Environmental Services Director
Picture it. It’s a beautiful spring day as you drive along a rural highway in North Dakota. The sun is out and your windows are down, when, suddenly, an offensive odor hits you right in the nostrils. Someone hit a skunk.
What is it about this smell that makes it so offensive? The sense of smell is comple. xOdors evoke a wide range of physiological and emotional reactions. Different people have different reactions to the same odor. Odors can be either energizing or calming. They can stimulate positive or negative reactions and memories.
There are many factors that play into odors that allow us to describe and measure them. Research from Penn State and the University of Minnesota identified five characteristics of odor:
1) Concentration – power of the odor.
2) Intensity – strength of the odor.
3) Persistence – how long the odor is in the air.
4) Hedonistic tone – pleasantness/ unpleasantness of an odor.
5) Description – type of odor.
Concentration and intensity are considered objective parameters and are used for scientific and regulatory measurements, while persistence, hedonistic tone and description are commonly considered subjective, as these differ from person to person.
After interviewing people who live around animal feeding operations, researchers found that neighbors reported lower odor if they knew and had a good relationship with the producer. Second, the more attractive and cleaner looking the operation, the less odor recorded by the neighbor.
Odor is the most common complaint associated with animal feeding operations, but it is one of the most challenging to measure. Unlike other air emissions, odor is not easily identified by a gas or molecular compound. Instead, odor is made up of hundreds of individual odorous compounds. Complicating this scenario is the fact that each person has a different perspective, tolerance and interpretation of what they are smelling. Because humans can detect more than 10,000 odors, it is helpful to categorize odors as pleasant, unpleasant or neutral.
For those wondering, North Dakota does have an odor law entitled “Restriction of Odorous Air Contaminants.” The law considers an odor objectable when a North Dakota Department of Health certified inspector or at least 30 percent of an odor panel exposed to the odor would deem that odor objectionable if the odor were present in their place of residence.
It’s illegal for a person to discharge into the ambient air any objectionable odorous air contaminant that measures seven odor concentration units or higher. There is an exemption in the law for applying manure to land in accordance with a nutrient management plan.
An odor measurement may be taken only with a properly maintained scentometer. A scentometer is a rectangular, clear plastic box with two nasal ports, two chambers of activated carbon with air inlets and several different size odorous air inlets. Trained individuals place the two nasal ports up to their nostrils and begin to breathe through the scentometer. All the odorous air inlets are closed so that the inhaled air must pass through the activated carbon and be deodorized. The individual begins sampling by opening the smallest odorous air inlet. More and larger odorous air inlets are opened until the individual detects an odor. The ratio of the odor-free air to the odorous air is used to calculate the odor concentration unit.
It’s important to note that the odor law is for any odor, urban or rural, that can be found objectionable and not just from agricultural operations.
Agricultural odors are complex and transient. More than 160 compounds have been identified in manure. Each individual compound contributes to the overall character, either by making the emission more offensive, easier to detect or harder to measure.
So, the next time you are driving along and smell that oh-so-familiar skunk, perhaps you will be able to distinguish the characteristics that go into the odor.
A few years back, NDSA President Dan Rorvig’s daughter Amy asked Dan why he had gray hair. He replied, “It’s from all those times you were naughty when you were little.” Amy shot right back, “So why does Grandpa have so much gray hair?”