Instrument (TROPOMI) and Ozone Monitoring Instrument (OMI). Over the core analysis period (2 August 2023-31 August 2024), aggregating daily matched pixels at the approximate native LEO resolutions (0.05° for TROPOMI and 0.2° for OMI) into 0.2° period-mean fields increases correlations (r) for tropospheric NO 2 (0.58-0.70 to 0.91-0.96) and total HCHO (0.34-0.36 to 0.71-0.89). Recalculating TROPOMI and OMI VCDs with TEMPO-consistent a priori profiles modestly improves correlations (Δr = 0.00-0.03) and shifts the normalized mean difference (NMD) of TEMPO V04 relative to TROPOMI (NO 2 : -11% to -21%; HCHO: -6% to ~0%) and OMI (NO 2 : -1% to -7%; HCHO: +7% to -1%). Comparable TROPOMI results persist over the extended record (August 2023-August 2026) for NO 2 (r = 0.96-0.98, NMD -13% to -23%) and HCHO (r = 0.89-0.92, NMD -7% to ~0%). Correlations are strongest in autumn (SON) for NO 2 and summer (JJA) for HCHO and weakest in winter (DJF) for both species. Single-scan comparisons show that TEMPO and TROPOMI resolve localized NO 2 enhancements and gradients associated with urban areas, power plants, and fires, whereas OMI captures the broader patterns. These findings provide guidance for the joint use of TEMPO and LEO records and for comparisons across the global air-quality constellation.