The use of plants to improve indoor air quality in small office space

Abstract

Exposure to volatile organic compounds (VOC) can cause a series of effects towards human health. VOC is also associated with Sick Building Syndrome and other building related illnesses. Common materials found in every home and place of business may cause elevated exposure to toxic chemicals. The aim of this study was to examine the best indoor plants that could be used to improve indoor air quality in a small office space. In this study, the concentration of VOC inside a room was monitored before and after the test, using Aeroquol Model S500 VOC Gas Detector and by using oil-based paint painted on a panel measuring 0.05 x 0.05 m in order to create a minimum of 3ppm of VOC. Three types of tropical indoor plants were used in this study; Nephrolepis exaltata, Rhapis excelsa and Dracaena fragrans. Data were monitored for eight hours at 10 minutes interval. The results showed no significant differences between the number of pots and the type of plants used in reducing VOC content in the real room environment. This was probably due to several factors, such as the interference of outside air and the condition of the experimental room. This experiment suggests that further experiments should be carried out in a controlled environment to improve our knowledge of how indoor plants can improve indoor air quality, and thus improve human health and well-being.

Full text

Pertanika J. Soc. Sci. & Hum. 20 (2): 493 - 503 (2012)
ISSN: 0128-7702 © Universiti Putra Malaysia Press
SOCIAL SCIENCES & HUMANITIES
Journal homepage: http://www.pertanika.upm.edu.my/
Article history:
Received: 14 October 2010
Accepted: 19 January 2011
E-mail addresses:
jasmin.ghazalli@gmail.com (Aini Jasmin, G.),
noorizan16@hotmail.com (Noorizan, M.), inakrisatia@yahoo.com
(Suhardi, M.), muradupm@yahoo.co.uk (Murad, A. G.),
shdi@yahoo.com (Ina, K.)
* Corresponding author
The Use of Plants to Improve Indoor Air Quality in
Small Ofce Space
Aini Jasmin, G.*, Noorizan, M., Suhardi, M., Murad, A. G. and Ina, K.
Department of Landscape Architecture, Faculty of Design and Architecture, Universiti Putra Malaysia, 43300
Serdang, Selangor, Malaysia
ABSTRACT
Exposure to volatile organic compounds (VOC) can cause a series of effects towards human health.
VOC is also associated with Sick Building Syndrome and other building related illnesses. Common
materials found in every home and place of business may cause elevated exposure to toxic chemicals.
The aim of this study was to examine the best indoor plants that could be used to improve indoor air
quality in a small ofce space. In this study, the concentration of VOC inside a room was monitored
before and after the test, using Aeroquol Model S500 VOC Gas Detector and by using oil-based
paint painted on a panel measuring 0.05 x 0.05 m in order to create a minimum of 3ppm of VOC.
Three types of tropical indoor plants were used in this study; Nephrolepis exaltata, Rhapis excelsa
and Dracaena fragrans. Data were monitored for eight hours at 10 minutes interval. The results
showed no signicant differences between the number of pots and the type of plants used in reducing
VOC content in the real room environment. This was probably due to several factors, such as the
interference of outside air and the condition of the experimental room. This experiment suggests that
further experiments should be carried out in a controlled environment to improve our knowledge of
how indoor plants can improve indoor air quality, and thus improve human health and well-being.
Keywords: Human health, indoor air quality, tropical indoor plants, volatile organic compounds
(VOC)
INTRODUCTION
Media reports regarding air pollution have
long been realized by the public. Awareness
towards the quality of air that we breathe is
important as people spend more than 80%
of their daily life indoors (e.g. home, ofce,
shopping malls and vehicles). Everyday,
people are exposed to a certain level of toxic
gases, both indoor and outdoor. However,
outdoor air pollution has always been seen
as the main problem regarding air quality;
but due to changes of lifestyle, the indoor

