Unexpectedly high concentrations of NO₂ have been noted in stack emissions from industrial gas turbines. NO₂ formation appears to occur through the so called "HO₂ mechanism II in which NO combines with HO₂ to produce NO₂ and OH. In this study, the formation of NO₂ was investigated through computer modeling and experimental testing.

Computer modeling utilized the CHEMKIN chemical kinetics program and a subset of a previously published C-H-O-N system mechanism. Experimental work was conducted using a high pressure flow reactor designed and built in the course of the study. The effects of pressure, temperature, and the presence of a NO₂ promoting hydrocarbon, methane, were investigated. It was discovered that as pressure increased from 1 atm. to 8.5 atm., the rate and amount of NO converted to NO₂ also increased. There also appeared to be a temperature "window" between approximately 800 and 1000 K in which NO to NO₂ conversion readily occurred. The presence of methane was seen to enhance NO conversion to NO₂, and a ratio of [CH₄]/[NO] was found to be a useful parameter in predicting NO₂ formation. Significant NO conversion to NO₂ was noted for [CH₄]/[NO] > 1 at the hydrocarbon injection point. Experimental results validated those trends obtained from modeling with a modified C-H-O-N mechanism.