Twelve years of global observations of formaldehyde in the troposphere using GOME and SCIAMACHY sensors I. De Smedt1, J.-F. Müller1, T. Stavrakou1, R. van der A2, H. Eskes2, and M. Van Roozendael2 1Belgian Institute for Space Aeronomy (BIRA-IASB), Avenue Circulaire, 3, B-1180, Brussels, Belgium 2Royal Netherlands Meteorological Institute (KNMI), Wilhelminalaan 10, 3732 GK, De Bilt, The Netherlands
Abstract. This work presents global tropospheric formaldehyde columns retrieved from
near-UV radiance measurements performed by the GOME instrument onboard ERS-2
since 1995, and by SCIAMACHY, in operation on ENVISAT since the end of 2002.
A special effort has been made to ensure the coherence and quality of the
CH2O dataset covering the period 1996–2007. Optimised DOAS settings are
proposed in order to reduce the impact of two important sources of error in
the derivation of slant columns, namely, the polarisation anomaly affecting
the SCIAMACHY spectra around 350 nm, and a major absorption band of the
O4 collision complex centred near 360 nm. The air mass factors are
determined from scattering weights generated using radiative transfer
calculations taking into account the cloud fraction, the cloud height and
the ground albedo. Vertical profile shapes of CH2O are provided by the
global CTM IMAGES based on an up-to-date representation of emissions,
atmospheric transport and photochemistry. A comprehensive error analysis is
presented. This includes errors on the slant columns retrieval and errors on
the air mass factors which are mainly due to uncertainties in the a priori
profile and in the cloud properties. The major features of the retrieved
formaldehyde column distribution are discussed and compared with previous
CH2O datasets over the major emission regions.
Citation: De Smedt, I., Müller, J.-F., Stavrakou, T., van der A, R., Eskes, H., and Van Roozendael, M.: Twelve years of global observations of formaldehyde in the troposphere using GOME and SCIAMACHY sensors, Atmos. Chem. Phys., 8, 4947-4963, doi:10.5194/acp-8-4947-2008, 2008.