Global Formaldehyde Products From the Ozone Mapping and Profiler Suite (OMPS) Nadir Mappers on Suomi NPP and NOAA-20

Abstract

We describe new publicly available, multi-year formaldehyde (HCHO) data records from the Ozone Mapping and Profiler Suite (OMPS) nadir mapper (NM) instruments on the Suomi NPP and NOAA-20 satellites. The OMPS-NM instruments measure backscattered UV light over the globe once per day, with spatial resolutions close to nadir of 50 × 50 km2 (OMPS/Suomi-NPP) and 17 × 17 km2 or 12 × 17 km2 (OMPS/NOAA-20). After a preliminary instrument line shape and wavelength calibration using on-orbit observations, we use the backscatter measurements in a direct spectral fit of radiances, in combination with a nadir reference spectrum collected over a clean area, to determine slant columns of HCHO. The slant columns are converted to vertical columns using air mass factors (AMFs) derived through scene-by-scene radiative transfer calculations. Finally, a correction is applied to account for background HCHO in the reference spectrum, as well as any remaining high-latitude biases. We investigate the consistency of the OMPS products from Suomi NPP and NOAA-20 using long-term monthly means over 12 geographic regions, and also compare the products with publicly available TROPOMI HCHO observations. OMPS/Suomi-NPP and OMPS/NOAA-20 monthly mean HCHO vertical columns are highly consistent (r = 0.98), with low proportional (2%) and offset (2 × 1014 molecules cm−2) biases. OMPS HCHO monthly means are also well-correlated with those from TROPOMI (r = 0.92), although they are consistently 10% ± 16% larger in polluted regions (columns >8 × 1015 molecules cm−2). These differences result primarily from differences in AMFs.