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Experimental study on variations of CO2 concentration in the presence of indoor plants and respiration of experimental animals


Abstract and Figures

This study aims to suggest an improved experimental method to reveal the ability of indoor plants to reduce CO2 concentrations, as well as to display the individual CO2 reduction characteristics of various indoor plants in accordance with this improved method. In previous studies, experiments were conducted under the condition in which the CO2 concentration in the experimental chamber is set only once to a high initial level of 1,000 ppm. However, in real conditions, CO2 concentration gradually increases in a room after the occupants enter. Hence, the existing experimental method can be improved in view of “light saturation and CO2 compensation”. Accordingly, in this study, the CO2 reduction characteristics of indoor plants under 2 conditions used in the existing method of measurement (Case 1) and the condition in the new method, which considers that CO2 concentration gradually increases through the respiration of experimental animals (Case 2)-were measured and compared against each other. For all plant samples, the level of CO2 reduction was higher in Case 2 than in Case 1, and the rate of CO2 reduction increases with time. The inflection point of CO2 concentration appeared at leaf areas of 9,000 cm2 in peace lily and areca palm, and 6,000 cm2 in weeping fig. Additional key wordsCO2 reduction quantity–compensation point–indoor air quality–respiration of experimental animals
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Experimental Study on Variations of C
2Concentration in the Presence of
Indoor Plants and Respiration of Experimental Animals
Geun Sug Oh, Gun Joo Jung*, Min Ho Seo, and Young Bin Im
Division of Architecture, College of Engineering, Pukyong National University, Busan 608-739, Korea
*Corresponding author:
Received August 12, 2010 / Accepted March 15, 2011
GKorean Society for Horticultural Science and Springer 2011
Abstract. This study aims to suggest an improved experimental method to reveal the ability of indoor plants to reduce CO2
concentrations, as well as to display the individual CO2 reduction characteristics of various indoor plants in accordance with
this improved method. In previous studies, experiments were conducted under the condition in which the CO2 concentration in
the experimental chamber is set only once to a high initial level of 1,000 ppm. However, in real conditions, CO2 concentration
gradually increases in a room after the occupants enter. Hence, the existing experimental method can be improved in view of
“light saturation and CO2 compensation”. Accordingly, in this study, the CO2 reduction characteristics of indoor plants under 2
conditions used in the existing method of measurement (Case 1) and the condition in the new method, which considers that
CO2 concentration gradually increases through the respiration of experimental animals (Case 2)-were measured and compared
against each other. For all plant samples, the level of CO2 reduction was higher in Case 2 than in Case 1, and the rate of CO2
reduction increases with time. The inflection point of CO2 concentration appeared at leaf areas of 9,000 cm2 in peace lily and
areca palm, and 6,000 cm2 in weeping fig.
Additional key words: CO2 reduction quantity, compensation point, indoor air quality, respiration of experimental animals
Hort. Environ. Biotechnol. 52(3):321-329. 2011.
DOI 10.1007/s13580-011-0169-6
Research Report
Previous studies have reported that urban residents spend
more than 80% of their whole day indoors despite their busy
and diversified lifestyles (Jenkins et al., 1992; Mølhave et
al., 2003; Orwell et al., 2004; US EPA, 2010; Wolkoff, 2003).
Particularly for office workers, who stay for a long time in a
single space, the quality of indoor air has a large influence
on the condition of the human body. However, as most
indoor air quality (IAQ) improvement methods suggested
thus far (US EPA, 2011) require large energy consumption
(Godish et al., 1989), their application ultimately and inev-
itably damage the balance among the components that provide
comfort to humans. For this reason, interest in utilizing plants
for passive methods such as cross-ventilating or mechanical
air conditioning of the interior of buildings is increasing, as
well as the number of researches reporting its efficacy.
From large trees that compose luxuriant forest to small
plants that grow under the shade of these trees (which humans
use as indoor plants under conditions of less-bright illumin-
ation), all plants create a microclimate environment around
their leaves and roots for survival. Plants undergo photo-
synthesis from which nutritive elements are generated, using
light, CO2, and H2O as raw materials (Wolverton, 1996).
During photosynthesis, air pollutants are eliminated as the
stomas of plants absorb the air pollutants together with CO2
(Kondo et al., 1992). Most of the absorbed pollutants are used
for plant growth (Chang et al., 2007; Winner, 1994). Moreover,
plants eliminate air pollutants absorbed into the soil through
the microorganisms in the rhizosphere (Orwell et al., 2004;
Wood et al., 2002). Therefore, the natural survival activity of
plants allows humans to live in a comfortable environment
with fresh air.
Previous studies have suggested that plants eliminate volatile
organic compounds such as benzene (Cornejo et al., 1999;
NASA, 1989; Orwell, 2004; Yoo et al., 2006), ethylbenzene
(Darlington, 2001), toluene (Cornejo et al., 1999; Darlington,
2001; Yoo et al., 2006), xylene (Darlington, 2001), and tri-
chloroethylene (Cornejo et al., 1999; NASA, 1989), even for-
maldehyde (Giese et al., 1994; NASA, 1989). Plants have also
been suggested to eliminate gas pollutants such as NOx (Fujii
et al., 2005; Henrik, 1986; Wolverton, 1985), O3 (Park et al.,
1998), CO (Wolverton, 1985), and CO2 (Fujii et al., 2005;
Han et al., 1996; Lee, 2004; Oh et al., 2009), as well as
Geun Sug Oh, Gun Joo Jung, Min Ho Seo, and Young Bin Im
particulate matter (Lohr, 1996).
However, plants do not consistently maintain equivalent
photosynthesis quantity [net photosynthesis quantity (NP)],
and the apparent gross photosynthesis quantity (GP) varies
depending on the environmental conditions. The formula for
GP is given below.
Gross photosynthesis (GP) = Net Photosynthesis (NP) +
Respiration (R)
If GP equals R, NP becomes zero. Relevant plants are
considered to be at the compensation point, which is an in-
dicator of the adaptability of a plant to the surrounding con-
ditions. Although NP increases in proportion to the quantity
of light, when the introduced light is small in quantity, in
cases where variable levels of light are used, the reaction
curve becomes horizontal. This means that another factor
(normally CO2 supply) besides the quantity of light limits
photosynthesis. This condition is referred to as light saturation
or CO2 limitation (Ridge, 2008).
