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The long-standing paradox of the linear polarization signal of the Na i D1line was recently resolved by accounting for the atom's hyperfine structure andthe detailed spectral structure of the incident radiation field. That modelingrelied on the simplifying angle-averaged (AA) approximation for partialfrequency redistribution (PRD) in scattering, which potentially neglectsimportant angle-frequency couplings. This work aims at evaluating thesuitability of a PRD-AA modeling for the D1 and D2 lines through comparisonswith general angle-dependent (AD) PRD calculations, both in the absence andpresence of magnetic fields. We solved the radiative transfer problem forpolarized radiation in a one-dimensional semi-empirical atmospheric model withmicroturbulent and isotropic magnetic fields, accounting for PRD effects,comparing PRD-AA and PRD-AD modelings. The D1 and D2 lines are modeledseparately as two-level atomic system with hyperfine structure. The numericalresults confirm that a spectrally structured radiation field induces linearpolarization in the D1 line. However, the PRD-AA approximation greatly impactsthe Q/I shape, producing an antisymmetric pattern instead of the more symmetricPRD-AD one, while presenting a similar sensitivity to magnetic fields between10 and 200 G. Under the PRD-AA approximation, the Q/I profile of the D2 linepresents an artificial dip in its core, which is not found for the PRD-AD case.We conclude that accounting for PRD-AD effects is essential to suitably modelthe scattering polarization of the Na i D lines. These results bring us closerto exploiting the full diagnostic potential of these lines for the elusivechromospheric magnetic fields.

The impact of angle-dependent partial frequency redistribution on the scattering polarization of the solar Na i D lines