Changes in transmission spectra for increasing enhancement of atmospheric oxygen by factors of 1–300× from top to bottom. The full spectra (orange lines) are compared to “hazeless” spectra for which the opacity contribution of haze was removed from the calculation (teal lines), revealing the otherwise muted molecular features of the gas-phase species. The transparent colored lines represent the full-resolution transmission spectra output by Exo-Transmit (spectral resolution of R = 1000), while the opaque, thick lines are smoothed for ease of visualization. The baseline case (1×) corresponds to Figure 3. The bulk composition of the atmosphere changes with increasing oxidation, and new molecular features of H₂O and CO₂ become apparent as their abundance increases. Haze dominates the transmission spectrum until oxygen has been added to the atmosphere at ∼50× its baseline value. At an oxygen enhancement of 300×, the production of haze is effectively suppressed, and its impact on the transmission spectrum is negligible. We note that the feature labeled as “Haze” near 7 μm is a spectroscopic feature resulting in a sharp rise in the extinction coefficient at that wavelength in the Haze model.