Photosynthesis generally varies in accordance with the
balance of light quantity and CO2 concentration in plant cells
(Zeiger et al., 1982). That is, stronger light induces a higher
photosynthetic rate and a lower concentration of CO2 in the
cells (Jarvis et al., 1981). If the CO2 concentration is limited,
the rates of stomatal conductance and photosynthesis also
become limited (Farquhar et al., 1980; Hall et al., 1980;
Tenhunen et al., 1984).
Oh et al. (2009) reported that plants adapted to low-light
conditions showed no large difference in the quantity of CO2
purification, even in the lower illumination intensity indoors
(1,000 lx), which is below the compensation point (3,000 lx),
if all other conditions are the same. Kil et al. (2008) also
suggests that the quantity of photosynthesis and formalde-
hyde elimination is influenced by the presence or absence of
light. However, the intensity of illumination almost has no
influence on these factors. In reality, light strength inside
offices is regulated by criteria on the illumination intensity
on the work surface in many countries [i.e., 300 - 1,000 lx; in
Korea, provision 3011 of KSA (Korean Standards Association
1991) is being implemented]. For indoor plants that are
already adapted to low and homogeneous illumination con-
ditions, CO2 concentration becomes the major limitation factor
for photosynthesis.
CO2, which is generated by individuals occupying a space
and by combustion apparatus, is an essential as well as limiting
factor, as described previously. CO2 is known to be an indoor
air pollutant and an indicator of IAQ (Wargocki et al., 2000).
Although CO2 does not inflict harm on the human body by
itself, an increase in its concentration sometimes indicates
the deterioration of the normal thermal condition or the in-
crease in different pollutant elements. High CO2 concen-
trations can also cause sick building syndrome (SBS) by
inducing metabolic disorders in individuals.
Regardless of the area, period, and time of inspection;
air-conditioning systems; presence or absence of occupants;
and nature of the office environment, the results of actual
measurements of CO2 inside offices conducted in many
countries after the year 2002 show that CO2 quantity is within
international regulation criteria (1,000 ppm by ASHRAE) or
the regulation criteria of the respective country (e.g., in Korea,
the criteria for IAQ in facilities of mass use, as set by the
Rule on Industrial Health Criteria, is 1,000 ppm) (Gupta et
al., 2007; Hong et al., 2008; Jeong et al., 2006, 2007; Mui et
al., 2008; Oh et al., 2010; Park et al., 2000; Sekhar et al.,
2002, 2003; Wargocki et al., 2002). However, Kim et al.
(1993) reported that more than half of the respondents of
their questionnaire experienced SBS symptoms. Moreover,
Lee et al. (1995) and Gupta et al. (2007) reported many cases
in which the measured quantity of CO2 satisfied the stipulated
regulation criteria but not the occupants staying in the indoor
space. In this regard, it seems that continuous reduction in
CO2 concentration is needed even for environments having a
CO2 concentration lower than the regulated values. Besides
playing a role in the elimination of indoor air pollutants, in-
door plants also contribute to conserving energy, providing
a positive psychological effect on individuals, and improving
the overall quality of indoor air.
However, since the initial study by NASA (1980), most
of the studies on the role of indoor plants in the improvement
of IAQ in many countries were conducted in which the
initial concentration of pollutants was set as the general air-
quality criteria regardless of the actual pattern of pollutant
generation. This existing research method may be appropriate
for comparison of IAQ improvement among various kinds
of plants, or among various kinds of plants in diverse en-
vironmental conditions. However, it is inappropriate for real
office conditions for which the means of maintaining CO2
levels are different.
In the studies by Wood et al. (2006) and Kim et al. (2009),
in which the plants were placed in real office space, the sug-
gested volume of plants needed to maintain appropriate
pollutant concentration was smaller than that suggested by
previous studies in which experiments were performed in a
chamber. This result was confirmed by a previous study (Oh
et al., 2010) that used peace lily as the experimental sample.
That is, CO2 reduction seems higher when the CO2 concen-
tration is continuously increasing, such as in real space,
compared to experiments in which the CO2 concentration is
set only once initially to a high extent, when the other
environment conditions related to photosynthesis of plants
are the same. Moreover, this difference in the reduction of
CO2 quantity increased with measurement time.
Accordingly, this study aims to reveal the air-purification
Hort. Environ. Biotechnol. 52(3):321-329. 2011. 323
Fig. 1. Experimental chamber system. (A) Glazing chamber 0.93
m × 0.6 m × 0.9 m, (B) Measurement and data logging system,
(C) Tube connection and air dryer, (D) Fan for air flow, (E) Seal
nut of the chamber frame, (F) Hamsters in the chamber.
characteristic according to plant kind. We added 2 more plants
to that used by Oh et al. (2010). This follow-up study suggests
a more substantial impact of indoor plants on indoor air im-
provement than was previously suggested.
The outcome of this study and the expected effect according
to this outcome are described below.
First, this study reveals that the air-pollutant-lowering effect
of indoor plants in real space is higher than the value reported
by the existing studies. Second, the experiments revealed the
largest value of leaf surface area that should be considered
in relation to the size of chamber. By applying this value into
real space, the optimal leaf surface area needed in relation to
the volume of the space can be determined. This value can be
utilized as a reference data for future studies on this subject.
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The experiment location is a room in the east side of the
4th floor of the Architecture Department Building at Pukyong
National University in Busan metropolitan area, Korea. A
chamber system for the experiment was installed at the
center of the room.
The chamber was small, on the scale of about 0.5 m3
volume (0.93 m × 0.6 m × 0.9 m); made of glass, the top
part of which can be opened and closed; and was designed
in such a way that air leakage can be reduced by the op-
pressing pressure exerted by the weight of the upper opening
part. Two units of silicon hose for gas exchange were installed
and fixed at a height of 1.2 m from the bottom, at 1 side of
the chamber. These hoses were connected to the gas inlet of
the CO2 measurement apparatus [IAQ Analyzer(ISR400) by
NDIR method] so that air can be constantly circulated between
the chamber and measurement apparatus. The sensor part
for the measurement of temperature, humidity, air velocity,
and illumination intensity, was installed on the side of the
chamber (at a height of 1.2 m from the bottom of laboratory),
and was connected to the measurement apparatus outside the
chamber. The schematic of the installation of the chamber
system is shown in Fig. 1.
The condition inside the chamber, except for CO2 concen-
tration, complies with the required environmental condition
for the comfort of occupants (ASHRAE Standard 55, 2004),
the values of which are similar to those set by existing studies.
