TROPOMI Level 2 Sulfur Dioxide (SO2) Total Column Products in NRT - Sentinel-5P

The retrieval of SO2 vertical column is performed in near-real time (i.e. typically 3 hours after measurement) based on the DOAS technique, involving two main steps: First, the effective slant column amount Ns (corresponding to the integrated SO2 concentration along the mean atmospheric optical path) is derived through a least-squares fit of the measured Earth reflectance spectrum to laboratory absorption cross-sections. Second, slant columns are converted into vertical columns by means of air mass factors (AMF) obtained from suitable radiative transfer calculations, accounting for the presence of clouds and aerosols, surface properties and best-guess SO2 vertical profiles. Beside the total column of SO2, enhanced levels of SO2 are flagged within the products. The recognition of enhanced SO2 values is essential in order to detect and monitor volcanic eruptions and anthropogenic pollution sources. Volcanic SO2 emissions may also pose a threat to aviation, along with volcanic ash.