Journal of Chromatography A, 1204 (2008) 72–80

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Journal of Chromatography A

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Evaluation of malodor for automobile air conditioner evaporator by usinglaboratory-scale test cooling bench

Kyung Hwan Kim, Sun Hwa Kim, Young Rim Jung, Man Goo Kim ∗

Department of Environmental Science, Kangwon National University, 192-1 Hyojadong, Chunchon, Kangwondo 200-701, South Korea

a r t i c l e i n f o

Article history:Received 26 March 2008Received in revised form 3 July 2008Accepted 3 July 2008Available online 17 July 2008

Keywords:OdorEvaporator

a b s t r a c t

As one of the measures to improve the environment in an automobile, malodor caused by the automobileair-conditioning system evaporator was evaluated and analyzed using laboratory-scale test cooling bench.The odor was simulated with an evaporator test cooling bench equipped with an airflow controller, airtemperature and relative humidity controller. To simulate the same odor characteristics that occur fromautomobiles, one previously used automobile air conditioner evaporator associated with unpleasant odorswas selected. The odor was evaluated by trained panels and collected with aluminum polyester bags.Collected samples were analyzed by thermal desorption into a cryotrap and subsequent gas chromato-graphic separation, followed by simultaneous olfactometry, flame ionization detector and identified by

Car air-conditioning systemGas chromatography–olfactometrySensory evaluation

atomic emission detection and mass spectrometry. Compounds such as alcohols, aldehydes, and organicacids were identified as responsible odor-active compounds. Gas chromatography/flame ionization detec-tion/olfactometry combined sensory method with instrumental analysis was very effective as an odorevaluation method in an automobile air-conditioning system evaporator.

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. Introduction

Over the past decades, automotive air-conditioning (A/C) sys-ems (ACS) have been undergoing constant improvements tochieve higher efficiency and also to address environmental con-erns [1]. Recently, the odor from inside of an automobile has beenecognized as one of indoor air pollutants, so it has become a dif-cult task to resolve in the automobile industry. More than 1500lastic components, seats, insulators and other interior materialsave been pointed out as the main cause of volatile organic com-ounds (VOCs) and odors emitted from new automobiles. Recently,ir conditioner evaporators have been suspected as one of the odorources in automobiles. Due to the odor mainly produced beforend after operating the air conditioner, consumer complaints havectually increased. Some automobiles may exhibit musty and nox-ous or sour odor coming from the climate control system. It is most

oticeable when the A/C is first turned on [2]. There have beeneveral studies concerning the odors of air-conditioning systems3–7].

∗ Corresponding author. Tel.: +82 33 250 8576.E-mail address: mgkim@kangwon.ac.kr (M.G. Kim).

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A Japanese research group focused on odor production mech-nism and odorants. They found that the odors caused byCS evaporators mainly occur when the surface of evaporatorecomes wet and dry (A/C off → on and A/C on → off). Fur-hermore, these odors stimulate drivers’ nose, and consequently

ake the drive unpleasant [3]. On the other hand, Americanesearch groups have focused on microorganisms to resolve ACSdor problems. Simmons et al. found that insulation materialshich absorb moisture and volatile organics appear to provide

uitable substrates for fungal colonization [5]. Simmons et al.lso found that climatic conditions (high humidity) and air-orne fungal populations are undoubtedly major factors in the

ncidence and severity of fungal colonization. Automobiles onceolonized by fungi may continually or sporadically emit nox-ous odors or sensitize products that affect the occupants ofhe automobile. In most cases, automobile engines and venti-ation fans are seldom kept running after the air-conditioningystem. Running the engines and ventilation fans for a shortime would reduce the moisture residues that are necessaryor the growth of the fungi [5]. A study on mixed biofilms

n automobile air-conditioning systems shows that bacteria andungi may form mixed, desiccation-resistant biofilms on the

etal heat exchanger fins within the core of ACS evaporatorss well as on forms, plastics, and other components. Theseixed biofilms when moistened may be major contributors to