The details of the experimental condition are as follows.
Temperature and humidity were set in the range of 21-25G
and 30-60%, respectively, by using an electric heat pump
(EHP)/cooler as well as a heater in the laboratory, and by
using a newly manufactured silica gel canister through which
vapor flow passage can be adjusted for setting the humidity.
The simple canister was installed in the part where air returns
to the chamber from the CO2 measurement apparatus. Air
current was set at 0.3-0.5 ms-1 by using a small ball-bearing
fan. The fan was installed about 5 cm from the glass surface
of the chamber. The air was directed toward the wall to reduce
the direct influence of air current on the plants. Light intensity
was set at 16 ± 5 ȝmolm-2s-1 (approximately 1,000 lx) by
controlling the volume of incoming daylight (skylight window
3.4 m × 1.6 m, pair glass) and using a fixed quantity of
artificial light (fluorescent lamp 32 W, 2 sets; daylight color
fluorescent lamp 45 W, 2 sets). This light intensity was con-
sistently maintained during experiment.
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To set the CO2 concentration similar to that in real offices,
experimental animals (i.e., hamsters) were placed inside the
Considering that the volume of the chamber is much
smaller compared to real office space, male junglian hamsters,
a kind of dwarf hamsters, were used. The breeding environment
was maintained such that the hamsters can sustain psycho-
logical and physiological stability as the experiment progresses.
To comply with the standards of Korea Good Laboratory
Practice (KGLP) (Korea Food and Drug Administration, KFDA,
2005) and ASHRAE (2004), the following conditions were
set: 23 ± 2Gtemperature, 40 ± 10% relative humidity, less
than 0.2 m/s air current, 150-300 lx illumination density, 12
h of illumination time, less than 60 dB noise, and less than
Geun Sug Oh, Gun Joo Jung, Min Ho Seo, and Young Bin Im
Fig. 2. Plants used in the small-chamber test. (A) Peace lily:
Spathiphyllum clevelandii, (B) Weeping fig: Ficus benjamina, (C)
Areca palm: Chrysalidocarpus lutescens.
20 ppm ammonia, which produces an offensive smell. To
avoid problems due to territoriality among the experimental
animals, the hamsters were bred separately.
A ball-type automatic water supply apparatus was installed.
Feed and water were supplied once a day in the evening. To
keep the chamber clean, the bedding was replaced twice a
Oh et al. (2010) reported that CO2 concentrations vary
according to the age of experimental animals (6-9 weeks).
The hamsters showed an increasing pattern in terms of CO2
concentration as time passes (more than 0.99 R2 value), and
the quantity of CO2 generation from respiration seems to be
similar among the experimental animals. In the experiment,
3 individual hamsters were grouped to maintain a continuous
CO2 generation pattern in accordance with time, like in the
real office condition. CO2 generation was measured every 1
min for 90 min. The resulting average linear tilt was 71.17
ppm/10 min (more than 0.99 R2 value), which is in the range
of 45-83 ppm/10 min, the linear tilt of CO2 generated by
occupants in a real office (Oh et al., 2010). The CO2 con-
centration after 90 min appeared to be similar to that of the
initial 1-time setting used in existing studies (1,000 ppm).
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Three species of indoor plants were used in the experiment:
peace lily (P, Spathiphyllum clevelandii), weeping fig (W,
Ficus benjamina), and areca palm (A, Chrysalidocarpus
lutescens). These plants have higher CO2 reduction effects
even at conditions of indoor illumination compared with
other foliage plants known to purify indoor air (Oh et al.,
2009). The sample plants are shown and described in Fig. 2.
Although peace lily shows higher CO2 reduction levels in
daylight than in artificial light, it can grow and survive in a
semi-sunny, semi-shaded, or completely shaded place.
As it has a high adaptability to shade-it can survive in
conditions in which more than 90% of sunshine is blocked,
in conditions under the criteria of a sunny summer day in
Korea (Korea National Institute of Horticultural & Herbal
Science; NIHHS, 2011)-peace lily exerts a high CO2 reduction
effect even under conditions of low illumination intensity,
such as at indoor places where the regulated illumination
intensity on the work surface, as required by law, is 300-
1,000 lx. As weeping fig grows and develops in regions with
distinct dry and rainy seasons, it sheds its leaves during the
dry season for survival, which shows its sensitivity to stress
induced by water shortage, as well as its adaptability to diverse
light intensities. Additionally, for rubber trees like weeping
figs, the light compensation point and required light intensity
for survival are low as they produce special proteins under
light-deprived conditions (NIHHS, 2011). Lastly, although
areca palm demands a somewhat higher light intensity (1,600-
4,300 lx) compared to the other experimental plants, it shows
a high CO2 reduction effect when both daylight and artificial
light are simultaneously considered, even when illumination
intensity is low (i.e., lower than 1,000 lx) (Oh et al., 2009).
In most plants, chlorophyll production and CO2 fixation
decrease in the absence or in low quantities of water. To
prevent this problem in the experimental plants, water was
supplied twice a week and culture medium was injected once
a week. To reduce the influence of variations in environmental
condition on the CO2 reduction effect, purification of experi-
mental plants was performed more than 4 weeks in advance,
under laboratory conditions, including temperature, humidity,
and illumination intensity, similar to those used in the ex-
The leaf areas of the plant samples were calculated such
that an average-sized leaf was primarily selected and scanned
Hort. Environ. Biotechnol. 52(3):321-329. 2011. 325
for computerization. The ratio of leaf vein length to leaf area
was calculated by the CAD program. Subsequently, the lengths
of veins of all leaves were measured, and the previously cal-
culated ratio was applied to these measured leaf vein lengths.
The leaf area per pot for all experimental plants was adjusted
to 3,000 cm2 by pruning. Moreover, to keep the CO2 reduction
effect uniform in the rhizosphere of each experimental plant,
the respective plants were individually planted in identical
soils (peat moss 50% + bark 20% + wood by-product 20% +
sand 10%) in black plastic pots(15 cm dia. × 20 cm ht.).
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For the experimental period, a number of sunny days, in
accordance with the criteria provided by the Korea Meteo-
rological Administration, were selected in the period of
December 2009-April 2010. Measurements were done every
1 min for 90 min between 10:00 and 16:00, when the natural
light was comparatively homogeneous. The experiment was
halted in cases when the measured light intensity is to below
16 ± 5 ȝmolm-2s-1 (approximately 1,000 lx).
