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
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
), total volatile organic compounds
(TVOCs), and particulate matters (PM
) 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
(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
(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
), eucalyptol (0.007–0.856 mg m
limonene (0.004–0.153 mg m
), r-cymene (0.019–0.141 mg m
), and terpinene-4-ol-1 (0.029–0.978 mg m
), 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
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,
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Corresponding author. Tel.: +8 8 6 6 275 2459;
fax: +8 8 6 6 274 3748.
E-mail address: email@example.com (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
) 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
; air change rate
(ACH): 1.8 h
) and one small ofﬁce (space volume:
; ACH: 1.3 h
) were chosen for the experi-
ment. Before evaporating, 30 min background
sampling was performed to measure background
levels of various indoor air pollutants, including
, total volatile organic compound
(TVOCs), and PM
, using continuous monitor.
Carbon dioxide (CO
) 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
was measured by Dust-track monitor (TSI
Inc., USA) with the detection range within
. 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
), 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
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-
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.
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H.-J. Su et al. / Atmospheric Environment 41 (2007) 1230–1236 1231
The average concentrations of CO
and CO were
signiﬁcantly higher (CO
: 543.21ppm and CO:
1.48 ppm) in the testing periods, compared to back-
ground levels (CO
(Table 1). The levels of PM
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
, when evaporating
lavender oil in the testing space. D-limonene was
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105 120 135 150 165
105 120 135 150 165
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
in testing ofﬁce and home, respectively. Terpinene-4-ol
highest levels when evaporating tea tree oils
). Eucalyptol (1,8-cineole) was
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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
(ppm) 18 435.47 (109.14) 543.21 (71.65) o0.01
) 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 30 60 120 180
0 30 60 120 180
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
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
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,
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
/terpene reactions are
important sources of secondary indoor air pollu-
tants including secondary hydroscopic organic
aerosols (SOAs) which are mainly of sub-micron
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Levels of indicative volatile organic compounds during the testing
periods (180 min)
) Ofﬁce Home
1st 2nd 3rd 1st 2nd 3rd
Linalool 533 496 604 987 779 594
D-limonene 12 6 2 32 21 28
Terpinene-4-ol 100 74 56 198 89 48
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 —
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
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-
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
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