Validation of OMPS Suomi NPP and OMPS NOAA-20 Formaldehyde Total Columns With NDACC FTIR Observations

We validate formaldehyde (HCHO) vertical column densities (VCDs) from Ozone Mapping and Profiler Suite Nadir Mapper (OMPS-NM) instruments onboard the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite for 2012–2020 and National Oceanic and Atmospheric Administration-20 (NOAA-20) satellite for 2018–2020, hereafter referred to as OMPS-NPP and OMPS-N20, with ground-based Fourier-Transform Infrared (FTIR) observations of the Network for the Detection of Atmospheric Composition Change (NDACC). OMPS-NPP/N20 HCHO products reproduce seasonal variability at 24 FTIR sites. Monthly variability of OMPS-NPP/N20 has a very good agreement with FTIR, showing correlation coefficients of 0.83 and 0.88, respectively. OMPS-NPP (N20) biases averaged over all sites are −0.9 (4) ± 3 (6)%. However, at clean sites (with VCDs < 4.0 × 10¹⁵ molecules cm⁻²), positive biases of 20 (32) ± 6 (18)% occur for OMPS-NPP (N20). At sites with HCHO VCDs > 4.0 × 10¹⁵ molecules cm⁻², negative biases of −15% ± 4% appear for OMPS-NPP, but OMPS-N20 shows smaller bias of 0.5% ± 6% due to its smaller ground pixel footprints. Therefore, smaller satellite footprint sizes are important in distinguishing small-scale plumes. In addition, we discuss a bias correction and provide lower limit for the monthly uncertainty of OMPS-NPP/N20 HCHO products. The total uncertainty for OMPS-NPP (N20) at clean sites is 0.7 (0.8) × 10¹⁵ molecules cm⁻², corresponding to a relative uncertainty of 32 (30)%. In the case of HCHO VCDs > 4.0 × 10¹⁵ molecules cm⁻², however, the relative uncertainty in HCHO VCDs for OMPS-NPP (N20) decreases to 31 (18)%.