In the U.S. and internationally odours remain at the top of air pollution complaints to regulators and government bodies. From state to state, in communities across the United States, and in other countries, odour issues are addressed by a variety of "odour laws", whether they are called an ordinance, rule, regulation, or policy.
Michael A. McGinley, P.E. and Charles M. McGinley, P.E.1
Competing interests: The author has declared that no competing interests exist.
Academic editor: Carlos N Díaz.
Content quality: This paper has been peer reviewed by at least two reviewers. See scientific committee here
Citation: M A. McGinley, P.E. and C M. McGinley, An overview of odour regulation throughout North America, Ist International Seminar of Odours in the Environment, Santiago, Chile, www.olores.org
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Keyword: nuisance, ordinance, rule, policy, inspection, field olfactometer, olfactometry
In the U.S. and internationally odours remain at the top of air pollution complaints to regulators and government bodies. From state to state, in communities across the United States, and in other countries, odour issues are addressed by a variety of "odour laws", whether they are called an ordinance, rule, regulation, or policy. An “odour law” is effective if and only if it uses a criterion or criteria to define compliance. Odour laws address community odour issues in several well-defined approaches that utilize compliance determining criteria. In the U.S., the Environmental Protection Agency (US-EPA) does not regulate odour; however, some states do specifically regulate odours with the common approach of setting ambient odour dilution-to-threshold (D/T) limits measured using a field olfactometer, i.e. Scentometer, Nasal Ranger, or other approved device or method. States that do not regulate odour authorize local governments, through general zoning or police powers, to adopt odour nuisance ordinances. Canadian provinces similarly regulate odours independent of the national Canadian government. With the exception of Ontario and Quebec, the individual Canadian provinces primary focus on agricultural odours.
Ambient air holds a mixture of chemicals from the everyday activities of industrial and commercial enterprises that make up modern day society. Exposure to those chemicals in the ambient air has become a part of modern day life. However, from time to time, citizens find the odours of these chemicals annoying and objectionable and at some point may declare them a nuisance.
An odour nuisance usually is a result of a series of odour episodes experienced by a citizen or citizens. The Frequency of these episodes, the Duration of each odour episode, the Intensity of the odours, and the character or Offensiveness of the odours contribute to the nuisance experience, i.e. “FIDO”. Additionally, the location or context of the odour episode can also affect the nuisance experience. Throughout North America, citizens seek relief from odour nuisance through either regulatory authority or personal legal action.
Elements of Odour Laws
From state to state and in communities across the United States and other countries odour issues are addressed by a variety of "odour laws", whether they are called an ordinance, rule, regulation, or policy. An odour law is effective only if it uses a criterion or criteria to define compliance. Odour laws address community odour issues in several well-defined approaches that utilize compliance determining criteria:
- Annoyance criteria (subjective categories);
- Complaint criteria (numbers of complaints);
- Ambient odour detection threshold criteria;
- Ambient odour intensity criteria;
- Ambient odorant criteria (mass concentration, i.e. mg/m3);
- Episode duration-frequency criteria (“odour-hours”);
- Source emission criteria (threshold or mass concentration); and
- Best available control technology criteria (i.e. industry standard).
These various approaches are not mutually exclusive; one odour law may include multiple approaches (McGinley, 2000).
The development and implementation of an odour law requires a scientific and an administrative infrastructure. Adequate regulatory resources are critical if the odour law is detailed and relies on on-going involvement of the regulatory agency staff. The planning and implementation of odorous emission sampling, odour testing, ambient odour monitoring, and related chemical testing are as essential as the administration of the odour law. The foundations of the odour law infrastructure include:
- Odour complaint mechanism (e.g. phone, internet);
- Air pollution inspectors with supplemental odour training;
- Administrative procedures for odour complaint review;
- Source odour and chemical sampling;
- Odour testing laboratory (e.g. source samples);
- Chemical testing laboratory;
- Odor modeling capabilities; and
- Procedure for odour prevention and odour control technology review.
