How do you measure farm odor?


SALEM, Ohio – Beauty is in the eye of the beholder and odor is in the nose of the neighbor.

But determining if, and how much, a farm smells may not be subjective for long.

Numbers game. In May 2003, neighbors of two hog operations in Paulding County filed a lawsuit claiming they had detrimental health effects from manure gases.

In October 2003, neighbors of a 690-head dairy in Putnam County filed a lawsuit claiming the farm was responsible for unreasonable odor and toxic gases.

A total of 35 plaintiffs are each seeking in excess of $20,000 for medical expenses. The dollar amount jumps tenfold when claims of emotional distress and property devaluation are included.

The questions at the crux of both the farms’ and public’s cases are: How much odor is too much and when are emissions excessive?

There aren’t any answers. But Ohio State University researchers are working to change that.

“Because of the lack of numbers, it’s easy for people to speculate that these farms are dangerous, and there’s no research to support or refute it,” said Glen Arnold, Putnam County extension agent.

Growing farms. As farmers build barns and apply for permits to add thousands of animals, public awareness is mounting.

Smell is the most prominent concern, said Lingying Zhao, Ohio State’s lead researcher on the project.

Starting last spring, Zhao, Arnold and another OSU researcher, Mike Brugger, tracked the airborne emissions from three farms in northwest Ohio: a 675-cow dairy, a 1,000-head hog farm, and an egg farm with 90,000 chickens. They ran three-day tests in March, June and August.

Importance. Researchers collected data all across the farms, including many points within the barn, hoping to show farmers where they need to pay attention to emissions.

For example, the owner of the poultry farm can look at the data and see the middle alley has the highest concentration of dust and then work on ventilation for that area.

Not only could the gases and dust be harmful to farmers and employees, but they can also jeopardize livestock performance, Arnold said.

The smell factor. Grab a sample of air in a bag. Shoot it through a machine. Get a printout of how bad it smells on the farm. Scientists wish it was this easy – and this objective.

Instead, the researchers gathered air samples at six locations on all three farms and overnighted them to Purdue University’s odor lab.

It ultimately goes to a panel of sniffing specialists. They take a whiff and assign a number to the odor based on how much fresh air is required to neutralize the sample.

It’s still subjective, but at least it’s something, experts say.

In the Ohio State study, odor levels inside the poultry and swine facilities were “above desirable,” Arnold said.

The smell at the base of the pit or manure holding pond at each of the farms was also high, he said.

But Arnold was most interested in the 500-foot downwind sample, more similar to a neighbor’s perspective.

All were under the human concern threshold.

Scoring the highest downwind score was the dairy. This came from an August reading, on a day when the manure pond was being agitated – a “worst-case scenario” for odor, Arnold said.

Toxic concern. Hydrogen sulfide is another major worry for farmers and neighbors.

Hydrogen sulfide forms when manure is stored anaerobically, meaning without oxygen.

If confined to a closed space, it can be a toxic gas nightmare.

But it must stay contained to be dangerous, Arnold said.

With an odor of rotten eggs, hydrogen sulfide’s odor detection level is between .7 and 1 parts per million (ppm), Arnold said.

Measurements hitting above this level were:

* inside the swine building (.200 ppm) in March; (.202 ppm) in June; and (.238 ppm) in August.

* at the dairy’s manure pit (1.44 ppm) in June and (.826 ppm) in August.

At 500 feet downwind, the highest reading came at the dairy in June. The level was .023 ppm.

Ammonia. Ammonia levels were low outside the facilities at all but the poultry operation.

Here, numbers were the highest, hitting 40 ppm in June near the manure pit.

Ammonia, released during manure storage, is considered average at 5-18 ppm and high at 40-50 ppm, Zhao said.

Inside the buildings, the highest number recorded at each farm was: 3 ppm at the dairy; 24.3 ppm at the poultry farm; and 5.7 at the swine operation.

At 500 feet downwind, all readings were at zero.

Dust? Next on the researchers’ list was dust, which is a particular concern for farmers because the finer the dust, the farther it settles in the lungs, Arnold said.

Readings inside the poultry building were the only ones to hit above the recommended 2 milligrams per cubic meter, Arnold said.

The numbers stayed at zero once downwind from the farms.

‘Snap shot.’ Researchers caution this data is only representative of 1 percent of the total days last year; it’s a “preliminary snap shot,” they say.

But, at this point, it’s all they have.

Although Minnesota and California have similar research, it can’t necessarily be useful in Ohio, Zhao said. Weather conditions and geography make the data difficult to transfer to other parts of the country, which is why it’s so pertinent for Ohio to conduct its own studies, she said.

She will continue the research and samples on other Ohio farms this year.

(Reporter Kristy Hebert welcomes reader feedback by phone at 1-800-837-3419, ext. 23, or by e-mail at


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