Evaluating TEMPO Satellite HCHO and NO2 Products Against Ground Based Pandora Instruments

Near-surface ozone can be hazardous to human and vegetation health. By measuring its two major atmospheric precursors, nitrogen oxides (NO_x) and volatile organic compounds (VOCs), and the ratio between them, the limiting factor in ozone production can be determined. This is critical in determining which compound to target to lower near-surface atmospheric ozone levels. The ratio between two proxies for these precursors, formaldehyde (HCHO) and nitrogen dioxide (NO₂), also known as FNR, is a well studied indicator for ozone formation sensitivity. The TEMPO satellite, a geostationary satellite launched over the United States in April 2023, is the first satellite to provide hourly measurements of these trace gasses over the US. The satellite provides unprecedented temporal and spatial resolution. This work used level 3 TEMPO products and data from 13 ground based Pandora spectrometer stations across three major ozone non-attainment US cities from May to June 2024. This work evaluated TEMPO atmospheric column measurements of NO₂ and HCHO against Pandora observations through linear regression analysis collocating points in space and time. While TEMPO showed a small upward bias against Pandora, the two instruments showed an overall strong agreement with R² = 0.76 for HCHO and R² = 0.75 for NO₂. Further, regressions and time series from both instruments showed greater discrepancies in urban locations over rural, however TEMPO did seem to follow the same diurnal trends as Pandora. This comparison provides a preliminary measure of the degree of error in the TEMPO instrument and further illuminates FNR patterns on a finer scale than before. This project will help inform future usage of newly released TEMPO data and improve understanding of diurnal and spatial variations in ozone sensitivity. This project is particularly beneficial for future work using this satellite data over more rural areas lacking ground-based measurements.