Odour Measurement in Odour Regulation
The term "odour" refers to the perception experience when one or more chemicals come in contact with the receptors on the olfactory nerves and "stimulate" the olfactory nerve. The term "odorant" refers to any chemical in the air that is part of the perception of odour by "stimulating" the olfactory nerves. Odour perception may occur when one odorant (chemical) is present or when many odorants are present. While some regulatory agencies have regulations to control specific chemical odorants, the remainder of this paper will focus on perception based odour laws.
The origins of sensory evaluation are in industries such as perfumes, coffee, tea, wine, liquors, meats and fish, with the development of smell or taste testing methods to determine the quality of products. Testing individuals became known as expert judges and were used to rate or grade products.
In the field of environmental engineering, odorous air samples are collected from emission sources. Odorous air samples need to be evaluated under controlled laboratory conditions following standard industry practices using trained panelists known as assessors. Four measurable, objective parameters of perceived odor are:
- Concentration – measured as dilution ratios and reported as detection threshold and recognition thresholds or as dilution-to-threshold (D/T) and sometimes assigned the pseudo-dimension of odour units per cubic meter.
- Intensity – reported as equivalent parts per million butanol, using a referencing scale of discrete butanol concentrations.
- Persistence – reported as the dose-response function, a relationship of odour concentration and odour intensity.
- Character Profiling - what the odour smells like using categorical scales and real exemplars (e.g. fruity à citrus à lemon: from a real lemon).
These odour parameters are objective because they are measured using techniques or referencing scales dealing with facts without distortion by personal feelings or prejudices. Additional measurable, but subjective, parameters of perceived odour are:
- Hedonic Tone - pleasantness vs. unpleasantness.
- Annoyance - interference with comfortable enjoyment of life and property.
- Objectionable - causes a person to avoid or causes physiological effects.
- Strength - word scales like “faint to strong”.
These odour parameters are subjective because individuals rely on their interpretation of word scales and on their personal feelings, beliefs, memories, experiences, and prejudices to report them. Written guidelines for subjective odour parameter scales assist individuals (citizens and air pollution inspectors) in reporting observed odour, however, the nature of these parameters remains subjective.
The ASTM International E-18 Sensory Evaluation Committee in 1957 approved and published a method for measuring environmental odors. This method was originally developed by the Los Angeles Air Pollution Control District (Mills et. al., 1963). ASTM standard D1391-78 “Measurement of Odor in Atmospheres” came to be known as the syringe static dilution method because it used 100-mL glass syringes to dilute the odorous air with odor free air (ASTM, 1978). The practice involved presenting assessors syringes of diluted odorous air samples along with syringes of odour-free air.
ASTM International published E679-79, “Standard Practice for Determination of Odor and Taste Thresholds by a Forced-Choice Ascending Concentration Series Method of Limits” in 1979 (ASTM, 1979). This method was based on the use of dynamic olfactometry to automatically perform the dilutions of the odorous air and then present the dilution mixture to the human assessors. ASTM E18 Committee officially withdrew the “Syringe Method”, D1391, from publication in 1985.
E679, was subsequently revised in late 1991, and again revised in 2004 to include reference to EN13725:2003 (ASTM, 2011). If a laboratory follows the EN13725 test method using a 3-Alternative (triangular) Forced-Choice presentation method, the laboratory will be meeting all requirements of ASTM E679-04. The additional requirements of EN13725 will improve the repeatability, reproducibility, dependability, and accuracy of all odour analyses performed by the laboratory (CEN, 2003).
