2. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
2 | P a g e
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Contents
1. Introduction ............................................................................................................................................. 3
2. A Hybrid Approach ................................................................................................................................... 4
3. Implementation........................................................................................................................................ 5
3.1 Phase 1 Description of the Field Odour Patrol ..................................................................................... 5
3.2 Selecting Points for Monitoring (Inside and Outside of Plant Boundary): .......................................... 6
3.3 Data gathered at each survey location ............................................................................................... 7
3.4 Selecting and Training the Odour Patrollers ....................................................................................... 8
3.5 Equipment used for Odour Patrol ....................................................................................................... 9
3.5 When each location should be surveyed: ........................................................................................... 9
3.6 Phase 2: Source sampling and olfactometric analysis ....................................................................... 10
3.7 Reverse Modeling .............................................................................................................................. 11
3.8 Predictive Modeling .......................................................................................................................... 12
4. Analyzing the Results and the Deliverables ........................................................................................... 13

3. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
3 | P a g e
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1. Introduction
This article will describe an approach to address odours at a gas/petroleum/oil refinery plant from a
practical perspective. Using traditional methods of source sampling and modeling for refineries has been
shown to be ineffective due to the vast number of sources within the plant. While stacks and lagoons can
be easily identified and the odour emission quantified, fugitive sources such as leaks, holding tank
openings, overpressure relief valves, flaring, and residual liquids can all significantly contribute to the total
odour emission from the plant. The odours from these processes will travel differently and will often have
adverse impact on residence up to hundreds of kilometers away.
This article will describe a new and innovative approach to odour emission assessment of petrochemical
refineries. This approach takes into account all sources both from stacks as well as from all fugitive sources.
The objective is to determine not only the impact of the plant but also to identify the most significant
sources to be targeted for remediation. The result of the study can also be used to implement electronic
continuous odour monitoring and complaint management system.

4. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
4 | P a g e
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2. A Hybrid Approach
Odour assessment of a refinery plant must utilize 3 main phases and technologies:
1. Field Odour Patrol using personal olfactometery and portable gas analyzers.
2. Source sampling and olfactometric laboratory analysis
3. Dispersion modeling
The addition of Odour Patrol using personal olfactometery is a critical step and differentiates this
methodology from all previous attempts using classical odour assessment. The classical approach of
source sampling, olfactometric analysis, and dispersion modeling was developed decades ago for dealing
with waste water treatment plants. This approach is not suited to a refinery without the use of an odour
patrol as way to tie real field measurements with predicted impact.
Field Odour Patrol is used for:
1. Source identification: determining the sources that need to be sampled and measured using
olfactometric laboratories
2. Baseline Study: assess the plants emission at the boundary and at the sensitive receptors (neighboring
residents)
3. Contribution Study: assess the impact of other nearby refineries or odour causing industries
4. Quality Assurance: assess the accuracy of predicted impact from dispersion model and source sampling
by comparing the results to real measured field data.
5. Determine the effect of certain process events (e.g. flaring) on odour impact of the plant.
Source sampling, olfactometric laboratory analysis and dispersion modeling are not used in this method
to assess the impact but rather to determine the contribution of each odour source to the total odour
impact of the plant. The ranking of odour sources are first based on contribution followed by ease/cost of
mitigation technology allowing the company to maximize their odour impact reduction with minimal
investment. Source testing also allows the plant to determine the mitigation efficiency of any solution that
is implemented.

5. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
5 | P a g e
S
3. Implementation
3.1 Phase 1 Description of the Field Odour Patrol
The first step in conducting a thorough odour survey is to select the locations that will be patrolled by the
field odour survey technicians. To conduct a full and comprehensive survey the odour patrol must cover
both inside and outside of the plant boundary.
Within the plan the ambient odour monitoring is done by measuring upwind and downwind of significant
sources in order to determine if the source is contributing to the total odour emissions. While individual
sources cannot be separated and easily identified in all cases, this method works well when sources are
considered in groups. For example in a natural gas refinery, each LNG train (liquefaction and purification
facility) can be considered as one group initially. Off‐spec ponds, holding tanks, and other visible sources
can be considered separate sources.
Within the plant boundary along the perimeter, a comprehensive odour survey using field patrollers can
determine odour levels at the property line caused from plant processes and distinguish it from those
entering from neighboring plants/sources. This distinction between what is produced by the plant
versus what odours enter the plant can have significant regulatory implications as well as considerable
impact on the investment required by the plant in mitigation technology. It is useful to not think of the
odour issues as the result of operation of any one plant, but rather the contribution of all odour causing
processes in a region. Odours often mix from various plants to produce a new, unique, and perhaps much
more foul odour. Unfortunately the mixture of odours with a refinery tends to have characteristics with
strong resemblance to the original odours emitted by the refinery; however the odour concentration can
be much higher because of the mixture of odours from neighboring processes. Therefore, while the
refinery is blamed and identified as the sole cause of the odour emissions, they are often one of the many

6. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
6 | P a g e
S
contributors to the issue. Proper boundary patrol can help the plant identify how much of the total odour
impact they are responsible for.
In addition to odour survey conducted within the plant boundary, additional measurement points must
be considered in the surrounding area around plant especially where sensitive receptors are located.
This survey allows the team to identify locations of possible complaints such as a residential community
impacted by the odour emissions. Field odour survey outside the plant can also provide valuable data for
validating dispersion models created in the source sampling and laboratory olfactometery phase.
3.2 Selecting Points for Monitoring (Inside and Outside of Plant Boundary):
The points selected for odour survey within the plant boundary will be based on plant layout, interviewing
field process engineers, and interviewing environmental officers. Outside of the plant boundary, the team
must rely on meteorological data, recorded complaint locations, and location of the sensitive receptors to
determine effective and practical survey points.
An initial assessment of the plant is the first and most critical step. This is where a sampling plan is
determined. The key to a successful odour monitoring program is to select areas where odour is
potentially or usually present. The engineer conducting survey may have a plant map, wind roses and
discussions with senior management and operators during an initial site visit for an assessment. A
valuable source of information during this initial assessment is to speak to field operators, who have
excellent knowledge into where odours may be present. Speaking to as many of these people will help
develop an effective plan from the beginning. Odour technicians in the initial days of measurement
should also engage field operators and covey any important information to the senior engineer to update
the sampling plan.
The selection of a point during the site visit and after reviewing the plant map may result in what appears
like a good point, yet may prove not as worthy. For example, selecting an elevated point on top of a tank
at a downwind distance of 300m of several process may appear a good option, but may actually yield
very few odour readings. Selecting these ambient monitoring points may require some ‘hunt and try.’
Since wind is a transporter of odour, wind roses are used to help pick ambient monitoring points in and
outside of the property line. A general wind direction can be determined and upwind and downwind
points be determined. Wind direction and speed change is influenced by season/month and time of day.
Depending on process and wind speed and direction, odours may move slightly in location of an area.
Although they may disappear, technicians may be able to capture readings with some frequency. For
example, on one side of road odours may be strong, yet on the other side no odour can be detected.

7. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
7 | P a g e
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It is tempting to use initial air dispersion modelling to predict potential points of highest odour. However
due to the large number of unforeseen odour sources at this stage of the project, any dispersion modeling
will be too simplified to yield any useful information on odour impact locations.
Once a complete list of survey points is created the team will validate the points by collecting odour
concentration measurement at each location for up to 30 days. The validation period will allow the team
to gather base levels for each location and discard locations that have less than 5% frequency of perceived
odour. Additional survey points may also be added during the validation period based on observation
and experience the team gains while conducting the odour patrols.
3.3 Data gathered at each survey location
At each data location, the odour patrol team records: date, time of measurement, GPS coordinate, odour
concentration based on personal olfactometery, description of the characteristic perceived odour, local
wind speed and direction, and optionally additional chemical readings (such as H2S or VOC) using portable
sensors such as the Scentroid OdoTracker. The team will encounter two types of odour, those that are
constantly present and those that are perceived intermittently. Intermittent drafts are usually due to wind
dusts and calm conditions below 1 m/s wind speeds. The drafts typically last between 20 to 60 seconds.
If drafts are below 20 seconds but repeat every few minutes, it is recommended to use a lung sampler to
capture a 10 min sample and analyze the sample using SM100 personal olfactometer at site. The team
will stay at the location and take an SM100 readings every 3 minutes for total duration of 10 minutes. This
will result in 3 readings over the 10 minute duration. The results are then used to determine the 10 min
average of the odours perceived. This will ensure any drafts are captured and also helps to correlate
with the 10 min interval in dispersion modelling. Technicians should face the wind direction when taking
odour measurements and avoid having nearby objects or structures upwind.
Significant odour readings that were not typical to a point were conveyed back to the process in order to
determine if a process event was responsible.
Tracer compounds can be measured, such as H2S and VOC’s, during ambient and source sampling to
determine if rises in specific compounds could be correlated to increases in odour. This information can
be used to implement a continuous total odour monitoring solution. H2S generally does not appear to
have a direct correlation with most refinery processes. Initial study shows total VOC to have some
correlation that could be used as part of continuous odour monitoring.

8. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
8 | P a g e
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3.4 Selecting and Training the Odour Patrollers
A properly trained technician is critical since they produce the crucial data of the odour survey. Odour
patrollers use the same technology used in olfactometric laboratories that conduct odour concentration
measurements to EN13725; meaning that they act as a panelist and use their olfactory sense with the
personal olfactometer to determine ambient odour concentration. Technicians need to be certified by n‐
butanol following the international odour standard EN13725. They should avoid smoking, alcohol, coffee,
gum, or other nerve stimulating chemicals. They need to have basic theory and practice (or training) on
odour perception and sampling methods. This will make them aware of issues such as odour fatigue which
can affect accurate recordings.
The ideal odour patrol consists of three technicians. Two technicians (panelists) are equipped with
SM100 personal olfactometers, and one ‘spotter’ whom performs initial survey and data collection. The
spotted will instruct the panelists when to start their measurement and will record other parameters such
as wind speed, direction, GPS coordinates, chemical readings, and odour characteristic. If panelists are
using the SM100i intelligent personal olfactometer, the unit will automatically record chemical levels,
odour concentration, GPS position, and wind speed/direction and therefore it may be possible to avoid
the use of the spotter.
The use of two panelists allows the for greater data reliability. Panelists should obtain results within a
maximum of 20% difference when conducting measurements at the same location and at the same time.
Results should be communicated to the spotter technician in private, so as not to influence the other
technician’s results, if not using the SM100i. Psychology plays a role in this matter and must be noted.

9. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
9 | P a g e
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3.5 Equipment used for Odour Patrol
Equipment used for ambient odour concentration measurement can be the SM100 or the SM100i. Both
devices work on the same principle of olfactometry as used in an olfactometric laboratory. Clean diluting
air is provided from a micro‐tank and is used to draw a sample and mix it at exact dilutions starting from
30,000 all the way to 2 times. The panelists breathe the mixture of ambient and diluting air and determine
at which concentration the odour becomes perceivable. The main difference between the two devices is
that the SM100i automatically controls the dilutions while the SM100 the panelist must manually decrease
the dilution if no odour is perceived.
Chemical sensors in the form of portable analyzers such as Scentroid OdoTracker or GC based portable
instruments can be used. The important characteristic that must be considered for any type of handheld
analyzer is the lower detection threshold. Certain chemicals such as H2S have an extremely low odour
detection threshold (e.g. H2S is 0.5 ppb). This means that at 0.5 ppb H2S has a perceived odour; therefore
sensors measuring H2S in ppm level are not useful for odour survey applications.
3.5 When each location should be surveyed:
The main objective when scheduling odour patrol shifts is
to ensure each location has data recorded at varying times
during the day over the survey period. It is recommended
to have two odour patrol teams: one for the locations
inside the plant and one team to survey the external
locations. The teams must measure concurrently to be able
to get as much correlated data as possible. The teams must
work on rotating shifts of day and night each lasting 10 to
12 hours. For example both teams would be on day shift
surveying locations from 7 am to 11 am and then again
from 2 pm to 6 pm. This shift schedule would last for 4
days then after a 2 day rest they would be switched to
night shift from 7 pm to 6 am. The order in which locations
are surveyed must also be changed every shift to ensure
odour concentration data is gathered from each location at
all hours of the day. Typical duration of the odour patrol
phase is a minimum of 30 days repeated once in summer season and once in the winter season to capture
different wind patterns.

10. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
10 | P a g e
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3.6 Phase 2: Source sampling and olfactometric analysis
The data collected by the odour patrol is then used to identify the odour sources within the plant. Some
of these sources may be practical to sample (e.g. off spec pond, holding tanks, stacks) and others may not
be practical to sample (in process leaks, over pressure relief valves, emission from liquid spilled on the
ground), referred to as fugitive sources.
For the point and area sources, the sampling team will use common sampling techniques as dictated by
the international odour standard EN13725. This includes flux chamber emission measurements for all area
sources both on land and on a liquid surface. Typical stacks in a refinery have high moisture and
temperature content and therefore must be properly pre‐diluted while sampling. A dilution probe with
capability to pre‐dilute up to 100 times is generally required to sample refinery stacks in accordance to
EN13725. All samples collected must be stored in PTFE bags as most compounds found in refineries (e.g.
benzene) escape easily from Nalophan and Tedlar bags. Samples of extremely high odour concentration
(over 10,000 OU) should be pre‐diluted at the source to avoid contamination of the olfactometer and to
minimize sample degradation.
If areas of the plant are identified by the odour survey to be of high odour impact but has no identifiable
point or area source then the odour is caused by fugitive odours. If an area has only fugitive sources, a
reverse modelling technique is required to quantify the emissions from the area to be used in dispersion
modeling. This technique assumes the entire area as a volume source and relies on measurements
collected during patrolling upwind and downwind of the location to determine the total odour emission.
Olfactometric analysis should be performed within 6 hours sampling in accordance to the VDI3880. Care
should be taken to ensure panelist are not exposed to full concentration of the odour as temporary
olfactory “blindness” is very common when exposed to contaminants found in refineries such as H2S and
Benzene.

