Content uploaded by Pei-Chih Wu
Author content
All content in this area was uploaded by Pei-Chih Wu on Jun 04, 2021
Content may be subject to copyright.
Atmospheric Environment 41 (2007) 1230–1236
The effects of evaporating essential oils on indoor air quality
Huey-Jen Su, Chung-Jen Chao, Ho-Yuan Chang, Pei-Chih Wu
Department of Environmental and Occupational Health, College of Medicine, National Cheng Kung University, 138 Sheng Li Road,
Tainan 70428, Taiwan, ROC
Received 8 May 2006; received in revised form 19 September 2006; accepted 22 September 2006
Abstract
Essential oils, predominantly comprised of a group of aromatic chemicals, have attracted increasing attention as they are
introduced into indoor environments through various forms of consumer products via different venues. Our study aimed
to characterize the profiles and concentrations of emitted volatile organic compounds (VOCs) when evaporating essential
oils indoors. Three popular essential oils in the market, lavender, eucalyptus, and tea tree, based on a nation-wide
questionnaire survey, were tested. Specific aromatic compounds of interest were sampled during evaporating the essential
oils, and analyzed by GC-MS. Indoor carbon monoxide (CO), carbon dioxide (CO
2
), total volatile organic compounds
(TVOCs), and particulate matters (PM
10
) were measured by real-time, continuous monitors, and duplicate samples for
airborne fungi and bacteria were collected in different periods of the evaporation. Indoor CO (average concentration 1.48
vs. 0.47 ppm at test vs. background), CO
2
(543.21 vs. 435.47 ppm), and TVOCs (0.74 vs. 0.48 ppm) levels have increased
significantly after evaporating essential oils, but not the PM
10
(2.45 vs. 2.42 ppm). The anti-microbial activity on airborne
microbes, an effect claimed by the use of many essential oils, could only be found at the first 30–60 min after the
evaporation began as the highest levels of volatile components in these essential oils appeared to emit into the air,
especially in the case of tea tree oil. High emissions of linalool (0.092–0.787 mg m
3
), eucalyptol (0.007–0.856 mg m
3
), D-
limonene (0.004–0.153 mg m
3
), r-cymene (0.019–0.141 mg m
3
), and terpinene-4-ol-1 (0.029–0.978 mg m
3
), all from the
family of terpenes, were observed, and warranted for further examination for their health implications, especially for their
potential contribution to the increasing indoor levels of secondary pollutants such as formaldehyde and secondary organic
aerosols (SOAs) in the presence of ozone.
r2006 Elsevier Ltd. All rights reserved.
Keywords: Essential oils; Indoor air quality; Airborne microbes; Terpenes; Formaldehyde; Secondary organic aerosols
1. Introduction
Essential oils and some extracted fragrance com-
pounds are widely adopted into modern society for
their capacity, at least reportedly, in generating
pleasant odors, and providing anti-bioactivity bene-
fits regardless of lacking sufficient scientific evidence
to elucidating the specific effects and their corre-
sponding mechanisms (Lahlou, 2004). Meanwhile, it
is only natural that use of essential oils and products
containing fragrances will release mixed volatile
organic compounds (VOCs) into the indoor air,
and many of these, such as terpenes and D-limonene,
have demonstrated a significant role in the formation
of secondary organic aerosols (SOA), often more
irritating or allergenic than the original substance,
ARTICLE IN PRESS
www.elsevier.com/locate/atmosenv
1352-2310/$ - see front matter r2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.atmosenv.2006.09.044
Corresponding author. Tel.: +8 8 6 6 275 2459;
fax: +8 8 6 6 274 3748.
E-mail address: amb.wu@msa.hinet.net (P.-C. Wu).
after oxidation (Wainman et al., 2000). Yet, whether
emission from evaporating or heating essential oils
can affect the profiles of indoor air quality has not
been investigated comprehensively thus far. We
therefore began by examining the emission patterns
of evaporating essential oils with burning candles
underneath incense evaporator in typical office and
residential environment to further characterize the
effects of evaporating essential oils on typical indoor
air pollutants (CO, CO
2
,andPM
10
) and airborne
microbes in these environments.
