During studies on the identification of the principal species produced in an N2/O2/H2O microwave discharge plasma, we succeeded in detecting the presence of NOx species, including NO2, in the gas phase. The Li+ ion adduct mass spectra of the discharge plasma, obtained by means of a direct sampling system, clearly showed various peaks, giving direct evidence that in addition to the familiar NO and N2O species, significant amounts of gas-phase neutral NO2, NO3, HNO2, and HNO3 were produced and detected in the N2/O2/H2O plasma. The influence of certain discharge variables on the yield and concentration of NOxLi+ was investigated also. Comparison of the present results with field observations of Earth's atmosphere demonstrated that laboratory simulation experiments can yield species comparable to the reactive nitrogen oxide species found in the troposphere.