Abstract Tropospheric Emissions: Monitoring of Pollution (TEMPO) is the first geostationary satellite instrument to monitor air pollutants across North America. This study uses Pandora observations to analyze the bias in TEMPO Level‐3 total column density of NO 2 (TOTNO 2 ) from August 2023 to December 2024. TEMPO achieves high accuracy at 5% cloud‐filtering threshold: correlation coefficient (R) of 0.86, index of agreement (IOA) of 0.91, mean absolute bias (MAB) of 1.423 × 10 15 molecules/cm 2 , and a percentage MAB (MABP) of 23.1%, corresponding to a 12% underestimation. Accuracy decreases when pixels with greater cloud‐cover are included. Solar zenith angle (SZA) of 10–20° yields the highest accuracy (R: 0.87, MABP: 22.7%), whereas SZAs of 70–80° yield the lowest (R: 0.71, MABP: 35.2%). Consequently, early‐morning or near‐sunset observations are less reliable than midday. This discrepancy could stem from inaccurate simulation of diurnal variations in the boundary‐layer height in the a‐priori, and from larger uncertainties in radiative transfer at high SZAs. TEMPO overestimates TOTNO 2 at low NO 2 levels and underestimates at high levels, with maximum biases of +16% (low) and −31% (high), respectively. Station‐to‐station performance varies considerably, with R ranging from 0.29 to 0.84 and MABP from 14.9% to 49.3%. Stations situated at higher altitudes relative to the ground show reduced agreement with TEMPO, as Pandora cannot detect NO 2 below the instrument's altitude, whereas TEMPO retrieves the full column. Validation of TEMPO TOTNO 2 at TROPOMI overpass time indicates that TEMPO's performance relative to Pandora (IOA: 0.93, MABP: 22.3%) closely matches that of TROPOMI (IOA: 0.92, MABP: 20.1%).
Ghahremanloo et al. (Thu,) studied this question.