The project aim was to study the seasonal cycles of two trace species of the Martian atmosphere: HCl and O3. The former was recently detected by ExoMars TGO and is the first halogen detected in the Martian atmosphere. Model work was then needed to try to reproduce and explain spacecraft observations. Ozone is a well-known compound of the Martian atmosphere, whose abundance is underestimated by models. We used newly measured vertical profiles from TGO to investigate this deficit.