of Field Olfactometry
St. Croix Sensory
The Nasal Ranger® Field Olfactometer is
the “state-of-the-art” in field
olfactometry for confidently measuring and quantifying
odor strength in the ambient air. The Nasal Ranger®
Field Olfactometer, a portable odor detecting and measuring
device, determines ambient odor “Dilution-to-Threshold”
(D/T) values objectively.
Field olfactometry can be used as a proactive
monitoring or enforcement tool for confident
odor measurement at property lines and in the neighboring
community. Quantifying ambient odor is often needed
for the following purposes:
- Monitoring daily operations (i.e. management performance
- Comparison of operating practices (i.e. evaluating
- Documenting specific events or episodes (i.e. defensible,
- Monitoring compliance (i.e. compliance assurance
- Determination of compliance (i.e. permit renewal),
- Determination of status (i.e. baseline data for
- Investigation of odor control effectiveness (i.e.
- Verification of odor dispersion modeling (i.e. model
- Determination of specific odor sources (i.e. investigation
- Verification of complaints (i.e. notice of violation).
The Nasal Ranger® Field Olfactometer, as a nasal
organoleptic instrument, provides field olfactometry
with a scientific method for dependable ambient odor
In 1958 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. The
Barnebey-Cheney Company originally manufactured a field
olfactometer instrument based on these grants, known
as a “scentometer”.
A Nasal Ranger® Field Olfactometer
creates a calibrated series of discrete dilutions by
mixing the odorous ambient air with odor-free (carbon)
filtered air. Field olfactometry defines each discrete
dilution level as a “Dilution-to-Threshold,”
D/T, ratio. The “Dilution-to-Threshold”
ratio is a measure of the number of dilutions needed
to make the odorous ambient air “non-detectable”.
Field olfactometry calculates
the “Dilution-to-Threshold” (D/T) ratio
Volume of Carbon-Filtered
D/T = ---------------------------------------
of Odorous Air
St. Croix Sensory
with the Nasal Ranger® Field Olfactometer is a cost
effective means to quantify odor strength in terms of
“Dilution-to-Threshold” (D/T) ratios.
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.
“protocols” are presented in brief
form as an application guide:
- On-Site Monitoring – Operators
have the unique ability to monitor odors 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 Nasal Ranger® Field Olfactometer
on-site may include odor observations at predetermined
locations, i.e. open doorways, driveways, storage
areas, and fence lines.
- Random Monitoring – A frequently
used method for ambient odor monitoring is 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 Nasal Ranger® Field Olfactometer
is a cost effective protocol.
- Scheduled Monitoring – Well-planned
scheduled monitoring can be limited to a daily “walk-about”
or “drive around”, or structured with
several visits to predetermined monitoring locations.
Data from a Nasal Ranger® Field Olfactometer can
be used to correlate the many parameters that influence
odor episodes, including meteorological conditions
and on-site operating activities.
- Intensive Odor Survey – An
in-depth evaluation of on-site odor generation and
off-site odor impact may be needed for permit renewal
or facility expansion. Extensive data collection with
the Nasal Ranger® 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 Nasal Ranger® Field Olfactometer.
- Citizen Monitoring – The
implementation of citizen odor monitoring with Nasal Ranger® Field 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 Nasal Ranger® 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 Nasal Ranger® Field Olfactometer will also
help in understanding the odor strength at which an
odor first becomes a nuisance.
- Complaint Response – The
use of “Odor Compliant Hot Lines” is a
common 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 Nasal Ranger® Field Olfactometer.
- Plume Profiling – Standard
and specialized air dispersion modeling predicts the
transport and dilution of odors by the wind. A protocol,
known as plume profiling, supplements and “calibrates”
air dispersion modeling. Several inspectors with Nasal Ranger® 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 the
Nasal Ranger® Field Olfactometer.
St. Croix Sensory
A field olfactometer device (“scentometer”)
is referenced in a
number of existing state odor regulations.
The “Dilution to Threshold”
(D/T) terminology and the method of
calculating the D/T are also referenced.
|The criteria of an odor regulation
often defines compliance as
that is less than 7 D/T” (7 used
for exemplary purpose only).
|The exact wording in a regulation
is important and may be stated in two ways:
||Compliance criteria: “…compliance
if…less than 7 D/T.”
criteria: “nuisance if…equal
to or greater than 7 D/T.”
|In these two examples, if
an air pollution inspector observed “odor”
with the field olfactometer set at a 7 D/T
||The “odor” would meet the
criteria for nuisance or
The ambient air would be “non-compliant”.
|Odor regulations that utilize field
olfactometry and a calibrated field olfactometer,
e.g. Nasal Ranger Field Olfactometer, also define
the number of observations needed and the time frame
of the observations.
For example, a regulation may read:
||“…Two field olfactometer observations
in a one-hour period separated by 15 minutes each…”
“…Two field olfactometer observations
not less than 15 minutes apart within a 1-hour period…”
|The “protocols” in this
Application Guide for Field Olfactometry are presented
in brief example form and are not mutually
exclusive, often being integrated into a comprehensive
odor management program. Likewise, the “odor
regulation” criteria for compliance and nuisance
are presented as examples only and are taken from
actual odor regulations.