Baseline correction to lab spectra of ice mixtures. In the left panels, we take the H₂O-rich mixtures of CH₄ and three O-COMs (CH₃CHO, C₂H₅OH, CH₃OCH₃) as examples. The original and the corrected spectra are plotted in solid blue and green, respectively. The polynomial is plotted in dashed orange, and the wavelength ranges that were selected to fit the polynomial are highlighted in orange panels. The right panels are similar to the left ones but for CH₃OH mixtures. SO₂, HCOOH, C₂H₅OH, and CH₃OCH₃ are taken as examples. The purple-shaded regions indicate the frequency ranges of CH₃OH bands.