Presently, international standards are in place, which dictate the scientific methods and practices of odour measurement. These international standard methods for quantifying odour are objective, quantitative, dependable, and reproducible. Specific examples are:
- EN13725:2003: Air Quality – Determination of Odour Concentration by Dynamic Olfactometry
- ASTM E679-04: Standard Practice for Determination of Odor and Taste Threshold by a Forced-Choice Ascending Concentration Series Method of Limits
- ASTM E544-10: Standard Practice for Referencing Suprathreshold Odor intensity (ASTM, 2010)
The U.S. Public Health Service sponsored the development of an instrument and procedure for field olfactometry (ambient odor strength measurement) through Project Grants A-58-541; A-59-541; and A-60-541 in 1958-1960 (Huey, et. al., 1960). The first field olfactometer, called a Scentometer, was manufactured by the Barnebey-Cheney Company, subsequently manufactured by the Barnebey Sutcliffe Corporation, and currently manufactured by Calgon Carbon Corporation. The Scentometer field olfactometer creates a series of dilutions by mixing the odorous ambient air with odour-free (carbon-filtered) air. The U.S. Public Health Service method defined the dilution factor as Dilution to Threshold, D/T. The Dilution-to-Threshold ratio is a measure of the number of dilutions needed to make the odorous ambient air non-detectable.
The National Air Pollution Control Administration of the US Public Health Service commissioned Copley International Corporation in 1970 to conduct a “National Survey of the Odor Problem”. The technical phase of the Copley Study found the Scentometer to be a utilitarian and effective tool for investigation of odour (Copley, 1970). The US Environmental Protection Agency commissioned a second Copley study in 1971, “Social & Economic Impacts of Odors” in the United States. The second Copley study found the Scentometer to be an effective and sensitive device and developed a Scentometer protocol for odour investigations (Copley, 1971). The US-EPA commissioned a third Copley study in 1972 for the “Development and Evaluation of a Model Odor Control Ordinance”. The third Copley Study recommended that odour regulation and enforcement be relegated to states and local jurisdiction using scientific approaches with trained inspectors using the Scentometer as well as source odour sampling (Copley, 1973).
In 2002 St. Croix Sensory, working with a consortium of universities (Duke, Iowa State, Minnesota, and Purdue) and agencies (Missouri Department of Natural Resources and US Department of Agriculture), developed a new version of a field olfactometer, the Nasal Ranger, US Patents 6,595,037 and 6,018,984, which operates on the same principles as the original Barnebey-Cheney Scentometer field olfactometer. Since 2010, several additional field olfactometers have been developed; Donald Wright (Georgetown, TX) US Patent 2011/0030450 A1; Christopher G. Henry (University of Nebraska) US Patent 13/421,048; and Ardevan Bakharti (IDES).
U.S. Odour Regulation
To this day, the US-EPA does not regulate odours directly; however, it does regulate certain chemical constituents that are accepted as having potential to cause an odour. In 1992, the EPA published a compilation of odour thresholds, “Reference Guide to Odor Thresholds for Hazardous Air Pollutants Listed in the Clean Air Act Amendments of 1990” (EPA, 1992).
Some U.S. states do specifically regulate odour. The most common approach is to set criteria based on observations in the field as outlined in the Copley Studies, using field olfactometry, i.e. Scentometer, Nasal Ranger, or other approved device. Ten states regulate odour using Dilution to Threshold (D/T) criteria. These are shown in black on the map in Figure 1.
- Colorado - Regulation No. 2
- Connecticut - Regulation 22a-174-23
- Delaware - Air Regulation Number 1119
- Illinois - Title 35, Subtitle B, Chapter 1, Part 245
- Kentucky - Regulation 401KAR53:010
- Missouri - Title 10, Chapter 6, Section 165
- Nevada - NAC 445B.22087
- North Dakota - Chapter 33-15-16
- West Virginia - Title 45, Series 4
- Wyoming - Chapter 2, Section 11
Other states, shown in grey on the map in Figure 1, have regulations with vague reference to odours and mention the field olfactometry or D/T method:
- North Carolina
Figure 1. States of the U.S. where odour regulations exist based on Dilution-to-Threshold, or D/T, indicated in black. The grey states have regulations with some reference to odour impacts.
