H2S concentrations measured at the perimeter of nine swine operations across the state indicated that for the sizes of operations investigated with this study, the dominating influence on perimeter H2S concentration was the influence of atmospheric stability, which in turn was a function of solar radiation and wind speed. The perimeter H2S concentration measured decreased dramatically with increased solar radiation. During the summer months, the sun will heat the ground causing air near the earth to rise. This rising air takes with it exhaust air from barns and outside manure storages expelling this air vertically, thereby decreasing the concentration measured near the ground at any given distance from the source. The highest average source perimeter H2S concentration was measured for a source with the highest ratio of total manured surface area as outside storage.
If an elevated H2S concentration was measured with monitors placed between a source and a near-by residence, an elevated H2S concentration in the ambient air near the residence was measured only if the separation distance was less than 2,149 ft from the source (GLD residence, Sources 5&6). These elevated levels measured at the residence required low solar and low wind speed conditions however. The time-weighted average H2S concentration measured in the ambient air surrounding residences did not reach a level even close to the Iowa proposed HEV of 30 ppb. The highest daily average H2S concentration in the ambient air near a residence was 11.4 ppb for the STC residence which was located 251 ft from a 4,800-hd deep-pit finishing site.
The NH3 concentrations measured at a residence in the ambient air and inside the home indicated that the inside home concentrations were higher and that these levels were in most every case not associated with downwind events from a source or elevated concentrations measured in the ambient air surrounding the residence. These results agree with one known short-term study conducted in Missouri where residences were monitored near a large swine finishing operation. The evidence suggests that inside home sources caused these elevated NH3 concentrations which is the topic of on-going research being conducted by the PI. The highest inside home NH3 concentrations were measured for residences where the occupants smoked or housed pets, both potential sources for NH3. If NH3 is being considered in the future for regulation, the results presented here make it mandatory that inside home NH3 concentrations must be considered before results measured in the ambient air surrounding a residence are assessed for compliance.