Analysis for Adsorbed Odor from
Car Air Conditioner Evaporator
Kazuhisa Uchiyama*, Osamu Kasebe**, Kengo Kobayashi***,
Shigeyuki Sato****, Hiroshi Ito*****
DENSO CORPORATION 1-1 Showa-cho Kariya-shi Aichi 448-8661 JAPAN
*[email protected], **[email protected], ***[email protected]
TOYOTA CENTRAL R&D LABS., INC.
41-1, Aza Yokomichi, Oaza Nagakute, Nagakute-cho, Aichi-gun, Aichi-ken, 480-1192, JAPAN
**** [email protected], ***** [email protected]
Abstract: As one of measures to improve the environment in a car, we have decreased the foul odor and the dusty
odor caused by the car air conditioner evaporator. However, the problem with adhesive odor is still left unresolved.
We analyzed the odor from cars with a sensory test and instrumental analysis. And we simulated the odor with an
evaporator desktop test bench with airflow controller, air temperature and humidity controller for testing odor from an
evaporator. We proved that the odor is composed mainly of substances from exhaust gas, tobacco smoke
and others. We found, (a) three principal components of adhesive odor with PCA (principal component
analysis), (b) a close correlation between odor sensory test data and instrumental analysis data with
multivariate analysis, and (c) specified main odor substances (ex. Lower fatty acids, Hydrocarbons and
Aldehydes). These odor substances tend to become noticeable while the air conditioner is operated with the
compressor turned on and off. This operating pattern is increasingly used recently for energy saving purpose.
With the evaporator desktop test bench, we found that hydrophobic odor substances (ex. Toluene) are released while
evaporator’s surface is changing from ‘Dry’ to ‘Wet’ (temperature falls down and flocculated water breaks out on the
surface). And while changing from ‘Wet’ to ‘Dry’, the flocculated water vaporizes and hydrophilic odor substances
(ex. Lower fatty acids) come up together. Consequently we have identified the components of inherent odors that
smell while H2O is condensing and vaporizing (= the compressor is turned on and off). And we clarify the odor
generation mechanism from an evaporator surface.
Key words: Air Conditioning, Human Engineering, Evaporator, Odor
1. Introduction
Heater core
For the past several years, we have been trying to
minimize the odor emitted from the car air conditioner
evaporator (Fig.1).
As the user's odor tolerance threshold
becomes lower, on the other hand, an unpleasant odor is still
emitted from the source of components collecting even after
Blower
Evaporator
Fig.1 Car Air Conditioner System and Evaporator
the current surface treatment capable of controlling an "uncomfortable odor" caused by bacteria and a "dusty
odor" resulting from corrosive products on the evaporator (Fig.2).
An odor from the evaporator surface-treated in the current process was traced by means of monitored vehicles
on a continuous basis. One of the 23 users of the monitored vehicles made a complaint about an annoying
"odor" in five months after the start of monitoring.
In contrast, four of the 23 users made a complaint
Odor Type
indicated a different type of odor unlike the
uncomfortable odor or dusty odor. In addition, we
counted the bacteria on the surface of six units
including these two and found out that the number
Resin Reacted Layer
?
Chromate Layer
Bacteria
Counter
-measure
Adsorption and
Desorption of Odor
Al(OH) 3
Odor
Mechanism
Sweat,Tobacco
Dusty
Growth of
Bacteria
Cause
in ten months.
A check for any odor from two of these units
Rotten
Odor
Evaporator
Evaporator
Biocide
New Coating
Odor
Evaporator
Filter
Fig.2 Odor of Car Air Conditioner
was below the odor-emitting minimum level, presenting no problem. We thereby cleaned up the two evaporators
so as to remove the collecting foreign material to a completely acceptable "odor" level and noticed that these
odors were caused by the collecting components, resulting in "adsorbed odors".
And when the compressor is set in control mode
Normal Pattern
intended for saving energy as currently observed, such
Comp ON
OFF
rising or lowering on the surface of the evaporator.
Evaporator
Temp.