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K.H. Kim et al. / J. Chrom

pisodic noxious odors in automobile air-conditioning systems [6].oisture retention, even episodic events, within the ACS in

onjunction with such biofilms appeared sufficient for odor pro-uction. The accumulation of bulk organic debris, leaves, insects,tc., of course could help in initiating the microbial problem, butost units with odors that were examined were free of such mate-

ials. Methods to reduce or eliminate the moisture retention inhe ACS, coupled with less susceptible or antimicrobial substrata,ould seem the most practical means for controlling microbial-

ssociated VOCs [7].However, both Japanese and American studies have limita-

ions in approaching the odor problems of ACS. The formerocused on odor production mechanisms of ACS throughdor sensory test and instrumental analysis separately andepended on statistical data correlation between sensory testsnd instrumental analysis. The latter only focused on microor-anisms which could possibly colonize on the ACS withoutdor sensory data since its main goals were not only mal-dor emitted from ACS but also the growth of microorgan-sms.

ACS evaporator consisting of aluminum absorbs heat from theabin air and removes its moisture, hence the odor could beaused by the matter accumulated when indoor and outdoor airasses through the evaporator’s fins. These matters could be useds nutrition for microorganisms [6,7] and converted into odorompounds by decomposition. Therefore, it is difficult to iden-ify odor-active compounds emitted from ACS only with simplenstrumental approaches. In odor research, it is well establishedhat the odor thresholds of volatile compounds can differ by

any orders of magnitude (e.g., parts per trillion up to odor-ess compounds) [8,9]. The relationship between concentrationnd odor intensity may also vary considerably between com-ounds. Because of the large variation in these two properties,he response of a chemical gas chromatography detector (e.g.,

flame ionization detector or a mass spectrometer) is not rep-esentative of odor activity. For example, the most abundantompounds in a chromatogram may not be the most importantdorant [10]. Consequently, the impact of a compound on thedor of a sample must be evaluated using human assessors [11].valuable tool for identifying character-impact odorants is gas

hromatography–olfactometry (GC–O), where human “sniffers” aresed to detect and evaluate volatile compounds as they elute fromGC column [8].

Therefore, the studies which have been used onlyC/flame ionization detection (FID) and mass spectrom-try (MS) so far had limitations for the identification ofdor-active compounds and their sources. Recently, thermalesorption–cryofocusing–GC/FID/olfactometry which combineswo detectors, olfactometry and flame ionization detector simul-aneously, has been effectively applied to the management ofdor-active compounds [12].

In this study, GC/FID/olfactometry combined sensory methodith instrumental analysis and a direct odor sensory evaluationith GC/MS, GC/atomic emission detection (AED) analysis wereerformed to identify odor-active compounds emitted from ACSvaporator. Malodor caused by the automobile air conditionervaporator was evaluated and analyzed using laboratory-scaleest cooling bench which could simulate the same odor charac-eristics that occur in automobiles. Samples were analyzed byhermal desorption into a cryotrap and subsequent gas chro-

atographic separation, followed by simultaneous olfactometry,ame ionization detector. Odor-active compounds were identi-

ed by GC/AED, GC/MS. Compounds such as alcohols, aldehydes,nd organic acids were identified as responsible odor-active com-ounds.

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. A 1204 (2008) 72–80 73

. Materials and methods

.1. Laboratory-scale test cooling bench system

To evaluate the odor produced from an ACS evaporator, aaboratory-scale test cooling bench was designed. The laboratory-cale test cooling bench was designed to control inflow air, bothn temperature and relative humidity. With this system, we couldvaluate only the odor produced from an evaporator with airurification equipment. We used a blower, blower controller andefrigerant (R-134a) used in real automobiles. One previously usedCS evaporator (mileage 4000 km) associated with unpleasantdors was selected to simulate the same odor characteristics. Toonitor temperature and relative humidity of the inlet and outlet

ir of evaporator, six temperature sensors and one relative humid-ty sensor were equipped at each position in both sides of thevaporator, respectively. The signal collected from each sensor wasonitored by data acquisition (34970A data acquisition unit, Agi-

ent Technologies, Santa Clara, CA, USA). The whole test benchystem is shown as in Fig. 1a and b.

Every required factor such as the outlet area of evaporator and airow rate was measured three times to evaluate the air-conditioningapacity of the laboratory-scale test bench to simulate the actualonditions. Engineering equation solver (EES) software was usedo evaluate air-conditioning capacity of the laboratory-scale testench to compare that of actual automobile.

