Left axis: polarization fraction at 353 GHz, P∕I, as a functionof the alignment parameter a_alig. Right axis: same for the polarization fraction in the V band p_V∕τ_V and the polarization ratio, R_S/V = P∕I∕(p_V∕τ_V). The vertical dotted line indicates the value of a_alig needed to reproduce the mean value of the Serkowski’s parameter λ_max of 0.55 μm observedin diffuse and translucent LOS. An empirical fit to the dependence of P∕I on a_alig is provided for convenience.