Jun 18, 2002 By Joann Loviglio Associated Press Writer 3 min read

PHILADELPHIA (AP) – The nose knows when it’s catching a whiff of something less than rosy, but deciding whether one thing stinks more than another is a subjective call.

Researchers at Penn State University, however, are developing a way to come up with a more objective way to gauge the olfactorily offensive: an “odor index.” “Just like any other sense, we smell things every day but how we interpret that is based on background, where we live, and a variety of other factors,” researcher Bradley A. Striebig, head of the environmental technology group at Penn State’s Applied Research Laboratory, said Monday. “What may smell to you may not smell to me.”

The odor index could replace a lot of the subjectiveness of scent with standardized lab procedures for analyzing air and sludge samples. That could help wastewater treatment plants, pig farms, landfills and other potentially smelly sites “mitigate (odor) before it becomes a public problem,” Striebig said Monday.

The scientists have devised an instrument-based system that sniffs out the gases a particular substance is giving off and determine how smelly it is, based on a scale from 0 to 1 million.

Here’s how it works: The scientists collect air samples from a site and bring them back to the lab. They freeze the gas, drawing out non-offending elements like oxygen and leaving the stinky ingredients behind. Then they turn it back into a gas and use a machine to measure the concentration of the gases.

Then, they measure the concentration of each gas against subjective standards about how much it takes an average person to smell it. The concentration and the subjective standards yield the odor index.

For example, an odor index value of 1,000 means that a scent would be barely detectable and a value of 10,000 means that the smell would be obvious but not nauseating. Raise that number to 100,000 or higher and, depending on the stinkiness of the chemical, the sniffer would be pretty sick to his stomach.

“Some (water treatment) systems that produce very little odor could be analyzed and duplicated in other systems that have odor problems,” Striebig said. “We also could more accurately measure whether an approach a plant is taking has improved or made odors worse.”

In the nine years that Pennsylvania has been regulating odors from wastewater plants, there has been debate about how to set standards for measuring odors. The research is possible now because of sophisticated and sensitive lab equipment that’s now available.

“The operators of most (waste) facilities want to be able to improve their odors but many don’t know how,” said Rich Giani, a state Department of Environmental Protection scientist who is working with the Penn State researchers on the project. “We want to have something so that the these operators can say, ‘I have a starting point – things to look for, what to do, how to do it.”‘

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On the Net:

Penn State University: http://www.psu.edu

Pennsylvania Department of Environmental Protection, http://www.dep.state.pa.us