The predominant reactive species of a gliding arc in humid air, 50% relative humidity (50% RH), are identified from emission spectroscopy measurements to understand and explain the glidarc plasma interaction with aqueous solutions. The rotational temperatures of the main particles (i.e., the OHdegrees and NOdegrees radicals) are derived from comparing experimental and synthetic spectra at various locations in the plasma stream with different airflow rates. The temperatures decrease rather moderately downstream from the starting section of the arc (the neck) and they rather steeply increase with increasing the mass flow rate. Density measurements are also performed for the same experimental conditions to determine their evolution in the non-equilibrium zone. Although they are quasi-constant along the plasma jet axis, the OH density is much higher than the NO one. The chemical processes, which may lead to a constant regeneration of these prevailing reactive particles in a humid air gliding arc plasma, are also discussed. The complex composition of the plasma gas makes other chemical processes fairly possible, which may result in abundant species depending on the compound proportions.