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A Model Farm for Emissions Studies
By Ann PerrySeptember 17, 2008
Anyone downwind of a pig barn knows that animal production facilities generate some notable emissions. Now Agricultural Research Service (ARS) scientists have reported that preliminary findings from wind tunnel studies indicate that positioning farm buildings perpendicular to prevailing winds could help reduce odors from downwind lagoons or tanks.
Wind speed and direction, topography, structures, facility management, climate and vegetative cover all influence airflow--and influence where these agricultural emissions end up.
ARS scientists Tom Sauer and Jerry Hatfield are using a wind tunnel to model how air emissions from animal production facilities travel across the landscape. They embarked on a 3-year study to see how the location and placement of buildings and waste-storage facilities affects the transport of odor constituents like ammonia and hydrogen sulfide.
The scientists, who both work at the ARS National Soil Tilth Laboratory in Ames, Iowa, used a 40-foot wind tunnel for their research. The “wind” was produced by a blower at one end of the tunnel that generated maximum wind speeds of 30 miles per hour.
Sauer and Hatfield built a test “farm” in the wind tunnel that had scale replications of swine finishing units, aboveground slurry tanks and lagoons. They arranged four of these model buildings on their “farm” in several different configurations with the model storage tanks.
The team also set up obstacles in the tunnel to create a surface boundary layer of air that would mimic the effects of the Earth’s atmospheric boundary layer. This helped to generate air turbulence which then flowed through and around the obstacles. Water vapor or smoke from dry ice substituted for ammonia and hydrogen sulfate emissions.
The researchers found buildings situated perpendicular to airflow disrupted the downwind airflow to a greater extent than buildings that were parallel to the airflow.
These findings also show that producers could derive a direct and permanent benefit of improved air quality with just the one-time cost of figuring out the best building placement.
Read more about the research in the September 2008 issue of Agricultural Research magazine.
ARS is a scientific research agency of the U.S. Department of Agriculture.