2. Research methods
Three best-sold essential oils, together comprising
more than 50% of total sale volume, were selected
for the field study based on market survey, including
lavender (Lavandula angustifolis), eucalyptus (Eu-
calyptus globules), and tea tree (Melaleuca alter-
nifolia). Bulk samples of these essential oils were
analyzed in our own laboratory by GC-MS to
characterize the chemical compositions following
the procedures reported previously (Chaintreau et
al., 2003), and 300 ml of each essential oil were
diluted with 50 ml water for use in incense
evaporator with burning candle.
Two different types of indoor environments, one
bedroom (space volume: 21.6 m
3
; air change rate
(ACH): 1.8 h
1
) and one small office (space volume:
28.2 m
3
; ACH: 1.3 h
1
) were chosen for the experi-
ment. Before evaporating, 30 min background
sampling was performed to measure background
levels of various indoor air pollutants, including
CO, CO
2
, total volatile organic compound
(TVOCs), and PM
10
, using continuous monitor.
Carbon dioxide (CO
2
) and carbon monoxide (CO)
were measured by using Q-track monitor (Model-
8550, TSI Inc., USA) with detection ranges within
0.04–1000 ppm for CO and 0–5000 ppm for CO
2
.
PM
10
was measured by Dust-track monitor (TSI
Inc., USA) with the detection range within
0.06–5000 mgm
3
. TVOCs was measured by using
ppbRAE air monitor (PGM-7240, RAE system
Inc., USA) with the detection range within
0–200 ppm. All real-time data were recorded by
one data per minute during the sampling period.
Airborne microbes were also collected before study.
Monitoring during evaporating essential oils began
after background profiles had been established, and
were continuously recorded for at least 3 h for each
round of test with triplicate tests completed for each
essential oil in each testing space. All real-time data
were recorded with the frequency of one data point
per minute during the sampling period. Duplicate
samples of airborne fungi and bacteria were
collected using Burkard sampler (Rickmansworth,
UK) with malt extract agar plates (MEA) and
tryptic soy agar (TSA) at a flow rate of 10 LPM
(Macher et al., 1995;Su et al., 2001). Airborne fungi
and bacteria were collected at 0, 30, 60, 120, and
180 min within the period of evaporating essential
oils. Fungi were cultured, incubated, and identified
before average concentrations of duplicated sam-
ples, as colony forming unit per cubic meter
(CFU m
3
), were calculated for the sampling site
(Wu et al., 2005).
Stainless-steel tubes filled with Tanex-TA and
Carboxen for absorbing VOCs (EPA-TO-17) were
equipped with a sample pump (SKC 223-3, U.S.A.),
and sampling at flow rate of 70 ml min
1
during the
period of evaporating each essential oils in the
testing space for VOCs sampling. Air samples were
sealed by stainless-steel cap and sent to laboratory
to be desorbed by automatic thermal desorption
system (ATD-400, PerkinElmer Inc., USA), and
directly transferred to GC-MS (Hewlett-Packard
GC-5890; Hewlett-Packard MS-5972)(Rastogi et
al., 2001). All procedures were completed within
30 min in our own laboratory. Specific VOCs,
including two monoterpene hydrocarbons (D-limo-
nene and r-cymene), one monoterpene ether (eu-
calyptol), and two monoterpene alcohols (linalool
and terpinene-4-ol) were chosen as indicators. They
were thermally extracted, analyzed, and quantified
by standard curve using GC-MS set at the identical
condition as for bulk sample analysis.
Wicoxon signed rank test was applied to compare
the indoor pollutants’ concentrations before and
after evaporating essential oils, and Friedman test
to examine whether the change of fungal or
bacterial concentrations at different sampling per-
iods.
3. Results
The effects of evaporating essential oils on indoor
TVOCs concentrations in the testing spaces are
shown in Fig. 1. The emissions of VOCs mostly
occurred, both at home and office environment,
during the first 20 min of initial evaporation of
eucalyptus and tea tree oil. The emissions of TVOCs
of lavender oil seemed to be slower than eucalyptus
and tea tree oils, yet, also reaching steady state
within 30–45 min, either at home or at office space.