An example state odour regulation is from the State of Colorado: “…areas predominantly for residential or commercial purposes, it is a violation if odors are detected after the odorous air has been diluted with seven (7) or more volumes of odor free air (7-D/T)” (Colorado DPHE, 2013). The Colorado regulation also designates a higher limit (15-D/T) for other land use areas, i.e. rural. However, Colorado limits ambient odour to only 2-D/T at the receptor near large swine facilities. Once an agency, such as the city of Denver, receives citizen complaints, enforcement personnel respond to the complaint location(s) and measure the D/T with field olfactometry every ten-minutes for one-hour. A violation exists if the enforcement agent twice measures the odour at 7-D/T or higher, with these measurements separated by at least 15-minutes, i.e. there is an odour above the limit with a measure of duration/frequency.
What about other States? What if a State does not regulate odours directly? What if a State does not give local governments (municipalities, cities, counties, etc.) expressed authority to regulate odours? Then authority to regulate odour is derived from general authority granted to local governments. These general authorities are know as:
- General zoning powers (state zoning legislation), which support local nuisance ordinances, including odour nuisance.
- Police powers (state legislation) grant municipality authority to abate “all nuisance”, including odour nuisance.
In most states, if the state has licensed the “odorous” facility, but does not expressly license the “odour”, then the local odour ordinance must “harmonize” with the state’s authority.
Local governments must also carefully “blend” any new odour ordinance with other nuisance ordinances already in place. This preferred “blending” links a new odour ordinance to existing nuisance ordinances, e.g. noise.
One example of a US municipal odour ordinance is from the City of Independence, Louisiana. Five stipulations of the Independence odour ordinance are:
- Unlawful to cause emissions of an odour nuisance or odorous air contaminant.
- Odour that is unreasonably unpleasant, distasteful, disturbing, nauseating, or harmful to a person of ordinary sensibilities and which is detectable after it is diluted with seven volumes of odour-free air by a field olfactometer, 7-D/T.
- City may issue a citation for violation.
- Any person may file a complaint and the City will investigate the complaint.
- $500 penalty on conviction; penalty does not preclude further actions to abate violations.
A second example of a US municipal odour ordinance is from the City of Des Moines, Iowa. Des Moines code enforcement officers respond to citizen complaints as part of their normal code enforcement duties, i.e. restaurant inspections. The City declares an “Odour Alert” when they receive ten complaints in a 24-hour time period. An inspector responds, measures the ambient odour, identifies the probable source, and serves a notice of violation. A facility that receives three notices of violations in a 90-day period is designated by the City as a “significant odour generator” and is required to submit an “odour management plan” that may include air stack testing and air dispersion modeling. The designated “significant odour source” may appeal to a citizen “Odour Board”, then the City Council, and then Municipal Court. The city of Des Moines’ citizen Odor Board is a unique, novel, and effective approach to addressing local odour nuisance.
Canada Odour Regulation
Canada, like the United States, does not regulate odours through the federal government, but leaves the responsibility with the provinces and territories. Various provinces have their own odour regulation or policy, typically aimed at agricultural sources.
Odours are controlled indirectly through several methods, such as facility setback distances, farming regulations, and concentration limits for specific odorants, e.g. H2S. Further, Right to Farm legislation partially shelters farms from odour nuisance complaints.
Some provinces also regulate odours directly through various approaches including general permitting, source limits, and ambient odour limits. Ontario has one of the most detailed odour control guidelines. A Certificate of Approval (permit) requires a facility to provide source testing and odour dispersion modeling to document odour levels at receptors. Ontario’s guideline approach has been to limit odors to 1-O.U. at a receptor, which is essentially no perceptible odour. Permits in other provinces, e.g. Alberta, Quebec, can have source odour level limits specifically written into the document.
