Tuesday, August 3, 2010

PS 47-173: Utilizing stable isotopes to characterize reactive nitrogen emissions and deposition

Joseph David Felix, University of Pittsburgh and Emily M. Elliott, University of Pittsburgh.

Background/Question/Methods

Reactive nitrogen, including nitrogen oxides (NOx = NO + NO2) and ammonia (NH3), are significant contributors to global water and air quality degradation – resulting in a myriad of human health and ecosystem impacts.  Natural and anthropogenic sources can be significant contributors to total reactive nitrogen; however source partitioning remains a challenge for researchers and policy makers. This research investigates the use of stable isotopes of NH3 and NOx as monitoring tools for understanding sources, transport, and fate of reactive nitrogen pollutants. Particular emphasis is placed on characterizing the isotopic composition of NOx15N-NOx) and NH315N-NH3) from livestock operations, fossil fuel combustion, cropland, pasture, and prairie ecosystems.

Results/Conclusions

For initial measurements of livestock NH3 emissions, a transect radiating outward from a 150 head dairy barn and downwind to the edge of a forest was sampled for NH3 using Ogawa passive samplers.  The δ15N-NH3 values inside the barn and adjacent to the ventilating fans range from -23‰ to -29‰ indicating a largely negative δ15N value for livestock waste emissions.  d15N values progressively increased away from the barn, indicating decreasing contributions of livestock emissions to ambient NH3.  Additionally, to characterize a major source of fossil fuel NOx, two coal-fired power plants, one using selective catalytic reduction (SCR) and one not using SCR, were sampled.  The δ15N-NOx values of the plant using the SCR and the non-SCR plant were ~+20‰ and ~+10‰ respectively. 
In addition to these initial measurements of NOx and NH3, field deployments in the spring and summer of 2010 will characterize d15N values from a conventionally managed corn field, a 30,000 head cattle concentrated animal feeding operation, vehicle emissions in a highly trafficked tunnel, and biogenic emissions from a tallgrass prairie.  This research will result in the most comprehensive survey to date of the isotopic composition of emission sources of reactive nitrogen and will serve as a critical foundation for subsequent studies aimed at the sources, transport, and fate of reactive nitrogen pollutants.