Examples of SO₂ maps recorded in September 2021. Top: maps of the line depth ratio of a weak SO₂ multiplet (around 1345.1 cm⁻¹) to the CO₂ transition at 1345.22 cm⁻¹, recorded in September 26, 27, 28, 29, and 30, 2021. Bottom: maps of the line depth ratio of a weak SO₂ multiplet (around 529.69 cm⁻¹) to the CO₂ transition at 529.81 cm⁻¹, recorded on the same days. Times refer to the beginning of the observations. The maps of September 27 correspond to the spectra shown in Figs. 2, 3, and 6–8.