Authored by:

Presented at

St. Croix Sensory Inc. / McGinley Associates, P.A.

3549 Lake Elmo Ave. N., P.O. Box 313

Lake Elmo, MN 55042 U.S.A.

+651-439-0177, 800-879-9231

stcroix@fivesenses.com

Copyright © 2002

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©2002 St. Croix Sensory, Inc.

St.Croix Sensory, Inc., 3549 Lake Elmo Ave. N., PO Box 313 Lake Elmo, MN 55042

Tel: 651-439-0177 ext. 18, E-mail: cmcginley@fivesenses.com

Ambient air holds a mixture of odorous chemicals from everyday activities of industrial

and commercial enterprises. From state to state and in communities across the United

States odor issues are addressed by a variety of odor ordinances, regulations and policies.

When air quality is compromised with odors, effective study, investigation, and

enforcement requires that odors be measured using standardized methods that are

dependable, reproducible, objective, and quantitative.

Point, area and volume emission sources can be sampled and tested for odor parameters

using standard practices published by the American Society of Testing and Materials

(ASTM E679 and E544) and by the European Union (European Normalization Standard,

EN 13725). The most common odor parameter determined during odor testing is “odor

concentration” (odor strength). This determination is made using an instrument called an

“olfactometer.” In the United States the standard followed for olfactometry is ASTM

Standard of Practice E679-91, “Determination of Odor and Taste Threshold by a Forced-

Choice Ascending Concentration Series Method of Limits.” In 2002 this ASTM standard

is under review to incorporate latest recommendations from the AWMA EE-6 “Odor

Committee” and elements from prEN 13725 – “Air Quality – Determination of Odour

Concentration by Dynamic Olfactometry”. The 18 countries in the European Union are

bound by the CEN/CENELEC International Regulations to implement this European

Standard. The new European standard has been adopted in Australia, New Zealand, and

much of the Pacific Rim. Therefore, “EN 13725” will become the de facto International

Standard for odor/odour testing.

Odor can also be measured and quantified directly in the ambient air using one of two

standard practices. ASTM E544-99, “Standard Practice for Referencing Suprathreshold

Odor Intensity”, is used to measure and quantify ambient odor intensity using an “Odor

Intensity Referencing Scale (OIRS). An air pollution inspector, plant operator, or

community odor monitor can observe the ambient odor and compare it to the OIRS (a

series of concentrations of a reference odorant, i.e. n-butanol).

A second standard method for measuring and quantifying odor in the ambient air utilizes

a field olfactometer. The standardized method (U.S. Public Health Service Project Grant

A-58-541) uses a portable odor detecting and measuring device known as a field

olfactometer (e.g. scentometer). The field olfactometer dynamically dilutes the ambient

air with carbon-filtered air in distinct dilution ratios known as “Dilution to Threshold”

dilution factors (D/T’s), i.e. 2, 4, 7, 15, etc.

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Community odors remain at the top of air pollution complaints to regulators and

government bodies around the U.S. and internationally. Ambient air holds a mixture of

odorous chemicals from everyday activities of industrial and commercial enterprises.

From state to state and in communities across the United States odor issues are addressed

by a variety of odor ordinances, regulations and policies. When odors compromise air

quality effective investigation and enforcement requires that odors be measured using

standardized methods that are dependable, reproducible, objective, and quantitative.

The quantification of odors is typically required for the following purposes:

1. Monitoring for compliance assurance.

2. Determination of compliance for permit renewal.

3. Determination of baseline status for expansion planning.

4. Determination of specific odor sources during complaint investigation.

5. Monitoring operations for management performance evaluation.

6. Comparison of operating practices when evaluating alternatives.

7. Monitoring specific events or episodes for defensible, credible evidence.

8. Comparison of odor mitigation measures during tests and trials.

9. Determination of an odor control system’s performance for warranty testing.

10. Verification of estimated odor impacts from dispersion modeling.

Odor is measurable using objective, quantitative, standardized scientific methods in odortesting

laboratories. Point, area and volume emission sources can be sampled and tested

for odor parameters such as odor concentration, intensity, persistence, and descriptors.

Odor can also be measured and quantified directly in the ambient air using one of two

standard practices by trained inspectors. The first method uses a standard “odor intensity

referencing scale” (OIRS) made up of the standard odorant, n-butanol, to quantify odor

intensity. The second method utilizes a field olfactometer, which dynamically dilutes the

ambient air with carbon-filtered air in distinct dilution ratios known as “Dilution-to-

Threshold” dilution factors (D/T’s).

