Domestic animals are the largest global source of atmospheric ammonia (NH3), with emission rates ranging from 20-35 Tg N yr-1, approximately 40% of natural and anthropogenic emissions combined. (One Tg=teragram is equal to approximately 1 million tons.) Environmental burdens associated with elevated atmospheric concentrations of NH3, including ammonium (NH4+) aerosol formation and enhanced deposition of reduced nitrogen (NHx = NH3 + NH4+), may therefore be more prevalent in downwind of regions of intense animal production. This research project addressed 1999 NPPC priority A.3: quantify atmospheric movement and deposition of nitrogenous compounds of swine manure storage or treatment structures, or land application areas. Specific objectives include: to obtain estimates of seasonal patterns in atmospheric NH3/ammonium concentrations in a region with a high density of large-scale swine production facilities; to make field measurements of NH3/ammonium dry deposition in this same region; to use 15N stable isotope ratio techniques to estimate the contribution of swine production facilities to atmospheric concentrations and deposition of NH3/ammonium; and to provide ground-truth data of atmospheric concentrations and depositions of NH3/ammonium for calibration of regional-scale models being used to predict fate and transport of NH3.
A unique database (over 1200 samples between 1999 and 2000) has been constructed of the temporal and seasonal ambient NH3 (annual mean = 5μg NH3-N m-3) and ammonium aerosol concentrations (annual mean = 5.5 μg (NH4)2SO4 m-3) in a region with relatively high-density of animal production facilities (eastern NC). This database has been constructed using a recognized U.S. EPA measurement technique. The data strongly suggests that there is strong local source term for NH3 emissions in the region that responds readily to changes in atmospheric temperature. Availability of a detailed database of ambient atmospheric NH3 and ammonium aerosol concentrations facilitates the estimation of dry deposition of these N-containing species, provided appropriate deposition velocity terms (vd) are available for plant canopies. Attempts to derive vd values for a corn canopy by measuring the flux of NH3 deposition demonstrated the limitations of current technology in achieving this goal, especially in regard to measuring NH3 gradients over plant canopies. Use of the delta-15N analysis may provide a potential direct link between ambient atmospheric NH3 and NH3 emissions in a region with a relatively high density of animal production facilities. However, the results presented here are only preliminary in nature and are subject to change. A suitable reference database is required regarding delta-15N values for NH3 released from various source materials by volatilization before this technique can realize its full potential. Work accomplished in this project supports NH3 fate and transport modeling efforts, such as the extended-RADM by providing measures of the ratio of NH3 to the total inorganic reduced-N (NHx = NH3 + NH4+). Modifications to the extended-RADM are now underway in an attempt to account for the ambient concentrations of NH3 and ammonium aerosols actually observed in eastern NC.
Support of this research demonstrates NPPC’s concern that development of best management practices (BMPs) for agricultural animal production must include the potential environmental consequences of implementing such BMPs on a regional scale basis. Much of the work detailed here continues under the direction of the principal investigator, and the support from NPPC to allow initiation of several aspects of this research is greatly acknowledged.