.2. Sampling

Canister (Restek, PA, USA) and bag (Top Trading, Seoul, Southorea) sampling methods were compared to determine which sam-ling method is effective. The odor from the test cooling benchas collected with the two sampling methods then the sampleas focused into a cryotrap (50 ml/min for 10 min) and analyzedy GC–O. The same procedure was repeated three times for repro-ucibility. Fig. 2 shows aluminum polyester bag (a) and its samplingethod (b).The samples could be focused into a cryotrap and ana-

yzed by GC–O. However, it was necessary to apply differentample introduction method for GC/MS and GC/AED analysisince it was difficult for GC/MS and AED to equip the thermalesorption–cryofocusing system. Furthermore, it was necessary tooncentrate large sample volume for GC–O analysis to detect odorluted from olfactory detection port (ODP) while small sample vol-me would be enough for the analysis of GC/MS and AED due to

imited sample volume. For these reasons, solid-phase microextrac-ion (SPME) method was considered. SPME method is a very simplend efficient, solventless sample preparation method and ideallyuited for MS application, combining simple and efficient sam-le preparation with versatile and sensitive detection [13]. In foodesearch field, it is well known that Carboxen/polydimethylsiloxaneCAR/PDMS) fiber is very effective to sample odors and aroma14,15]. Therefore, SPME fiber (CAR/PDMS) was applied to absorbdor compounds from collected sample in aluminum polyester bag.he standard n-alkanes (C5–C18) were analyzed in GC/FID with bag-hermal desorption–cryofocusing method and GC/MS, AED withag-SPME method to ensure the identification data reliable. Theollected sample in bag was absorbed on SPME fiber (CAR/PDMS;5 �m thickness; Supelco, Bellefonte, PA, USA) for 2 h at 25 ◦C inconstant temperature oven and then introduced to the GC/MS

raph at the temperature and time suggested by manufacturers270 ◦C for 2 h). The odor components were thermally desorbedrom SPME fibers at each injector (250 ◦C) and focused at the fore

74 K.H. Kim et al. / J. Chromatogr. A 1204 (2008) 72–80

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art of the column with liquid nitrogen for 10 min and then ana-yzed.

.3. Odor sensory evaluation

According to the Korean official test method for offensivedor [16], five panels were selected among 10 candidates. Therere four different test solutions for the selection of odor pan-ls: acetic acid (99% Daejung, Gyeonggi, Korea), trimethylamine40%, w/w, Sigma–Aldrich, St. Louis, MO, USA), methyl cyclopen-anol (99%, Sigma–Aldrich), and �-phenylethyl alcohol (60-12-8,igma Aldrich); their concentrations were 1.0, 0.1, 0.32, 1.0% (w/w),

espectively. In this test, panels should be able to recognize eachest solution odor and evaluate their characteristics and intensityetween 3 and 4. Selected panels perceived the odor intensityetween 3 and 4 and expressed the right odor characteristics forhe test solutions.

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agram (lower) of lab-scale test bench.

Panelists recorded odor characteristics and intensity when eval-ating. The odor intensity was classified 0–5. Odor intensity 0

ndicates odorless, 1 indicates very faint odor (threshold), 2 indi-ates weak odor, 3 indicates moderate odor, 4 indicates strong odor,indicates very strong odor (from odor intensity 2, panels must

xpress odor characteristics) [17]. Each selected panel was trainedo express and classify the odor.

Before the odor evaluation, the test room was ventilated enoughnd all of the windows, doors were closed when evaluating. Pan-ls evaluated the odor right in front of the evaporator outlet. Fig. 3hows the odor evaluation schematically. Five panels (A–E) evalu-ted the odor in turn.

.4. Odor reproduction tendency

To find out the odor reproduction tendency during the evapo-ator operation, five times of odor reproduction experiment wereerformed. The inflow air temperature was set at 25 ◦C and rel-

K.H. Kim et al. / J. Chromatogr

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Q(FSfhtwas 250 ◦C. The same sample introduction was applied for GC/AEDanalysis. The analytical conditions of GC/FID-O, MS, and AED aredetailed as shown in Table 1.

