Stone, ZacharyShen, YueBurke, Colin JChen, Yu-ChingYang, QianLiu, XinGruendl, R AAdamow, M.Andrade-Oliveira, F.Annis, JamesLidman, Christopher2026-02-262026-02-260035-8711https://hdl.handle.net/1885/733806610We study the optical gri photometric variability of a sample of 190 quasars within the SDSS Stripe 82 region that have long-term photometric coverage during ∼1998-2020 with SDSS, PanSTARRS-1, the Dark Energy Survey, and dedicated follow-up monitoring with Blanco 4m/DECam. With on average ∼200 nightly epochs per quasar per filter band, we improve the parameter constraints from a Damped Random Walk (DRW) model fit to the light curves over previous studies with 10-15 yr baselines and 100 epochs. We find that the average damping time-scale τDRW continues to rise with increased baseline, reaching a median value of ∼750 d (g band) in the rest frame of these quasars using the 20-yr light curves. Some quasars may have gradual, long-term trends in their light curves, suggesting that either the DRW fit requires very long baselines to converge, or that the underlying variability is more complex than a single DRW process for these quasars. Using a subset of quasars with better-constrained τDRW (less than 20 per cent of the baseline), we confirm a weak wavelength dependence of τDRWλ0.51 ± 0.20. We further quantify optical variability of these quasars over days to decades time-scales using structure function (SF) and power spectrum density (PSD) analyses. The SF and PSD measurements qualitatively confirm the measured (hundreds of days) damping time-scales from the DRW fits. However, the ensemble PSD is steeper than that of a DRW on time-scales less than ∼a month for these luminous quasars, and this second break point correlates with the longer DRW damping time-scale.ZS and YS acknowledge support from NSF grants AST- 1715579 and AST-2009947, and NASA grant 80NSSC21K0775. This research made use of MATPLOTLIB , a PYTHON library for publication quality graphics (Hunter 2007 ).application/pdfen-AU© 2022 The Author(s)202210.1093/mnras/stac12592023-10-01