Final abundances for the major nitrogen species obtained with the full chemical network. Solid curves show ice abundances, dashed curves show gas abundances. Thin curves are for low ionisation level, and thick curves are for high ionisation level. The physical conditions and initial abundances in Fig. 5a are identical to those considered in Figs. 3a and c. Likewise, for Fig. 5b the assumptions are identical to those in Figs. 3b and d. The arrow on the right-hand side of each plot indicate the initial abundances of N₂ and NH₃. They have the same initial abundances and hence share arrow. The grey, dashed, vertical line in panel a) indicates the iceline position of NH₃. The position of the iceline is the same in panel b). The iceline of N₂ is at 30 AU, and therefore not seen.