Development of a long-term SO2 column data record from satellite nadir UV sensors

As part of its Climate Change Initiative extension program (CCI+), the European Space Agency started a new activity aiming to develop space-based long-term climate data records for precursors gases involved in the formation of aerosols and ozone (https://climate.esa.int/en/projects/precursors-for-aerosols-and-ozone/about/). The targeted trace gases are NO₂, SO₂, HCHO, CHOCHO, CO and NH₃.

For SO₂ in particular the project relies on recent developments for Sentinel-5 Precursor/TROPOMI based the Covariance-Based Retrieval Algorithm (COBRA). This algorithm will be used to build consistent column retrievals from a series of four satellite sensors (GOME, SCIAMACHY, OMI and TROPOMI), covering nearly three decades of observations.

Here, we give an overview of the SO₂ development activities in the Precursors CCI+ project. To achieve the project objectives, an extensive comparison of results is performed in the form of a round Robin exercise. This includes comparison of different algorithms, but also testing of various processing options for ancillary data such as cloud and surface reflectance parameters. First results from the round Robin exercise are presented with a focus on OMI, in particular the comparison between COBRA and Principal Component Analysis (PCA) column retrievals. Preliminary results using COBRA for the historical sensors GOME and SCIAMACHY are also shown.