Evaluation of Pandora HCHO and NO2 Columns with In Situ AEROMMA Observations in New York City

Formaldehyde (HCHO) and nitrogen dioxide (NO₂) are precursors to the formation of tropospheric ozone. The Pandora Global Network (PGN) is a system of ground-based spectrometers that report column and vertical profiles of HCHO and NO₂ through Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). The PGN offers a continuous dataset of HCHO and NO₂ around the globe and is a key component of the validation plan for the geostationary satellite Tropospheric Emissions: Monitoring of Pollution (TEMPO), however studies on the Pandora HCHO products are limited. In this analysis, we compare the MAX-DOAS retrievals observed by nine Pandoras in NYC to in situ data taken during NOAA’s airborne campaign Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) in the summer of 2023 by the Goddard ISAF instrument (HCHO) and the NOAA NOy-LIF instrument (NO₂). Our findings indicate that the Pandoras in NYC accurately represent the spatial and daily variability of HCHO and agree with the in situ vertical profiles within the range of uncertainty. Both the Pandora columns and vertical profiles capture the sharp horizontal gradient of NO₂ and are sensitive to the instrument’s viewing angle. TEMPO (version 3) exhibits good agreement with the overall Pandora tropospheric HCHO column in NYC during the AEROMMA flights, though this is highly dependent on the presence of clouds.