Two reduced Io spectra, showing the difference in the SO₂ absorption features between the anti-Jovian hemisphere (central longitude of 165^∘W) and the sub-Jovian hemisphere (central longitude of 336^∘W). The data were obtained on two consecutive nights (2023 July 25 for (a) and 2023 July 24 for (b)). The data are shown in black with the noise in gray. The spectra have each been divided by a Callisto spectrum, flattened and normalized. The corresponding best-fit model spectrum is shown in red.