Three sources of NOx
Source http://en.wikipedia.org/wiki/NOx
There are three sources of NOx emanating from combustion processes:
 Thermal NOx
 Fuel NOx
 Prompt NOx
Thermal NOx refers to the high temperature oxidation of atmospheric N2. Given
high temperatures (usually above 1600C) and enough time for reactions to occur
three sorts of reactions (primarily) occur:
1) N2 + O>>>>NO +N
2) N + O2>>>>NO + O
3) N +OH>>>>NO+H
Fuel NOx when burning nitrogen rich fuel such as coal or oil the nitrogen in the fuel
forms free N2 or NO.
NOx produced through pathways other than that described above is referred to as
prompt NOx. This third mode of production involves atmospheric N2 coming with C,
CH, and CH2.