OMI Collection 4 Formaldehyde Retrievals: Towards a Multi-Sensor, Multi-Satellite and Multi-Decadal Dataset

Earth's atmosphere formaldehyde originates from anthropogenic, pyrogenic and biogenic processes. It can be directly emitted or be a by-product in the oxidation pathways of other volatile organic compounds, resulting on formaldehyde being one of the most abundant non-methane volatile organic compound (NMVOC) in the troposphere. Formaldehyde amounts in the atmosphere are sufficiently large to induce spectral signatures in backscatter solar radiation strong enough to allow its observation from nadir sounding satellite instruments. Given formaldehyde short lifetime, these satellite observations can be used as proxy observations of other NMVOC. Starting in the late 1990s, with observations by the GOME instrument (Chance et al., 1999), satellite formaldehyde has become an important tool to study the oxidative capacity of the atmosphere and emissions of NMVOCs emissions.

This paper presents Ozone Monitoring Instrument collection 4 formaldehyde retrievals, provides a description of the new retrievals and shows how it differs from its predecessor collection 3 dataset. The discussion addresses the impact of using OMI collection 4 radiances with improved calibration, updates in spectroscopy and spectral fitting as well as new ancillary datasets used in online air mass factor calculations. Results from validation studies against ground-based observations from the Network for the Detection of Atmospheric Composition Change show excellent performance at most locations. Finally, the paper highlights the continuity and consistency between OMI collection 4, OMPS-NPP and OMPS-N20 formaldehyde retrievals, providing an ongoing consistent data record starting in 2004. All three products use the Smithsonian Astrophysical Observatory retrieval framework, which is also the basis of the upcoming TEMPO formaldehyde retrievals.