Top: abundances relative to H nuclei and right-to-left accumulated column densities of NH₃ and NH₃ ice in the modelled protoplanetary disc as a function of height above the midplane at a radius of 105 AU. Also shown for species with a single ¹⁵N substitution (dotted curves). Bottom: ratios of abundances and column densities of ¹⁴N- and ¹⁵N-bearinge species. Also indicated is the elemental ratio (dashed line).