Detection of trace species in the troposphere using backscatter spectra obtained by the GOME spectrometer

Atmospheric UV/visible backscatter spectra obtained by the Global Ozone Monitoring Experiment (GOME) spectrometer on board the European ERS-2 satellite can be used to retrieve column amounts of key trace species (formaldehyde, nitrogen dioxide) associated with biomass burning events and anthropogenic activities. The GOME sensor is a nadir looking spectrometer with a scan swath of ±31° (corresponds to 960 km on ground). The full forward scan lasts 4.5 seconds, and comprises three 1.5 second steps, each with corresponding footprint size 320x40 km² . The single flyback scan lasts 1.5 seconds. With this scan strategy, global coverage is achieved in three days at the equator. The spectral resolution is 0.2 nm to 0.4 nm between 240 nm and 790 nm in the UV/visible spectral range. The differential optical absorption spectroscopy fitting technique is applied to GOME backscatter data for the retrieval of trace gas total column amounts along the viewing path of the instrument (“slant columns”). Vertical column amounts are then determined by dividing the slant columns with appropriate air mass factors, taking into account the cloudiness of the ground scene. For the SE Asia burning event of 1997, GOME overpasses from the end of September over Indonesia were analysed for the content of NO₂ and H₂CO respectively. In such a biomass burning scenario, H ₂CO concentrations are expected to be large in the troposphere, where hydrocarbon oxidation is greatly enhanced. NO₂ is generated in natural and man-made burning processes. The distribution of NO₂ has a marked diurnal cycle and typically shows an enhanced tropospheric content. A series of GOME overpasses from January 1996 over the heavily populated eastern side of North America were also analysed for enhanced NO₂ content due to anthropogenic activity