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Monitoring Ambient Ammonia Concentrations and Ammonia Dry Deposition Using Passive
Samplers at the Pocosin Lakes National Wildlife Refuge in Eastern North Carolina

Wayne P. Robarge*
North Carolina State University, Department of Soil Science, Raleigh, NC 27695-7619

John T. Walker
U.S. Environmental Protection Agency, NRMRL, Research Triangle Park, NC 27711

Sara Ward
U.S. Fish and Wildlife Service, Raleigh Ecological Services Field Office, Raleigh, NC 27636


Confined animal feeding operations in North Carolina (especially in the Coastal Plain region) constitute the largest sources of ammonia (NH3) emissions in the state. A moratorium on construction of new swine facilities during the past 8 years has essentially capped the NH3 emissions from this segment of the animal industry. However, expansion of the poultry industry continues for broiler, layer and turkey production. This project is monitoring the potential impact of a new layer facility (eventual flock population 3.5 million birds) on local dry deposition of NH3 to the nearby Pocosin Lakes National Wildlife Refuge, which lies within 1.6 km of the northern boundary of the new layer facility. For approximately one year prior to arrival of birds at the layer facility, background ambient ammonia chemistry was monitored using annular denuder technology at a fire tower within the refuge located approximately 9 km north of the facility. Annual mean concentrations of NH3 and ammonium (NH4) for 2005-2006 are summarized below:

Statistic    Aerosol    NH3   NH4   Na

- ug NH3/m3 -    - ug NH4/m3 -    - ug Na/m3 -

Mean    0.491   0.482   0.124

Std. Deviation    0.456   0.387   0.103

Count    365   359   355

Minimum    0.011   0.003   0.007

Maximum    5.42   3.77

Gaseous SO4    - ug SO4/m3 -

3.67   2.02   358   0.024   13.4   0.720

Weekly average NH3 concentrations along transects extending across the northern boundary of the layer facility were monitored prior to January 2007 using GRADKO® passive samplers. No NH3 concentrations were detected above the calculated detection limit of ~2 ug NH3/m3, which is consistent with the background weekly average NH3 concentrations recorded using annular denuder technology. With arrival of birds in January 2007, the GRADKO® passive samplers were replaced with ALPHA® passive samplers which have a calculated detection limit of <0.1ug NH3/m3. Use of the more sensitive ALPHA® passive samplers has recorded elevated concentrations of NH3 along transects extending across the northern boundary of the layer facility. Occurrences of elevated NH3 concentrations are consistent with potential plumes of NH3 originating from the layer facility. Weekly average NH3 concentrations derived using passive samplers will be combined with micrometeorological data to calculate dry deposition. Backwards Lagrangian models will be used to model source strength of the facility and potential movement of NH3 plumes deeper into the refuge.