Community levels of atmospheric ammonia near industrial hog operations

Background: Industrial hog operations release ammonia to the atmosphere that may create potential health hazards for nearby human populations. Limited work has been performed to measure, map, and estimate NH3 at the community level to assess potential human exposure. To address this issue, a study was designed to characterize NH3 levels near industrial hog farms and human populations in Eastern NC. Methods: NH3 was collected using passive diffusion tubes for one week at a time. Sampling occurred continuously from October 2003 to October 2004 at varying distances from farms in close proximity to homes and schools. Geographic Information Systems (GIS) and the Bayesian Maximum Entropy (BME) framework were used to map and predict spatiotemporal variation in community levels of atmospheric ammonia. Results: Mean levels near homes and schools was 4 to 12 times greater than ambient background levels (1-3 ppb), reaching as high as 80 ppb. Exposed sites (less than 2 km from a hog farm) had mean levels which were three times higher than less exposed sites (greater than 2 km from a hog farm). GIS was successfully used to construct spatiotemporal maps that showed “zones of exposure” for communities located near industrial hog farms. Conclusions: The study established that passive sampling in conjunction with GIS methodologies could effectively show NH3 variation in space and time. The collected data and constructed maps act as indicators of relative exposure for communities near industrial hog farms.