Evaluation of Satellite Retrievals of Total Column Formaldehyde over the Tropical Western Pacific and Central United States

Atmospheric formaldehyde (HCHO) is primarily formed in situ through the oxidation of methane and shorter-lived organic compounds, such as acetaldehyde and isoprene.  Because of its short lifetime of ~2 hours, knowledge of the HCHO distribution can also aid in the determination of the emissions of these short lived precursor species.  Satellite retrievals are instrumental in understanding the HCHO distribution and isoprene emissions but need to be evaluated through comparison to in situ observations.  Here, we use observations over the remote tropical western Pacific (TWP) during the CONTRAST campaign and over the central United States from the DC3 campaign to evaluate five retrievals of HCHO from the OMI, OMPS, and GOME2 instruments.  We find an almost uniform low bias in total column HCHO among all retrievals in both domains as compared to in situ derived columns (~20-50% low in the central US and 10% high to 80% low in the TWP), with each retrieval varying in accuracy between the two regions. In the TWP, the underestimate likely results partially from a low bias in the background column obtained from various chemical transport models.  Additional contributors to the discrepancy between the remotely sensed and in situ derived columns are investigated