Ambient hydrogen sulfide concentrations were monitored for several months at the property line of a wean-to-finish swin production facility. Data was analyzed to determine apparent influences of slurry characteristics, wind speed and time of day. It was also analyzed to evaluate the apparent potential effectiveness of a commercial manure additive, limited aeration and permeable geotextile/straw cover on reducing ambient hydrogen sulfide levels. The addition of the manure additive, combined with the warm weather and 41 days of aeration in late summer, apparently reduced volatile fatty acids, sulfide and BOD in the lagoon slurryy and also the ambient hydrogen sulfide concentrations. The actual effect could not be determined due to the absence of a control lagoon. Concentrations were twice as high at night than during the day. Mean ambient hydrogen sulfide concentrations with the cover was only 13% of the mean concentrations before the cover was installed.