Odor Monitoring for a Confined Animal Feed Operation

An often overlooked area of environmental concern is odor. Odors, and living with odors, are typically associated with paper mills, landfills, some manufacturing and confined animal feeding operations (CAFO). Although not commonly thought of, odors can be a real concern for people living in an odor’s footprint.

What is an Odor? An odor is a sensation produced by chemical stimulation of chemeoreceptors in the olfactory epithelium of the nose. A chemeoreceptor is a sensory cell or organ that is responsive to chemical stimuli and the epithelium is a membrous tissue composed of layers of compact cells—think of the nasal passage. The volatile molecules that stimulate olfactory senses are odorants. Many in the environmental arena are used to dealing with volatile chemicals such as benzene. When we “smell” gasoline, maybe while filling our cars, benzene is the stimulant that activates the chemeoreceptor in the epithelium creating the sensation of an odor.

What are the properties of odors? The first is the odor threshold. If an odor is not detectable, then by definition, there is no odor. Detection is an awareness of an odor, the point where it can be said, “yes I smell something, but I’m not sure what it is.” An odor threshold is the minimum concentration of an odorant stimulus that is perceived by 50% of the population. This can be statistically calculated in a laboratory from a group’s response to an odorant. Recognition is, again, 50% of the population that can say, yes that odor is “gasoline” or “rotten eggs.”

A second property of an odor is its intensity. Odor intensity is the perceived strength of odor sensation. This intensity property is used to locate the source of odors and perhaps most directly related to odor nuisance. We typically think of odors as having a “bad” smell, but a good example of odor intensity is flowers. Flowers, to most people have a pleasant or even desirable odor, however, the intensity of the odor that cut flowers emit is dependent on their age. Cut flowers will reach a peak intensity, hopefully shortly after we bring them home, and then the intensity will diminish with time.

Character is the third odor trait. It can be thought of as; what does the odor smell like? The character of an odor is a critical element in assessing an odor. This property is the ability to distinguish different odors and is only descriptive. First a basic description is used such as sweet, pungent, acrid, fragrant, warm, dry, or sour. The odor is then referenced to a source, typically an odor “wheel,” similar to a wine wheel, which can then be followed to reference a specific chemical such as acids or gasoline.

The fourth property of an odor is hedonic tone. Hedonic assessment is the process of scaling odors on a scale ranging from extremely unpleasant, neutral and up to extremely pleasant. It is important to note that intensity and hedonic tone, whilst similar, refer to different things. That is, the strength of the odor (intensity) and the pleasantness of an odor (hedonic tone). Moreover, it is important to note that perception of an odor may change from pleasant to unpleasant with increasing concentration, intensity, time, frequency, and previous experience with a specific odor; all factors determining a response.

What Affects Odor Perception? The sensitivity to odors causes a reaction by the individual. However the reaction varies from one individual to the next. Factors that impact perception are fatigue and tolerance. The olfactory nerves can become desensitized to an odor by overexposure.

As suburban sprawl has encroached upon historically undeveloped areas that may contain landfills or livestock production, the public complaints regarding odors has risen. In fact, odor associated with CAFOs has become a favorite of plaintiff attorneys in recent years. A recent article in the Kansas City Star noted that complaints have included comments that the “odor is worse than death” or “hell on earth.” A trained odor monitoring technician can collect data that can quantify the odor nuisance and assist the odor emitter and the receiver in finding a solution.

A person trained to use St. Croix Sensory, Inc.’s Nasal Ranger can provide affordable, real time data. The Nasal Ranger is calibrated and filters the incoming air allowing a determination of threshold, intensity and hedonic scale. The character of an odor is a more subjective task, and as state earlier, usually involves the use of standard descriptors as a reference.

The odor monitoring technique, includes identifying wind direction so that data collection is performed facing into the wind to prevent odor “blow-by.” Climatic conditions at the time of odor data collection is an important element of odor monitoring. Wind direction, wind speed, air temperature and cloud cover are all climatic elements that should be recorded each time odor data is collected.

Once the climatic conditions have been recorded, the actual odor monitoring with the nasal ranger can begin. After facing into the wind, the first step, is to purge the olfactory senses. This procedures involves taking 10 deep breathes with the nasal ranger set on 99% filtered air (the highest setting) and then proceeding down the scale of filtered air. Once the purging has been completed the odor monitor can move to the next settings (the settings are logarithmic) and then will breathe at that setting for approximately 10 seconds and will ask: “do I smell anything?” If not, then odor monitor moves to the next setting on the nasal ranger and repeats the process through all of the settings. If no odor is detected, then that is recorded. If an odor is detected, the nasal ranger setting that the odor is detected at is recorded and then the odor is identified, typically by use of the odor wheel. This process is repeated every 15 minutes for up to four hours. At the end of a 4-hour period, the odor monitor needs to leave the area and desensitize for a minimum of four hours prior to resuming data collection.

In the CAFO scenario, odor data was collected from sunup to sundown, seven days a week from March 1st to December 1st. This required a large team of odor monitoring technicians so that they could be cycled in and out over the course of the day to allow for continuous odor data collection but also making allowance for the time necessary to desensitize.