Analysis for Adsorbed Odor from Car Air Conditioner Evaporator
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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
*kazuhisa_uchiyama@denso.co.jp, **osamu_kasebe@denso.co.jp, ***kengo_kobayashi@denso.co.jp
TOYOTA CENTRAL R&D LABS., INC.
41-1, Aza Yokomichi, Oaza Nagakute, Nagakute-cho, Aichi-gun, Aichi-ken, 480-1192, JAPAN
**** e0291@mosk.tytlabs.co.jp, ***** hiroshi-ito@mosk.tytlabs.co.jp
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
Blower Evaporator
emitted from the source of components collecting even after 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. Odor Type Rotten Dusty Sweat,Tobacco
In contrast, four of the 23 users made a complaint Cause
Growth of Al(OH) 3 Adsorption and
Bacteria Desorption of Odor
in ten months. Odor Resin Reacted Layer Odor
A check for any odor from two of these units Bacteria
Chromate Layer
?
Mechanism
indicated a different type of odor unlike the Odor
uncomfortable odor or dusty odor. In addition, we Evaporator Evaporator Evaporator
Counter
counted the bacteria on the surface of six units -measure
Biocide New Coating Filter
including these two and found out that the number 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
an odor would be enhanced in addition to temperature No Odor
Evaporator
rising or lowering on the surface of the evaporator. Temp.
(Fig.3) An Example of Eco-mode Pattern
ON
Comp
The purpose of this study is to identify the OFF
causative substance of such an "odor" possibly Wet to Dry
Dry to Wet
resulting from the components accumulating on the Wet enough
Evaporator
surface of the evaporator and determine the odor Temp. Odor
mechanisms components through the analysis, clarify 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 Brain
analyzed how an odorous stimulus was transmitted. Olfactory
Epithelium Odor Measurement
Substances
The odorous stimulus first stimulates the olfactory Odor
Substances Chemical
Analysis Odor
cells on the "olfactory epithelium" as olfactory Recognition Emotion
receptors in the nasal cavities, then goes through the First Study, Restudy Sensory Test
Memory
olfactory nerve, and finally reaches the brain. At this Decision Image
Fig.4 Flow of Stimulus and Measurement
time, if the concentration of the odorous components is
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 *PCA:Principal Component Analysis
Odor Sensory Test Factor 2
evaluation strategy for relating the test values by Sampling Bag
2.72
Odor B
Cars
means of instrumental analysis with the odor sensory
evaluation values of the same samples. To correlate PCA*
0.00 Factor 1
Odor C
the results of analysis to the odoring evaluation values,
Odor A
Questionnaire
we focused on relationships between the types of odor -2.72
-2.72 0.00 2.72
Fig.5 Sensory Test and PCA
and the causative substances. Analysis on the chief
ingredients of the results of the odoring evaluation will identify
Partial Regression
judgment criteria, which are available to group the plots (Fig.5).
The odoring evaluation values in these vehicles are selected as Y = β1X1 + β2X2 + β3X3 + . . . + βpXp
objective parameters while the odor component analysis values are Observed
Value Explanatory Variate
specified as descriptive parameters. Since the intensity of an odor (Instrumental Analysis
Data)
Fig.6 Multiple Regression Analysis
in the vehicle is supposed to be highly correlated with the level of
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.
SampleNo. Date Name
(1) Panels: Invoked were general engineers and office workers who
1. Check on the number that you feel.
had little preliminary knowledge of odors and were not interested in [odor intensity] [Odor Pleasantness
/ Unpleasantness]
this evaluation. 5 Intense Odor 2 Pleasant
4 Strong Odor 1 Rather Pleasant
(2) Samples for evaluation: With an odorless specimen added as a 3 Odor Easily Sensed Odor 0 Neither
-1 Rather Unpleasant
blank, all the samples were resorted on a random basis irrespective 2 Weak Odor
1 Barely Recognizable Odor -2 Unpleasant
of the sampling sequence from the vehicles in such a manner that 0 No Odor -3 Very Unpleasant
