δ15N values of atmospheric N species simultaneously collected using sector - based samplers distant from sources Isotopic inheritance and fractionation

The nitrogen isotope ratios (delta N-15) of atmospheric N species are commonly suggested as indicators of N emission sources. Therefore, numerous research studies have developed analytical methodologies and characterized primary (gases) and secondary emission products (mostly precipitation and aerosols) from various emitters. These previous studies have generally collected either reduced or oxidized N forms, and sampled them separately prior to determining their delta N-15 values. Distinctive isotopic signals have been reported for emissions from various sources, and seasonality of the delta N-15 values has been frequently attributed to shifts in relative contributions from sources with different isotopic signals. However, theoretical concepts suggest that temperature effects on isotopic fractionation may also affect the delta N-15 values of atmospheric reaction products. Here we use a sector-based multi-stage filter system to simultaneously collect seven reduced and oxidized N species downwind from five different source types in Alberta, Canada. We report delta N-15 values obtained with a state-of-the-art gold-furnace pre-concentrator online with an isotope ratio mass spectrometer (IRMS) to provide representative results even for oxidized-N forms. We find that equilibrium isotope effects and their temperature dependence play significant roles in determining the delta N-15 values of the secondary emission products. In the end, seasonal delta N-15 changes here are mainly caused by temperature effects on fractionation, and the delta N-15 values of only two N species from one source type can be retained as potential fingerprints of emissions. (C) 2017 Natural Resources of Canada (Government of Canada). Published by Elsevier Ltd.