Aini Jasmin, G., Noorizan, M., Suhardi, M., Murad, A. G., and Ina, K.
494 Pertanika J. Soc. Sci. & Hum. 20 (2): 494 - 504 (2012)
air quality (IAQ) is also seen as a problem
as well.
Acceptable temperature and relative
humidity, controlled airborne contaminants
and adequate distribution of ventilated air
are some elements that promote good IAQ.
Some examples of common indoor air
pollutants include radon, carbon monoxide
and ozone. One of the pollutions that is
widely found indoors is VOCs. VOCs
are organic chemical compounds that
have high enough vapour pressures under
normal conditions to signicantly vaporize
and enter the atmosphere. Many VOCs
are human-made chemicals and used
as industrial solvents. Some of VOC
sources are formaldehyde and methane.
Formaldehyde is found in many building
materials, such as paints, adhesives and
wall boards. Many VOCs are neurotoxic,
nephrotoxic or hepatotoxic, or carcinogenic
and many can damage the blood components
and the cardiovascular system and cause
gastrointestinal disturbances (Leslie, 2000).
Indoor air pollution can even increase the
chance of long-term and short-term health
problems for indoor occupants, reduce in
productivity and degrade students’ learning
environment and comfort (Lee & Chang,
2000).
VOCs are emitted by various types of
products that can be found indoors, such as
paints and lacquers, cleaning agents, building
materials and furnishings, ofce equipment
like copiers and printers, correction uids
and carbonless copy paper, permanent
markers, and photographic solutions. Table
1 shows some common emissions and their
sources (Wolverton, 1997). However,
VOCs did not only originate from internal
sources but are influenced by outdoor
sources as well (Ekberg, 1994).
People now build well-sealed homes
and install insulation and other materials to
conserve energy. This reduces movement
of air through a building and increases the
concentration of many indoor pollutants.
Dependencies on air-conditioning and bad
ventilation system worsen the condition and
quality of the indoor air. There are several
TABLE 1
Some common emissions and their sources (Wolverton, 1997)
Sources of Chemical Emissions
Formaldehyde Xylene Benzene Alcohols Acetone
Adhesives √ √ √ √
Carpeting √
Computer VDU screens √
Draperies √
Fabrics √
Ofce correction uid √
Paints √ √ √ √
Plywood √
Upholstery √

The Use of Plants to Improve Indoor Air Quality in Small Ofce Space
495Pertanika J. Soc. Sci. & Hum. 20 (2): 495 - 504 (2012)
effects caused by poor indoor air quality
and a common symptom associated with
poor indoor air quality is the Sick Building
Syndrome (SBS).
SBS is dened as a set of sub-clinical
symptoms with no specically identied
cause. It is a collection of symptoms
experienced when a person is exposed
to high concentrations of certain gasses,
specically those living or working inside
a building. The SBS symptoms include
irritation in the eyes, blocked nose and throat,
complaints in upper airways, headache,
dizziness, sensory discomfort from odours,
dry skin, fatigue, lethargy, wheezing, sinus,
congestion, skin rash, irritation, nausea,
difculty in concentrating, fatigue and can
even cause the occupants to be sensitive to
odours (Gupta et al., 2007).
The toxicity level of certain VOCs
can be carcinogenic. Among other,
formaldehyde has been long considered as
a probable human carcinogen (Group 2A
chemical) based on experimental animal
studies and limited evidence of human
carcinogenicity. However, the International
Agency for Research on Cancer (IARC)
reclassified formaldehyde as a human
carcinogen (Group 1) in June 2004 based
on the ‘‘sufcient epidemiological evidence
that formaldehyde causes nasopharyngeal
cancer in humans’’ (Zhang et al., 2008). The
chemical characteristic of VOCs indicates
that these chemicals decline with time.
Newer materials emit higher concentration
of VOC. It was concluded that common
materials found in every home and place of
business may cause elevated exposures to
toxic chemicals (Wallace et al., 1987).
There are three common ways to
improve indoor air quality; these include
source control, good ventilation systems to
exhaust contaminated air, and air cleaning.
Other methods include phytoremediation,
photocatalytic oxidation, adsorption and
by using plants. Recently, using plants
as a bioltering system is widely advised.
Plants not only serve as an ornament but
they can also promote a better indoor air
condition. This does not apply only to
indoor environment but also the outdoor
(Jim & Chen, 2008). Most plants transpire
through their stomata. During the process,
plants absorb indoor air pollution (Song
et al., 2007). Gaseous pollutants could
be absorbed into plant tissues through
the stomata, together with CO2 in the
process of photosynthesis, and with O2 in
respiration. After entering the plant, transfer
and assimilation could x the pollutants in
the tissues (Jim & Chen, 2008).
Plants also have psychological effects
on humans. A review suggests that indoor
plants can and provide psychological
benefits such as stress-reduction and
increased pain tolerance (Bringslimark
et al., 2009). Despite the fact that many
research has been carried out in this area
(Oyabu, 2003; Raza, 1991; Song et al.,
2007), little emphasizes on the effectiveness
of indoor plants in reducing indoor pollution
in the tropical, as well as work done in real
room or office environment. Therefore,
this study was conducted to investigate
the effectiveness of three different species
and treatments of indoor plants in reducing
indoor pollutants in real working or ofce
environment.