Table 1Analytical condition of GC/FID/O, GC/AED, GC/MS

CryofocusingCoolant Liquid N2

1st Loop (6.35 mm I.D.), sample focusing: 50 ml/min for10 min

2nd Loop(0.80 mm I.D.) for 10 min

Thermal desorptionTemperature 100 ◦C boiling water

Transfer line temperature: 200 ◦C

GC/FID/OColumn UA-1(15 m × 0.53 mm I.D. × 0.5 �m film, Frontier Lab)Column flow FID: 3.0 ml/min, ODP: 0.5 ml/minOven temperature 40 ◦C(5)–10 ◦C/min–80 ◦C(0)–15 ◦C/min–250 ◦C(10 min)Injector temperature 200 ◦C

ig. 2. Bag sampling method: (a) aluminum polyester bag and (b) lung sampler.

tive humidity ranged from 50 to 70%. The evaporator operationime was varied to find the relationship between evaporator oper-tion time and odor reproduction. Evaporator operation time, inletemperature and relative humidity of the evaporator, 100% rela-ive humidity continuation time at the outlet of evaporator, odorontinuation time, and odor intensity were measured.

.5. Gas chromatography–olfactometry

Three olfactometry panelists, trained in GC-sniffing and odorecognition, sniffed the humidified effluent of GC and recorded

Fig. 3. Odor evaluation.

G

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. A 1204 (2008) 72–80 75

he intensity and characteristics of each odor simultaneously. Dur-ng the sniffing sessions, the panelists were instructed (i) to signalach odor perceived by pressing a button for as long as the odoras perceived, (ii) to describe the odors reported in written, and

iii) to quantify their intensity on a scale, in the present case withve levels (1, very weak; 2, weak; 3, moderate; 4, strong, and 5,ery strong) [18]. A five point scale was preferred to that proposedy Ferreira et al. [19]. The output of the variable potentiometeras connected to a separate channel in the autochro-GPC softwaresed to collect GC/FID data, and time intensity data from ODP wereontinuously recorded. Flow rate ratio between FID and ODP washosen experimentally to ensure the best compromise betweenhromatographic resolution and sufficient effluent at the sniffingort.

.6. Mass spectrometry and atomic emission detection

The same odor sample was injected splitless into a GCMS-P2010 (Shimadzu, Kyoto, Japan) with a capillary column

UA-5, 60 m × 0.25 mm I.D., 0.1 �m film thickness; Frontier Lab,ukushima, Japan) by using SPME fiber (Carboxen/PDMS, 75 �m,upelco, Bellefonte, PA, USA). The temperature was programmedrom 40 to 250 ◦C at 5 ◦C/min with a 10-min final temperatureold. The MS (electron impact ionization) conditions were: ioniza-ion energy, 70 eV; mass range, 27–400 m/z. Injector temperature

FID temperature 250 ◦CGas H2: 30 ml/min, air: 300 ml/min, make-up: 15 ml/minOlfactometry Transfer-line temperature: 100 ◦CGas Humidified air: 100 ml/min, make-up: 5 ml/min

C/AEDColumn UA-5 (30 m × 0.25 mm × 0.1 �m)Column flow 1.0 ml/min, HeOven temperature 40 ◦C(0 min)–5 ◦C/min–250 ◦C(10 min), 57 min analysis

timeInjector temperature 250 ◦CActivation MIP (microwave-induced plasma)Channels C 193 nm, O 171 nm, N 174 nm, S 181 nmReagent gas O2, H2, 10% CH4 in N2

C/MSColumn UA-5 (60 m × 0.25 mm × 0.1 �m)Column flow 1.0 ml/min, HeOven temperature 40 ◦C(0 min)–5 ◦C/min–250 ◦C(10 min), 57 min analysis

timeInjector temperature 250 ◦CIonization EI (70 eV)Scan range 27–400 m/zInterface temperature 250 ◦C

76 K.H. Kim et al. / J. Chromatogr. A 1204 (2008) 72–80

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ature and relative humidity monitored at the evaporator inlet afterthe modification. This fluctuation was observed over 100 min andthe same observations were carried out to check the cooling benchsystem. It is recommended that before testing evaporator, it is nec-essary to stabilize the test bench system at least for 20 to 30 min

Fig. 5. Fluctuation of temperature and relative humidity monitored at the evapora-tor inlet.