ARTICLE IN PRESS
H.-J. Su et al. / Atmospheric Environment 41 (2007) 1230–1236 1231
The average concentrations of CO
2
and CO were
significantly higher (CO
2
: 543.21ppm and CO:
1.48 ppm) in the testing periods, compared to back-
ground levels (CO
2
:435.47andCO:0.47ppm)
(Table 1). The levels of PM
10
were observed to have
a minor increase during the evaporating test, yet
without statistical significance (p¼0.053). Indoor
concentrations of total airborne bacteria appeared to
decrease after evaporating lavender, eucalyptus, and
tea tree oils regardless of being in office or home
environment, and the lowest level was found at
30 min after evaporating when the highest levels of
volatile components of these essential oils appeared
to have emitted into the air (Fig. 2). Unfortunately,
their effects on airborne bacteria did not seem to
persist through time especially in the naturally
ventilated home. Similar phenomenon was also
observed with airborne fungi when airborne fungal
levels began to decrease after the first 30min.
The levels of indicator VOCs during the testing
periods (180 min) were shown in Table 2.Thelevelof
linalool, a major composition of lavender oil, was
between 496.04 and 986.90 mgm
3
, when evaporating
lavender oil in the testing space. D-limonene was
ARTICLE IN PRESS
0
0.5
1
1.5
2
2.5
-150 1530456075
90
105 120 135 150 165
Time (min)
TVOC (ppm)
Lavender
Eucalyptus
Tea tree
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
TVOC (ppm)
Lavender
Eucalyptus
Tea tree
-150 1530456075
90
105 120 135 150 165
Time (min)
(a)
(b)
Fig. 1. The effects of evaporating essential oils on the indoor TVOCs concentrations in the testing spaces ((a) homes and (b) office).
H.-J. Su et al. / Atmospheric Environment 41 (2007) 1230–12361232
released from all three essential oils, and the
concentrations were between 2.37 and 69.32 mgm
3
in testing office and home, respectively. Terpinene-4-ol
wasalsofoundinthreeessentialoils,showing
highest levels when evaporating tea tree oils
(467.68–954.18 mgm
3
). Eucalyptol (1,8-cineole) was
ARTICLE IN PRESS
Table 1
Levels of indoor air pollutants during background and evaporating periods
Pollutants (unit) Cycles of testing Average concentrations (SD) p-value
Background (30 min) Evaporating period (180 min)
CO (ppm) 15 0.47 (0.87) 1.48 (1.13) o0.01
CO
2
(ppm) 18 435.47 (109.14) 543.21 (71.65) o0.01
PM
10
(mgm
3
) 17 2.42 (1.44) 2.45 (1.42) 0.05
TVOCs (ppm) 18 0.48 (0.30) 0.74 (0.45) o0.01
0
500
1000
1500
2000
2500
3000
0 30 60 120 180
min
Bacteria (CFU/m3)
Lavender_Office
Eucalyptus_Office
Tea tree_Office
Lavender_Home
Eucalyptus_Home
Tea tree_Home
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0 30 60 120 180
min
Fungi (CFU/m3)
Lavender_Office
Eucalyptus_Office
Tea tree_Office
Lavender_Home
Eucalyptus_Home
Tea tree_Home
(b)
(a)
Fig. 2. The effects of evaporating essential oils on airborne bacteria (a) and fungi (b).
H.-J. Su et al. / Atmospheric Environment 41 (2007) 1230–1236 1233
a major compound in eucalyptus and tea tree oils, and
the higher levels were observed when evaporating
eucalyptus oils (203.09–1540.62 mgm
3
). r-Cymene
showed a strong presence both in eucalyptus and tea
tree oils, and higher levels were found when evaporat-
ing the latter (72.25–173.23 mgm
3
).
