A Review of the Techniques Used for Measurements of Nitrogen Isotopes in Atmospheric Aerosols

This review of the methods used for measurements of stable nitrogen isotopes in gases and aerosol particles also summarizes some of the latest research on nitrate, ammonium, nitrogen oxides and ammonia in the atmosphere. The main methods used for the determination of N isotopes in nitrate and nitrogen oxides are one that makes use of denitrifying bacteria and a two-step chemical reduction method (cadmium + hydrazoic acid). A commonly used method for measuring nitrogen isotopes in ammonia and ammonium ion is a chemical conversion that uses sodium azide in an acetic acid buffer or hydroxylamine hydrochloride. A common characteristic of these methods is that nitrous oxide is the final analysis product, and the isotopes are determined by mass spectrometry. The precision of the analyses are typically very high (~ 0.25‰), and the methods require a small amount of sample, usually tens of nmols is sufficient. Some improvements to these methods and collection methods have been made in recent years, and these advances will facilitate research on nitrogen isotopes in the atmosphere.