Satellite observations of formaldehyde over North America from GOME

Formaldehyde (HCHO) is an important indicator of tropospheric hydrocarbon e missions and photochemical activity. We present HCHO observations over Nort h America for July 1996 from the GOME instrument on-board the ESA ERS-2 sat ellite. Slant columns are determined to <4x10(15) molecules cm(-2) sensitiv ity by directly fitting GOME radiance measurements. These show a distinct e nhancement over the southeastern United States, consistent with a large reg ional source from oxidation of non-methane hydrocarbons including in partic ular isoprene. Conversion of slant to vertical columns is done by combining species vertical distribution information from the GEOS-CHEM 3-D troposphe ric chemistry and transport model with scattering weights from the Smithson ian Astrophysical Observatory LIDORT multiple scattering radiative transfer model. The results demonstrate the ability to measure HCHO from space in t ypical continental atmospheres, and imply that space-based measurements of HCHO may provide valuable information on emission fluxes of reactive hydroc arbons.