DEVELOPMENT OF ODOR WHEEL AS PRIMARY ASSESSMENT TOOL

FOR ODOR

Nastaein Qamaruz Zamana, Ros Nadiah Rosli and Ahmad Shukri Yahya

School of Civil Engineering, Universiti Sains Malaysia, 14300, Nibong Tebal, Penang, Malaysia

a Corresponding email : cenastaein@eng.usm.my

ABSTRACT

The aim of this paper was to develop an effective odor wheel to

evaluate or rank an odor. Emission of odor can be measured using

various types of techniques around the world. Odor wheel was used as

indicator for primary observation to detect odor characteristic and

intensity. Five sources of odor within coverage of 2 km radius from

this Universiti Sains Malaysia (Engineering campus) were sampled and

brought to lab for analysis. With two colors presented on the wheel,

blue and red, darker color tone respectively represents increase in

odor pleasantness and characteristic. In this study, pictures were

also added to be represented the smell and combined together with

color tone to let the assessor easily detect the odor. The odor wheel

was designed to be rotatable, as assessor can scale odor based on

their experience of smell. However, the assessor needs to pass the

screening test so that the test will be valid. Details of panel such

as gender, level of education and age are also recorded. Results are

presented by combination of pleasantness and characteristic of sample.

Mean of pleasantness for each odor sample are gathered statistically.

This study introduces an easy tool to the community to detect odor

nearby their place.

Keyword: odor wheel development, hedonic tone, odor characteristic

INTRODUCTION

There is no specific unit for odor. Odor concentration is usually

reported in terms of dilution per threshold or odor unit per meter

cube (OU/m3). The odor concentration value is obtained from number of

dilution of a sample to an individual detection (threshold) level.

There are various techniques of measuring odor concentration either

manual or automatic. Most developed countries had developed their odor

measurement tool and regulation standard for example, the Japanese

introduced Triangular Odor Bag more than thirty years ago and it was

applicable until now (Iwasaki, 2003). The Canadian recently develop a

highly technology and practical odor measurement tool for field and

in-lab assessment named as Scentroid SM100 (Benzo et al., 2012).

Nevertheless, the whole world agreed that the Olfactometer, standard

that used by the European as the standard to measure odor and it was

stated on EN13725 Air Quality – Determination of Odour Concentration

by Dynamic Olfactometry. In Malaysia, the Malaysian Standard MS 1963:

2007 similar to the EN13725 is used as the guideline for in-lab odor

assessment. The Olfctometer can only analyze odor concentration of

odor; nevertheless, the ICH (Intensity, Characteristic, and Hedonic

tone) measurement is still under development.

There are many types of odor wheel, for example odor wheel for odors

drinking water, wastewater, compost and urban environment (Suffet and

Rosenfeld, 2007). Also, McGinley et al. (2002) described that there

are eight classes for odor that are floral, fruity, vegetable, earthy,

offensive, fishy, chemical and medicine. But, until now, there is no

specific odor wheel that contained all human descriptor for odor.

Meanwhile, study conducted by Castro et al. (2013), determined ten

cluster of human odor descriptor by statistical methods. However, all

the cluster group are in the form of wording that is quite difficult

and take longer time to think before the assessors give the answer.

Sakai et al. (2005) and Saito et al. (2006) suggested that picture and

color evoke common mental image for objects and this mental image lead

to form expectation to the odor.

By using odor wheel, it is introduce to measure odor based on their

characteristic and hedonic tone (pleasantness) instead of odor

concentration value. An odor wheel is expressed in terms of

“descriptors” that describe a characteristic of an odor. Hedonic tone

is one of odor parameter that define pleasantness or unpleasantness of

an odor (Stuetz et al., 2001). It usually is presented in form of

scales, either increasing or decreasing number to represent the

pleasantness. However, the normal scales is nine level scales, -4

(extremely unpleasant odor) to +4 (extremely pleasant odor) (Guideline

VDI 3882 Part 2, 1994). Importantly, hedonic tone address odor

complaint especially if the unpleasantness smells keeps continuing at

long time. In order to evaluate acceptability of odor, simply

referring to hedonic tone is not sufficient (Nimmermark, 2011).

Since odor is very subjective, sometimes it is very difficult to

characterize the odor. For this case, the people might face difficult

situation on complaining if the odor source is not recognized.

However, there is still an optional solution where the odor can be

characterize based on chemical component inside the odor or based on

the similarity of odor. Therefore, the purpose of odor wheel is to

check the odor character as well as the pleasantness of an odor.

The problem statement is what would be the best odor representation;

is it sufficient only to measure odor concentration or needed some

additional tool to help people identify the odor. Thus, the aim of

this study is to investigate the effectiveness of using odor wheel to

describe odor. Combination of hedonic tone and odor characteristics

are attached together in the odor wheel, since none of previous

researches combined that parameter.

