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

RATIONALE Ammonia (NH 3 ) emissions are a substantial source of nitrogen pollution to sensitive terrestrial, aquatic, and marine ecosystems and dependable quantification of NH 3 sources is of growing importance due to recently observed increases in ammonium (NH 4 + ) deposition rates. While determination of the nitrogen isotopic composition of NH 3 (δ 15 N‐NH 3 ) can aid in the quantification of NH 3 emission sources, existing methods have precluded a comprehensive assessment of δ 15 N‐NH 3 values from major emission sources. METHODS We report an approach for the δ 15 N‐NH 4 + analysis of low concentration NH 4 + samples that couples the bromate oxidation of NH 4 + to NO 2 – and the microbial denitrifier method for δ 15 N‐NO 2 – 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 δ 15 N‐NH 3 values from major emission sources (including livestock operations, marine sources, vehicles, fertilized cornfields) collected using passive sampling devices. RESULTS The δ 15 N‐NH 4 + analysis approach developed has a standard deviation of ±0.7‰ and was used to analyze passively collected NH 3 emissions with a wide range of ambient NH 3 concentrations (0.2 to 165.6 µg/m 3 ). The δ 15 N‐NH 3 values reveal that the NH 3 emitted from volatilized livestock waste and fertilizer has relatively low δ 15 N values (–56 to –23‰), allowing it to be differentiated from NH 3 emitted from fossil fuel sources that are characterized by relatively high δ 15 N values (–15 to +2‰). CONCLUSIONS The isotopic source signatures presented in this emission inventory can be used as an additional tool in identifying NH 3 emission sources and tracing their transport across localized landscapes and regions. The insight into the transport of NH 3 emissions provided by isotopic investigation is an important step in devising strategies to reduce future NH 3 emissions, a mounting concern for air quality scientists, epidemiologists, and policy‐makers. Copyright © 2013 John Wiley & Sons, Ltd.