Best-fit extinction model for SDSS J1630+3119. Panel a: observed data and 2175 Å bump feature in spectrum. The quasar spectra, including the original spectrum (black curve) and reddened quasar composites with the best-fitting extinction curves with and without the bump component (solid and dashed green curves) are overplotted for comparison. The sky blue region between them is the extinction bump of the MW-like dust. The multi-band magnitudes from the SDSS, 2MASS, and WISE are presented by orange squares. Panel b: observed extinction (orange squares and black curve) and modelled extinction (green curve). The dashed grey and solid sky blue lines present the underlying linear and bump components of the best-fitting extinction curve. The extinction curve rapidly decreases with increasing wavelength into the infrared spectrum, and the extinction is an unlimited approach to zero with λ → ∞.