An odorous air sample can be collected from a point emission source and from surface

and volume emission sources. “Whole-air” samples for laboratory odor testing are

typically collected in 10-liter Tedlar gas sample bags for transport to the odor-testing

laboratory.

In the early years of odor testing a syringe dilution technique measured odors in the

“Standard Test Method for Measurement of Odor in Atmospheres (dilution method)”.

The syringe dilution technique used a series of dilutions known as "dilution ratios". In

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Thresholds by a Forced-Choice Ascending Concentration Series Method of Limits” was

1991, and published in October 1991, as ASTM E679-91. This standard defines a

method of dynamically diluting the odor sample with an instrument called an

olfactometer.

When practicing ASTM E679-91 during an odor test, the odor panelist (assessor) sniffs a

dilute sample of the odor as it is discharged from the olfactometer as one of three sample

presentations (one presentation with the dilute odor and two with odor free air). The

assessor sniffs all three of the presentations and must select the one of the three that is

different from the other two, even if they must guess. This statistical approach is called

“triangular forced-choice.” The assessor declares to the test administrator if the selection

is a “guess”, a “detection” (the selection is different from the other two), or a

“recognition” (the selection smells like something) as defined by ASTM E679-91.

The assessor is then presented with the next set of three presentation choices, one of

which contains the diluted odor sample. However, this next set of three samples presents

the odor at a higher concentration (e.g. two times higher). The assessor continues to

additional levels of higher concentration (lower dilution) presentations following the

“triangular forced-choice” procedure and the required designation of “guess”, “detect”, or

“recognition”. This statistical approach of increasing levels of sample presentation is

called “ascending concentration series.”

In the 1980’s countries in Europe began developing standards of olfactometry. Some of

these standards developed and published include:

France AFNOR X-43-101, Method of the Measurement of the Odor of a Gaseous

Effluent, Bureau de Normalisation, Paris, France (drafted in 1981 & revised in 1986)

Germany VDI 3881, Parts 1-4, Richtlinien, Olfactometry, Odour Threshold

Determination, Fundamentals. Verein Deutsche Ingenieure Verlag, Dusseldorf, Germany

(drafted in 1980 & revised in 1989)

Netherlands NVN 2820, Provisional Standard: Air Quality. Sensory Odour

Measurement using an Olfactometer. Netherlands Normalization Institute, The

Netherlands (drafted in 1987 & issued in 1995)

Various inter-laboratory studies as well as collaborative projects involving multiple odor

testing laboratories in the 80’s showed that laboratory results still differed significantly

The development of a draft odor-testing standard in the Netherlands led to an Inter-

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used as standard odorants for the study. Through 1990 to 1992 the results of this Dutch

Inter-Laboratory study led to the development of strict assessor performance criteria.

During the first year, the inter-laboratory repeatability was in the range of factors from

3 to 20. An analysis of the data from this first year showed the majority of variability

was between assessors. Individual assessors were repeatable within a factor 3 to 5. The

researchers found that the only way to meet agreed upon repeatability criteria was to

control the instrument sensor, the human assessors, by selecting assessors who were all

similar in sensitivity.

Standards were set for assessor performance to the standard odorant n-butanol. Only

assessors who met predetermined repeatability and accuracy criteria were allowed to

continue as assessors. Over the next two years, these new criteria were implemented

within each of the labs involved in the study.

The work of this inter-laboratory study led to the final Dutch standard released in 1995

and set the foundation for the development of the new European odor testing standard.

A working group was formed within the Committee European de Normalisation (CEN)

Technical Committee 264 – “Air Quality” to develop a unified olfactometry standard.

This working group saw a need to help industry and regulators develop a consistent basis

for monitoring and testing odors, and, thus help determine the potential for odor nuisance.

This was to be accomplished by developing a method that:

1. Improved consistency within each laboratory (repeatability);

2. Achieved comparable results among laboratories (reproducibility); and

3. Connect the results to a traceable reference material, e.g. n-butanol (accuracy)

In order to achieve these goals, the committee focused on the following issues: sampling

procedures, sample containers, olfactometer construction and operation, the olfactometer

and assessor interface, the odor testing room, methods of data processing, and assessor

selection, training, and performance

The first complete draft of the European olfactometry standard was released in 1995.