Fig. 4. Odor e

.7. Identification of odor-active compounds

The complex odor emitted from the evaporator was measuredith a direct odor sensory test as shown in Fig. 4. Collected samplesere analyzed by thermal desorption into a cryotrap and subse-

uent gas chromatographic separation, followed by simultaneouslfactometry, flame ionization detector and identified by GC/AEDnd GC/MS.

Odor-active compounds were identified by n-alkanes linearetention indices (C5–C18) on UA-1 and UA-5 columns and withdor quality. Most of the odor-active compounds were confirmedy retention indices. Library mass spectra and some standardompounds were also used. The odor-active compounds wereonclusively determined by the information collected from eachest and analysis (Fig. 4). Furthermore, nasal impact frequencyNIF) was used to identify each odor compound separated fromC/FID/O system among odor compounds. Although previously

wo research groups proposed to calculate peak detection frequen-ies from odors perceived by a panel of 6–10 assessors to improvehe reliability of aromagrams, NIF was calculated by the resultsrom three assessors in this study due to lack of sample (totalolume of the sample was 5 l). NIF indicates the detected odor fre-uency (%) at olfactory detection port by a panel of three assessors20].

. Result and discussion

.1. Air-conditioning capacity of the laboratory-scale test bench

With the EES software, theoretical condensed water and air-onditioning capacity were calculated. Calculated air-conditioningapacity was 2.088 kW which is similar to the air-conditioningapacity of real automobiles. The difference between calculatedondensed water and collected condensed water was 0.02 g/minhich meant the calculated air-conditioning capacity was correct.

urthermore, the set temperature (25 ◦C) and relative humidity50%) were monitored to check the function of laboratory-scaleest bench. Fig. 5 shows the fluctuation of temperature and relativeumidity monitored at the evaporator inlet. The set temperaturend relative humidity were satisfied within 5% (temperature: ±3 ◦C,elative humidity: ±5%).

It was difficult to make the set value stable for the first experi-ent. Especially, the relative humidity fluctuation ranged from 20

o 30% since the sensitivity of humidifier was not good. After know-ng that both temperature and relative humidity sensors were notensitive enough, those sensors were changed into more sensitivenes and the sensing time was adjusted from 10 to 5 s interval.urthermore, each sensor was uncapped to get better sensitivity

tion method.

gainst the air flow. Fig. 5 shows the fluctuation of the tempera-

Fig. 6. Change of odor characteristics during the evaporator operation.

atogr. A 1204 (2008) 72–80 77

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Table 2Evaporator operation time and change of odor continuation time, odor intensity

1st 2nd 3rd 4th 5th

Evaporator operation time (min) 10 10 20 20 74Inlet temperature (◦C) 25 25 25 25 25Inlet relative humidity (%) 50 60 50 70 50100% R.H. continuation time (min) 9 14.3 23 45.5 23.5Odor continuation time (min) 0.3 2.4 1.5 11.5 14.7Odor intensitya 4 3 3-4 2-3 2

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epending on the outside air conditions (temperature and relativeumidity).

.2. Odor characteristics during the evaporator operation

According to a previous study [3], there is a relationship betweenhange of odor characteristics and that of evaporator surface con-ensed and vaporized (when the compressor is turned on andff). Furthermore, many consumer complaints were induced whenrivers turn on and off their air-conditioning system as well. There-ore, air-conditioning operation was monitored with the changef temperature and relative humidity, and the odor was evaluatedy the trained panelists to find the relationships between them.here were significant changes in odor characteristics during thevaporator operation (Fig. 6).

