  The detected Na/Mg ratio in a sample of 17 Na-enhanced and Na-rich meteors is
investigated based on obtained spectral, orbital and structural data. We
utilize the meteor observations of the AMOS network obtained within a survey of
medium-sized meteoroids supplemented by higher-resolution spectra observed on
the Canary Islands. Ground-based meteor observations are then compared with
high-resolution Echelle spectra of simulated ablation of known meteorite
samples in a high-enthalpy plasma wind tunnel. It was found that most
Na-enhanced and Na-rich spectra can be explained by the effect of low meteor
speed related to low ablation temperatures and generally do not reflect real
meteoroid composition. Spectra obtained by the laboratory experiment simulating
low meteor speeds show corresponding Na-rich profiles irrespectively of the
meteorite composition. We estimate that for an H-type ordinary chondrite with
speed of $\approx$ 10 km/s, the Na line intensity is increased by a factor of
40 to 95. The dynamical analysis has revealed that all Na-rich meteors
originated on Apollo-type orbits and exhibit consistent chondritic material
strengths. For more clarity in the classification of Na-enhanced and Na-rich
meteoroids, we propose new speed-dependent boundaries between the spectral
classes. Real compositional Na enhancement was confirmed in five cometary
meteoroids: two Perseids, an $\alpha$-Capricornid, $\nu$-Draconid and a
sporadic. The two Na-enhanced Perseids were linked with increased material
strength suggesting that the detected increase of volatile content has
implications for the meteoroid structure.