The purpose of this study is to identify the
ON
Comp
OFF
an odor would be enhanced in addition to temperature
(Fig.3)
No Odor
An Example of Eco-mode Pattern
causative substance of such an "odor" possibly
resulting from the components accumulating on the
surface of the evaporator and determine the odor
Wet to Dry
Evaporator
Temp.
mechanisms components through the analysis, clarify
Wet enough
Dry to Wet
Odor
Car Running
Car Stopping
Fig.3 Comp. Operation Mode and Odor
how the adsorbed odor arose.
2. Materials and Methods
Before developing an odor evaluation method, we
analyzed how an odorous stimulus was transmitted.
The odorous stimulus first stimulates the olfactory
cells on the "olfactory epithelium" as olfactory
receptors in the nasal cavities, then goes through the
olfactory nerve, and finally reaches the brain. At this
Brain
Olfactory
Epithelium
Odor
Substances
Recognition
First Study, Restudy
Memory
time, if the concentration of the odorous components is
Decision
Odor
Substances
Emotion
Image
Measurement
Chemical
Analysis
࡮
࡮
Odor
Sensory Test
Fig.4 Flow of Stimulus and Measurement
at a sufficiently high level for the stimulative pulse from the olfactory cells to exceed a definite level (the
concentration of the odorous components at this time is called as "threshold concentration"), then the signal is
perceivable as an odor to determine the kind of odor (Fig.4).
A search of those parameters objectively identified in the process from the generation of an odorous stimulus
to the recognition of the odor will indicate that data can be collected through instrumental analysis for an "odorous
component" and through odoring evaluation questionnaires for an "emotion or image."
2.1 Identifying Odor causative substances
2.1.1 Samples for Odor sensory test and Instrumental analysis
We picked samples, and divide in two for instrumental analysis and the odor sensory evaluation value.
2.1.2 Odor sensory test for PCA and multiple regression analysis
At first step, we made an attempt to develop a new
evaluation strategy for relating the test values by
means of instrumental analysis with the odor sensory
*PCA:Principal Component Analysis
Odor Sensory Test
2.72
Sampling Bag
Cars
evaluation values of the same samples. To correlate
PCA*
the results of analysis to the odoring evaluation values,
and the causative substances.
Fig.5 Sensory Test and PCA
Analysis on the chief
ingredients of the results of the odoring evaluation will identify
objective parameters while the odor component analysis values are
specified as descriptive parameters. Since the intensity of an odor
in the vehicle is supposed to be highly correlated with the level of
Odor C
-2.72
-2.72
0.00
2.72
Partial Regression
judgment criteria, which are available to group the plots (Fig.5).
The odoring evaluation values in these vehicles are selected as
Factor 1
0.00
Odor A
Questionnaire
we focused on relationships between the types of odor
Factor 2
Odor B
Y = β1X1 + β2X2 + β3X3 + . . . + βpXp
Observed
Value
Explanatory Variate
(Instrumental Analysis
Data)
Fig.6 Multiple Regression
Analysis
the component characterizing the odor of cigarette smoke, we believe that those components closely correlated to
the odoring evaluation values are imported into the descriptive parameters when the variables are selected by
performing multiple regression analysis (Fig.6).
Each of the individual groups consists of similar members, based on the evaluation quadrants for people. The
samples collected from the actual vehicle and prepared for odoring evaluation were divided into two and shared
by instrumental analysis.
Placed in odor bags, these samples were submitted to the panels (or testers) to receive
responses by means of an SD method questionnaire.
(1) Panels: Invoked were general engineers and office workers who
had little preliminary knowledge of odors and were not interested in
this evaluation.
(2) Samples for evaluation: With an odorless specimen added as a
blank, all the samples were resorted on a random basis irrespective
of the sampling sequence from the vehicles in such a manner that
the contents of the samples were unperceivable. Then, they were
SampleNo.
1. Check on the number that you feel.
[odor intensity]
5 Intense Odor
4 Strong Odor
3 Odor Easily Sensed Odor
2 Weak Odor
1 Barely Recognizable Odor
0 No Odor
smoking was selected to conduct a test by means of curtains
blocking off the direct rays of the sun under a temperature and
humidity condition not making the panels feel uncomfortable.
(4) Questionnaire: The terms indicating the types of odors were
previously selected through several prior tests.