2. Fill in the box that you feel.
the contents of the samples were unperceivable. Then, they were
3 : Very much so
named with alphabetic characters to conduct a blind test. 2 : Considerable
1 : Little so
(3) Evaluation environment: A silent chamber facing south without blank : Not at all
smoking was selected to conduct a test by means of curtains
Acid Sweet Burnt Acrid
Fish and meat Festering trash Dusty Tobacco
blocking off the direct rays of the sun under a temperature and Exhaust gas Sweat Cosmetics Garbage
Fusty Damp mop Dirty sock Fishy
humidity condition not making the panels feel uncomfortable. Interior odor
Comment ( )
(4) Questionnaire: The terms indicating the types of odors were Thank you
previously selected through several prior tests. By making 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 Intense Odor
4 Strong Odor
ranked at six intensity levels and seven degrees 3 Odor Easily Sensed
2 Weak Odor with the Kind of Recognizable Odor
respectively (Tables 1 and 2). 1 Barely Recognizable Odor
0 No Odor
2.1.3 Instrumental analysis for multiple regression analysis
We have decided to perform analysis by means of the possibly
Table 2. Odor Pleasantness / Unpleasantness
optimum strategy for each kind of "odorous" components supposed
3 Very Pleasant
to exist in the odor for each sort of sources and the actual vehicle. 2 Pleasant
1 Rather Pleasant
Under the conditions shown in Appendix A, instrumental 0 Neither Pleasant nor Unpleasant
-1 Rather Unpleasant
analysis was performed on each sort of components. A blank test -2 Unpleasant
-3 Very Unpleasant
was definitely conducted before and after sampling a specimen in
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 Temperature-controlled Room
Conditioned
new desktop test bench (hereafter called the "mini Clean Out Air Air Conditioner Sampling Bag
Unit
core bench" as shown in Fig.9) incorporating a
small-size evaporator (hereafter called the "mini
Exhaust
core") and intended for laboratory evaluation. R134a
Canister
Internally covered with stainless steel to
facilitate cleaning, the onboard car air conditioner 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. Sampling Bag
Mini-Core
On the other hand, the mini core (a small size evaporator) IN
Conditioned
Circulation Systems
Clean N2
built in the mini core bench is of a small size and low thermal Hot Cold
capacity. 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 Fig.9 Mini-Core Benchtemperature 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 Table 3. Test Conditions
Assembly Mini-Core
20°C and a relative humidity between 40 % and 60 % from Test Bench Bench
the typical conditions as described above. Temperature (degree) 20 ~ 30 20 ~ 25
Humidity (%RH) 40 ~ 60 30 ~ 60
We ranked the intensity of odor and the degree of
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
Factor
Table 4. Test Conditions
Eigenvalue Contribution Accumulated
performed analysis on the principal components.
As a result of the principal component analysis, three
5.309 0.531
Contribution
0.531
1
2 2.549 0.255 0.786
principal components having eigenvalue more than one were 3 1.059 0.106 0.892
4 0.482 0.048 0.940
identified. Additionally, since the degree of contribution was
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
Table 5. Test Conditions
components as the judgment criteria (Table 5).