The faint odors were perceived right before and during the evap-rator operation but their odor intensity and unpleasantness werensignificant. However, sour, vinegar-like odor was perceived for0 min after turning off the evaporator. Relative humidity at theutlet of the evaporator was gradually decreased from 100% whenhe strong odors were perceived. The relative humidity was rapidlyecreased 23 min after turning off the evaporator and the odor

ntensity was further stronger. Odor sampling was performed athis point of time for three times. The odors became faint 30 minfter stopping the evaporator. This similar tendency occurred fiveimes for the replicated odor reproduction experiments. All of theanelists perceived strong odors when the relative humidity at theutlet of the evaporator was gradually or rapidly decreased from00% relative humidity. This odor production tendency was theame as the result of the previous study [3]. However, those ten-encies greatly depended on both the controlled air conditionse.g. temperature, relative humidity) and air flow rate from thelower (e.g. levels 1–6). Table 2 shows the evaporator operation

ime and change of odor continuation time, and odor intensity.00% relative humidity continuation time and odor continuationime and odor intensity were changed depending on the evap-rator operation time. Furthermore, it was found that when thevaporator operation time is longer, the odor continuation time

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ir flow was 200 m3/h. Odor was perceived after the 100% R.H. continuation time.a Odor intensity: 0, odorless; 1, faint (threshold); 2, weak; 3, moderate; 4, strong;

, very strong.

ecomes longer but the odor intensity becomes weaker. On theontrary, when the evaporator operation time is shorter, the odorontinuation time becomes shorter but the odor intensity becomestronger (more detailed results are described in Section 3.4). There-ore, when sample collection is carried out for the odor emittedrom the evaporator, short evaporator operation time is stronglyecommended to get better results. Otherwise, it would be veryhallengeable to collect and identify the odor from the evaporator.

.3. Odor sampling

Canister (6 l, Restek) and aluminum polyester bag (5 l, Toprading) sampling methods were compared to determine whichampling method is effective. Between the two methods, canis-er had very low background compared to bags (data not shown).owever, it was difficult to collect odor sample by using canister

ince it has high sampling flow rate and the collected odor cannote perceived by panelists to check if the odor has the same char-cteristics. Although a bag method had a little higher backgroundevel compared to the canister method, more odor peaks could beerceived from the used bags in GC/FID/O analysis. Furthermore,

t was possible to collect the odor effectively using bags since theampling flow rate is not so high and the collected odor could beerceived by panelists. The odor was collected in both canisters andags at the same time (n = 3) and they were analyzed three times

tion of the references to color in the text, the reader is referred to the web version

78 K.H. Kim et al. / J. Chromatogr. A 1204 (2008) 72–80

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or each sample by GC/FID/O. No odor was perceived from canisteramples. On the contrary, several odors were perceived from bagamples. The average perceived odor peaks were 3.7 times for theag sample while canister sample had no odor peak. A bag blankas also analyzed by putting pure nitrogen gas in GC/FID/O, GC/MS,

nd GC/AED analysis. No odor was perceived in GC/FID/O and theevel of bag blank was similar to SPME blank in GC/MS and GC/AEDnalysis. Furthermore, bag blanks by putting outside air and airrom the laboratory room were analyzed in GC/FID/O analysis. Theesults from blank test in GC/FID/O are shown in Fig. 7. The blackolid line chromatogram indicates FID signal and the red solid linet the bottom of each chromatogram indicates ODP signal.

.4. Odor reproduction tendency

Table 2 shows evaporator operation time, inlet temperature andelative humidity of the evaporator, 100% relative humidity contin-ation time at the outlet of evaporator, odor continuation time, anddor intensity during the five times of odor reproduction experi-

ents.Table 2 shows the effect of 100% relative humidity continuation

ime, odor continuation time, and the odor intensity correspond-ng to the evaporator operation time. Several facts were found fromhis result. First, by the evaporator operation time and relative

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ig. 9. Total ion chromatogram of odor from an evaporator by SPME-GC/MS. (For interpref the article.)

tom, inverted). (For interpretation of the references to color in the text, the reader

umidity of inflow air, the 100% relative humidity continuationime increases in proportion to the amount of water which can beondensed on the surface of evaporator after stopping evaporatorperation. Second, the odor continuation time increases propor-ionally with the 100% relative humidity continuation time. Third,he odor intensity decreases inversely proportional to the odor con-inuation time.

All things taken together, the odor production in real automo-iles could appear corresponding to the condensed water on theurface of the evaporator. For example, after a driver turns off theutomobile air conditioner, the condensed water on the surfacef evaporator will be gradually or rapidly vaporized correspond-ng to the inflow air and comes inside the automobile and finallyhe driver will perceive the odor. The vaporized water can includeydrophilic odor compounds. When the fact is considered that ifhe odor continuation time is longer, the odor intensity becomeseaker, the evaporator operation time has to be short from 10 to0 min (inflow air temperature: 25 ◦C; inflow air relative humidity:0%; air flow amount: 200 m3/h) for effective odor sampling and

valuation.