By making
[Odor Pleasantness
/ Unpleasantness]
2 Pleasant
1 Rather Pleasant
0 Neither
-1 Rather Unpleasant
-2 Unpleasant
-3 Very Unpleasant
2. Fill in the box that you feel.
3 : Very much so
2 : Considerable
1 : Little so
blank : Not at all
named with alphabetic characters to conduct a blind test.
(3) Evaluation environment: A silent chamber facing south without
Name
Date
Acid
Sweet
Burnt
Acrid
Fusty
Interior odor
Damp mop
Dirty sock
Fishy
Fish and meat
Exhaust gas
Festering trash
Sweat
Comment (
Dusty
Cosmetics
Tobacco
Garbage
)
Thank you
Fig.7 Questionnaire
inquiries about (1) Intensity of odor, (2) Degree of comfort / uncomfortableness, and (3) Type of odor in addition
to (4) Miscellaneous requesting comments without restriction. Regarding the type of odor, the checkers were
requested to respond with "3", "2","1" or "blank" as the degree of consistency with the word representing the
odor used for the questionnaire. These results "3", "2" and "1" were then converted into 3 points, 2 points, and
1 point respectively when being totalized. (Fig.7)
In the questionnaire, the intensity of odor and the degree of
Table 1. Odor Intensity
unpleasantness were adopted as the evaluation items and
5
4
3
2
1
0
ranked at six intensity levels and seven degrees
respectively (Tables 1 and 2).
2.1.3 Instrumental analysis for multiple regression analysis
We have decided to perform analysis by means of the possibly
optimum strategy for each kind of "odorous" components supposed
to exist in the odor for each sort of sources and the actual vehicle.
Under the conditions shown in Appendix A, instrumental
analysis was performed on each sort of components. A blank test
was definitely conducted before and after sampling a specimen in
Intense Odor
Strong Odor
Odor Easily Sensed
Weak Odor with the Kind of Recognizable Odor
Barely Recognizable Odor
No Odor
Table 2. Odor Pleasantness / Unpleasantness
3
2
1
0
-1
-2
-3
Very Pleasant
Pleasant
Rather Pleasant
Neither Pleasant nor Unpleasant
Rather Unpleasant
Unpleasant
Very Unpleasant
each test to keep checking the background value when conducting this test.
2.2 Clarifying adsorbed odor mechanisms
At the second step, we tried to not only determine the odor-emit ting components through PCA and multiple
regression analysis but also clarified how the adsorbed odor arose.
2.2.1 Samples
A smoking device was used to introduce and familiarize a cigarette odor along with cigarette smoke to the
evaporator placed on the car air conditioner test bench and the mini core bench (After-mentioned. See 2.2.2.). In
order to simulate the actual familiarizing conditions, the evaporator temperature was kept cycled between the
condensing point and the vaporizing point to apply the odor.
2.2.2 Odor sensory test on Test bench and Mini-core bench
We prepared the onboard car air conditioner ‘Test Bench’ (see Fig.8 for further information) traditionally used
on an evaluation chamber basis and fabricated a
new desktop test bench (hereafter called the "mini
Temperature-controlled Room
Conditioned
Clean Out Air
Air Conditioner
Unit
core bench" as shown in Fig.9) incorporating a
small-size evaporator (hereafter called the "mini
core") and intended for laboratory evaluation.
Internally covered with stainless steel to
facilitate cleaning, the onboard car air conditioner
R134a
Sampling Bag
Exhaust
Canister
Fig.8 Test Bench
evaluation bench is capable of controlling the evaluation chamber at a specified temperature and humidity and
running the car air conditioner placed in the chamber. The evaluation panels enter this chamber to odor and
evaluate the odor in turn.
Additionally, to avoid raising the intensity of the odor in the chamber, the system is
designed in such a manner that the ambient air is deodorized through an active carbon filter and always introduced
at a constant rate.
On the other hand, the mini core (a small size evaporator)
built in the mini core bench is of a small size and low thermal
capacity.
Mini-Core
Sampling Bag
Hot
Cold
Furthermore, the temperature controls are simplified
OUT
by means of a noncombustible liquid heat film in place of
chlorofluorocarbons.