Then in the spring and summer of 1996, nineteen laboratories from five countries

participated in an Inter-laboratory Comparison of Olfactometry (IOC) study. The

purpose of this study was to validate the requirements, methods, and procedures outlined

1. All quality requirements and performance criteria were attainable for all testing

methods studied (Forced-Choice and Yes/No); and

2. Those following the standard for the longest period of time performed the best with

regards to accuracy and repeatability.

The CEN olfactometry standard was released to the public at the end of 1999 through the

standard organizations of each participating country. The standard was released as

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Proposed CEN standard #13725 (prEN 13725) “Air Quality – Determination of odour

January 2000. Comments were submitted to each country’s standardization body

separately. These comments were reviewed in early 2000. The working group met in

2000 to review all comments and issue a final revision of the standard. The final revision

was sent to the CEN organization in 2001 for official acknowledgement and approval.

The final CEN standard approval will obligate all countries of the European Union to

adopt the standard and withdraw any conflicting or redundant national standards. These

countries include: Austria, Belgium, Denmark, Finland, France, Greece, Germany,

Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,

Switzerland, and the United Kingdom.

The final standard will be published in three official languages: English, French, and

German. The standards are distributed through the individual country standardization

boards. For example, an English language copy can be obtained from the British

Standards Institute (BSI).

The new European standard has been adopted in Australia, New Zealand, and much of

the Pacific Rim. Therefore, “EN 13725” will become the de facto International Standard

for odor/odour testing.

The proliferation of large scale animal confinement facilities (i.e. feedlots) throughout the

United States, as well as the general trend of urban sprawl moving people closer to

odorous industrial facilities, wastewater treatment facilities, and agricultural facilities has

created a resurgence in funding for odor related research. In 1995, universities and

research institutions in the United States and Canada began to develop and expand odor

testing laboratories for conducting odor research in agricultural facilities, municipal solid

waste facilities, and other odorous industries. Odor research laboratories founded or

expanded in the past five years include:

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In 1995 the AWMA EE-6 Odor Committee formed a subcommittee on the

“Standardization of Odor Measurement”. The EE-6 Subcommittee developed

and submitted them for review on August 23, 2002, to the ASTM International E18

Sensory Committee.

In October, 2002, the EE-18 Sensory Committee of ASTM International initiated a

comprehensive review of ASTM E679-91 and elements of the AWMA guidelines and

the EN13725 Standard.

EN13725 standardizes the following elements of odor testing (olfactometry) and exceeds

the existing ASTM standard:

1. Ascending concentration series sample presentation (same as ASTM E679-91)

2. Binary or triangular forced-choice selection (ASTM requires triangular)

3. Dilution ratio of “2” for the presentation series (ASTM allows 3)

4. “Odor free” dilution and blank air (same as ASTM)

5. Olfactometer materials of Teflon, stainless steel, or glass (same as ASTM)

6. Presentation flow rate of 20-liters per minute (ASTM does not specify)

7. ISO 5725 Accuracy of Measurement and Results (exceeds ASTM)

8. Requires periodic olfactometer calibration (exceeds ASTM)

9. Requires assessor certification (exceeds ASTM)

10. Uses the traceable reference odorant n-butanol (exceeds ASTM)

The objective of the ASTM review is to achieve repeatability, reproducibility, and

accuracy in odor testing that was achieve by EN13725:

Odor can also be measured and quantified directly in the ambient air using one of two

standard practices by trained inspectors. The first method uses a standard “odor intensity

referencing scale” (OIRS) made up of the standard odorant, n-butanol, to quantify odor

intensity. The second method utilizes a field olfactometer, which dynamically dilutes the

ambient air with carbon-filtered air in distinct dilution ratios known as “Dilution-to-

Threshold” dilution factors (D/T’s).

Odor intensity of the ambient air can be measured objectively using an "Odor Intensity

Referencing Scale" (OIRS) [ASTM E54475, 88, “Standard Practice for Suprathreshold

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air to the odor intensity of a series of concentrations of a reference odorant. A common

reference odorant is n-butanol. Sec-butanol is an alternative to n-butanol for a standard

referencing odorant. The air pollution inspector, plant operator, or community odor

monitor observes the odor in the ambient air and compares it to the OIRS. The person

making the observation must use a carbon-filtering mask to "refresh" the olfactory sense

observer's olfactory sense would become adapted to the surrounding ambient air or

become fatigued from any odor in the surrounding air. The adaptation of an observer's

olfactory sense is a common phenomenon when attempting to evaluate ambient odors,

i.e. a wastewater treatment plant operator monitoring treatment plant odors "off-site".

