The emission of greenhouse gases, such as N2O and fluorinated gases, has been increasingly regulated in the semiconductor industry. Pressure effects on the abatement of N2O and CF4 were investigated in a low-pressure plasma reactor by using Fourier transform infrared (FTIR) spectroscopy. The destruction and removal efficiency (DRE) of N2O and CF4 was significantly lowered below 0.2 Torr. When the pressure was increased, the DRE of CF4 with H2O as the reactant gas increased continuously, but that with O-2 or without any reactant gas first increased and then decreased. A larger electrode length yielded a higher DRE of N2O and CF4, especially at lower pressures. To understand this phenomenon, the electrical waveforms for the discharge in N2O were analyzed in conjunction with its optical emission profiles, and the rotational temperatures for different electrode lengths were compared using the N-2 (+) ion band (lambda = 391.4 nm). They provided insights into the mechanism involved in terms of plasma property and gas residence time.