4. Discussion
Our finding suggests that most VOCs in the
essential oils would emit into the air within the first
30 min, while the emission patterns varied in each
evaporating test. The most likely rationale to justify
these variations might be attributable to various
burning temperatures associated with different
candles. Combustion-related emissions products,
including CO
2
and CO also significantly increased
during the evaporating period as expected. Such a
phenomenon might suggest the need of fresh air
intake when evaporating essential oils using an
incense evaporator with a burning candle. Com-
pared to other claims, the anti-microbial activity of
essential oils has been the one with more scientific
evidences, and documentations for bioactivity of
lavender, tea tree, and eucalyptus oils under
diffusion or contact study-setting were available
(Viljoen et al., 2003;Lis-Balchin and Hart, 1999;
Hammer et al., 1999;Inouye et al., 2001;Pattnaik et
al., 1997). Our study is, thus far, the first to
demonstrate the effects of using essential oils on
reducing airborne microbial levels. These results
implied that the reduction of airborne microbes
when evaporating essential oils could only be
observed during the first 30–60 min when the highest
levels of volatile components in these essential oils
appeared to emit into the air. The effect, yet, did not
seem to persist through, and was easily disturbed by
outdoor sources and other contributions of fugal
levels from indoor human activities. While benefits
of using various essential oils have been advocated
for commercial purpose, only a few studies in the
literature have aimed to elucidate the specific effects
of these essential oils, and the mechanisms of their
bioactivities. The reported bioactivities of essential
oils have included insecticidal activity, anti-micro-
bial activity, effects on musculoskeletal system,
neurological effects, blood pressure action, gastro-
protective effect, sedative, and antispasmolytic
actions (Lahlou, 2004). Yet, with increasing usage
and exposure to essential oils and related fragrant
compounds, concerns on clarifying more specifically
their potential health and environmental impacts
have arisen in recent decades. Meanwhile, a large
quantity of VOCs with complex mixture is also
likely to be emitted into indoor air when using
essential oils and products containing rich fra-
grance. The major constituents of these three testing
oils often include linalool, eucalyptol (1,8-cineole),
D-limonene, r-cymene, g-terpinene, and terpinene-4-
ol-1 belong to the family of terpenes. Terpennoids
are a group of unsaturated hydrocarbons and
oxygen-containing compounds mainly emitting
from plants in nature. Previous studies have
indicated that these monoterpenes (hydrocarbons,
alcohols, and ethers) with one or more unsaturated
carbon–carbon bonds may easily interact with
oxidants, such as ozone, hydroxyl and nitrate
radicals, in general environments, and generate
consequently a variety of secondary organic pollu-
tants in gas and particle phase (Weschler, 2000). The
oxidation products of terpenes, such as D-limonene,
a-pinene, and linalool, have been characterized by
atmospheric chemists to include a number of higher
molecular weight oxidation products include alde-
hydes, ketones, organic aicds, and diacids (Grosjean
et al., 1992;Reissell et al., 1999;Grosjean et al.,
1993;Shu et al., 1997;Hakola et al., 1994). One
major product derived from reaction between
oxidants and terpenes is formaldehyde, and serial
studies have shown O
3
/terpene reactions are
important sources of secondary indoor air pollu-
tants including secondary hydroscopic organic
aerosols (SOAs) which are mainly of sub-micron
ARTICLE IN PRESS
Table 2
Levels of indicative volatile organic compounds during the testing
periods (180 min)
Compounds (mgm
3
) Office Home
1st 2nd 3rd 1st 2nd 3rd
Lavender
Linalool 533 496 604 987 779 594
D-limonene 12 6 2 32 21 28
Terpinene-4-ol 100 74 56 198 89 48
Eucalyptus
Eucalyptol 523 1541 503 263 203 522
D-limonene 69 36 34 13 13 32
r-Cymene 58 46 — 14 16 28
Terpinene-4-ol 71 77 33 31 27 —
Tea tree
Eucalyptol 94 97 42 80 53 34
D-limonene 23 19 6 3 5 —
r-Cymene 132 119 72 173 157 91
Terpinene-4-ol 882 903 623 954 840 468
H.-J. Su et al. / Atmospheric Environment 41 (2007) 1230–12361234
particles (Sarwar et al., 2004;Iinuma et al., 2004).
These oxidation products have attracted rising
concerns as many of them seem to be more irritating
than their precursors (Karlberg and Dooms-Goos-
sens, 1997;Wolkoff et al., 1999;Wolkoff et al.,
2000), and fine to ultra-fine particles are known to
penetrate into lower respiratory system more easily.
The concentration levels reported in this investiga-
tion can be of great importance as they may well be
the first set of field concentrations for various
terpenes measured during the evaporation of
essential oils in general indoor environments. These
data indicate that evaporating essential oils could be
another hidden source of indoor terpenes, and
deserve more attention for its potential impacts on
indoor air quality, especially on the levels of
secondary pollutants such as formaldehyde and
SOAs.
