Naming the Smell: How the Odor Wheel Turned a Subjective Complaint Into Scientific Evidence
By Paul E. Rosenfeld, M.S., Ph.D., Principal Environmental Chemist, RoseyFields LLC, Santa Monica, California
The problem with “it smells bad”
Long before odor nuisance became a litigation category, Dr. Paul E. Rosenfeld, M.S., Ph.D. recognized a basic evidentiary problem: lay descriptions of odor, “foul,” “nauseating,” “chemical”, are subjective, inconsistent between witnesses, and difficult for a court to weigh against a defendant’s evidence of regulatory compliance. His research career addressed this gap directly by developing structured odor classification tools.
Building an odor wheel for compost and biosolids facilities
Working with colleagues, Dr. Rosenfeld developed an odor wheel classification specifically for evaluating human health risk criteria at compost facilities, organizing odorant categories into a visual, structured framework analogous to a wine-tasting wheel, allowing community members and investigators to characterize odor complaints using a shared, repeatable vocabulary rather than ad hoc description (Rosenfeld et al., 2007).
Generalizing the framework beyond composting
A companion publication extended the odor wheel concept to drinking water, wastewater, and the broader urban environment, establishing that the underlying classification methodology, organizing odorants by chemical family and sensory character, generalizes across very different odor-generating industries rather than being limited to a single facility type (Rosenfeld & Suffet, 2007).
Quantifying, not just classifying, the underlying odorants
Classification alone does not establish a health-relevant exposure; Dr. Rosenfeld’s research also directly measured odorant emissions from composting operations, quantifying biosolids odor and odorant emissions from windrows, static piles, and biofilters to determine actual emission rates at each stage of the composting process (Rosenfeld et al., 2004).
Reduced sulfur compounds as a recurring health-relevant odorant class
Much of the health-relevant odor from composting, wastewater, and biosolids facilities traces to reduced sulfur compounds, including hydrogen sulfide, which has both a distinctive odor threshold well below its regulatory exposure limits and documented respiratory and neurological effects at higher concentrations, making it a frequent focus of both odor characterization and health-risk analysis (ATSDR, Hydrogen Sulfide).
Testing engineering controls in the peer-reviewed literature
Beyond measurement, Dr. Rosenfeld’s research tested specific odor-control technologies, including high-carbon wood ash amendments and two-stage biofilters, publishing quantitative before-and-after odor reduction data that gives litigation opinions about “available control technology” a documented, peer-reviewed evidentiary basis rather than a bare assertion (Rosenfeld & Suffet, 2004; Rosenfeld & Grey, 2003).
Applying the framework across a wide range of facility types
The same odor wheel and quantification methodology has proven applicable across a wide range of subsequent matters, from a Washington State industrial composting facility to a Iowa corn wet-milling plant, illustrating that a well-designed classification tool developed for one industry can transfer effectively to structurally different odor sources.
Why odor evidence often intersects with, but is distinct from, toxic exposure evidence
An odor can be present, and constitute an actionable nuisance, at concentrations well below any recognized toxic threshold, meaning odor nuisance litigation and toxic exposure litigation require separate analytical frameworks even when they involve the same chemical compounds and the same facility.
The absence of a federal odor standard as a recurring evidentiary gap
Because no federal regulation directly limits “odor” as a measurable parameter, litigants and courts rely heavily on state and local nuisance law standards, industry-specific best-practice guidance, and structured scientific classification tools like the odor wheel to establish what constitutes an unreasonable interference with property use, in the absence of the bright-line numeric standard available for criteria air pollutants.
Why a twenty-year publication record matters more than a single litigation opinion
Because the odor wheel classification and odorant quantification methodology has been developed, tested, and published over roughly two decades in peer-reviewed journals independent of any specific litigation, it offers courts a scientific foundation considerably more durable than a methodology developed solely for a single case. More information on Dr. Rosenfeld’s odor and air-quality nuisance research is available through RoseyFields.com.
References
1. Rosenfeld PE, Clark JJJ, Hensley AR, Suffet M. The use of an odor wheel classification for evaluation of human health risk criteria for compost facilities. Water Sci Technol. 2007;55(5):345-357.
2. Rosenfeld PE, Suffet IH. The anatomy of odour wheels for odours of drinking water, wastewater, compost and the urban environment. Water Sci Technol. 2007;55(5):335-344.
3. Rosenfeld PE, Grey MA, Sellew P. Measurement of biosolids odor and odorant emissions from windrows, static pile and biofilter. Water Environ Res. 2004;76(4):310-315.
4. Rosenfeld PE, Suffet IH. Control of compost odor using high carbon wood ash. Water Sci Technol. 2004;49(9):171-178.
5. Rosenfeld PE, Grey MA. Two stage biofilter for biosolids composting odor control. Seventh International In Situ and On-Site Bioremediation Symposium; June 2003; Orlando, FL.
6. Rosenfeld PE, Suffet IH. Understanding odorants associated with compost, biomass facilities, and the land application of biosolids. Water Sci Technol. 2004;49(9):193-199.
7. Rosenfeld PE, Henry CL. Wood ash control of odor emissions from biosolids application. J Environ Qual. 2000;29:1662-1668.
8. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Hydrogen Sulfide. Atlanta, GA: US Department of Health and Human Services; 2016.
9. Rosenfeld PE, Henry CL, Bennett D. Wastewater dewatering polymer affects on biosolids odor emissions and microbial activity. Water Environ Res. 2001;73(4):363-367.
10. Rosenfeld PE, Henry CL. Activated carbon and wood ash sorption of wastewater, compost, and biosolids odorants. Water Environ Res. 2001;73:388-393.
11. US Environmental Protection Agency. Clean Air Act National Emission Standards for Hazardous Air Pollutants. 40 CFR Part 63.
12. Rosenfeld PE. RoseyFields LLC: Odor and Air Quality Assessment for Waste and Composting Facilities. Santa Monica, CA: RoseyFields LLC; 2026.
13. In re Grain Processing Corporation Litigation (Muscatine County, Iowa nuisance class action, filed 2012); settlement approved 2019.
14. Davis M, Davis J, et al. v Cedar Grove Composting Inc. Case No. 13-2-03987-5, Superior Court of the State of Washington, County of Snohomish.