The detected FTIR absorbance spectrum of the arc and the DBD plasma jet as function of wavenumber. For the arc plasma jet the spectrum contains major contributions of NO and NO2 and minor contributions of N2O and HNO2. For the DBD jet, the absorbance of O3 and an influence of the residual H2O and CO2 content on the absorbance spectra were identified. Measured absorbance values below zero are due to a higher residual gas content during the acquisition of the background spectrum. In the case of H2O, this can visually mask an absorption of NO2 between 1540 and 1660 cm−1. Therefore, the reference functions for both NO2 and H2O were fitted mutually as a sum function in this wavenumber region to allow a distinction between both substances.