Although, the scientific evidence regarding the
effects of these aromatic compounds remains
limited, they have been at least suggested to be
sensitization agents (Buckley et al., 2003). Exposure
to fragrance and essential oils from the air has also
induced or worsened respiratory problems including
decrease of pulmonary function and increase of
chest tightness, wheezing and exacerbates asthma in
susceptible subjects (Kumar et al., 1995;Millqvist et
al., 1999;Millqvist and Lowhagen, 1996;Galdi et
al., 2004). In addition, fragrances are also accounted
for the cause to occupational asthma (Baur et al.,
1999;Lessenger, 2001), and respiratory symptoms
and other nonspecific symptoms in susceptible
subjects triggered by exposure via airway and other
sensory pathway (Millqvist et al., 1999), with many
of them being similar to those described in multiple
chemical sensitivity and sick building syndromes
(Millqvist et al., 1999;Opiekun et al., 2003). Our
investigation illustrates the range of concentrations
that may potentially result from evaporating essen-
tial oils in a manner commonly employed by a great
proportion of Taiwanese population. The findings
warrant a need for further evaluation on health
consequences of applying essentials in the above-
discussed fashion.
Acknowledgments
The authors are in great debt to the building
owners for their understanding and cooperation
during the long process and sampling activities.
We also thank our colleagues participating in the
field investigations, and helping in the laboratory
task. Taiwan National Science Council (NSC
93-2320-B-006-070) grants have in part, supported
this study. It is to be noted that partial data
reported in this work have appeared as preliminary
results and were published in the proceedings of
indoor air 2005.
References
Baur, X., Schneider, E.M., Wieners, D., Czuppon, A.B., 1999.
Occupational asthma to perfume. Allergy 54, 1334–1335.
Buckley, D.A., Rycroft, R.J.G., With, I.R., Mcfadden, J.P., 2003.
The frequency of fragrance allergy in patch-tested patients
increases with their age. British Journal of Dermatology 149,
986–989.
Chaintreau, A., Joulain, D., Marin, C., Schmidt, C.O., Vey, M.,
2003. GC-MS quantitation of fragrance compounds sus-
pected to cause skin reactions. Journal of Agricultural and
Food Chemistry 51, 6398–6403.
Galdi, E., Perfetti, L., Calcagno, G., Marcotulli, M.C., Moscato,
G., 2004. Exacerbation of asthma related to eucalyptus
pollens and to herb infusion containing Eucalyptus. Monaldi
Archives for Chest Disease 59, 220–221.
Grosjean, D., Williams II, E.L., Seinfeld, J.H., 1992. Atmo-
spheric oxidation of selected terpenes and related carbonyls:
Gas phase carbonyl products. Environmental Science and
Technology 26, 1523–1526.
Grosjean, D., Williams II, E.L., Grosjean, E., Andino, J.M.,
Seinfeld, J.H., 1993. Atmospheric oxidation of biogenic
hydrocarbons: reaction of ozone with a-pinene, D-limonene,
and trans-caryophyllene. Environmental Science and Tech-
nology 27, 2754–2758.
Hakola, H., Arey, J., Aschmann, S.M., Atkinson, R., 1994.
Product formation from the gas phase reactions of OH
radicals and O
3
with a series of monoterpenes. Journal of the
Atmospheric Chemistry 18, 75–102.
Hammer, K., Carson, C., Riley, T., 1999. Antimicrobial activity
of essential oils and other plants extracts. Journal of Applied
Microbiology 86, 985–991.
Iinuma, Y., Bo
¨ge, O., Gnauk, T., Herrmann, H., 2004. Aerosol-
chamber study of the a-pinene/O
3
reaction: influence of
particle acidity on aerosol yields and products. Atmospheric
Environment 38, 761–773.
Inouye, S., Tsuruoka, T., Uchida, K., Yamaguchi, H., 2001.
Effect of sealing and Tween 80 on the antifungal susceptibility
testing of essential oils. Microbiology Immunology 45,
201–208.
Karlberg, A.T., Dooms-Goossens, A., 1997. Contact allergy to
oxidized D-limonene among dermatitis patients. Contact
Dermatitis 36, 201–206.
Kumar, P., Caradonna-Graham, V.M., Gupta, S., Cai, X., Rao,
P.N., Thompson, J., 1995. Inhalation challenge effects of
perfume scent strips in patients with asthma. Annals of
Allergy, Asthma, and Immunology 75, 429–433.
Lahlou, M., 2004. Essential oils and fragrance compounds:
bioactivity and mechanisms of action. Flavour and Fragrance
Journal 19, 159–165.
Lessenger, J.E., 2001. Occupational acute anaphylactic reaction
to assault by perfume spray in the face. Journal of the
American Board of Family Practice 14, 137–140.
