Reanalyzed bi-daily IASI/Metop-B ULB-LATMOS sulphur dioxide (SO2) L2 product (columns and altitude)

The reanalyzed IASI/Metop-B bi-daily sulphur dioxide (SO2) dataset includes retrievals produced with a new version of the ULB-LATMOS algorithm for fast, simultaneous retrieval of SO2 column and altitude. The retrievals rely primarily on the calculation of hyperspectral range indices (HRIs), which provide enhanced detection sensitivity and retrieval accuracy, especially for weak SO2 abundances and low-altitude plumes, and on brightness temperature differences for saturated SO2 signals. Algorithm improvements and meteorological inputs data sourced from the ERA5 ECMWF reanalysis [(Hersbach et al., 2020)](https://doi.org/10.1002/qj.3803) ensure the homogeneity of the retrievals over time and across the different IASI instruments. The dataset includes the SO2 altitude retrieved from IASI observations, the SO2 total column retrieved assuming the gas is located at the retrieved altitude, and SO2 columns retrieved assuming that all SO2 is confined to fixed altitudes ranging from 1 to 60 km. These fixed-altitude columns can be used to construct total column averaging kernels. The dataset also includes SO2 altitude and total column distributions gridded at 0.125° x 0.125°, the global atmospheric SO2 mass, and the global SO2 mass as function of altitude. Strict quality flags were applied to the data and the values “0” indicate that SO2 retrieval was not possible. The labels “AM” and “PM” in the file names refer to retrievals from the daytime and nighttime IASI overpasses, respectively. See Clarisse et al. (2026, ESSD), An 18-year record of atmospheric sulphur dioxide (SO2) derived from IASI measurements, for a detailed description of the algorithm, the data contents, and comparisons with independent measurements.

The dataset is available on a global scale between 10 July 2007 and 15 October 2021 (IASI/Metop-A), from 22 January 2013 (IASI/Metop-B), and from 12 April 2019 (IASI/Metop-C).

Current Version: V4.5.0R