I have a combustion process where Im using spectroradiometers for sensing the flame, my doubt appears since I have in one hand (a) two spectral measurements in the vis region (400-700nm) composed by a continuous black body type background and some emission peaks (Sodium and potasium mainly), if the continuum total intensity and temperature (about 1800K, retrieved with two color pyrometry) are similar in both of them, what could be the reason that intenisty from those line emissions are so different between the two spectra? (about 3 times greater for one), the only thing that changed in the experiment was the fuel/oxygen ratio, then my question is, appart from temperature, is there any (i.e. thermodynamic issue) other cause for molecules or atoms to emit more radiation?.

On the other hand (b) for the same kind of fuel, I measured spectra at a laboratory scale flame (small one) and at a flame in an industrial burner (greater flame), both spectra produced similar temperatures (again, retrieved with two color pyrometry) but in the industrial spectrum appeared the same emission peaks plus new ones, I think in this case it has to be with the population of excited species, which I assume is greater for the new ones in the industrial flame. What are other factor to cause a stable spontaneous emission? I found some answers looking at Boltzmann distribution function, but I think there is something else Im not looking at.

Thanks in advance