Carbon Monoxide – CO
CO plays a central role in tropospheric chemistry because it is the leading sink of the hydroxyl radical, which itself determines the oxidising capacity of the troposphere to a large extent. Therefore, CO is of prime importance for the troposphere’s self-cleansing efficiency and for the concentration of greenhouse gases such as CH4. CO also has a large impact on air quality because it is toxic and is a precursor of tropospheric ozone, a secondary pollutant which is associated with respiratory problems and decreased crop yields.
CO detection with SCIAMACHY is an ambitious task. Carbon monoxide vertical columns can be retrieved from a number of CO absorption lines located around 2.3 mm in the SWIR range. The retrieval is not straightforward because these lines are relatively weak, much weaker than the absorption structures of the overlapping absorbers water vapour and CH4. In addition, CO retrieval is hampered by a number of calibration issues that are mainly related to large variable dark signals and changing instrument characteristics as a result of the growth of an ice layer on the channel 8 detector (e.g. Gloudemans et al. 2005). Nevertheless, a first survey of global CO over land had been performed which shows elevated CO in the case of fires due to biomass burning. These results are consistent with MOPITT and model predictions to a large degree (de Laat et al. 2006, Buchwitz et al. 2007b). Gloudemans et al. (2009) also succeeded in deriving CO over the ocean, when using scenes with low maritime clouds. This yielded a five-year CO dataset over both land and clouded ocean scenes between 2003 and 2007 (fig. 3-12).