11. Scentroid, A division of IDES Canada Inc
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
11 | P a g e
3.7 Reverse Modeling
Reverse modeling is used in two stages within the odour impact assessment of a refinery. In the first stage, the entire data
collected by the odour patrol is used to conduct reverse modeling of the plant as a whole. In this model, the plant is
assumed to be a large volume source and data collected over the patrol period along with the associated metrological
data is then used to determine the total odour emission of the plant. Scentroid has developed automation tools to make
the reverse modeling more efficient and cost effective.
Reverse modeling can also be used to determine total odour emission from a small portion of the plant, in which the
odour survey was identified as a high impact area containing only fugitive odours. The reverse modeling and total odour
emission is then used in a predictive model to determine the exact impact of the specific area on the total odour impact
of the plant. This result can be used to rank the odour sources (both fugitive and source) based on their impact for more
efficient and economically feasible odour abatement implementation.

12. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
12 | P a g e
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3.8 Predictive Modeling
The predictive model can be
created once all odour sources
are identified and their total
odour emission is measured. As
mentioned previously, all fugitive
odour sources must have a total
odour emission based on reverse
modeling. The predictive model is
created to determine how much
each source contributes to the
odour levels perceived at
different locations. While some
odours may have a high total
odour emission, their impact on
the sensitive receptors may be insignificant. Generally, odours from low level sources (e.g. off‐spec pond)
close to the ground travel less than odour from high level sources (e.g. tall stacks). Certain odours travel
more due to their temperature or their flow velocity from the source.
The predictive model allows us to create a list of sources with their odour contribution as a percentage of
the total odour perceived at the sensitive receptor. Those with highest impact should be targeted for
remediation if the total odours are to be reduced. Sources must also be ranked based on the cost of
remediation to ensure a feasible and economically efficient remediation plan is created.
The predictive model can also be used as a validation of the sampling and olfactometric process. Predictive
model can be executed for meteorological conditions during surveying and the theoretically predicted
odour levels can be compared to those obtained in the field. While some errors may be expected due to
omission of certain odour sources, uncertainty in measurement in the field and in the laboratory, a strong
correlation should be observed. This correlation will validate that the process of the predictive model was
correctly performed and matches the actual readings.

13. Scentroid, A division of IDES Canada Inc.
431 Alden Rd. #3 Markham, ON, L3R 3L4
T: 416.479.0078 or 1.888.988.IDES (4337)
www.Scentroid.com
13 | P a g e
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4. Analyzing the Results and the Deliverables
One of the key deliverables from the odour impact assessment will be the effect of process events on total
odour impact. During the odour patrol, field odour concentration is collected and compared with any
irregular process events. Results from each data point is analyzed to find instances where odour
concentration exceeded the 90th percentile. For each of those instances, the plant log book is studies to
determine if any potentially odour causing event had occurred. If there is correlation found between the
events and the change in odour impact, the plant can be notified to change the process or if possible, to
schedule the event to minimize the odour impact. The scheduling can be based on meteorological
conditions (when wind speeds exceed certain velocity or are not blowing to the sensitive receptors or
certain ambient temperatures), or based on time of day (late night when the odour impact may not be
noticed). The knowledge of odour impact of each process event can play a significant role in reducing the
odour nuisance of a plant.
The odour survey will also produce graphs showing frequency, duration, concentration and offensiveness
of the odour at each location. The maps and graphs will clearly show the impact of the plant and can be
used as a comprehensive baseline study. Repetition of the survey after mitigation technologies have been
implemented, can show the effectiveness of these solutions and demonstrate due diligence. The graphs
can also be used to determine when and how often the plant can expect to impact the neighbouring
residents.
The odour impact through survey can be combined with results from predictive and reverse modeling
to show using exactly the impact of the plant as a percentage of the total odour impact. The data can also
be used to determine where other external odour emitters are located and quantify their contribution.
At the end of the study the plant will have exact knowledge of their own odour impact, what events and
processes cause the adverse effects, and what may be done to reduce their odour emission.