Measurement of the optical depth to reionization (${\tau }_{\mathrm{reio}}$) is largely driven by the large-scale EE polarization data of cosmic microwave background (CMB) ($\ell <30$). Removing the low-$\ell$ EE data potentially alleviates various cosmological tensions. In this work, we study the effect of the low-$\ell$ EE polarization measurements on the Chevallier-Polarski-Linder (CPL), Jassal-Bagla-Padmanabhan (JBP), and Barboza-Alcaniz (BA) dark energy parametrizations using CMB data from Planck and Atacama Cosmology Telescope Data Release 6, combined with a Dark Energy Spectroscopic Instrument baryon acoustic oscillation and PantheonPlus compilation of type Ia supernovae. We find that excluding low-$\ell$ EE data shifts ${\tau }_{\mathrm{reio}}$ and $A_s$ to higher values through the unbroken $A_s-{\tau }_{\mathrm{reio}}$ degeneracy with a $\sim (1.4–1.8)\sigma$ shift in $A_s$ for $\mathrm{\Lambda }\mathrm{CDM}$ (cold dark matter) and JBP, and a milder $\sim 1\sigma$ shift for CPL and BA. The equation of state (EOS) for all three parametrizations moves toward the quintessence regime [$w(z)>-1$] upon exclusion of low-$\ell$ EE data, driven primarily by the strengthening of the $w_a-A_s$ and the $w_a-{\tau }_{\mathrm{reio}}$ correlations, with a small effect from the correlations of $w_0$ with $A_s$ and ${\tau }_{\mathrm{reio}}$. The most prominent effect occurs in JBP, where the EOS lies entirely within the quintessence regime at $1\sigma$ when excluding low-$\ell$ EE data. Model comparison through the Akaike information criterion shows positive evidence in favor of CPL and BA and weak evidence in favor of JBP, robust to the inclusion of low-$\ell$ EE data and CMB data used. The deviance information criterion model comparison shows strong evidence in favor of CPL and BA when low-$\ell$ EE data are included, and positive evidence when they are excluded. For JBP, we get positive (weak) evidence when including (excluding) low-$\ell$ EE data over $\mathrm{\Lambda }\mathrm{CDM}$.

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• Cosmology