Aini Jasmin, G., Noorizan, M., Suhardi, M., Murad, A. G., and Ina, K.
496 Pertanika J. Soc. Sci. & Hum. 20 (2): 496 - 504 (2012)
MATERIALS AND METHODS
Characteristics of the Plants
The plants chosen for this study were divided
into three categories of characteristics;
palms, herbaceous and ferns. The selected
plants were Rhapis excelsa, Dracaena
fragrans and Nephrolepis exaltata. These
plants were chosen to represent leaf
characteristic groups. Rhapis excelsa
represents the palm group, Dracaena
fragrans represents the herbaceous group
and Nephrolepis exaltata represents the fern
group. The characteristics of the plants are
shown in Fig.1 to Fig.3. All the three plants
are known to have the ability to purify the air
in a previous study (Wolverton, 1997) and
are therefore suitable to be used as indoor
plants. All plants were planted in a standard
clay pot and the soil mixture used was the
John Innes 3:2:1 compost. The soil mixture
consisted of three parts of loam, 2 parts of
peat and 1 part of sand. This soil mixture
is widely used and it is known as a standard
soil mixture for plants in Malaysia. Plants
were randomly selected from a total of 10
plants from each group and divided into
three different treatments (one, three and six
pots). No plants were used for the control.
The Experimental Room
The experiment was conducted at the
Landscape Research Laboratory, Faculty of
Design and Architecture, Universiti Putra
Malaysia. The room measures 0.3m width
x 0.5m length x 0.3m height, with four
window panes, a door and a personal air-
conditioning unit. In order to imitate a real
small ofce condition, the air-conditioning
was set at 21oC, with a medium speed
fan and lights were turned on during the
experiment.
Measurement of VOC
The source of VOC came from a panel
painted with oil paint. Oil-based paint
was chosen because the emission rate
Fig.1: Dracaena fragrans (herbaceous plant group)

The Use of Plants to Improve Indoor Air Quality in Small Ofce Space
497Pertanika J. Soc. Sci. & Hum. 20 (2): 497 - 504 (2012)
is slower as compared to water based
spray paint. A few guidelines suggested a
minimum of four hours to collect air sample
(Environmental Protection Agency, 2007).
For this experiment, however, the data were
measured for a duration of eight hours,
from 9.30 a.m. to 5.30 p.m., which are the
standard working hours (Ministry of Human
Resources, 2005).
Measurement of VOC was carried
out using a hand-held data logging device
Aeroqual 500 Series, with a maximum
measurement limit of 25ppm. The relative
humidity and temperature was recorded
using the MC-83 Relative Humidity-
Temperature meter. The recorded data
will show if the temperature and humidity
levels are within human comfort level. The
Fig.2: Rhapis excelsa (palm group)
Fig.3: Nephrolepis exaltata (fern group)