Variate Factor1 Factor2 Factor3 Factor4
The first principal component was named as the
Intensity -0.163 0.979 -0.014 -0.076
"Unpleasantness" presenting high factor loadings Unpleasantness 0.831 0.372 0.216 -0.174
Acid -0.803 0.511 -0.170 0.161
with the "Odor Pleasantness / Unpleasantness" and Sweet -0.868 0.450 -0.079 0.062
Burned 0.815 0.448 -0.219 -0.017
the terms presenting unpleasant odors such as Dusty 0.871 0.066 -0.267 0.104
Tobacco 0.721 0.529 -0.242 -0.276
"burning, dusty, smoky, and exhaust gaseous" and
Exhaust Gas 0.753 0.274 -0.024 -0.024
"acid, sweet, and cosmetics" (with the Cosmetics -0.827 0.454 -0.222 -0.007
Interior Materials 0.038 0.471 0.866 0.045
uncomfortable quadrants defined to be positive due
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 withthe 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 Factor 2 Factor 3
1.0 1.0
each term plotted about the principal Intensity Interior
Odor
component axis. These plots indicate 0.5 Acid Tobacco Burned 0.5
Cosmetic Interior
Unpleasantness
that the evaluation quadrants are clarified Sweet
Odor Exhaust Gas
Intensity Unpleasantness
0 Dusty Factor 0 Factor
with the three evaluation axes, indicating 1 Sweet Exhaust Gas Burned 1
Acid
Tobacco
Cosmetic Dusty
how closely the term is related to the -0.5 -0.5
degree of uncomfortableness for the
-1.0 -1.0
samples used this time. -1.0 -0.5 0 0.5 1.0 -1.0 -0.5 0 0.5 1.0
Fig.10 Factor Loading
3.1.3 Principal component score
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.
Intensity Interior Odor
2nd principal component: Vehicles 2.2 2.2
with a strong smoky odor placed (+)
Very
Plastic
䊶䊶Vinyl
Smoky Almost New
䊶䊶
1.1 1.1
on the intensive (positive) side. Uses
(+) Strong
Interior Odor
Perfumes 䇭
3rd principal component: Vehicles
Group (+) Unplea (+) Unplea
0 -santness 0 -santness
with a strong interior or plastic
Uses
Perfumes
odor placed on the intensive -1.1
Smoking
-1.1 Group Smoking
Group
Group
interior odor (positive) side.
-2.2 -2.2
We acquired these results and -2.2 -1.1 0 1.1 2.2 -2.2 -1.1 0 1.1 2.2
: Smoking Car : Aromatic, Cosmetics, Perfumes : Others
found out that each principal Fig.11 Principal component score
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
the component analysis values used as the descriptive parameter. At this
Odor Intensity
4
3
time, the component analysis values were converted into logarithmic 2
variables for this analysis because the logarithmic physical values such as 1
0
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 ޓޓޓ ޓޓޓ
Unpleasantness = 0.469*log(Substanece-A)+0.449*log( -B)+0.204*log( -C)+ …
R:0.987, R**2:0.908
ޓޓ
acquired a high-precision regression
equation to identify those odor causative
ޓޓޓޓޓ
Intensity = 0.326*log(Substanece-D)+0.537*log( -E)+0.253*log( -F)+ …
R:0.978, R**2:0.910
substances. ޓޓޓޓޓ
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
Furthermore, we checked for the
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 Odor Intensity Unpleasantness
Mode 0 1 2 3 4 5 +1 0 -1 -2 -3
vertical axis of the graph refers to the operation modes of
Dry
the air conditioner, indicating the changes of Dry (with the
ON
blower), ON (with the compressor turned on), and OFF ON
(continual)
(with the compressor turned off). The horizontal axis refers
OFF
to the intensity of odor and the degree of unpleasantness.
OFF
(continual)
By allowing five evaluators to odor in turn, it is difficult to
Fig.14 Result of Odoring evaluation
conduct continuous evaluation with a limited number of
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 Concentration (ppb)
Mode 0 0.2 0.4 0.6 0.8 1.0
unpleasant component is described. In a part, a negative
Dry
value resulted by subtracting the blank value (as marked with
ON ND
"ND" on the graph) and, therefore, a significant difference is 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), and OFF (with the mini core at normal 4
Dry ON OFF
Intensity
3
temperature and the compressor turned off in reproduction 2
NG Intensity
mode). The vertical axis refers to the intensity of odor 1 Good
0
Unpleasantness
on the upper side and the degree of unpleasantness on the -1
Good Unpleasantness
-2
lower side (Fig.16). NG
-3
-5 0 5 10 15 20 25 30 35
Unlike the results with the onboard car air conditioner Time (min)
Fig.16 Result of Odoring evaluation
evaluation bench described above, it was possible to
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.
