Iowa State Researchers Present Findings on Air Quality Monitoring

April 21st, 2002

AMES, Iowa — Recent research by two Iowa State University agricultural engineers illustrates the complex nature of an issue that is generating plenty of public debate — the effect livestock production has on air quality.

Dwaine Bundy and Steven Hoff presented two papers April 13 on a project that involved air quality monitoring at five swine production facilities. The presentations took place at the mid-central conference of the American Society of Agricultural Engineers in St. Joseph, Mo.

Hydrogen sulfide and odor measurements were taken at various distances from the five facilities over several months. Measurements were taken both during the day and at night. Weather data including temperature, sky cover, wind speed and direction also was recorded.

The facilities ranged in size from 2,500 to 8,000 animals per site. Breeding-gestation, farrowing and finishing facilities were included in the study.

Hydrogen sulfide levels were measured using a Jerome meter, a portable instrument that can detect hydrogen sulfide in a range from 1 to 4,000 parts per billion (ppb).

Bundy and Hoff found hydrogen sulfide levels were highest near the facilities, and decreased as the distance from the facilities increased.

There was an average of 16 ppb of hydrogen sulfide 500 feet or less from the facilities. The average was 8 ppb for 500 to 1,000 feet and 2 ppb for 1,000 to 1,500 feet. Although no standards for hydrogen sulfide yet have been established in Iowa, the most frequently discussed number is 15 ppb when the measurement is taken at any nearby residence or public use area.

Odors were evaluated using a scentometer. An odor threshold above 7 is often defined as an annoyance odor by most regulatory bodies that use odor as a standard. An odor threshold at or above 15 is often defined as a strong odor.

Bundy and Hoff found that at distances greater than 1,500 feet downwind from a source, with all types of units combined, 10 percent of the readings were at or above the annoyance odor level of 7. There were no readings of 15 at this distance. Only a few readings of 15 were found, and these were at distances of less than 500 feet from a facility. There were no odors or hydrogen sulfide detected from the swine facilities at any distances when not in the path of the air passing over the odor source.

While no standards for odor currently exist in Iowa, proposals being discussed range from 7 to 15, depending on where the measurement is taken.

Bundy and Hoff say this project shows that most Midwest livestock production facilities probably wouldn't have much trouble complying with proposed standards under discussion in Iowa for hydrogen sulfide or odor. Ammonia standards also are being discussed but the researchers say effective portable monitoring equipment isn't available. Their project didn't include ammonia measurements.

Another aspect of this project was to see how the local weather patterns impacted the dispersion of gases from the livestock facilities. In general, the researchers found that gas levels were lower on clear, sunny days and higher on calm, cloudy days.

"During the day, the sun plays a big role in atmospheric dispersion of gases, especially close to the source," Bundy says. "When the sky is clear, the atmosphere is generally unstable and a great deal of turbulence exists which tends to dilute gases at a high rate. During cloudy conditions, the atmosphere is more stable, and less turbulence is available to mix with emitted air."

In a related project, Bundy and Hoff are developing a computer model that can help determine how far gases from livestock production facilities will travel under a variety of atmospheric conditions. They took some of the data from the air monitoring project and plugged it into this model to see how closely the measured results would match the predicted results.

"In general, the modeled results for hydrogen sulfide and odor were quite close," Hoff says. "Data collection on source and downwind hydrogen sulfide, ammonia and odor levels are planned and will be used to provide additional calibration data for the model for a wide range of weather conditions."

Hoff says the model could be used as a tool to help determine the best places to build future livestock confinement facilities. Initial funding for the modeling project came from the Iowa Pork Producers Association. The second phase of the project is being funded by the Iowa Farm Bureau Federation.


Dwaine Bundy, Agricultural and Biosystems Engineering, (515) 294-1450

Steven Hoff, Agricultural and Biosystems Engineering, (515) 294-6180

Susan Thompson, Agriculture Communications, (515) 294-0705