Nitrogen and triple oxygen isotopes in near‐road air samples using chemical conversion and thermal decomposition

RATIONALE The determination of triple oxygen (δ18O and δ17O) and nitrogen isotopes (δ15N) is important when investigating the sources and atmospheric paths of nitrate and nitrite. To fully understand the atmospheric contribution into the terrestrial nitrogen cycle, it is crucial to determine the δ15N values of oxidised and reduced nitrogen species in precipitation and dry deposition. METHODS In an attempt to further develop non-biotic methods and avoid expensive modifications of the gas-equilibration system, we have combined and modified sample preparation procedures and analytical setups used by other researchers. We first chemically converted NO3– and NH4+ into NO2– and then into N2O. Subsequently, the resulting gas was decomposed into N2 and O2 and analyzed by isotope ratio mass spectrometry (IRMS) using a pre-concentration system equipped with a gold reduction furnace. RESULTS The δ17O, δ18O and δ15N values of nitrate and nitrite samples were acquired simultaneously in one run using a single analytical system. Most importantly, the entire spectrum of δ17O, δ18O and/or δ15N values was determined from atmospheric nitrate, nitric oxide, ammonia and ammonium. The obtained isotopic values for air and precipitation samples were in good agreement with those from previous studies. CONCLUSIONS We have further advanced chemical approaches to sample preparation and isotope analyses of nitrogen-bearing compounds. The proposed methods are inexpensive and easily adaptable to a wide range of laboratory conditions. This will substantially contribute to further studies on sources and pathways of nitrate, nitrite and ammonium in terrestrial nitrogen cycling. Copyright © 2012 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.