The experiment was conducted by separating Case 1 (in
which the CO2 concentration was set only once at an initial
value of 1,000 ppm, which is higher than in real space and is
similar to that used in the existing studies) and Case 2 (in
which the CO2 concentration was set at 350-450 ppm, which
was initially similar to that in the natural condition, but
increased to G1,000 ppm through the respiration of hamsters)
according to the criteria of CO2 concentration variation pattern.
Moreover, the leaf surface area varied from 3,000 cm2 to
15,000 cm2, with an interval of 3,000 cm2, for all the ex-
perimental plants. The measurements were conducted 5 times
per leaf-area classification, and results in which 3 out 5 meas-
urements showed a stable variance pattern of CO2 concentration
were used for analysis. To determine the net CO2 reduction
quantity among all plants, the variation of CO2 concentration
from an initial value of 1,000 ppm was measured in an empty
chamber 3 times for 24 h. The resulting variation was lower
than 10 ppm, which is within the range of measurement error.
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In view of ‘light saturation and CO2 compensation’, the
photosynthesis rates of plants vary in accordance with the
variation of CO2 concentration in a space having indoor
illumination. As the existing studies were conducted at a
higher CO2 concentration (set once at an initial concentration
of 1,000 ppm) than that in real office conditions, the rate of
photosynthesis is limited by CO2 concentration. The effect
of plants on the improvement of indoor-air quality may be
underestimated because the photosynthesis rate of the experi-
mental plants is estimated to be lower than that in reality.
This study investigated the CO2 reduction characteristics of
experimental plants in a chamber in which the CO2 concen-
tration gradually increases due to the respiration of experimental
animals (i.e., hamsters). This condition is similar to the CO2
variation pattern in real offices. The experiment was conducted
according to leaf-area classification, after dividing Case 1 and
Case 2 according to the CO2 generation pattern in the chamber.
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The experimental value of the variation in CO2 concentration
is suggested by the average value in an interval of 10 min.
The variation patterns of CO2 concentration for the above-
described experiments are shown in Fig. 3-5.
The pattern of CO2 concentration variation was similar
among all experimental plants with the passage of time. The
R2 values were significant at 0.97-0.99. While in Case 1, the
variation tilt of CO2 concentration (negative value) became
steeper as the leaf area of the plants increased, in Case 2, the
variation tilt of CO2 concentration (positive value) became
gentler as the leaf area of the plants increased. This means
that the difference in the tilt of CO2 concentration increased
as the respiration of hamsters increased. That is, for both Case
1 and Case 2, the larger the leaf area, the higher the CO2
reduction effect of indoor plants.
As Oh et al. (2010) suggested, for all experimental plants,
the CO2 reduction effect seemed to be higher in the later part
of the measurement period for Case 1, while it is higher in
the earlier part of the measurement period for Case 2. Hence,
it is believed that in real space, the improvement effect of
indoor plants on IAQ will continuously increase. However,
CO2 reduction quantities differed according to the increase
in leaf area among the experimental plants. This issue will
be examined in the next section.
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The resulting values of CO2 reduction quantities (ppm/1.5
h) by the experimental plants were converted to CO2 reduction
quantities (1.5 h) in proportion to the volume of the chamber
(about 500 L), as shown in Fig. 6.
For all experimental plants, the values of Case 2 were
higher than those of Case 1, and the differences were 0.005-
0.04 L for peace lily, 0.01-0.06 L for weeping fig, and
0.025-0.06 L for areca palm. Therefore, the CO2 reduction
effect of the plants is believed to be higher in real offices,
where the CO2 concentration increases continuously due to
occupants, than the values in the existing studies, in which
the CO2 concentration was set at a higher value than what
exists in real space. From the experimental results, it seems
that areca palm has the highest CO2 reduction effect: The
CO2 reduction values (L/1.5 h) were 0.07-0.13 for peace lily,
0.04-0.13 for weeping fig, and 0.11-0.17 for areca palm.
This implies that areca palm can be preferentially selected
as an indoor plant for the purpose of reducing indoor CO2
Geun Sug Oh, Gun Joo Jung, Min Ho Seo, and Young Bin Im
Fig. 3. CO2 variation patterns of peace lily. Leaf Area (cm2). (A)
3,000, (B) 6,000, (C) 9,000, (D) 12,000, and (E) 15,000.
Fig. 4. CO2 variation patterns of weeping fig. Leaf Area (cm2). (A)
3,000, (B) 6,000, (C) 9,000, (D) 12,000, and (E) 15,000.
Hort. Environ. Biotechnol. 52(3):321-329. 2011. 327
Fig. 5. CO2 variation patterns of areca palm. Leaf Area (cm2). (A)
3,000, (B) 6,000, (C) 9,000, (D) 12,000, and (E) 15,000.
Fig. 6. Volume of CO2 removal as influenced by leaf area at 1.5
hrs after the initi ation of the experiment. (A) Peace lily: Spathiphyllum
clevelandii, (B) Weeping fig: Ficus benjamina, (C) Areca palm:
Chrysalidocarpus lutescens.
concentrations in regions with a temperate climate.
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By varying the leaf area up to 15,000 cm2 for all 3 ex-
perimental plants, the amount of CO2 reduction was found
to vary only minutely despite the increase in leaf area. It is
assumed that the leaf areas considered were the maximum
plant quantities that the chamber can accommodate.
For peace lily and areca palm, the inflection point appeared
at the leaf area of 9,000 cm2. If these experimental plants
had more than 9,000 cm2 of leaf area for a 500-L chamber
volume, the ratio of leaves in which photosynthesis can be
actively generated would be lowered due to the high-density
arrangement, as these plants have characteristically large
leaf area and grow with boughs extended and spread toward
Geun Sug Oh, Gun Joo Jung, Min Ho Seo, and Young Bin Im
all directions. Hence, it becomes difficult for the plants to
further increase the apparent gross photosynthesis quantities,
and the variation in the quantities of CO2 reduction becomes
minute. Unlike the other 2 experimental plants, the inflection
point of CO2 reduction quantity appeared at 6,000 cm2 of
leaf area in weeping fig. As weeping fig has a characteristically
small leaf area and grows tall, even in the case of a high
input volume of this plant into the chamber, the ratio of sun
leaves versus shade leaves was almost unchanged. Despite
these characteristics, it is believed that the inflection point
appears at 6,000 cm2 of leaf area because this size offers
adaptability to diverse environmental conditions as the plant
grows naturally in places with distinct rainy season and dry
season. As the weeping fig sheds all its leaves to survive
during the dry season in nature, it is believed to adjust its
photosynthesis quantity by itself in conditions beyond the
requirement for adequate survival and growth, such as very
high plant density; in conditions of lower illumination density;
or some other conditions.