The above interpretation about the relationship between thedor production, intensity and evaporator operation time and themount of air condensed on the surface of evaporator is consider-bly related to the fact that a lot of consumer complaints related to

tation of the references to color in the text, the reader is referred to the web version

atogr. A 1204 (2008) 72–80 79

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Table 4Odor characteristics and compounds with each system’s retention indices

No. Retention indices Odor characteristics Compoundsa

ODP MS AED (O)

1 <500b <500b <500b Plastic ∼Ketone2 <500b <500b <500b ?c ∼Ether3 603 595 595 Sour ∼Acid4 630 626 634 ?c ∼Alcohol5 673 661 –d ?c ∼Alcohol6 675 685 670 Burnt, sour ∼Acid7 923 948 949 Cutting plastic ∼Pinene8 945 972 976 Fragrant ∼Aldehyde9 960 –d –d Sour Unknown

10 1032 1028 1028 Greasy, oil like ∼Alcohol11 1083 –d –d ?c Unknown12 1091 1105 1108 Unpleasant ∼Aldehyde

a Identified compounds were indicated as their kinds since the information aboutthe odorants are confidential.

b Retention indices below 500: Peaks which cannot be indicated as retentionindices, were indicated their retention time.

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heir air-conditioning system mainly happen in spring and autumn.n fact, relative humidity is very high in summer (annual aver-ge: 80%, Korea Meteorological Administration, 2006) and the usersormally use their air conditioners for a long time, which makes

ess odor productions, faint odor intensity, and characteristics. Thisact makes the odor complaints few in summer. Conversely, rel-tive humidity is relatively lower in Spring and Autumn (annualverage: 50–60%, Korea meteorological administration, 2006) thanummer and users normally use their air conditioners for a shortime to make it cool temporally or to remove the moisture fromheir windshield, which makes high odor productions and strongdor intensity and characteristics. This fact induces many consumeromplaints in spring and autumn.

.5. Sensory evaluation

To simulate the same characteristics of odor that occur inutomobiles, one previously used automobile air conditioner evap-rator associated with unpleasant odors was selected for theaboratory-scale test bench. The main odor sensory evaluationas performed when the evaporator was: off, from off to on, andn, from on to off. The odor was evaluated by the trained pan-lists. When the evaporator was turned off from the operationas the most unpleasant odor occurrence mode in this study. Thedor intensity was three and the produced odors had sour, rottenour, and vinegar like characteristics. With these sensory results,C/FID/O analysis was performed to separate a single odor from

he complex odors and compare the odor characteristics.

.6. GC/FID/olfactometry

Fig. 8 shows the comparison between FID chromatogram andIF profile. Abbott et al. [21] proposed to objectify a single odor,hich panels perceived at the ODP, as averaged perceived odor

requencies. From this comparison, one inversed peak againstID chromatogram indicates one perceived odor. For example,hen n = 3, if one odor of the same retention time was perceived

hree times, three peaks accumulate to the NIF profile (coincidentesponse chromatogram) as shown below.

Out of 12 peaks, the total peaks which panels perceived threeimes were 6 (peak number 1, 3, 6, 7, 8, and 10). The rest of peaksere perceived twice. Table 3 shows the odor characteristics and

etention indices perceived at ODP. The odor characteristics per-eived at ODP was very similar to the odor sensory evaluation result.

able 3dor characteristics of each odor peak perceived at olfactory detection port and their

etention indices

o. Panels Odor characteristics

A B C

1 0.95a 0.96a 0.98a Plastic2 1.12a 1.30a – ?b

3 630 633 629 Sour4 675 673 – ?b

5 675 681 – ?b

6 731 731 733 Burnt, sour7 921 922 923 Cutting plastic8 939 945 949 Fragrant9 959 965 – Sour

10 1032 1033 1037 Greasy, oil like11 1083 1083 – ?b

2 1091 1098 – Unpleasant

a Retention time: Peaks which cannot be indicated as retention indices, werendicated their retention time.

b The panels indicated question mark when they smell something slightly butould not express what the smell was.

