This project was designed to address the National Pork Board objective of needing to know ambient concentrations of gases emitted from swine operations (in particular ammonia, NH3) both near and distant from these operations. Published scientific studies have either measured or modeled ambient concentrations of NH3 in regions with relatively high densities of swine production (such as Sampson and Duplin Counties in eastern North Carolina), with the conclusion that the presence of these operations have impacted local atmospheric chemistry. However, the majority of these studies are based on measurements at a single location on the landscape and it is assumed that the data collected at these relatively few locations is representative of the region. This project used passive sampler technology to look more closely at how NH3 disperses away from swine facilities (housing units with anaerobic lagoons) at ground level.
Passive samplers have been proven to provide reliable quantitative measures of average atmospheric NH3 concentrations without the need for costly infrastructure such as electrical power, shelters and constant attention by trained personnel. They allow affordable replication of measurements and can be deployed in relatively large numbers at very modest cost. Passive samplers were deployed around animal operations (swine and turkey; April 2007 to June 2008) in eastern North Carolina at various distances and orientation to provide a range of weekly observations (total 24 sampling sites). The NH3 concentrations were compared to those measured using US Environmental Protection Agency approved annular denuder technology at two locations (urban, and rural with no animal facilities) during the same time period to determine the degree to which observed NH3 was elevated above expected normal background levels.
The data gathered in this study demonstrate that regardless of orientation the weekly average ground level concentration of NH3 drops off very rapidly as one moves away from an animal facility, and that even in regions with relatively high densities of animal operations it is possible to observe low ambient NH3 concentrations (within 2 miles) similar to those found in urban areas and rural areas without animal facilities nearby. When combined with the appropriate geographical information system (GIS) data, a spatial representation of the weekly mean NH3 concentrations as a function of distance from nearby animal facilities showed how ambient concentrations of NH3 varies across the landscape, being a function of distance between adjacent facilities, herd size and type of facility, and season of the year. This project illustrates that attempts to measure impact of animal facilities on ambient atmospheric NH3 concentrations as compared to “remote” locations has limited applicability. Measurements of increased ambient concentrations of NH3 near animal facilities are more a measure of the frequency and orientation (wind direction) of ground-level plumes of NH3 moving away from the facility than any consistent regional elevation of ambient atmospheric concentrations. As such, closeness to the nearest facility, as well as relative density of facilities, will dictate measured ambient NH3 concentrations as observed at a particular time or location on the landscape. This work also demonstrates that passive sampler technology for atmospheric gases such as NH3 is a viable, affordable measurement approach that can be used for monitoring average gas concentrations within the immediate vicinity of swine facilities.