The mini core is shielded from the
outside with the sampling bag in such a way that the
IN
Circulation Systems
Fig.9 Mini-Core Bench
Conditioned
Clean N2
temperature and humidity of the nitrogen running in the bag can be controlled at discretion. Table 3 lists typical
test conditions.
By means of these test benches, we performed odoring evaluation and instrumental analysis. The
odoring evaluation was completed at a low temperature of
20°C and a relative humidity between 40 % and 60 % from
the typical conditions as described above.
We ranked the intensity of odor and the degree of
Table 3. Test Conditions
Assembly
Test Bench
Temperature (degree)
Humidity (%RH)
Mini-Core
Bench
20 ~ 30
40 ~ 60
20 ~ 25
30 ~ 60
unpleasantness at six intensity levels and seven degrees (Table 1 and Table 2).
In advance, a T&T-Olfactometer was used to select approximately ten evaluation panels that were not
handicapped in olfactory capability, followed by training to an odor intensity evaluation error between 0.5 and 1.0
among the individuals. Three or five panels were selected to mark the samples and find the average.
2.2.3 Instrumental analysis on a Test bench and on a Mini-core bench
Sampling on test bench, we firstly collected the odor in Tedler-bag and a canister, and then condensed odor
samples from them, on Tenax-TA or other devices (DNPH-Silica, Sr(OH)2 glass beads, Chromosorb 101 and
others). Sampling on mini-core bench, we could collect the odor to a canister or condensed odor samples directly.
Instrumental analysis conditions are the same (see Appendix A).
3. Results and Discussions
3.1 Correlation between instrumental analysis values and the odor sensory evaluation values
3.1.1 PCA result
By wrapping up the above-mentioned questionnaires, we
performed analysis on the principal components.
As a result of the principal component analysis, three
principal components having eigenvalue more than one were
identified. Additionally, since the degree of contribution was
Table 4. Test Conditions
Factor
Eigenvalue
1
2
3
4
Contribution
5.309
2.549
1.059
0.482
0.531
0.255
0.106
0.048
Accumulated
Contribution
0.531
0.786
0.892
0.940
found sufficient over 80 percent and at approximate 90 percent for up to the third chief ingredient, the adsorbed
odor evaluation quadrants would be reproducible with the first to third principal components only (Table 4).
Next, we started to characterize the principal
components as the judgment criteria (Table 5).
The first principal component was named as the
"Unpleasantness" presenting high factor loadings
with the "Odor Pleasantness / Unpleasantness" and
the terms presenting unpleasant odors such as
"burning, dusty, smoky, and exhaust gaseous" and
"acid,
sweet,
and
cosmetics"
(with
the
uncomfortable quadrants defined to be positive due
Table 5. Test Conditions
Variate
Intensity
Unpleasantness
Acid
Sweet
Burned
Dusty
Tobacco
Exhaust Gas
Cosmetics
Interior Materials
Factor1
Factor2
-0.163
0.831
-0.803
-0.868
0.815
0.871
0.721
0.753
-0.827
0.038
0.979
0.372
0.511
0.450
0.448
0.066
0.529
0.274
0.454
0.471
Factor3
Factor4
-0.014
0.216
-0.170
-0.079
-0.219
-0.267
-0.242
-0.024
-0.222
0.866
-0.076
-0.174
0.161
0.062
-0.017
0.104
-0.276
-0.024
-0.007
0.045
to the converted parameters). While the terms on the uncomfortable side reading a positive factor load present
no problem, the other terms of the comfortable side have the term "acid" typically expressing an unpleasant odor,
raising a suspicion. We thereby interviewed the panels to make a survey to find out that the samples marked this
time with "acid" were of a "citrus fragrance (deodorant)" odor and with a judgment for a preferable odor in
addition to a description of "deodorant" noted in the voluntary response column, presenting no inconsistency with
the results.
Likewise the second principal component was named as "intensity" because the "intensity" factor loading was
found at a high level.
For the three remaining principal components, only "interior odor" presented a high factor
loading.