ASTM E544-75, 88, "Standard Practice for Referencing Suprathreshold Odor Intensity",

presents two methods for referencing the intensity of ambient odors: Procedure A -

Dynamic-Scale Method and Procedure B - Static-Scale Method. Field inspectors

commonly use the Static-Scale Method and it has become incorporated as a standard of

practice by a number of odor laboratories, because of its low cost of set-up compared to a

dynamic-scale olfactometer device (Procedure A).

Using the OIRS, the intensity of the observed ambient air is expressed in "parts per

million" (PPM) of n-butanol (or sec-butanol). A larger value of butanol means a stronger

odor. An important aspect of using a butanol intensity referencing scale is knowing that a

variety of scales are available. Common butanol static-scales include:

The OIRS serves as a standard practice to quantify the odor intensity of the ambient air

objectively. To allow comparison of results from different data sources and to maintain a

reproducible method, the equivalent butanol concentration is reported or the number on

the OIRS is reported with the scale range and starting point.

An example 5-point OIRS with a geometric progression of three is:

Reference Level n-Butanol PPM in Air

0 0

1 25

2 75

3 225

4 675

5 2025

Field air pollution inspectors (field odor inspectors), using a standard odor intensity

referencing scale (OIRS), can provide measured, dependable, and repeatable observations

of ambient odor intensity.

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In 1958, 1959, and 1960 the U.S. Public Health Service sponsored the development of an

instrument and procedure for field (ambient) odor measurement (olfactometry) through

manufactured by Barnebey-Cheney Company and subsequently manufactured by

Barnebey Sutcliffe Corporation.

The U.S. Public Health Service method defined the dilution factor as "Dilution to

Threshold", D/T. The method of producing "Dilution to Threshold" (D/T) with the field

olfactometer consists of mixing two "volumes" of carbon-filtered air with specific

"volumes" of odorous ambient air. The method of calculating "Dilution to Threshold"

(D/T) for the field olfactometer is:

D/T = Volume of Carbon Filtered Air / Volume of Odorous Air

The field olfactometer instrument, the “Dilution to Threshold” (D/T) terminology, and

the method of calculating the “D/T” are referenced in a number of existing agencies’ odor

regulations and permits. Therefore, a field olfactometer instrument, in the hands of

trained air pollution investigators or monitors, is a realistic and proven method for

quantifying ambient odors.

Common “Dilution-to-Threshold” (D/T) ratios used to set ambient odor guidelines are:

D/T’s of 2, 4, and 7. Field olfactometers typically have additional D/T’s (dilution ratios)

such as 15, 30, 60 and higher dilution ratios.

Field olfactometry with a calibrated field olfactometer is a cost effective means to

quantify odor strength. Facility operators, community inspectors, and neighborhood

citizens can confidently monitor odor strength at specific locations around a facility’s

property line and within the community when using a calibrated field olfactometer.

The following “protocols” are presented in brief exemplary form as an application guide

for field olfactometry:

throughout the day with field olfactometry. Operator monitoring can include odor

observations of arriving materials, outdoor process activities, and fugitive air

emissions. Monitoring with a field olfactometer on-site may include odor

observations at predetermined locations, i.e. open doorways, driveways, storage

areas, and fence lines.

the “random inspection” approach. Random monitoring leads to a compilation of

data that can be correlated with meteorological information and on-site activities.

Managers and regulators alike find that random odor monitoring with a field

olfactometer is a cost effective protocol.

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daily “walk-about” or “drive around”, or structured with several visits to

predetermined monitoring locations. Data from a field olfactometer can be used

to correlate the many parameters that influence odor episodes, including

meteorological conditions and on-site operating activities.

off-site odor impact may be needed for permit renewal or facility expansion.

