## 3 Results and Discussion
### EGA Fast Pyrolysis of Sole NNN  
Figure 6 shows the spectra obtained at the three temperatures studied for NNN in the He atmosphere. As can be seen, at 300 \({}^{\circ}\)C the chromatogram presents two major peaks where the largest corresponds to NNN (at around 18 min retention time). When the temperature increases, the intensity of the NNN peak decreases, disappearing at 500 \({}^{\circ}\)C. The peak of myosmine (at around 15 min retention time) presents a maximum at 400 \({}^{\circ}\)C, whereas the other peaks observed increase their intensity with increasing temperature. Figure 7 shows the spectra obtained for NNN in the air atmosphere at the six temperatures studied. Figure 6: Chromatograms of the pyrolysis of NNN at different temperatures under the He atmosphere. Under air atmosphere, the NNN (18 min) is less stable and the peak of myosmine (15 min) at 300 \({}^{\circ}\)C is already the major peak. At 400 \({}^{\circ}\)C the NNN has almost disappeared. Under He atmosphere, 94 peaks have been assigned, and 93 under air atmosphere. Appendix Table A1 shows the list of compounds assigned in all experiments that represent more than 0.5% area and have a match-quality factor higher than 80%. We assigned 1H-pyrrol [2,3-b] pyridine and 5,6 dimethyl-3H Pyrrol [2,3-b] pyridine by interpreting their mass spectra and considering the probability of obtaining such structures from the NNN pyrolysis. Figure 8 shows the evolution of the % area of NNN versus temperature for the two atmospheres. It can be seen that the NNN is more stable in the He atmosphere than in air, showing a marked degradation at 300 \({}^{\circ}\)C under oxidizing conditions. Figure 7: Chromatograms of the pyrolysis of NNN at different temperatures under the air atmosphere. Figure 9 shows the evolution of the main compounds detected under inert conditions versus temperature. Myosmine (compound number 29) is the main compound at the three temperatures considered, reaching a yield of around 27% at 400 and 500 \({}^{\circ}\)C. 3-pyridincarbonitrile (compound 13) is the second major compound at 500 \({}^{\circ}\)C, and presents a marked increase with temperature reaching 23%. 1H-pyrrolo [2,3-b] pyridine (compound 27) levels its yield at 400 \({}^{\circ}\)C at 12.7%. Nornicotine (compound 28) and nornicotyrine (compound 34) present a maximum yield at 400 \({}^{\circ}\)C, as a consequence of their first formation from NNN and the subsequent pyrolysis reactions they undergo. 3-ethenylpyridine, 3-pyridinecarbonitrile, isoquinoline, nicotine, myosmine, nicotyrine and nornicotyrine were also detected by [PERSON] et al. [26], who also obtained myosmine and 3-pyridinecarbonitrile as the majority compounds when studying the degradation of NNN. Figure 8: Evolution of NNN with temperature in the He and air atmospheres. Figure 9: % area vs temperature of the majority compounds detected in the pyrolysis of NNN under inert atmosphere. Nitric oxide (2), 1-propene (3), 3-ethenyl-pyridine (11), 3-pyridinecarbonitrile (13), isoquinoline (20), nicotine (24), 1H-pyrrolo [2,3-b] pyridine (27), nornicotine (28), myosmine (29), 3,4-dimethyl-pyrrolo(1,2-a) pyrazine (30), nornicotyrne (34). Figure 10 shows the evolution of the products obtained under the air atmosphere as a function of temperature. Myosmine (compound 29, that reached around 37% of the total area at 400 \({}^{\circ}\)C) and 3-pyridinecarbonitrile (compound 13, that represents 28% at 425 \({}^{\circ}\)C),are the main compounds, as observed under the inert atmosphere. Nevertheless, their behavior is somewhat different, since mysomine presents a maximum with temperature while 3-pyridinecarbonitrile shows an increasing trend with temperature throughout the range studied. Carbon dioxide (compound 1) and water (compound 8) also present an increasing trend with temperature reaching 5 and 6.6% respectively, at 425 \({}^{\circ}\)C. Nicotyrine (compound 31) is practically not observed, contrarily to the case of the pyrolysis of nicotine and NNK (39).