The reason why the "interior odor" was identified as a judgment criterion would be that the panels who were
closely connected as occupants to vehicles were familiar with such an interior odor like the vehicles and, therefore,
the odor is separately perceived and assessed unlike the typical uncomfortable odors such as exhaust emissions.
3.1.2
Factor loading
Fig.10 shows the factor loadings for
each term plotted about the principal
component axis.
Factor 2
1.0
Factor 3
1.0
Interior
Odor
Intensity
These plots indicate
Acid
0.5
that the evaluation quadrants are clarified
0
with the three evaluation axes, indicating
how closely the term is related to the
Cosmetic Interior
Sweet
Tobacco
Odor Exhaust Gas
Burned
Unpleasantness
Dusty
Factor 0
1
-0.5
degree of uncomfortableness for the
-0.5
-1.0
-1.0
samples used this time.
-0.5
0
0.5
Fig.10 Factor Loading
3.1.3 Principal component score
0.5
1.0
-1.0
-1.0
Sweet
Acid
Cosmetic
Intensity
-0.5
Unpleasantness
Factor
Exhaust Gas Burned 1
Tobacco
Dusty
0
0.5
1.0
The scores of the principal components from the results of "odor" evaluation in the actual vehicle are plotted
with ‘• ○’ about the three axes.
Furthermore, (1) Smoking vehicles are plotted with ‘•’ and (2) Vehicles using
odorants (or aromatics) are plotted with ‘○’ to enclose each segments.
In addition, those vehicles with a short actual driving period (i.e., almost new vehicles) and those with
comments indicating a plastic and vinylic odor are encompassed (Fig.11).
1st principal component: Smoking vehicles on the uncomfortable (positive) side and deodorant using vehicles on
the comfortable (negative) side.
2nd principal component: Vehicles
with a strong smoky odor placed
on the intensive (positive) side.
1.1
3rd principal component: Vehicles
0
with a strong interior or plastic
odor placed on the intensive
interior odor (positive) side.
We acquired these results and
found
out
that
each
principal
Intensity
2.2
(+)
Uses
Perfumes
Group
-1.1
-2.2
-2.2
2.2
Very
Smoky
(+)
1.1
Plastic
Vinyl
䊶䊶
Unplea
-santness 0
Smoking
Group
-1.1
Interior Odor
-1.1
Uses
Perfumes
Group
-2.2
0
1.1
2.2
-2.2
-1.1
: Smoking Car
: Aromatic, Cosmetics, Perfumes
Fig.11 Principal component score
(+)
Almost New
Strong
Interior Odor
(+)
䊶䊶
䇭
Unplea
-santness
Smoking
Group
0
1.1
: Others
2.2
component definitely corresponded to the vehicle and that the odors could unequivocally be segregated by means
of these evaluation axes.
3.1.4 Discussion about determining the odor causative substances
Having identified the evaluation axis for the adsorbed odors by performing analysis on the principal
components through the odoring evaluation, we describe correlations between the results of this odoring
evaluation and the findings of the analysis.
Multiple regression analysis was performed with the representative
Odor Intensity
= k log (Odor Substance Concentration) + a
element for each evaluation axis used as the objective parameter and with
5
4
3
2
1
0
Odor Intensity
the component analysis values used as the descriptive parameter. At this
time, the component analysis values were converted into logarithmic
variables for this analysis because the logarithmic physical values such as
odor component concentration are widely known to be in proportion as the
0.1
1
10
100
Concentration (ppb)
Weber-Fechner’s low (Fig.12).
Fig.12 Weber-Fechner’s low
The questionnaire item “Odor Pleasantness / Unpleasantness”" was used
for the first principal component element “Unpleasantness”, the item “Intensity of odor” was used for the second
principal component “Intensity,” and the item “New vehicle odor and interior” was used for the third principal
component “Interior odor”. As a result of
the multiple regression analysis, we
acquired
a
high-precision
regression
equation to identify those odor causative
substances.
