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Assessing the Use of NH₃ Isotopic Composition Collected by Passive Samplers to Indicate Regional NH₃ Emission Sources

J. David Felix^* and Emily M. Elliott
University of Pittsburgh

Given the growing concern regarding the increasing NH₄⁺ deposition rates in both wet and dry deposition across the U.S., there is heightened interest in improving our understanding of NH₃ emission sources, the processes controlling the formation of NH₄⁺ aerosols subject to long-range transport, and ultimately the deposition of NH₃ products in wet and dry deposition. As a result of this growing concern, the NADP and CASTNET programs are collaborating on a new monitoring program, the “Ammonia Monitoring Network (AMoN).” In collaboration with this initiative, our research aims to assess the utility of adding δ¹⁵N-NH₃ measurements to the monitoring protocol. Beginning in July of 2009, ALPHA passive samplers equipped with phosphorous acid-coated filters were deployed at multiple NADP sites to collect NH₃ emissions for isotopic analysis. Sites were chosen based on their proximity to NH₃ emission sources including concentrated livestock operations, power plants, urban areas and intensive rowcrop operations. As part of this effort, we are also characterizing the isotopic composition of major NH₃ emission sources including livestock waste, fossil fuel combustion, and fertilizer. These source isotope compositions will be used to construct mixing models for each site to characterize the relative contribution of individual NH₃ sources to gaseous NH₃ concentrations. To aid mixing model formulations, δ¹⁵N-NH₃ values will be compared with monthly NH₃ emission estimates from local and regional emission sources and ongoing NH₃ concentration measurements at individual sites. δ¹⁵N-NH₃ values will also be examined for temporal variations, as well as correlations with NH₃ concentrations, temperature, and wind/speed direction. The results from this work will constitute an annual record of monthly δ¹⁵N-NH₃ values recorded at multiple monitoring sites throughout the U.S. characterized by a range of NH₃ concentrations and associated emission sources.

*Department of Geology & Planetary Science,4107 O'Hara Street SRCC, Room 200 Pittsburgh PA 15260-3332, , 717 385 3191