The relative abundance of 14N and 15N is practically constant in the atmosphere but can vary elsewhere, due to natural isotopic fractionation from biological redox reactions and the evaporation of natural ammonia or nitric acid.
Kelimpahan relatif 14N dan 15N hampir konstan di atmosfer tetapi dapat bervariasi di tempat lain, karena fraksinasi isotop alami dari reaksi redoks biologis dan penguapan amonia atau asam nitrat alami.