Furthermore, we checked for the
‫ޓޓޓ ޓޓޓ‬
‫ޓޓޓޓޓ‬
‫ޓޓޓޓޓ‬
Unpleasantness = 0.469*log(Substanece-A)+0.449*log( -B)+0.204*log( -C)+ …
R:0.987, R**2:0.908
‫ޓޓ‬
Intensity = 0.326*log(Substanece-D)+0.537*log( -E)+0.253*log( -F)+ …
R:0.978, R**2:0.910
Interior Odor = 0.301*log(Substanece-G)+0.615*log( -H)+0.362*log( -I)+ …
R:0.961, R**2:0.846
Fig.13 Result of the Multiple Regression Analysis
adsorbed odor from the evaporator by means of those components incorporated in the regression equation and
those not incorporated. As a result, the components imported into the regression equation presented a higher
odor intensity than that of the other components not imported, backing the results of the analysis. (Fig.13)
3.2 Adsorbed odor mechanisms
3.2.1 Result of the test bench
This section describes the findings of the evaluation on the air conditioner test bench.
(1) Results of odoring evaluation
Fig.14 shows the results of the odoring evaluation. The
vertical axis of the graph refers to the operation modes of
the air conditioner, indicating the changes of Dry (with the
blower), ON (with the compressor turned on), and OFF
Mode
2
3
4
5
+1
Unpleasantness
0
-1
-2
-3
ON
ON
(continual)
By allowing five evaluators to odor in turn, it is difficult to
(continual)
conduct continuous evaluation with a limited number of
Odor Intensity
1
Dry
(with the compressor turned off). The horizontal axis refers
to the intensity of odor and the degree of unpleasantness.
0
OFF
OFF
Fig.14 Result of Odoring evaluation
odoring times and only five times was available for evaluation on a spot basis all over the modes. While the odor
varied in a consecutive manner, a long time lag required each time for exchanging the panels resulted in
fluctuations.
Additionally, in the cigarette odor-familiarizing test conducted this time, a part of the panels complained about
uncomfortableness due to a highly intensive odor and about olfactory fatigue as the odor accumulated in the
evaluation chamber, indicating an error expansion factor.
(2) Results of instrumental analysis
Fig.15 shows the results of the instrumental analysis. Likewise the vertical axis of the graph refers to the
operation modes and the horizontal axis refers to the concentration (in ppb) of the odorous component.
As an example, the behavior of i-Valeric acid known as an
unpleasant component is described.
Mode
In a part, a negative
0
0.2
Concentration (ppb)
0.4
0.6
0.8
1.0
Dry
value resulted by subtracting the blank value (as marked with
"ND" on the graph) and, therefore, a significant difference is
ON
ND
ON
ND
(continual)
unlikely between the analysis values, indicating difficult
OFF
analysis even by highly sensitive analyzing strategy.
OFF
ND
(continual)
3.2.2 Mini core bench
Fig.15 Result of Instrumental Analysis: i-Valeric Acid
Next, the results of the odoring evaluation on the mini
core bench are shown along with the findings of the analysis in Fig.16 and Fig.17.
(1) Results of odoring sensory evaluation
The horizontal axis refers to the elapse time, indicating the changes of Dry (with blower only and the mini core
at normal temperature), ON (with the mini core at low temperature and the compressor turned on in reproduction
mode). The vertical axis refers to the intensity of odor
on the upper side and the degree of unpleasantness on the
lower side (Fig.16).
Unlike the results with the onboard car air conditioner
evaluation bench described above, it was possible to
Intensity
temperature and the compressor turned off in reproduction
4
Dry
ON
OFF
3
Intensity
NG
2
1 Good
0
Good
Unpleasantness
-1
-2
NG
-3
-5
0
5
10
15
20
Time (min)
Fig.16 Result of Odoring evaluation
Unpleasantness
mode), and OFF (with the mini core at normal
25
30
35
evaluate the samples at short time intervals without causing olfactory fatigue by fitting the nose with the silicon
tube connected with the outlet only when the odor is smelt. While omitted in the figure, the fluctuations among
the panels were limited below 0.5 because of no olfactory fatigue.
This section describes the results of the instrumental
analysis. In the same manner, the horizontal axis refers to
the elapse time and indicates the changes of the Dry, ON,
and OFF modes and the bar graphs along the vertical axis
refer to the concentration of the component (Fig.17).
