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Pollution of the atmosphere from various sources, including factories and automobiles, is a serious problem worldwide and should be controlled and reduced. Nonthermal plasma is studied by various groups and has been applied for exhaust gas treatment and indoor air purification. Microplasma, which is atmospheric pressure nothermal plasma, has recently been studied by many researchers. Although nonthermal-plasma diagnosis by emission spectroscopy has been applied by many authors, the mechanisms are not sufficiently understood. In this paper, the diagnosis of the microplasma discharge in gas and gas mixture are presented. An experimental Marx generator with MOSFET switches was used to generate pulsed output voltages of up to 1.8 kV. Emission spectra were observed by a spectrometer with intensified charge-coupled device camera and a photomultiplier tube. The formation of radicals was confirmed by NO- band, second positive band, and first negative system. Time evolution of light emission that is measured by the photomultiplier tube showed differences between the NO- band and the second positive band. This condition is suggested to be the result of different light emission mechanisms; the second positive band is excited by direct electron impact, and the NO- band is excited by collisions of metastables.