Monitoring Sulphur dioxide
The PROMOTE Air Quality Service provides global sulphur dioxide (SO2) columns from GOME and SCIAMACHY satellite measurements. Sulphur dioxide enters the atmosphere as a results of both natural phenomena and anthropogenic activities, such as fossil fuel combustion, oxidation of organic materials in soils, volcanic eruptions and biomass burning. Changes in the abundance of SO2 have an impact on atmospheric chemistry and on the radiation field, and hence on the climate. Consequently, global observations of SO2 are important for atmospheric and climate research.
The technique used to retrieve SO2 column from GOME and SCIAMACHY UV-measurements is the Differential Optical Absorption Spectroscopy (DOAS). Volcanic emissions are clearly detected with this retrieval technique, as well as strong pollution events. The detected volcanic SO2 plumes are important information for air traffic organisations.
The SO2 column product consists of a collection of global maps (monthly, composite 3-days and daily maps). Higher resolution maps over pre-defined regions known for SO2 emission from anthropogenic pollution or from volcanic activity are provided as well. The monthly maps are calculated by averaging data over a complete month, composite 3-days maps are calculated by averaging data on periods of 3 days, the minimum period necessary to achieve global coverage at the equator with GOME and SCIAMACHY.
In the next phase of PROMOTE, a HDF data archive will be created for the SO2 column product. The data archive will be made available to the users via the PROMOTE Web-site.
The derivation of high quality quantitative SO2 columns from GOME and SCIAMACHY measurements is a major challenge. In addition to DOAS fitting difficulties the retrieval of SO2 columns is characterised by large uncertainties related to clouds, SO2 profile shape and aerosols. In the next two years, an improved retrieval method for the tropospheric SO2 column will be developed, based on a combined DOAS slant column retrieval and modelling approach. GOME and SCIAMACHY SO2 slant columns will be assimilated in the chemistry-transport model TM, which is driven by high-quality meteorological fields and provides best-guess profiles of SO2, based on the latest emission inventories, atmospheric transport, photochemistry and removal processes. With the data-assimilation approach, the accuracy of the SO2 column product will be improved, and a daily global coverage can be achieved.