Finally, the maximum density was converted to leaf area
per 1 m3 of plant volume to allow application in real space
which gave values of 18,000 cm2m-3 for peace lily and areca
palm, and 12,000 cm2m-3 for weeping fig.
Ac know ledg ement: This research was supported by Basic
Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Edu-
cation, Science and Technology (2010-009430).
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... Therefore, the existing studies of indoor plants could be roughly summarized into two aspects: air quality improvement [7] and human health influence in physiology and psychology [8]. For air quality improvement, phytoremediation is one of the most effective, economical and environmentally friendly indoor air purification methods, and the benefits of air quality provided by indoor plants include improving indoor thermal comfort and reducing volatile organic compounds (VOCs) [9][10][11], as well as removing carbon dioxide from the air and producing oxygen [12,13]. Meanwhile, the indoor plants have positive impacts on human physiology and psychology, especially the positive psychology influences on improving learning and work efficiency [14][15][16], relieving negative emotions [17][18][19] and promoting the recovery of physical and mental health [20][21][22]. ...
... The experimental results showed that indoor plants could effectively remove 65-100% of formaldehyde and had the higher efficiency in the light environment. Oh et al. [12] measured the carbon dioxide reduction ability of three indoor plants under the condition of increasing carbon dioxide concentration. They found that indoor plants could alleviate the increase in carbon dioxide concentration and the carbon dioxide removal rate was related to its concentration. ...
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Indoor plants have great benefits to humans, including physical health, cognition and emotion through their repair and purification capabilities, but most of these positiv e effects have not been quantified and valued. In this study, the Corona Virus Disease 2019 (COVID-19), when people must be self-isolated at home and avoid outdoor activities in China, was utilized adequately and the influence of indoor plants was analyzed via the 2031 valid questionnaires, in which indoor plant status, interest degree, interaction frequency and anxiety alleviation were surveyed. Results showed that indoor plants were widely cultivated especially in the living room. Compared to before the COVID-19, the interest degree with indoor plants increased by ∼33% and their overall interaction frequency increased by ∼78% during the COVID-19. More than 70% of the surveyed people exhibited anxiety during the COVID-19, and the overall anxiety level was 1.17 (between 'Slight anxiety' and ' Anxiety'). And ∼61% of the surveyed people supported that indoor plants could alleviate self-isolation anxiety, and the anxiety alleviation degree was 0.79 (tend to 'Releasing the certain anxiety'), which showed that indoor plants had also shown to have an indirect psychological effect on anxiety alleviation.
... The innate biophilic qualities of these systems are often desirable for indoor environments due to their therapeutic psychological effect of building occupants [16][17][18][19]. However, a commercially underappreciated aspect of living walls is their ability to remove indoor air contaminants such as volatile organic compounds, particulate matter and CO 2 [1, [21][22][23][24][25][26]. Through photosynthesis, living walls are able to effectively reduce the concentrations of CO 2 from indoor environments, however lighting conditions have a strong influence on the efficacy of this process [27]. ...
... If changes to plantscape design or lighting infrastructure could support an average light intensity greater than 100 μmol m − 2 s − 1 , it may be plausible to increase the rate of elevated indoor CO 2 removal by 1.5-7-fold (Fig. 3), and thus reduce building reliance on HVAC ventilation by some degree, if adequately sized living walls can be used. Our findings confirm the positive correlation between light intensity and CO 2 assimilation rates by ornamental plants observed in previous studies [21,23,54] and highlight the need for technical guidelines to be established for the lighting of indoor living walls. ...
Vertical greening systems, or living walls, are becoming increasingly used indoors for improving the sustainability of buildings, including for the mitigation of excess CO2 levels, derived from human respiration. However, light provision within indoor environments is often insufficient for the efficient functioning of many plant species, leading to low photosynthetic CO2 removal rates, and the need for supplementary light sources. In this study, we investigated the performance of supplementary lighting employed for indoor living wall systems, and whether optimised lighting conditions could lead to improved CO2 removal. In situ trials with several medium-large indoor living walls were performed to sample the lighting scenarios currently employed. We concluded that the majority of plants in existing systems were exposed to suboptimal lighting and will have a net-zero CO2 removal efficiency. Sealed chamber experiments using two common living wall plant species were conducted to explore the effect of varying lighting conditions on CO2 removal efficiency. Comparisons on optimal and “best case” in situ conditions were carried out, showing that CO2 removal efficiency was significantly correlated with both leaf and stem angles, which suggest phototropism may influence in situ CO2 removal. After a ten-day experimental period, the highest CO2 removal efficiency for both test plant species was observed at 200 μmol m⁻² s⁻¹ light flux density (∼10500 lux) at 15° from the vertical growing surface. Our results indicate that most current lighting systems are inadequate for healthy plant photosynthesis and CO2 removal, and that modified lighting systems could improve this performance. The estimation of the CO2 removal ability of a 5 m² passive living wall decreases from an ACH of 0.21 h⁻¹, achieved in an optimal light exposure condition, to only 0.03 h⁻¹ when plants are exposed to sub-optimal conditions. To reduce maintenance costs, technical guidelines for indoor living wall lighting should be established, and lighting suppliers should recognise the developing niche market for specialised indoor living wall lighting.
... Figures 1 and 2 show the foreground of the target building and the floor plan of the target lecture room. The target plant, areca palm ( Figure 3), is recognized worldwide as one of the best indoor air purification plants, absorbing CO2 and producing O2 to detoxify its surroundings by removing air pollutants such as formaldehyde (CH2O), xylene (C8H10) and toluene (C7H8) [61,62]. Among the houseplants that can grow under low indoor illumination (300- The target plant, areca palm ( Figure 3), is recognized worldwide as one of the best indoor air purification plants, absorbing CO 2 and producing O 2 to detoxify its surroundings by removing air pollutants such as formaldehyde (CH 2 O), xylene (C 8 H 10 ) and toluene (C 7 H 8 ) [61,62]. ...
