Zolal Ayazpour

and 31 more

This study presents the Ozone Monitoring Instrument (OMI) Collection 4 formaldehyde (HCHO) retrieval developed with the Smithsonian Astrophysical Observatory’s (SAO) Making Earth System Data Records for Use in Research Environments (MEaSUREs) algorithm. The retrieval algorithm updates and makes improvements to the NASA operational OMI HCHO (OMI Collection 3 HCHO) algorithm, and has been transitioned to use OMI Collection 4 Level-1B radiances. This paper describes the updated retrieval algorithm and compares Collection 3 and Collection 4 data products. The OMI Collection 4 HCHO exhibits remarkably improved stability over time in comparison to the OMI Collection 3 HCHO product, with better precision and the elimination of artificial trends present in the Collection 3 during the later years of the mission. We validate the OMI Collection 4 HCHO data product using Fourier-Transform Infrared (FTIR) ground-based HCHO measurements. The climatological monthly averaged OMI Collection 4 HCHO vertical column densities (VCDs) agree well with the FTIR VCDs, with a correlation coefficient of 0.83, root-mean-square error (RMSE) of 2.98 × 1015 molecules cm-2, regression slope of 0.79, and intercept of 8.21 × 1014 molecules cm-2. Additionally, we compare the monthly averaged OMI Collection 4 HCHO VCDs to OMPS Suomi NPP, OMPS NOAA-20, and TROPOMI HCHO VCDs in overlapping years for twelve geographic regions. This comparison demonstrates high correlation coefficients of 0.98 (OMPS Suomi NPP), 0.97 (OMPS NOAA-20), and 0.90 (TROPOMI).

Karn Vohra

and 6 more

Caroline R. Nowlan

and 14 more

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 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 air mass factors.