Air Emissions and Animal Agriculture

Understanding odor

Olfaction, the sense of smell, is the least understood of the five senses. This, among other factors, makes the task of reducing livestock odors a considerable challenge.

As perceived by humans, odors have five basic properties that can be quantified:

1) intensity

2) degree of offensiveness

3) character

4) frequency, and

5) duration

All of these contribute to peoples’ attitude toward odor, as well as the business generating the odor. It is generally accepted that the extent of objection and reaction to odor by people is highly variable. The reaction can be based on previous experience, relationship to the odor-producing enterprise and the sensitivity of the individual.  Weather (temperature, humidity, wind direction) affects the volatility of compounds, preventing or enhancing movement into the gaseous phase where an odor can be dispersed downwind. Most of us will accept even a strong odor for a short period of time, provided we don’t have to smell it often. But we have a threshold for the frequency and duration of the odor, above which our tolerance is exceeded and we view the odor as a nuisance. These thresholds are person-specific.

While it is the frequency and duration of an odor that often triggers a nuisance complaint, odor measurement procedures typically focus on the first three traits (intensity, offensiveness and character). From a human health standpoint, exposure time is an essential measure in predicting any negative effects that may occur and this encompasses frequency and duration, as well as concentration (intensity). As a result, regulatory procedures often include concentration, frequency and duration as part of the compliance protocol.

Last Updated 06/29/2011