Precise measurement of the CMB anisotropy and polarization requires the removal of foreground emissions, including the rotational line emission of carbon monoxide (CO) from the interstellar medium. While CO emission is concentrated in the Galactic plane, faint, diffuse high-latitude CO clouds and extragalactic CO lines contaminate the "clean" CMB maps used for cosmology. Planck studies estimate that residual CO contamination could affect the measured CMB power spectrum by 1-10% at specific frequencies (e.g., 100, 217 GHz), potentially biasing parameter estimation and mimicking or masking primordial signals like $B$-modes or non-Gaussianity (Planck Collaboration 2014; Rizzuto et al. 2024).