Ozone (O$_{3}$) is important in the stabilisation of CO$_{2}$ in the Martian atmosphere and thus it is important to study the spatio-temporal variability of O$_{3}$. We retrieve two years of total columnar O$_{3}$ from raw spectral data provided by the SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument aboard the Mars Express. The seasonal variability is studied in tropical, mid- and high latitudes and is compared with simulations by a photochemical coupled general circulation model (GCM). The high latitudes exhibit the largest seasonal variations in O$_{3}$, with a winter high and a summer low and a comparison with GCM results is good in general. We have studied the correlation of O$_{3}$ with dust, retrieved simultaneously from SPICAM observations. In southern tropical latitudes, the columnar O$_{3}$ is seen to increase during a global dust storm year (Martian year (MY) 28) compared to the O$_{3}$ column values during a year without global dust storm (MY27), although the water vapour column between these years remains unchanged. This indicates the radiative impact of dust on O$_{3}$ and its retrieval. We also study the ozone–carbon monoxide correlation as a tracer of dynamics. The dynamical contribution to the O$_{3}$ column is found to be the highest during winter over the southern polar region.