Aini Jasmin, G., Noorizan, M., Suhardi, M., Murad, A. G., and Ina, K.
498 Pertanika J. Soc. Sci. & Hum. 20 (2): 498 - 504 (2012)
devices were placed in the middle of the
room. Some previous experiments (see
Wallace et al., 1987; Chan et al., 2009; Sohn
et al., 2007) indicated that the experimental
device should be put between 1 meter to
1.5 meter above the oor level. However,
according to the manufacturer of the device
used in this experiment, the Aeroqual 500
Series, can be placed anywhere in the
experimental room. Fig.5 shows the layout
of the experiment.
Statistical Analysis
The one-way analysis of variance (ANOVA)
and Fisher least significant difference
(LSD) tests were used to determine the
differences between the group of plants
and the treatment used in reducing VOC
concentration.
RESULTS AND DISCUSSION
From the analysis, no signicant difference
was found between the plants species and
even the number of pots. Nonetheless, there
were still decrements in the concentration of
VOC. The results derived from the analysis
are as follows:
TABLE 2
ANOVA test results for Nephrolepis exaltata
Sum of
Squares Df Mean
Square FSig.
Between
Groups
.016 3.005 .322 .809
Within
Groups
.333 20 .017
Total .349 23
TABLE 3
ANOVA test results for Rhapis excelsa
Sum of
Squares df Mean
Square FSig.
Between
Groups
.009 3.003 .087 .966
Within
Groups
.719 20 .036
Total .729 23
TABLE 4
ANOVA test results for Dracaena fragrans
Sum of
Squares df Mean
Square FSig.
Between
Groups
.024 3.008 .440 .727
Within
Groups
.362 20 .018
Total .386 23
In general, however, a decrease in VOC
was found in the number of plants, ranging
from 70% to 77% in Nephrolepis exaltata,
63% to 72% in Dracaena fragrans and 75%
to 81% in Rhapis excelsa, with the highest
value recorded in 6 plants. From Table 5,
and by disregarding the control treatment,
Rhapis excelsa (3 pots) has the highest value
(0.8078), while the lowest is Dracaena
fragrans (1 pot), with a value of 0.6320.
The decrement in the percentage of Rhapis
excelsa (3 pots) is the highest (81%) as
compared to other species and the numbers
of pots. The lowest percentage is Dracaena
fragrans (1 pot) with 63%.
When the results of the experiments
with the plants and no plants (control)
in the room were compared, the VOC
concentration still seemed to decrease.
This could be due to the interference of air

The Use of Plants to Improve Indoor Air Quality in Small Ofce Space
499Pertanika J. Soc. Sci. & Hum. 20 (2): 499 - 504 (2012)
Fig.4: The experimental room
Fig.5: The layout of the experiment
Fig.6: The experimental devices

Aini Jasmin, G., Noorizan, M., Suhardi, M., Murad, A. G., and Ina, K.
500 Pertanika J. Soc. Sci. & Hum. 20 (2): 500 - 504 (2012)
which entered the room from outside (i.e.
from beneath the door, windows and air-
conditioning). VOC is not mainly reduced
by plants but by dilution of air. According
to Wallace et al. (1987), the concentrations
of several VOCs (ethylbenzene, l,l,l-
trichloroethane, xylenes) declined sharply
over time, indicating that building materials
or nishings (paints, carpets, adhesives, etc.)
were likely the sources. Assuming a decline
in emissions with age, the newer materials
used in the chamber should lead to higher
concentrations than in the building.
Based on the findings presented in
the tables above, there is no significant
difference between the numbers of pots in
all the three species of plants used in the
experiment. Each species was tested with
several numbers of pots. 1 pot, 3 pots, 6
pots and control treatment were used to
compare the plants ability in improving
indoor air quality. From the results, the
plant with the best ability to purify the air
was Rhapis excelsa, with 3 pots in one room.
This nding indicates that different types of
foliage can inuence the reduction of VOC.
According to Lohr (1992), plants
can increase indoor relative humidity by
releasing moisture into the air. During
photosynthesis, the nal products are glucose
(C6H12O6), oxygen (O2) and water (H2O).
Plants with large leaf surface area emit more
water vapour during photosynthesis, and
thus increase the humidity level in a space.
Relative humidity can affect temperature.
It gets warmer if the relative humidity
increases (Swanson, 2006). According
to Zhang et al. (2007), temperature is
one of the environmental parameters that
inuences VOC emissions from building
materials, together with air velocity and
humidity (Wolkoff, 1998). Bremer et al.
(1993), Cox et al. (2005) and Yang (1999)
reported that the emitted substances were
temperature dependant.
Meanwhile, the emission of
formaldehyde from particle-board was
also observed to be strongly dependent on
relative humidity which has to be taken into
account when examining these materials in
climate chamber studies (Sollinger et al.,
1994). Therefore, the use of plants is not
only to lter the air but can help maintain a
good relative humidity and temperature in
order to control airborne pollutants.
Previous research indicates that the
plants, Crassula portulacea, Cymbidium
Golden Elf, and Hydrangea macrophylla,
have very high removal rates (60-80%) of
the pollutant benzene (Liu et al., 2007).
On the contrary, no signicant difference
was found between all the three plant
TABLE 5
Decrement value of VOC by plant species and treatment (data are means ± standard error)
Species Treatment
1 pot 3 pots 6 pots Control
Nephrolepis exaltata 0.70 ± 0.05 0.74 ± 0.07 0.77 ± 0.05 0.75 ± 0.04
Dracaena fragrans 0.63 ± 0.06 0.69 ± 0.07 0.72 ± 0.04 0.67 ± 0.05
Rhapis excelsa 0.75 ± 0.07 0.81 ± 0.07 0.77 ± 0.08 0.72 ± 0.09

