Satellite observations of formaldehyde over North America from GOME

Formaldehyde (HCHO) is an important indicator of tropospheric hydrocarbon emissions and photochemical activity. We present HCHO observations over North America for July 1996 from the GOME instrument on-board the ESA ERS-2 satellite. Slant columns are determined to <4x10(15) molecules cm(-2) sensitivity by directly fitting GOME radiance measurements. These show a distinct enhancement over the southeastern United States, consistent with a large regional source from oxidation of non-methane hydrocarbons including in particular isoprene. Conversion of slant to vertical columns is done by combining species vertical distribution information from the GEOS-CHEM 3-D tropospheric chemistry and transport model with scattering weights from the Smithsonian Astrophysical Observatory LIDORT multiple scattering radiative transfer model. The results demonstrate the ability to measure HCHO from space in typical continental atmospheres, and imply that space-based measurements of HCHO may provide valuable information on emission fluxes of reactive hydrocarbons.