Effect of b ± Δb on the transmission spectra of three different groups of exoplanets (groups A, B and C), showing an introduced slope and an offset for different b values. Black dots show the synthetic spectra of each subgroup, and black squares show the respective derived spectra with the variationin b. The colored areas illustrate the error envelope for each case. Dashed black lines show the linear regression fits on each spectrum, and dotted green lines indicate two atmospheric scale heights from the predefined input value for R_p ∕R_s.