On the mini core bench, unlike the results with the
Concentration (ppb)
(2) Results of instrumental analysis
0.6 Dry
ON
i-Valeric Acid
Toluene * 1/10
0.4
0.2
0.0
OFF
-5
0
5
10
15
20
Time (min)
Fig.17 Result of Instrumental Analysis
25
30
onboard car air conditioner evaluation bench, the concentration of the odorous component in each mode presented
a significant difference from the blank and the concentration of the component also presented a significant
difference between the modes.
For example, variations in i-Valeric acid and toluene are shown as functions of time.
Judging from the results of odoring evaluation (Fig.16) and the instrumental analysis (Fig.17), the remarkable
point is that the behavior of toluene and i-Valeric acid varies depending whether the unit is turned on or off.
With the unit turned on, the concentration of water-repellent toluene was at a high level when condensed water
was present. With the unit turned off, on the other hand, the concentration of the water-soluble i-Valeric acid
component was at a high level with the odor intensity also at a high level when the condensed water was
vaporized. In other words, these results imply all over again that the collection odor would be caused by and
closely related with condensed water.
In addition, these findings indicate that the degree of unpleasantness is highly related to the amount of
i-Valeric acid and these odorous components accelerate the degree of unpleasantness.
3.2.3 Discussions about odor mechanism
The reason why it was difficult to perform instrumental analysis on the onboard car air conditioner evaluation
bench was as follows:
1.Adversely affected by the ambient air to result in an unstable blank.
2.High wind velocity reduced the odor generation period of time and allowed differences between the bag
sampling individuals and adsorption to the bag.
These factors seem to have degraded quantitativeness. In contrast, on the mini core bench, the blank was kept
at a low level by using the mini core in a clean environment and it was possible to reproduce the behavior of
condensed water on the surface of the evaporator at a low air flow rate to enable the testers to evaluate the
odorous components on a stable basis.
As described above, we have succeeded in identifying how an odor is familiarized with the car air conditioner
by relating the generation or evaporation of condensed water due to evaporator temperature rising and lowering
and the emission of the odorous components of the collection odor through the odoring evaluation and the
instrumental analysis (Fig.18).
As
shown
in
the
figures,
the
water-repellent components represented
by toluene from among the odorous
components collecting on the surface of
the evaporator are emitted in the form of
displacement with moisture in response to
the start of water condensation with the
compressor turned on and this is felt as the
collection odor when the unit is turned on.
Next,
condensed,
as
additional
the
moisture
evaporator
is
surface
temperature is lowered in the continuous
turn-on mode with the evaporator covered
1. Dry
Hydrophobic Substance
Hydrophilic Substance
H2O
Odor Substances
䇭
Evaporator’s Surface
3. ON Continual : Wet enough
Hydrophilic Substance’s Elution
2. ON : Dry to Wet
Hydrophobic Substance Released
Ex. Toluene
Flocculated Water
Odor Intensity: Strong
4. OFF : Wet to Dry
Hydrophilic Substance’s Vaporization
Ex. i-Valeric acid
Flocculated Water
Odor Intensity: Weak
Odor Intensity: Very Strong
Fig.18 Adsorbed Odor Mechanism
with water on the surface, the emission of the odorous components is reduced, and the intensity of the odor
transfers at a low level.
During this, the water-soluble components such as less-carbon fatty acids represented by
i-Valeric acid increasingly dissolve from the surface of the evaporator into the condensed water.
Finally, with the compressor turned off, the moisture evaporates and the water-soluble components dissolved
in the condensed water vaporize with the moisture and felt as an odor when the unit is turned off (at the lower
right corner of Fig.18).
4. Conclusions
To determine the odor cause, we performed instrumental analysis and odor sensory evaluation. We found out
for the first time that the instrumental analysis values of the adsorbed odor were highly correlated to the odor
sensory evaluation values and identified the odor causative components.
These causative substances adsorbed on the evaporator surface tend to become noticeable while the air
conditioner is operated with the compressor turned on and off for energy saving purpose. With the evaporator
‘Mini-core bench’, we simulated adsorbed odor and found that
• Hydrophobic odor substances (ex. Toluene) are released while evaporator’s surface is changing from ‘Dry’ to
‘Wet’ (temperature falls down and flocculated water breaks out on the surface).