ARTICLE IN PRESS
H.-J. Su et al. / Atmospheric Environment 41 (2007) 1230–1236 1235
Lis-Balchin, M., Hart, S., 1999. Studies on the mode of action of
the essential oil of lavender (Lavandula angustifolia P Miller).
Phytotherapy Research 13, 540–542.
Macher, J.M., Chatigny, M.A., Burge, H.A., 1995. Sampling
airborne microorganisms and aeroallergens. In: Air sampling
instruments for evaluation of atmospheric contaminants,
Cincinnati, Ohio, American Conference of Governmental
Industrial Hygienists, pp. 589–617.
Millqvist, E., Lowhagen, O., 1996. Placebo-controlled challenges
with perfume in patients with asthma-like symptoms. Allergy
51, 434–439.
Millqvist, E., Bengtsson, U., Lowhagen, O., 1999. Provocations
with perfume in the eyes induce airway symptoms in patients
with sensory hyperreactivity. Allergy 54, 495–499.
Opiekun, R.E., Smeets, M., Sulewski, M., Rogers, R., Prasad, N.,
Vedula, U., Dalton, P., 2003. Assessment of ocular and nasal
irritation in asthmatics resulting from fragrance exposure.
Clinical and Experimental Allergy 33, 1256–1265.
Pattnaik, S., Subramanyam, V.R., Bapaji, M., Kole, C.R., 1997.
Antibacterial and antifungal activity of aromatic constituents
of essential oils. Microbiology 89, 39–46.
Rastogi, S.C., Heydorn, S., Johansen, J.D., Basketter, D.A.,
2001. Fragrance chemicals in domestic and occupational
products. Contact Dermatitis 45, 221–225.
Reissell, A., Harry, C., Aschmann, S.M., Atkinson, R., Arey, J.,
1999. Formation of acetone from the OH radical- and O
3
-
initiated reactions of a series of monoterpenes. Journal of
Geophysical Research 104, 13869–13879.
Sarwar, G., Olson, D.A., Corsi, R.L., Weschler, C.J., 2004.
Indoor fine particles: the role of terpene emissions from
consumer products. Journal of the Air and Waste Manage-
ment Association 54, 367–377.
Shu, Y., Kwok, E.S.C., Tuazon, E.C., Atkinson, R., Arey, J.,
1997. Products of the gas phase reactions of linalool with OH
radicals, NO
3
radicals and O
3
. Environmental Science and
Technology 31, 896–904.
Su, H.J., Wu, P.C., Chen, H.L., Lee, F.C., Lin, L.L., 2001.
Exposure assessment of indoor allergens, endotoxin and
airborne fungi for homes in southern Taiwan. Environmental
Research 85, 135–144.
Viljoen, A., Vuuren, S.V., Ernst, E., Klepser, M., Demirci, B.,
Baser, H., van Wyk, B.E., 2003. Osmitopsis asteriscoides
(Asteraceae)-the antimicrobial activity and essential oil
composition of a Cape-Dutch remedy. Journal of Ethno-
pharmacology 88, 137–143.
Wainman, T., Zhang, J., Weschler, C.J., Lioy, P.J., 2000. Ozone
and limonene in indoor air: a source of submicron particle
exposure. Environmental Health Perspectives 108, 1139–1145.
Weschler, C.J., 2000. Ozone in indoor environments: concentra-
tion and chemistry. Indoor Air 10, 269–288.
Wolkoff, P., Clausen, P.A., Wilkens, C.K., Hougaard, K.S.,
Nielsen, G.D., 1999. Formation of strong airway irritants in a
model mixture of (+)-a-pinene/ozone. Atmospheric Environ-
ment 33, 693–698.
Wolkoff, P., Clausen, P.A., Wilkens, C.K., Nielsen, G.D., 2000.
Formation of strong airway irritants in terpene/ozone
mixture. Indoor Air 10, 82–91.
Wu, P.C., Li, Y.Y., Lee, C.C., Li, F.C., Huang, C.Y., Chiang,
C.M., Su, H.J., 2005. Changing microbial concentrations
associated with ventilation performance in Taiwan’s air-
conditioned office buildings. Indoor Air 15, 19–26.
ARTICLE IN PRESS
H.-J. Su et al. / Atmospheric Environment 41 (2007) 1230–12361236
