Characterizing the isotopic composition of atmospheric ammonia emission sources using passive samplers and a combined oxidation-bacterial denitrifier approach

RATIONALE: Ammonia (NH3) emissions are a substantial source of nitrogen pollution to sensitive terrestrial, aquatic, and marine ecosystems and dependable quantification of NH3 sources is of growing importance due to recently observed increases in ammonium (NH4+) deposition rates. While determination of the nitrogen isotopic composition of NH3 (delta N-15-NH3) can aid in the quantification of NH3 emission sources, existing methods have precluded a comprehensive assessment of delta N-15-NH3 values from major emission sources. METHODS: We report an approach for the delta N-15-NH4+ analysis of low concentration NH4+ samples that couples the bromate oxidation of NH4+ to NO2- and the microbial denitrifier method for delta N-15-NO2- analysis. This approach reduces the required sample mass by 50-fold relative to standard elemental analysis (EA) procedures, is capable of high throughput, and eliminates toxic chemicals used in a prior method for the analysis of low concentration samples. Using this approach, we report a comprehensive inventory of delta N-15-NH3 values from major emission sources (including livestock operations, marine sources, vehicles, fertilized cornfields) collected using passive sampling devices. RESULTS: The delta N-15-NH4+ analysis approach developed has a standard deviation of +/- 0.7% and was used to analyze passively collected NH3 emissions with a wide range of ambient NH3 concentrations (0.2 to 165.6 mu g/m(3)). The delta N-15-NH3 values reveal that the NH3 emitted from volatilized livestock waste and fertilizer has relatively low delta N-15 values (-56 to -23 parts per thousand), allowing it to be differentiated from NH3 emitted from fossil fuel sources that are characterized by relatively high delta N-15 values (-15 to +2 parts per thousand). CONCLUSIONS: The isotopic source signatures presented in this emission inventory can be used as an additional tool in identifying NH3 emission sources and tracing their transport across localized landscapes and regions. The insight into the transport of NH3 emissions provided by isotopic investigation is an important step in devising strategies to reduce future NH3 emissions, a mounting concern for air quality scientists, epidemiologists, and policy-makers. Copyright (C) 2013 John Wiley & Sons, Ltd.