• While changing from ‘Wet’ to ‘Dry’, the flocculated water vaporizes and hydrophilic odor substances (ex.
i-Valeric acid) come up together.
• We clarify the odor generation mechanism from an evaporator surface.
To improve comfortableness in the occupant compartment, these odors possibly emitted from the air
conditioner must be minimized in the future by, for example:
• Determining the sources of the odor-emitting components in question to minimize the rate of the odorous
components flowing into the air conditioner by eliminating the causative factors and;
• Installing a deodorization filter allowing only a limited part of the odorous components to flow into the
upstream of the evaporator to prevent the odorous components from adhering.
These measures are noticeable.
References
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three-point comparison type odor bag strategy, - from a odoring test procedure study report by the
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and developing the bad-odor olfactory test procedure, Environment and measurement technology, vol.9, No.10,
(1982).
3. Toshiyuki Tanaka; Sampling organic chemical compounds gases in the air by the adsorption and capture
strategy at normal temperature Part 1, Basic principles, Environment and measurement technology, vol.16,
No.1, (1989).
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strategy at normal temperature Part 2, Actual atmospheric measurement and sample measurements,
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Appendix A
Table 6. Aldehyde Analysis Conditions
Trapping: DNPH Silica Cartridge (Waters SepPak)
Instrument (HPLC): Shimazu LV-10VP, Detector: UV (350nm)
Column: Inertsil ODS-80A (GL Science)
Mobile Phase: CH3CN/H2O = 55/45, 1.5mL/min
Column compartment: 40 degree
Injection Volume: 25µL
Table 7. Ammonia Analysis Conditions
Trapping: Impinger 10ml H2O
Instrument (IC): DIONEX DX-120, Conductivity Detector
Column: IonPacCS12A, Guard Column: IonPacCG12A
Eluent: 20mM CH3SO3H, Flow Rate: 1.0mL/min
Suppresser: CSRS-1 (Recycle Mode), Column Temp.: 40 degree
Table 8. Nitrogen Compound Analysis Conditions
Trapping: 6L Canister → Tenax-TA (at -78 degree)
Instrument (GC): Shimazu GC-14B
Column: UnicarbonB-2000, Carrier Gas: He 50ml/min,
Oven Temp.: 70 degree for 5min, 70-120 degree at 8 degree/min
Inj Temp.: 200 degree, Detector: FTD
Table 9. Sulfur Compound Analysis Conditions
Trapping: 6L Canister → Chromosorb 101 (at –78 degree)
Instrument (GC): Shimazu GC-9A
Column: β, β’-ODPN 4m
Carrier Gas: N2 70ml/min, Oven Temp.: 70 degree Isothermal
Inj Temp.: 120 degree, Detector: FPD
Table 10. Low Boiling HC Analysis Conditions
Trapping: 6L Canister
Instrument: Entech 7000 + GC/MS: HP 6890 + 5972A
Column: HP-1, Length: 60m, Film: 1µm, ID: 0.32mm
Carrier He: 1.0ml/min,
Oven Temp.: 35 degree for 5min, 35-80 degree at 4 degree/min,
80-240 degree at 10 degree/min,
240 degree for 20min
Detector: MSD, Interface Temp.: 280 degree
Table 11. High Boiling HC Analysis Conditions
Trapping: Tenax-TA (at RT) Thermal Desorption: 280 degree
Instrument (GC/MS): Gerstel TDS + Agilent 6890+Agilent 5973N
Column: HP-1, Length: 60m, Film: 1µm, ID: 0.32mm
Carrier He: 1.0ml/min,
Oven Temp.: 35 degree for 5min, 35-80 degree at 4 degree/min
80-240 degree at 10 degree/min, 240 degree for 20min
Detector: MSD, Interface Temp.: 280 degree
Table 12. Lower Fatty Acid Analysis Conditions
Trapping: Sr(OH)2 Coated Glass Beads
Instrument (GC): Shimazu GC-14B
Column DB-Wax, Length: 60m, Film: 0.25µm, ID: 0.32mm
Carrier He: 1.0ml/min, Oven: 120-240 degree at 8 degree/min
Inj Temp.: 250 degree, Detector: FID