EE (left panel) and BB (right panel) power spectra of the S-PASS polarization maps computed on the set of isolatitude masks described in Sect. 2.2 (colored curves). Solid lines show the best fit curve obtained by fitting the model in Eq. (1) to the data (we note that in this figure the amplitude of D_ℓ = ℓ(ℓ + 1)C_ℓ/2π is plotted). Gray curves represent the polarization spectra computed on the whole sky region observed by S-PASS where the signal is strongly contaminated by the Faraday rotation effects on the Galactic plane.