Comprehensive Analysis of Bias in TEMPO NO₂ Column Densities Through Pandora Observations

Area of Science:

• Atmospheric Science
• Remote Sensing
• Air Quality Monitoring

Background:

• The Tropospheric Emissions: Monitoring of Pollution (TEMPO) is a pioneering geostationary satellite instrument for observing North American air pollutants.
• Accurate measurement of nitrogen dioxide (NO2) is crucial for understanding air quality and pollution dynamics.

Purpose of the Study:

• To assess the bias and accuracy of TEMPO Level-3 total column density of NO2 (TOTNO2) data.
• To compare TEMPO's NO2 measurements with ground-based Pandora observations and satellite TROPOMI.

Main Methods:

• Analysis of TEMPO TOTNO2 data against Pandora ground-based measurements from August 2023 to December 2024.
• Evaluation of TEMPO's accuracy under varying cloud-filtering thresholds and solar zenith angles (SZAs).
• Comparison of TEMPO validation results with TROPOMI satellite data during coincident overpasses.

Main Results:

• TEMPO achieves high accuracy (R: 0.86, IOA: 0.91, MABP: 23.1%) with a 5% cloud-filtering threshold, but accuracy degrades with increased cloud cover.
• Optimal accuracy is observed at SZAs of 10-20°, while higher SZAs (70-80°) show reduced reliability.
• TEMPO exhibits overestimation at low NO2 levels (+16%) and underestimation at high levels (-31%), with significant station-to-station variability.

Conclusions:

• TEMPO provides a valuable dataset for monitoring NO2, with accuracy dependent on cloud cover and solar zenith angle.
• Midday observations with minimal cloud cover yield the most reliable TEMPO NO2 data.
• TEMPO's validation performance against Pandora is comparable to that of the TROPOMI satellite.