Three methods have been examined for evaluating the concentration of nitrogen atoms in the afterglow of a nonequilibrium, helium-stabilized, atmospheric pressure plasma, These are nitric oxide titration, absolute emission intensity of N-2(B (3)Pi (g)) and temporal decay of the N-2(B (3)Pi (g)) emission. To employ the second method, the rate constants for the recombination of N atoms into N-2(B (3)Pi (g)), at different vibrational levels of the B state, it-ere determined. The third newly developed method has three advantages over the other two techniques: (1) it can predict the N-atom density for the entire after glow, (2) it does not require calibration of the N-2(B (3)Pi (g)) emission intensity, and (3) it does not disturb the gas flow. According to these measurements, the atmospheric pressure plasma produced a high density of nitrogen atoms, exceeding 4.0 x 10(15) cm(-3) at the edge of the discharge for 10 Torr N-2 in 745 Torr He at 375 K and 15.5 W/cm(2).