... The target plant, areca palm ( Figure 3), is recognized worldwide as one of the best indoor air purification plants, absorbing CO2 and producing O2 to detoxify its surroundings by removing air pollutants such as formaldehyde (CH2O), xylene (C8H10) and toluene (C7H8) [61,62]. Among the houseplants that can grow under low indoor illumination (300- The target plant, areca palm ( Figure 3), is recognized worldwide as one of the best indoor air purification plants, absorbing CO 2 and producing O 2 to detoxify its surroundings by removing air pollutants such as formaldehyde (CH 2 O), xylene (C 8 H 10 ) and toluene (C 7 H 8 ) [61,62]. Among the houseplants that can grow under low indoor illumination (300-1000 lx), it was selected due to having a high CO 2 reduction effect in previous studies [63,64]. ...
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The objective of this paper is to investigate the effect of improving indoor air quality with indoor plants. As a methodology, two target classrooms with the same size (120.64 m2) and 32 students per room were selected. Then, 48 areca palm pots (average leaf area of 300 cm2/pot) were placed, and the plant density was 14.68% of the floor area. Subjective assessment for general questions, learning motivation, perceived air quality, and SBS symptoms was conducted at 5 min after the class started and 5 min before the class ended. The results showed that the CO2 concentration by respiration of the students (average of 1873 ppm) exceeded the regulatory standard (1000 ppm), but the students did not recognize the indoor CO2 concentration. The increase in CO2 concentration in the classroom was lower in the case with plant placement (624 ppm) compared with the case without plant placement (about 1205 ppm). It was statistically proven that the CO2 concentration by respiration could be reduced by 50% if the indoor plant leaf area density were maintained at about 14.68% of the floor area. In the case with plant placement, the students perceived the indoor air quality to be 40% fresher and showed a 140% higher acceptability. Moreover, the complaining of SBS symptoms was improved by 108%, and the students’ perception that it was better to focus on learning increased by about 120%. As the awareness of sustainability increases, indoor plants will be more actively placed in the United Arab Emirates. Indoor plants not only provide a visual green effect to improve human comfort but also purify indoor air pollutants.
... Although some VOCs present in indoor air can directly be taken up and further metabolised by plants, the VOCs are more extensively removed by microorganism mostly present in the rhizosphere around the roots of the plants (Pacheco-Torgal et al. 2015). However, the removal of carbon dioxide, sulfur dioxide, nitrogen dioxide and ozone appear to be partially or solely plant facilitated (Fikiey et al. 1981;Pacheco-Torgal et al. 2015;Oh et al. 2011;Torpy et al. 2014a). These VICs are generally taken up by the plant stomates (gaseous compound exchange pores) during daylight hours (Pacheco-Torgal et al. 2015). ...
... The use of biology to remove indoor CO 2 offers opportunities that have received limited research attention, while indoor plants have proven to be able to reduce CO 2 in indoor environments. Oh et al. (2011) and Pennisi and van Iersel (2012) studied the capacity of several indoor plant species to reduce CO 2 and concluded that an impractical large quantity of indoor plants would be needed due the limited photosynthetic rate to significantly reduce the indoor CO 2 concentration. Plant-based green wall technology increases the efficiency of capturing CO 2 compared to passive potted plants, because plant density and thus photosynthetic rate increases, along with the ease to increase the light intensity (Torpy et al. 2014b). ...
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Studies on human exposure to indoor air pollution reveal that indoor environments could be at least twice as polluted as outdoor environments. Indoor air pollution has not received as much attention than outdoor air pollution, despite an adult spending now most of the time indoors as a result of the global shift in the economy from the manufacturing sector towards the service and knowledge-based sectors, which operate in indoor office environments. Additionally, the health threats caused by a long-term exposure to indoor air pollution have become more apparent over the last decades as buildings are progressively sealed against the outside climate conditions to obtain heating and cooling energy cost savings and in response to stricter safety guidelines. Currently there is not a single technology that can efficiently provide a complete and satisfactory purification of indoor air. Biological systems for improving indoor air quality are promising, but challenges need to be examined to properly address the bioavailability of low pollutant concentrations, guarantee microbial safety, and incorporate CO2-removal. This study presents the recent research advances in biological indoor air purification methods as a ‘green’ alternative to physical–chemical methods, with emphasis on current challenges and opportunities it can provide for improving Indoor Environment Quality, building energy cost savings and improvements on indoor comfort and well-being. Graphical abstract
... Studies have shown that hydroponic farming system has the potential of removing atmospheric carbon dioxide (Park et al., 2010). This air which is produced through human respiration and Volatile organic compounds (VOCs) heavily contaminates indoor surroundings (Aydogan and Montoya, 2011;Kim et al., 2008;Oh et al., 2011). Carbon dioxide is a narcotic (Milton et al., 2000) which has been associated with decline in student academic performance and work performance when increased in circulation (Seppänen et al., 2006;Shaughnessy et al., 2006). ...
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Agriculture is the economic back-borne of majority of developing countries worldwide. The sector employs over 50% of the working population and contributes about 33% of the Gross Domestic Product (GDP) in majority of African states. However, such contribution by the agricultural sector is likely to be affected by climate change, increasing human population and urbanization which impact on available agricultural land in various ways. There is thus an urgent need for developing countries to create or adopt technologies such as; soil-less farming that will not only address climate change challenges but also enhance crop production for improved food security. This paper reviews the science, origin, dynamics and farming systems under the soil-less agriculture precisely hydroponic farming to assist in widening the scope of knowledge of the hydroponic technologies and their implementation in Africa.
... While CO 2 , SO x , NO x and O 3 appear to be taken up directly through the stomates of plants during daylight, VOCs are mostly degraded by microorganisms present in the rhizosphere. A symbiotic relationship between plants and microorganisms may be achieved (Moya et al., 2019;Oh et al., 2011;Pacheco-Torgal et al., 2015;Torpy et al., 2014;Yang et al., 2009). The performance of botanical technologies is still lower than that of other conventional technologies (Table 4). ...
