Estimating Hydrogen Sulfide Emissions and Ambient Air Concentrations from Beef Cattle Feedlot Operations

摘要

Hydrogen sulfide (H_2S) is a colorless, highly toxic gas that has a characteristic odor of rotten eggs. H_2S is released through bacterial decomposition of organic matter containing sulfur, such as manure. H_2S emissions from concentrated animal feeding operations (CAFOs), such as beef cattle feedlots, can result in occupational and community exposures and possible health concerns. Accurate measurement of H_2S emissions and concentrations on or near large cattle feedlots can be challenging and sometimes infeasible because of the variety of emission sources and variations in daily and seasonal levels. Sophisticated sampling and analytical instruments are also needed, and sampling can be time-consuming, and costly. This makes dispersion modeling a desirable alternative method for exposure investigations associated with CAFOs. We used the American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) with published emission rates, closest national weather station data and feedlot capacity to estimate receptor ambient concentrations in varying downwind distances from the source. Published H_2S emission rates ranged from 0.025 g/s to 3.6 g/s. The respective maximum hourly measured concentrations onsite were 4.2 μg/m~3 (3 ppb) in dry conditions and 2.0 mg/m~3 (1,440 ppb) during worst case conditions, e.g., rainfall, agitation of liquid manure lagoon. The maximum hourly modeled ambient air concentration at the closest populated census block receptor (i.e. less than half kilometer) is 300 μg/m~3 (214.3 ppb) downwind of a typical 55,000 cattle head and approximately 85 hectares of feedlot pen surface. Among many factors, moisture content, temperature of air and manure, the daily sulfur intake of the animals, the size of feedlot, the housing type, and lot design influence air emissions and ambient air concentrations. An exposure assessment strategy that combines air dispersion modeling with air sampling and monitoring will provide a better understanding of H2S emission rates, concentrations at the source, and potential exposures in communities near feedlots.