METHODOLOGY

Odor Threshold Test

All samples were measured using Odor Threshold Test, developed method

from Japanese Triangular Odor Bag. The test involved three bags filled

with odorless air. Only one bag was selected to be diluted with

odorous compound. Panels need to choose which bag contained odorous

compound. More details of Odor Threshold Test can be referred to

Higuchi (2003).

Odor Wheel Test

Table 1 shows ten clusters suggested by Castro et al. (2013). Cluster

1 (W1), Cluster 3 (W3) and Cluster 7 (W7) are group of pleasant odor,

while Cluster 4 (W4), Cluster 5 (W5) and Cluster 9 (W9) are the group

of very unpleasant smell. The remaining cluster, Cluster 2 (W2),

Cluster 6 (W6), Cluster 8 (W8) and Cluster 10 (W10) having a neutral

odor. From the table, few odor characters of each cluster are taken in

the form of picture into odor wheel shown in Figure 1. The selected

picture was based on character in the cluster group. Each of the

cluster group is divided into three colors which are pink (good

smell), red (neutral) and dark red (bad smell). The hedonic tone, also

called as pleasantness scales (Naddeo et al., 2013) in blue color is

attached together with the wheel and able to rotate to let combination

affect of pleasantness and character of certain smell. A pin is placed

in the middle of odor wheel to let the rotation. The color was chosen

randomly as red and blue just to represent color tone that describe

odor. There are nine level of classification, ranging from -4 to +4.

The color tone (blue color) increased as unpleasant smell increased.

Pictures representing various odor characteristics were presented to

the panelist at the end of the Odor Threshold Test. The panel judged

the odor based on hedonic tone and give characteristic of the odor.

Odorous compound for each cluster are shown in Table 2.

Table 1 Odor Characteristic for each cluster group (source: Castro et

al., 2013)

W 1 W 2 W 3 W 4 W 5 W 6 W 7 W 8 W 9 W 10fragra

ntwoody,resinous

fruity,otherthancitrus

sickening

chemical minty,peppermi

nt

sweet popcorn sickening

lemon

floral musty,earthy,mo

ldy

sweet putrid,

foul,decaye

d

etherish,

anaesthetic

cool,cooling

vanilla

burnt,smoky

garlic,

onion

fruity,

citrus

perfume

cedarwood fragrant

rancid medicinal

aromatic fragra-nt

peanutbutter

heavy fragra-nt

sweet herbal,green,

cut grass

aromatic

sweaty disinfectant,

carbolic

anise(licoric

e)

aroma-tic

nutty(walnut

)

burnt,smoky

oran-ge

rose fragrant light sour,vinega

r

sharp,pungent,

acid

fragrant choco-late

oily,fatty

sulfidic

light

aromatic

aromatic pineapple

sharp,pungent,

acid

gasoline,

solvent

medicinal

malty almond sharp,pungen

t,acid

sweet

light light cherry(berry)

fecal(like

paint spicy almond

heavy household

cool,cool-

manure)

gas ing

cologne

heavy strawberry

sourmilk

cleaningfluid

sweet cara-mel

warm putrid,

foul,decaye

d

aroma-tic

herbal,

green,cutgrass

spicy perfumery

musty,earthy

,moldy

alcoholic

eucaliptus

light musty,earthy,moldy

sewer herbal,

green,cut

grassviolet

sburnt,smoky

banana heavy turpentine (pine

oil)

camphor warm woody,resinou

s

burntrubber

sharp,

pun-gent,acid

Table 2 Odor compound for each cluster group (source: Castro et al.,

2013)

Figure 1 Rotatable odor wheel

Panelist selection

A panel screening test was first carried out to select suitable

panelists for the olfactometry test. Panels are selected using the 5-2

method (Saiki, 2003) where the candidates had to guess two strips of

the same odor of standard references which are β-phenylethyl alcohol,

methyl cyclopentenolone, isovaleric acid, γ-undecalactone and skatole.

If the candidate can guess two of the standard references out of five,

the procedure is repeated for the other four standard references.

Twenty five candidates are tested with the standard references.

Fourteen of candidates are male and the remaining is female. Their

ranges of age are within 23 to 32 years old. Out of twenty five

candidates, only eight did not pass the screening test. Eight female

and nine male candidates who passed the test were appointed as the

panelist.

Odor sampling

The odor samples were taken at five odor sources around Universiti

Sains Malaysia (Engineering Campus), involving cow and chicken farm,

poultry processing factory, palm oil factory and paper and pulp

factory. Gas samples were collected using Nalophan bag inside Eco-

drum, equipment was used to collect the odor. After that, the samples

were brought to the lab for analysis. The odor sampling and analysis

were done in the same day for each sample, to minimize error due to

sample loss or diffusion through the bags. The samples are then

continued for the assessment using odor wheel after analysis of Odor

Threshold Test. Presentation of results are compared either to choose

the Odor Threshold Test, Odor Wheel (by wording only) or Odor Wheel

(with picture). By using the same sample, the panelists are asked to

choose hedonic tone scale together with the characteristics in the

odor wheel.