Indoor air pollution has traditionally received less attention than outdoors pollution despite indoors pollutant levels are typically twice higher, and people spend 80–90% of their life in increasing air-tight buildings. More than 5 million people die every year prematurely from illnesses attributable to poor indoor air quality, which also causes multi-millionaire losses due to reduced employee’s productivity, material damages and increased health system expenses. Indoor air pollutants include particulate matter, biological pollutants and over 400 different chemical organic and inorganic compounds, whose concentrations are governed by several outdoor and indoor factors. Prevention of pollutant is not always technically feasible, so the implementation of cost-effective active abatement units is required. Up to date no single physical-chemical technology is capable of coping with all indoor air pollutants in a cost-effective manner. This problem requires the use of sequential technology configurations at the expenses of superior capital and operating costs. In addition, the performance of conventional physical-chemical technologies is still limited by the low concentrations, the diversity and the variability of pollutants in indoor environments. In this context, biotechnologies have emerged as a cost-effective and sustainable platform capable of coping with these limitations based on the biocatalytic action of plants, bacteria, fungi and microalgae. Indeed, biological-based purification systems can improve the energy efficiency of buildings, while providing additional aesthetic and psychological benefits. This review critically assessed the state-of-the-art of the indoor air pollution problem and prevention strategies, along with the recent advances in physical-chemical and biological technologies for indoor pollutants abatement.
With the urban development, indoor air quality (IAQ) is of growing public health concern due to that fact people spend 80%–90% of their time indoors, which has prompted the use of plants to reduce the air pollution through the phytoremediation from interior spaces, especially in the enclosed rooms with air-conditioning and heating. Indoor plants have been proved to improve the indoor environment, relieve anxiety, and reduce CO2 concentration. However, the comprehensive review has not been published to summarize the development status and potential deficiencies of indoor green plants after 2018. The 50 published articles related to indoor green plants were selected by the primary retrieval system and the later manual screening. This review mainly focused on the effects of green plants on the indoor thermal environment and indoor pollutants including volatile organic compounds (VOCs), and CO2 concentration, while the application efficiency of green plants was described on learning or productivity efficiency, patients' post-operative recovery and emotion comprehensively.
Plants can purify indoor air quality; in particular, plant transpiration can facilitate indoor air movement, purify air by removing pollutants effectively, and provide clean indoor air. In this study. The first and second stages mainly focused on selecting plants with superior performance in the indoor spaces. In the final stage, the effects of different arrangements of grow lights and air conditioners were investigated. The arithmetic mean and regression analysis results demonstrated that the plants illuminated with grow lights had superior performance. Plants that performed photosynthesis and transpiration simultaneously could lower the average temperature, increase indoor humidity (to make up for the lack of cold room humidity), and lower CO 2 concentration. Our results demonstrated that placing plants together at a location across the air conditioner and under grow light illumination afforded the most effective indoor air purification and CO 2 removal.
Indoor plants can improve indoor thermal environment, relieve the anxiety, and reduce the CO2 concentration especially in enclosed rooms with air-conditioning and heating. However, owing to the space limitation and the light requirement, it is very difficult to maintain traditional large-scale plantings indoors. To improve indoor planting efficiency and thermal environment, the living wall was introduced to be combined with air-conditioning. Two identical rooms were built to analyze the efficiency of combining a living wall with air-conditioning. One room contained a living wall and air-conditioning, while the other room only with air-conditioning was served as a reference. The indoor thermal environment and CO2 concentration were monitored, while the 64 participants were questioned to display their subjective feelings in two rooms. The results showed that combining the living wall lowered the relative humidity by 2.6%, maintained the indoor air speed at 0.20 m/s∼0.30 m/s and reduced the CO2 concentration by approximately 10%, while it increased the uniformity of these environmental parameters. The average skin temperature in the room with the living wall was 0.2 °C higher than that in the referred room and closer to the neutral mean skin temperature. The living wall significantly improved the subjective evaluation on indoor environment, especially in air movement and air freshness, with the thermal comfort level from 0.13 (Slightly higher than ''Neutral (0)'') to 0.73 (Slightly lower than ''Comfortable (+1)'').
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Urban civilization has a high impact on the environment and human health. The pollution level of indoor air can be 2–5 times higher than the outdoor air pollution, and sometimes it reaches up to 100 times or more in natural/mechanical ventilated buildings. Even though people spend about 90% of their time indoors, the importance of indoor air quality is less noticed. Indoor air pollution can be treated with techniques such as chemical purification, ventilation, isolation, and removing pollutions by plants (phytoremediation). Among these techniques, phytoremediation is not given proper attention and, therefore, is the focus of our review paper. Phytoremediation is an affordable and more environmentally friendly means to purify polluted indoor air. Furthermore, studies show that indoor plants can be used to regulate building temperature, decrease noise levels, and alleviate social stress. Sources of indoor air pollutants and their impact on human health are briefly discussed in this paper. The available literature on phytoremediation, including experimental works for removing volatile organic compound (VOC) and particulate matter from the indoor air and associated challenges and opportunities, are reviewed. Phytoremediation of indoor air depends on the physical properties of plants such as interfacial areas, the moisture content, and the type (hydrophobicity) as well as pollutant characteristics such as the size of particulate matter (PM). A comprehensive summary of plant species that can remove pollutants such as VOCs and PM is provided here. This review will help in making informed decisions about integrating plants into the interior building design.
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Air pollutants cause various types of damage to plants: the retardation of growth, the promotion of ageing, the abscission of leaves and withering. Air pollutants are absorbed by plants mainly through the stomata of their leaves. The absorbed pollutants produce toxic substances in plants: SO2 produces SO3²⁻, NO2 produces NO2⁻ and all pollutants produce active oxygen species, such as O2-, H2O2 and ¹O2, as secondary toxic substances to some extent. These substances destroy or inactivate various cellular components like proteins and lipids and cause damage to plants. On the other hand, plants have metabolic pathways to scavenge these toxic substances and can avoid damage when the amount of absorbed air pollutant is low. The degree of damage to plants caused by air pollutants depends on the degree of stomatal opening and the potentials to produce and to scavenge toxic substances in plants. Plants also show dynamic responses to air pollutants: stomata tend to close when plants get contact with air pollutants and various activities to scavenge toxic substances in plants increase with the contact of plants with low concentrations of pollutants. The activities of active-oxygen-scavenging enzymes, superoxide dismutase and catalase, were shown to increase with SO2 and activities of other such enzymes, ascorbate peroxidase and glutathione reductase increased with O3. By contrast, the activity of nitrate reductase which produces toxic NO2⁻ was shown to decrease with NO2. Genetic engineering technique is being used to change the tolerance of plants to air pollutants, based on these findings.
