Column density ratio between SO₂ and H₂ for sources in different evolutionary stages. Red, green, and blue symbols represent sources from Perseus, Ophiuchus, and Taurus, respectively. Dots indicate Class 0 sources, squares represent Class I sources, and diamonds show Class I/II and Class II sources. Empty triangles indicate upper or lower limits. Values for IRAS 16295 were taken from Drozdovskaya et al. (2018) and Jørgensen et al. (2016). Perseus sources are from this work, Ophiuchus Class I sources correspond to IRS 67, GSS30-IRS1, IRS 44, IRS 43, and Elias 29, from left to right, studied by Artur de la Villarmois et al. (2019), and Taurus sources are taken from Garufi et al. (2022) and represent DG Tau (outer disk), HL Tau (inner disk), HL Tau (outer disk), IRAS 04302, and T Tau S, from left to right. The upper limit for IRAS 16293 is given by the optically thick continuum emission and lower limits for Perseus and Taurus sources are given by optically thick SO₂ emission. The PEACHES sample and Class I Ophiuchus sources are ordered by T_bol.