Signal-to-noise ratio of the detection of H₂O and CO as a function of extinction affecting the emission spectrum of the planet. Assuming PDS70 b has the same chemical composition as HR 8799 c, an additional extinction with A_V ≈ 16−17 mag (A_K ≈ 1.2 mag, using the extinction law from Wang & Chen 2019) is required in order not to detect molecules with S∕N > 5. The vertical dashed line shows the maximum value obtained by SED fitting from Wang et al. (2021). This extinction would have revealed molecules in the planet atmosphere with S∕N ~ 7–9.