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Foliage plants of Hedera helix L. (english ivy), Spathiphyllum wallisii Regal (peace lily), Syngonium podophyllum Schott, (nephthytis), and Cissus rhombifolia Vahl. (grape ivy) were evaluated for their ability to remove two indoor volatile organic air pollutants, benzene and toluene. Removal was monitored when the aerial portion of plants was exposed singly to 1 μL·L-1 or to 0.5 μL·L-1 of each gas in a closed environment over 6-hour periods during the day and the night. Selected physiological processes were assessed before and immediately after treatment to determine the effect of the gases on the plants. The effectiveness of plants in the removal of air pollutant(s) varied with species, time of day, and whether the gases were present singly or as a mixture. When exposed to a single gas, S. wallisii, S. podophyllum, and H. helix displayed higher removal efficiencies (ng·m-3·h-1·cm-2 leaf area) of either gas than C. rhombifolia during the day. The efficiency of removal changed when both gases were present; H. helix was substantially more effective in the removal of either benzene or toluene than the other species, with the removal of toluene more than double that of benzene. When exposed singly, the removal of both compounds was generally higher during the day than during the night for all species; however, when present simultaneously, H. helix removal efficiency during the night was similar to the day indicating that stomatal diffusion for english ivy was not a major factor. The results indicated an interaction between gases in uptake by the plant, the presence of different avenues for uptake, and the response of a single gas was not necessarily indicative of the response when other gases are present. Changes in the rates of photosynthesis, stomatal conductance, and transpiration before and after exposure indicated that the volatiles adversely affected the plants and the effects were not consistent across species and gases. Deleterious effects of volatile pollutants on indoor plants may be critical in their efficacy in improving indoor air quality and warrant further study.
Results are presented of an investigation into the capacity of the indoor potted-plant/growth medium microcosm to remove air-borne volatile organic compounds (VOCs) which contaminate the indoor environment, using three plant species, Howea forsteriana (Becc. (Kentia palm), Spathiphyllum wallisii Schott. 'Petite' (Peace Lily) and Dracaena deremensis Engl. 'Janet Craig'. The selected VOCs were benzene and n-hexane, both common contaminants of indoor air. The findings provide the first comprehensive demonstration of the ability of the potted-plant system to act as an integrated biofilter in removing these contaminants. Under the test conditions used, it was found that the microorganisms of the growth medium were the "rapid-response" agents of VOC removal, the role of the plants apparently being mainly in sustaining the root microorganisms. The use of potted-plants as a sustainable biofiltration system to help improve indoor air quality can now be confidently promoted. The results are a first step towards developing varieties of plants and associated microflora with enhanced air-cleaning capacities, while continuing to make an important contribution to the aesthetics and psychological comfort of the indoor environment.
Human activity is altering the chemistry of the atmosphere, which, in turn, is affecting the physiology and growth of plants. The purpose of this article is to develop four ideas that are currently emerging from the work of a diverse group of plant scientists. (1) Air pollution definitions: The definition of air pollution has been broadened, and research activities are expanding to include analysis of plant responses to a wide range of atmospheric chemicals emitted from anthropogenic sources but not previously considered as air pollutants. Thus experiments with CO2 and other trace gases are being pursued with approaches developed in air pollution research. (2) Air pollution uptake: Efforts are increasing to better quantify air pollution absorption rates through stomata in order to calculate actual dose vs, plant responses. The flux rates of gaseous pollutants into leaves, especially O-3, are largely dependent upon stomatal conductance. Approaches are being developed to calculate stomatal absorption of gaseous pollutants, based on stomatal conductance values for water vapor and ambient air-pollution concentrations. Calculation of air pollution absorption rates will allow responses of plants to pollutants to be assessed in toxicological frameworks and will help characterize the strength of vegetation as sinks for some gaseous pollutants. (3) Compensatory responses: Plant responses to air pollutants can be interpreted as compensatory, i.e., a physiological adjustment to an environmental stress that maximizes productivity above that which would have occurred in the absence of compensation. Examples of compensatory responses to air pollutants are shifts in root-to-shoot ratio and accelerated rates of leaf maturation. Recognition of compensatory responses to air pollutants allows these responses to be placed in a framework that relates to whole-plant processes and ecosystem functions. (4) Air pollution and multiple stresses: Air pollution stress seldom occurs in isolation, and research approaches are being developed around the concept of multiple interacting stresses. Multiple-stress experiments are important because factors such as plant water status, light, and nutrient availability are known to alter plant responses to air pollutants. Multiple-stress studies will involve experiments with model plant species and high degrees of environmental control and monitoring.
The amount of formaldehyde removal was assessed according to various light intensity, and correlations between formaldehyde removal and photosynthesis factors were determined by potted Fatsia japonica and Epipremnum aureum. The amount of formaldehyde removal by potted F. japonica and E. aureum did not significantly increase with light intensity, whereas it had considerable differences between the light and the dark (0 μ㏖·m-2·s-1). The amount of formaldehyde removal by F. japonica and E. aureum was positively correlated with photosynthesis rate, but negatively correlated with intercellular CO₂ at 2 and 5 h after exposure. In addition, photosynthesis rate tended to decrease with time at high light intensity, which was attributable to the reduction of CO2 concentration in a chamber. Stomatal conductance and transpiration rate increased with light intensity during exposure of gaseous formaldehyde in a chamber, whereas intercellular CO₂ decreased. As a result, we considered that formaldehyde removal by potted plants was little affected by indoor light intensity (20-60 μ㏖·m-2·s-1).
The concentrations of HCHO(formaldehyde), (particulate matter), (carbon dioxide) and TBC(total bacteria counter) distribution in schools(Chung-Nam Area) were examined, and the results were compared with the recommended criterion of the administration law of indoor air. The subjects were an elementary school, a middle school and a high school in Chung-Nam area, and the concentration of TBC was examined by Single Stage Air Cascade Sampler, which applied the inertia collision catching method of 28.29L/min(flux) during 5 months from March, 2007 to July, 2007. The instrument(LD-3B, SIBATA Company)was used to examine , by a light scattering method and a light transmission method. The instrument(Airboxx(KD Engineering) was used to examine . The instrument(Z300XP(Environmental sensor)was used to examine HCHO. The result indicated that the average concentrations of the surveyed classrooms were in Spring and in Summer. The average concentration of the surveyed schools were 576 ppm in the classroom and 527 ppm in the stateroom. The average concentration of TBC were in an elementary school, in a middle school, in a high school. The HCHO average concentration of the surveyed schools were 0.03 ppm in the classroom, 0.02 ppm in the stateroom.