The Use of Plants to Improve Indoor Air Quality in Small Ofce Space
501Pertanika J. Soc. Sci. & Hum. 20 (2): 501 - 504 (2012)
species used in the experiment in this study.
This might e due to the use of a real room
condition. The previous experiments were
mainly done in sealed gas chambers to test
the plants’ capability to purify the air. The
chamber’s size ranges from 1m³ (Raza et
al., 1995) to a set of four interconnected,
cylindrical Plexiglas chamber measuring
40cm in diameter x 60cm tall (Liu et al.,
2007) to 3.5 m x 3.5 m x 2.4m (Song, Kim,
& Sohn, 2007). These chambers are air-
tight, i.e. there is no outside air interference
that can dilute the contaminated air.
This experiment was done in a real room
environment. Even though the laboratory
size used by Liu et al. (2007) is about the
same as the experimental room used in
this study, the reading of VOC may vary
because the room used for the experiment is
more airtight and has no ventilation system,
whereas this study imitated the real personal
office environment. Salthammer (1997,
as cited in Guieysse et al., 2008), indoor
VOC concentrations depend on the total
space volume, the pollutant production and
removal rates, the air exchange rate with
the outside atmosphere, and the outdoor
VOC concentrations. This also shows that
different sizes of experimental room may
give different VOC readings.
CONCLUSIONS
There have been a lot of changes in the
world we live in today. The effects of
global warming have caused people to
spend more time indoors. Even outdoor
activities have been brought indoors because
of heat and polluted air. Technological
advancements have caused people to be
dependant to alternatives sources. Even
though it positively improves the way of
living, it can also negatively affect human
health at the same time.
The issue regarding indoor air quality
is of every field’s concern. Architects,
landscape architects and even interior
designers must always put human health
and comfort as priorities in their designs.
Architects have been known to be the
main persons in a building design process.
Therefore, an architect must produce a good
design, not only to beautify the building, but
also to make it environmentally friendly for
humans.
Similarly, ventilation system plays a
big role as big ofces depend on it to bring
in fresh air. Natural aeration is always the
best but issues, such as outdoor air pollution
and safety in high buildings, often make it
not possible. According to Wargocki et al.
(2002), periodical air refreshing is often not
efcient because many indoor air pollutants
are constantly released. Hence, forced
ventilation is still one the most common
methods used for air treatment (Guieysse
et al., 2008). A central air conditioning re-
circulates air in order to save energy, but it
also circulates airborne biological materials.
There are numerous effects on health due
to airborne biological materials. These
include a range of infections and allergic
diseases, such as extrinsic allergic alveoli,
allergic rhinitis and asthma and perhaps
even lung cancer (Leslie, 2000). A central
air conditioning must be installed with
some sort of device that can lter the air.

Aini Jasmin, G., Noorizan, M., Suhardi, M., Murad, A. G., and Ina, K.
502 Pertanika J. Soc. Sci. & Hum. 20 (2): 502 - 504 (2012)
However, the lter system must be properly
maintained because the lter is seen as the
main pollution source (Bitter & Fitzner,
2002). At the same time, indoor air must
be brought outside and fresh air from the
outside be brought inside, provided that the
outdoor environment allows a better outdoor
air quality. In this study, the ventilation
system is the main suspect for the null
hypothesis.
Plants have always been seen as a
good biological lter for both indoor and
outdoor. They do not only serve as the
green lung of the earth, but also bring
physiological benefits to humans. The
focus of this study was to identify which
tropical indoor plant in Malaysia has better
efciency in improving indoor air quality.
Nevertheless, only three plant species were
experimented in this study. To provide
further insights into how plants can reduce
indoor pollution and improve our health
and working environment, more plants
need to be tested, and a more controlled
environment is needed as well.
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