Afterglows of R/x(N-2-5%H-2) (R=Ar or He) flowing microwave discharges are characterized by optical emission spectroscopy. Absolute densities of N atoms and N-2(A) and N-2(X,v>13) molecules and estimated densities of NH and H atoms are determined after calibration of the N atom density by NO titration. It is determined the variations of active species densities along the post-discharge tube from the early afterglow to the late afterglow region. Conditions allowing to obtain a high concentration of H-atoms in dominant N-atoms have been found in the early afterglow region of the R/x(N-2-5%H-2) mixture for x<5%. From these densities, the destruction probabilities of the H-atoms on the afterglow quartz tube wall is found to be: HHe=(2-3)x10(-4) and HAr=(3-4)x10(-3). The interest of these results concerns the enhancement of surface nitriding by combined effects of N and H atoms inclusion in afterglow conditions.