a) Cylindrical map of the CO₂ column density for 0.5 ≤ tangent altitude ≤ 1 km at any LST. VIRTIS-M pixels are identified on the surface by means of the position of the tangent point. Points having a column density exceeding the maximum value indicated by the colour ramp are marked in white. The same maps for different altitude bins (1 ≤ tangent altitude ≤ 2.0 km, 1.0 ≤ tangent altitude ≤ 3.0 km and for tangent altitude ≥ 3.0 km) are also shown (panels from b) to d)).