(2) Results of instrumental analysis
0.6 Dry ON OFF
This section describes the results of the instrumental
Concentration (ppb)
analysis. In the same manner, the horizontal axis refers to 0.4 i-Valeric Acid
Toluene * 1/10
the elapse time and indicates the changes of the Dry, ON, 0.2
and OFF modes and the bar graphs along the vertical axis
0.0
refer to the concentration of the component (Fig.17). -5 10 0 15 20 5 25 30
Time (min)
On the mini core bench, unlike the results with the Fig.17 Result of Instrumental Analysis
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 1. Dry 2. ON : Dry to Wet
water-repellent components represented Hydrophobic Substance
Hydrophilic Substance Hydrophobic Substance Released
by toluene from among the odorous
Ex. Toluene
H2O
Odor Substances
Flocculated Water
components collecting on the surface of
the evaporator are emitted in the form of
displacement with moisture in response to
䇭
Evaporator’s Surface
Odor Intensity: Strong
the start of water condensation with the 3. ON Continual : Wet enough 4. OFF : Wet to Dry
compressor turned on and this is felt as the Hydrophilic Substance’s Elution Hydrophilic Substance’s Vaporization
collection odor when the unit is turned on.
Ex. i-Valeric acid
Flocculated Water
Next, as additional moisture is
condensed, the evaporator surface
Odor Intensity: Weak Odor Intensity: Very Strong
temperature is lowered in the continuous
Fig.18 Adsorbed Odor Mechanism
turn-on mode with the evaporator covered
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 1. Special Pollution Section, Atmospheric Integrity Bureau, Environment Agent; Technical guidelines for the three-point comparison type odor bag strategy, - from a odoring test procedure study report by the Environment Agent -, Environment and measurement technology, vol.9, No.9, (1982). 2. Special Pollution Section, Atmospheric Integrity Bureau, Environment Agent; Fundamental data for teaching 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). 4. Toshiyuki Tanaka; Sampling organic chemical compounds gases in the air by the adsorption and capture strategy at normal temperature Part 2, Actual atmospheric measurement and sample measurements, Environment and measurement technology, vol.16, No.2, (1989). 5. Toshiyuki Tanaka; Performance of the Tenax-GC sampling tube for analysis on volatile organic chemical compounds at ppb level in the air, Air pollution society paper, Volume No.19, Number 6, (1984). 6. Nobuyuki Kashihira; Effect of sample injection through gas chromatography - Measuring a sulfide by means of GC-FPD -, Environment and measurement technology, vol.16, No.2, (1989). 7. Emiko Sudo; Measuring methods in environmental analysis, Environment and measurement technology, vol.12, No.9, (1985). Tomohiko Ishiguro; Details of how to measure the public specified bad-odor substances along with instructions, Environment and measurement technology, vol.14, No.1, (1987). 8. Kazuhisa Uchiyama, et al.; Analysis on odors adsorbed by the car air conditioner - Analyzing sensory odor evaluation and instrumental analysis data by means of multivariate analysis -, Compilation before Academy Lecture Meeting by Society of Automotive Engineers of Japan, Inc. Nos.981, 293, (1998), and 9831919. 9. Shigeyuki Sato; Quality of air in the passenger compartment, Toyota Central Laboratory Research and
Development review, Vol.33, No.4, (1998).
10. Shigeyuki Sato et al.; Study in relation to odors of automobiles, Compilation before Academy Lecture Meeting
by Society of Automotive Engineers of Japan, Inc. Nos.981, (1998), and 9831892.
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: FIDYou can also read
