International audienceThe ExoMars Trace Gas Orbiter (TGO), a mission by ESA and Roscosmos, was launched in March 2016. After a long aerobraking phase, it reached its final, near-circular 400 km orbit in February, 2018 then started its operational scientific phase in March, 2018. On board TGO, the ACS-TIRVIM instrument has the capability to map the thermal structure of the Martian atmosphere and its aerosol load at a great variety of local times. In this abstract, we describe our retrieval algorithm used to analyse TIRVIM data. We discuss synthetic retrievals performed for a great variety of scenes to fine-tune and evaluate the performance of our algorithm, then present results obtained from the first orbits of TGO. In a second step (see EPS...