Extensive data collection with a field olfactometer will identify which sources or

operations cause odor and which ones do not cause odor off-site. All potential

odor sources and operations could be ranked and their relative contributions

determined. Short-term trials or tests of odor mitigation measures, e.g. odor

counteractants, would also require an intensive period of data collection using a

field olfactometer.

olfactometers can be part of an interactive community outreach program. The

primary function of citizen odor monitoring is to collect information, through

accurate record keeping, which represents real conditions in the community.

Citizens recruited and trained to measure odors using field olfactometers would

also report odor descriptors. Citizen odor monitoring will assist in determining

prevalent times and prevalent weather conditions of odor episodes. Citizen odor

monitoring with field olfactometers will also help in understanding the odor

strength at which an odor first becomes a nuisance.

method used by facilities and communities to respond to odor episodes. A

complaint response plan, with designated “on-call” responders, creates

opportunities for verifying odor episodes, tracking odor sources, and quantifying

odor strength with a field olfactometer.

transport and dilution of odors by the wind. A protocol, known as plume

profiling, supplements and “calibrates” air dispersion modeling. Several

inspectors with field olfactometers, spaced cross wind and down wind from an

odor source, would measure and record the odor strength as “D/T” values. The

odor plume profile would then be documented and overlaid on the local terrain

map. Therefore, the air dispersion modeling and the local topography would be

integrated with actual odor measurements from a field olfactometer.

These “protocols” are presented in brief exemplary form as guide and are not mutually

exclusive, often being combines into a comprehensive odor management program.

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Odor is measurable using objective, quantitative, standardized scientific methods in odortesting

laboratories and out in the ambient air by trained inspectors. Point, area and

volume emission sources can be sampled and tested for odor parameters such as odor

concentration, intensity, persistence, and descriptors. Odor can also be measured and

quantified directly in the ambient air using one of two standard practices by trained

inspectors. The first method uses a standard “odor intensity referencing scale” (OIRS)

made up of the standard odorant, n-butanol, to quantify odor intensity. The second

method utilizes a calibrated field olfactometer, which dynamically dilutes the ambient air

with carbon-filtered air in distinct dilution ratios known as “Dilution-to-Threshold”

dilution factors (D/T’s).

The stakeholders for standardized odor measurement are:

With the knowledge of fundamental odor testing an objective approach can be taken to

addressing community nuisance odors and problematic odorous emissions. The

subjectivity of nuisance odors can be replaced with objective, scientific methods of odor

measurement with laboratory olfactometry and field olfactometry.

The author thanks Michael A. McGinley, P.E. for his guidance and recommendations.

1. ASTM D1391: Standard Test Method for Measurement of Odor in Atmospheres

(dilution method), American Society for Testing and Materials, Philadelphia, PA,

1978.

Thresholds By a Forced-Choice Ascending Concentration Series Method of

Limits, American Society for Testing and Materials, Philadelphia, PA, 1991.

3. Heeres, P. & H. Harssema. “Progress of the Standardization of Olfactometers in

the Netherlans.” Staub Reinh. Der Luft, 1990, vol. 50, pp 185-187.

4. Hermans, L. “Ringonderzoek Olfactometers.” Publikatiereeks Lucht No. 80,

1989. Ministry of the Environment, Leidschendam, the Netherlands.

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5. Van Harreveld, A.Ph., Heeres, P., Harssema, H. “A Review of 20 Years of

Standardization of Odor Concentration Measurement by Dynamic Olfactometry

in Europe.” Journal of the Air and Waste Management Association, June 1999.

Vol. 49, No. 6: pp. 705-715.

Olfactometry, Technical Committee CEN/TC 264, European Committee for

Standardization, September, 1999.

"Guidelines for Odor Sampling and Measurement by Dynamic Dilution

Olfactometry DRAFT", Air & Waste Management Association EE-6 Odor

Committee, August 23, 2002.

8. ASTM E544-75,88: Standard Practice for Suprathreshold Intensity Measurement,

American Society for Testing and Materials, Philadelphia, PA, 1989.

9. McGinley, Charles M., etal, "ODOR SCHOOL Curriculum Development for

Training Odor Investigators”, AWMA Odors: Indoor and Environmental Air,

International Specialty Conference, Bloomington, MN, September, 1995.

10. Huey, Norman A., “Objective Odor Pollution Control Investigations”, JAPCA,

Volume 10, No. 6, December 1960.

dilution-to-threshold

dilution ratio

odor concentration

odor intensity

odor

olfactometer

olfactometry