Quenching constants for NO2 fluorescence were obtained for 13 different inert gases. Quenching cross sections range from 1/25 to 1/2 of gas kinetic and increase with increasing molecular complexity, and dipole moment. No unusual resonance effect for quenching by ground-state NO2 was found. The present data are consistent with a single radiative lifetime of 4.4×10−5 sec for excited NO2. The apparent Stern—Volmer quenching ratios are shown to be functions of both the excitation and fluorescence frequency, and the fluorescence spectrum shows the corresponding red shift at high quenching pressure. This indicates that quenching is a multistep process, although qualitative considerations suggest that a large fraction of the excess internal energy of NO2* is likely to be transferred in a single effective collision.