Preliminary Work for Specialized Retrieval Algorithms Over Canada from Tropospheric Emissions: Monitoring of Pollution (TEMPO)

Tropospheric Emissions: Monitoring of Pollution (TEMPO) is an instrument designed to monitor air quality over North America, planned to be launched in early 2022. TEMPO, along with the European Sentinal-4 and the Korean Geostationary Environment Monitoring Spectrometer (GEMS), are positioned in geostationary orbits, which allows for unprecedented temporal resolution to accompany modern spatial resolution. The result will be a wealth of information on key pollutants which captures daily variations, a feat which was previously infeasible, and which can resolve features on an urban scale. This data will be invaluable for improving air quality forecasts, improving inventories of emission sources, informing emission control efforts, and driving health impact studies.

TEMPO measures the atmosphere by measuring scattered and reflected sunlight, which contains spectral information about the atmospheric species it interacted with along the way. It will take these measurements as far south as Mexico City and as far north as the Canadian oil sands: at these northern Canadian latitudes there are some unique challenges which must be addressed to produce high quality data. Firstly, at these latitudes the instrument is looking through the atmosphere at a shallow angle, which increases the importance of accurately considering the curvature and the horizontal variation in the atmosphere. Secondly, the sun is lower in the sky, which also increases the importance of these factors in addition to reducing the strength of the measured signal. Lastly, snow has historically not been treated robustly for these types of measurements, which is a problem at northern latitudes where snow cover is pervasive for much of the year.

Preliminary results are presented for the development of specialized algorithms for TEMPO measurements over Canada which address these challenges. This work sets the stage for future developments such as explicit treatment of snow and improved separation of snow and cloud features, and leveraging the shallow sun and observation angles, along with the density of TEMPO measurements, to improve the separation of surface level pollutants from those higher in the atmosphere. Such developments would allow Canada to maximize its benefit from TEMPO measurements.