Auditing and Assessing Air Quality in Concentrated Feeding Operations1,2,3

Professional Animal Scientist, Feb 2008 by Cole, N A, Todd, R, Auvermann, B, Parker, D

In its gaseous form, atmospheric ammonia can travel from rural to urban areas and neutralize acid gases such as sulfates and nitrates (products of fossil fuel burning) in the atmosphere, converting these gases into small particulates (PM25) that may pose a potential health risk to some individuals (Watson et al., 1998; Neas, 2000; McCubbin et al., 2002). Ammonia that travels downwind may also be deposited via wet or dry deposition onto the soil or water bodies and become a nutrient source. In ecologically sensitive areas, ammonia deposition may provide an oversupply of N for the native flora, resulting in modifications of the native ecosystem (Hutchinson and Viets, 1969; Wolfe et al., 2003; Todd et al., 2004). From an economic perspective, ammonia losses also represent a loss of potentially valuable N fertilizer.

Atmospheric ammonia concentrations at AFO vary greatly and there appears to be a notable diel pattern with highest concentrations during the day and lowest concentrations at night (Omland, 2002; Todd et al., 2005, 2007). Ammonia concentrations in open-lot feedyards rarely exceed 3 ppm (Todd et al., 2005, 2007); however, concentrations within animal houses can frequently exceed 25 ppm, the threshold limit value for worker safety in Denmark (Omland, 2002). Ammonia emissions from AFO may be affected by many factors including diet (protein quantity and degradability, carbohydrate degradability, acid-base balance), pen surface, retention pond, or lagoon conditions (total ammonium concentration, pH, temperature, moisture, solids), weather, ventilation rate, manure storage method, and animal age (Dewes, 1996; Ni, 1999; Ni et al., 1999; Cole et al., 2005, 2006; Todd et al., 2006, 2007).

Some current ammonia emission factors used by the EPA are in doubt because incorrect assumptions were made and because many values are based on European data in which different managing systems were used (Asman, 1992; Battye et al., 1994) that may not be applicable to American production systems. In addition, a single emission factor for ammonia and many other pollutants is difficult to justify because so many environmental factors can affect emissions.

Hydrogen Sulfide

Hydrogen sulfide forms in livestock operations primarily from anaerobic fermentation by sulfate-reducing bacteria. In solution, sulfide ions develop an equilibrium with hydrogen ions (Shurson et al., 2000). Under basic conditions (pH > 8), most reduced S exists in solution as HS^sup -^ and S^sup 2-^ ions, and the quantity of free H^sub 2^S is small. At pH

Reported hydrogen sulfide emission rates from swine and dairy manure storage tanks and anaerobic lagoons are highly variable (Parker et al., 2005a) ranging from 146 (Zahn et al., 2001) to 46,260 (Hobbs et al., 1999) �g/m^sup 2^ per min. Hydrogen sulfide concentrations downwind of feedyard pens in Nebraska (Koelsch et al., 2004) and Texas (Rhoades et al., 2003) ranged from 0.003 to 0.13 ppm; however, fewer than 1% of measurements exceeded the state regulated value of 0.1 ppm. Hydrogen sulfide emissions from feedyard pens averaged approximately 3.7 kg per 1,000 head daily, and emissions from retention ponds ranged from 102 to 1,348 �g/m^sup 2^ per min (0.54 to 11.2 kg per 1,000 head daily; Rhoades et al., 2003).