Ambient odour measurement, the most prevalent strategy in the U.S., also has been used by Provinces (e.g. Manitoba; Alberta; and Saskatchewan) and regional authorities in other areas (e.g. Region of Peel in Ontario) for regulatory screening and surveys to identify and quantify significant odour sources.
Within the United States, odour regulation is considered by the federal government to be a local issue with authority relegated to individual states. Most states with odour regulations utilize measurement of ambient odours. Most recent activity in the U.S. has been at the lowest levels of government, with counties and cities attempting to address local odour issues caused by various industries. These local governments must blend a new odour ordinance with their other nuisance ordinances and also harmonize with state regulatory authority.
Canada similarly has odour regulation at the Provincial level of government; however, the methodology used varies more widely than in the U.S. While, many provinces have minimal enforcement through odour perception measurement protocols, several utilize odour measurement in the permitting process or utilize ambient odour measurement for regulatory screening and surveys.
ASTM International. 1978. D1391-78: Standard Method for Measurement of Odor in Atmospheres (Dilution Method). Philadelphia, PA. USA.
ASTM International. 1979. E679-79: Standard Practice for Determination of Odor and Taste Threshold by a Forced-Choice Ascending Concentration Series Method of Limits. Philadelphia, PA. USA. (Obsolete-Out of Print)
ASTM International. 2010. E544-10: Standard Practice for Referencing Suprathreshold Odor Intensity. Philadelphia, PA. USA.
ASTM International. 2011. E679-04(11): Standard Practice for Determination of Odor and Taste Threshold by a Forced-Choice Ascending Concentration Series Method of Limits. Philadelphia, PA. USA.
Colorado Department of Public Health and Environment. 2013. 5 CCR1 001-4: Regulation Number 2 Odor Emission. Colorado Air Quality Control Commission. Available on-line at: http://www.colorado.gov/cs/Satellite?c=Document_C&childpagename=CDPHE-Main%2FDocument_C%2FCBONAddLinkView&cid=1251599389740&pagename=CBONWrapper
Committee for European Normalization (CEN). 2003. EN13725: Air Quality – Determination of Odour Concentration by Dynamic Olfactometry. Brussels, Belgium.
Copley International Corporation. 1970. National Survey of the Odor Problem – Study of Social and Economic Impact of Odors - Phase I. PB-194-376. U.S. Environmental Protection Agency. Distributed by National Technical Information Services – U.S. Department of Commerce.
Copley International Corporation. 1971. National Survey of the Odor Problem – Study of Social and Economic Impact of Odors - Phase II. PB-205-936. U.S. Environmental Protection Agency. Distributed by National Technical Information Services – U.S. Department of Commerce.
Copley International Corporation. 1973. National Survey of the Odor Problem – Study of Social and Economic Impact of Odors - Phase III: Development and Evaluation of a Model Odor Control Ordinance. PB-223-589. U.S. Environmental Protection Agency. Distributed by National Technical Information Services – U.S. Department of Commerce.
EPA. 1992. Reference Guide to Odor Thresholds for Hazardous Air Pollutants Listed in the Clean Air Act Amendments of 1990. Air Risk Information Center, U.S. Environmental Protection Agency. EPA600/R-92/047. Research Triangle Park, NC.
Huey, N.A., Broering, L.C., Jutze, G.A., and Gruber, C.W. 1960. Objective Odor Pollution Control Investigations. J. Air Pollution Control Assoc. 10(6), 441-444.
McGinley, C.M., Mahin, T.D., and Pope, R.J. 2000. Elements of Successful Odor Laws. Presented at the Water Environment Federation 2000 Specialty Conference on Odors and VOCs. WEF. Cincinnati, OH. 16-19 April 2000.
Mills, J.L., Walsh. R.T., Luedtke, K.D., and Smith, L.K. 1963. Quantitative Odor Measurement. J. Air Pollution Control Assoc. 13(10).
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