Map of the SO₂/CO₂ line depth ratio derived from the 1350.16 cm^-1 SO₂ line and the 1350.40 cm^-1 CO₂ line (Jan. 10 and 12) and the 1366.48 cm^-1 SO₂ line and the 1366.41 cm^-1 CO₂ line (Jan. 11). All frequencies correspond to Doppler-shifted transitions. On Jan. 10 and 11, Area 1 (maximum SO₂ line depth) is indicated by a black circle. Area 2 (maximum CO₂ line depth) is located around the subsolar point, which is indicated by the white spot. At 1350 cm^-1 (Jan. 10 and 12), a depth ratio of 0.45 corresponds to a SO₂ mixing ratio of 60 ppm. At 1366 cm^-1 (Jan. 11), a depth ratio of 1.5 corresponds to a SO₂ mixing ratio of 100 ppm. (see text, Sect. 3.4).