RESULTS AND DISCUSSIONS

Laboratory test on develop odor wheel

After development of odor wheel, it is tested by using five standard

references that was used for panelist selection. The purpose of this

test is to check validity and suitability of that odor wheel before

proceeding to the real odor site. Table 3 shows response from ten

panelists about standard references given to them. Five females and

five males at age of 23 to 28 years old take part for this test. They

describe the odor differently because it depends on a person

experience and sense to judge the odor. Since all standard references

can be described using the developed odor wheel, the odor wheel can

proceed for the real site.

Table 3 Results obtained from preliminary study

Characteristic and pleasantness of the five standardreferences

assess by panelistPanel β-

phenylethyl alcohol

methylcyclopenteno

lone

isovalericacid

γ-undecalact

one

skatole

A Fragrant,0

Woody, -2 Pungent, -4 Chemical,-3

Decay, -1

B Fragrant,+2

Decay, -2 Pungent, -3 Decay, -3 Decay, -1

C Fragrant,-2

Woody, -1 Pungent, -4 Decay, -2 Decay, 0

D Sweet, -2 Chemical, -1 Pungent, -4 Decay, -3 Woody, -2

E Fragrant,-3

Woody, -2 Pungent, -4 Chemical,-1

Decay, -1

F Sweet, 0 Woody, -1 Pungent, -2 Chemical,-2

Decay, -3

G Fragrant,-1

Chemical, -1 Lemon, -4 Chemical,-2

Decay, 0

H Sweet, +2 Decay, -2 Pungent, -3 Decay, -2 Woody, -1

I Fragrant,0

Chemical, -1 Pungent, -3 Chemical,-3

Decay,-3

J Sweet, 0 Decay,-1 Lemon,-4 Decay, -2 Decay,-1

On-site result using Odor Threshold Test

Six panelists take part on one session of the test. There are total of

12 sessions, where one site is divided into two sessions; morning and

evening. While, for palm oil factory, there are two type of emissions,

at point source (stacks) and area source (the pond). The results shows

that the palm oil factory produced the highest odor concentration

value, followed by poultry processing factory, farms and paper and

pulp factory. Details are as shown in Table 4.

Table 4 Odor concentration value using Odor Threshold Test

Odorconcentration

(OU/ m3)No.

Odor Source Type ofemission source

A.M. P.M. Average

1. Cow farm Area 412 550 4812. Chicken farm Area 232 309 2713. Poultry processing

factoryArea 733 412 573

4. Palm oil factory PointArea

13032317

17383090

15212704

5. Paper and pulpfactory

Area 158 158 158

On-site result using Odor Wheel

Response towards odor concentration using odor wheel are taken based

on an average of each sample using six panels. The purpose of this

test is also to measure the effectiveness of describing odor, either

by picture or words. Table 5 shows the result of assessment using odor

wheel with picture. From results, all odor source are categorized as

cluster 9 (W9) from odor wheel except paper and pulp which is in

cluster 5 (W5) as referred to odor wheel in Figure 1. After that, they

are asked to describe the odor in words, however, by this time Table 1

is shown to them. Table 6 shows the response from panelist by using

words.

Table 5 Odor assessment result using odor wheel (by picture)

Odor Source Odor Character Hedonic Tone Cow farm W9 -1

Chicken farm W9 -1Poultry processing

factoryW9 -3

Palm oil factory W9 -4Paper and pulp factory W5 -1

Table 6 Odor assessment result without picture (by word)

Odor Source Odor Character Hedonic Tone Cow farm sickening -1

Chicken farm sickening -1Poultry processing

factoryputrid, foul -3

Palm oil factory rancid -4Paper and pulp factory cleaning fluid -1

Based on either results, either using picture or wording, the odor

character is still in the same group. It is no problem in using both

methods. A survey is carried out to the panelist to ask about

efficiency of using word and picture. Most of them prefer by using

picture because it is quite confusing to determine the accurate word

to describe the odor. In addition, words that describe the group for

each odor character are presented as picture on the odor wheel.

An assessment of odor is sufficient by determination of odor

concentration to check the quality of odor. If a person wanted to know

the character or pleasantness of an odor that lead to complaint or

treatment, the analysis by using odor wheel should be carried out.

CONCLUSION

Odor can be measured not only in terms of odor concentration. Other

parameter such as offensiveness, intensity or character can also

describe odor as well. The odor wheel is different from others with

additional picture, and hedonic tone scale is attached together with

the wheel. It helps assessors to identify types of odor more easily

compared to older odor wheel that describe using words, as agreed by

the panel. Psychologically, this increased ability to choose answer by

looking at picture either than thinking the accurate word to describe

the odor. The odor wheel was designed to be rotatable to make it

easily to combine the odor characteristic and hedonic tone parameter.

Also, by looking at the combination of color, if both darker tone

colors joined together, it means that the odor has very bad unpleasant

smell.

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