Snow‐Covered Insights From Above and Below: High‐Frequency Measurement of Nitrogen Dioxide From Space and Ground

Abstract The Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite provides hourly air quality measurements over North America. This study evaluates TEMPO observations over snow‐covered surfaces, highlighting its ability to capture sharp spatial and temporal gradients in vertical column densities and surface concentrations, key parameters for assessing air quality and public health impacts. Data from the 2024 Study of Winter Air Pollution in Toronto, including in situ and mobile Multi‐Axis Differential Optical Absorption Spectroscopy measurements, are used to assess TEMPO's precision and accuracy. Additional evaluations are performed at Pandora sites across North America to examine wintertime performance. Comparisons show strong correlations between TEMPO and surface observations, with significant improvements in bias after applying corrections to air mass factors, cloud fraction, and surface albedo (from −32% to −9% over snow).