Time-resolved, absolute NO and N atom number densities are measured by NO Laser Induced Fluorescence (LIF) and N Two-photon Absorption LIF in a diffuse plasma filament, nanosecond pulse discharge in dry air, hydrogen-air, and ethylene-air mixtures at 40 Torr, over a wide range of equivalence ratios. The results are compared with kinetic modeling calculations incorporating pulsed discharge dynamics, kinetics of vibrationally and electronically excited states of nitrogen, plasma chemical reactions, and radial transport. The results show that in air afterglow, NO decay occurs primarily by the reaction with N atoms, NO + N → N2 + O. In the presence of hydrogen, this reaction is mitigated by reaction of N atoms with OH, N + OH → NO + H, resulting in significant reduction of N atom number density in the afterglow, additional NO production, and considerably higher NO number densities. In fuel-lean ethylene-air mixtures, a similar trend (i.e. N atom concentration reduction and NO number density increase) is observed, although [NO] increase on ms time scale is not as pronounced as in H2-air mixtures. In nearstoichiometric and fuel-lean ethylene-air mixtures, when N atom number density was below detection limit, NO concentration was measured to be lower than in air plasma. The results show the need for further kinetic modeling to provide quantitative insight into NO kinetics in hydrocarbon-air plasmas.