Monthly grids are available (L3). You will find below one zip file per year, containing 12 monthly TXT files. See readme_SkT.txt, latitude.txt, longitude.txt and IASI_Flux_and_Temperature.pdf (Data Manager Plan OPIDoR).
Metop-A data are available starting September 2007.
Metop-B data are available starting January 2013.
Metop-C data are available starting October 2019.