Gatmrs

GtTtwfiul1pci

toata

c The panels indicated question mark when they smell something slightly butould not express what the smell was.

d Peak that was not able to be found in other systems.

t ODP, complex odor can be separated as a single odor. For thiseason, separated single odors can have very different odors.

Three different trained panelists (A–C) perceived the eluteddors at ODP. The panelists wrote the odor characteristics whilehey were evaluating odors. Although the same odor sample wasnalyzed and evaluated, the odor peaks perceived by panelists werelightly different from each other since each of them had differentensitivity against the odors. Panel A had an excellent sensitivity, Bad a normal sensitivity, and C was a little insensitive to the odorsompared to others. However, it was useful to have this result sincehe main or strong odor could be implicated from this result.

.7. GC/AED, GC/MS analysis

With GC/AED analysis, characteristic oxygen peaks were iden-ified and their retention indices were same as the peaks foundn GC/FID/O analysis. Nine of twelve compounds were detected inC/AED oxygen analysis. No peaks were found in the GC/AED sulfurnd nitrogen analysis. GC/MS analysis was performed to identifyhe name of odor-active compounds. Fig. 9 shows total ion chro-

atogram of odor sample by using GC/MS with odor peaks. Theed lines indicate the odor peaks identified in GC/FID/O analy-is.

Among 12 odor peaks, 10 odor peaks could be identified withC/MS analysis. Identified odor-active compounds mainly con-

ain “oxygen.” They were mostly alcohols, aldehydes, and acids.hese compounds had over 90% similarity. The US National insti-ute of Standards and Technology (NIST) and Wiley (7th edition)ere used as standard spectrum libraries. To ensure the identi-cation, standard chemicals and standard retention indices weresed. Fig. 10 shows mass spectra between sample and standard

ibrary. It shows two odor-active compounds (A and B) among0 identified odor-active compounds. Identified odor-active com-ounds are confidential since this study was supported by aompany (identified odor-active compounds with only their groupsn Table 4).

Identified odor-active compounds and their odor characteris-

ics with each retention indices are shown in Table 4. Identifieddor peaks, retention indices of each system and odor compoundsre shown in this table. From the odor compound identification,he odor peaks having “sour” characteristics were identified ascid group. The two odor peaks having retention time below 500

80 K.H. Kim et al. / J. Chromatogr. A 1204 (2008) 72–80

een sa

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4

dpossathaatoratusfe

A

R

R

[

[[

[[[

[

Fig. 10. Mass spectra betw

ere identified only with their retention time. With a bag-thermalesorption–cryofocusing–GC/FID/olfactometry system, the sampleould be concentrated enough to be analyzed and evaluated since00 ml sample was focused. However, it was little difficult to iden-ify all the odor compounds in GC/AED, MS analysis since differentample introduction method was used. As a result of it, some identi-ed odor peaks in GC/O analysis could not be identified in GC/AED,S analysis. To get better results, it is recommended to use the

ame sample introduction method.

. Conclusion

With the laboratory-scale test bench simulating the odor pro-uced from an automobile’s air conditioner evaporator, the sameroblematic odor was reproduced. The characteristics of odorccurrence were similar to the real automobile’s one and also theame characteristics of odor were reproduced using laboratory-cale test cooling bench system. The odor produced from anutomobile air conditioner evaporator has very different charac-eristics from ordinary odor samples. It has high relative humidity,igh linear velocity, and is emitted at very low concentration,nd its production is intermittent. To resolve these difficulties,bag-thermal desorption–cryofocusing–GC/FID/olfactometry sys-

em was designed and the application was effective. Produceddors emitted from the evaporator used in this study had sour,otten sour, and vinegar like characteristics. Compounds suchs alcohols, aldehydes, and organic acids were identified as

he main odor-active compounds emitted from the evaporatorsed in this study. GC/FID/olfactometry combined direct odorensory method with instrumental analysis was very effectiveor odor evaluation method in an automobile air conditionervaporator.

[[[[[

mple and standard library.

cknowledgement

This research was supported by the advanced engineering team,&D center, Halla Climate Control Corp., Daejeon, Korea.

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