T-Jump/FTIR spectroscopy was employed to flash pyrolyze a series of energetic compounds in an air atmosphere for comparison with an argon atmosphere. The O-NO2, compounds (NG, NC. and PETN), N-NO2, compounds (RDX and HMX), and C-NO2 compounds (DNT, TNT. and NTO) were studied. The effect of the surrounding atmosphere on the pyrolysis gases roughly correlates with the trend in the vapor pressure of the parent energetic material (i.e. DNT>NG>TNT>NTO>PETN approximate to RDX > NC approximate to HMX). For high vapor pressure compounds, the gaseous phase reactions dominate and the dependence on the surrounding atmosphere is strong. For low vapor pressure compounds. the condensed phase decomposition dominates and the dependence on the surrounding atmosphere is weak. That is, the extent of condensed phase vs. gas phase decomposition is the major factor in the effect of the surrounding atmosphere on the decomposition gases. The main reactions in the air are CO with 0, which is fast, and NO with 0, which is slow. However, these pyrolysis products for the nitrate esters, the nitramines, and the C-NO2, compounds behave differently suggesting that a common process, such as surface catalysis, is not responsible for the behavior seen. There is little effect of the relative humidity (0-60% range) except in the case of HMX.