Ion-attachment mass spectrometry is capable of accurate and in situ analysis of multicomponent gases that may even include unknown components. We developed a compact apparatus that uses this method and examined its performance for perfluoro compounds, a class of greenhouse gases, using typical standard gases, and subsequently applied the method to the in situ analysis of exhaust gases from a dry-etching machine, where c-C4F8/O-2/Ar plasma is generated. Perfluoro compounds of low concentration can be detected as quasimolecules without any fragmentation. In the exhaust gases, many components that are not considered in the current measurement protocol [J. Meyers, D. Green, P. Maroulis, and W. Reagen, Equipment Environmental Characterization Guidelines, Rev. 3.0 (INTEL, 1999)] are measured, as well as components already reported.