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Investigation of A Potted Plant (Hedera helix) with Photo-Regulation to Remove Volatile Formaldehyde for Improving Indoor Air Quality

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Formaldehyde is the most common volatile organic compound (VOC) emitted from household materials and is associated with many health risks, including sick building syndrome. A potted Hedera helix was used as an air purifier to remove the gaseous formaldehyde. Development of a test platform is necessary to evaluate the indoor performance of air cleaning protocols. The box modulation with a novel volatile pollutant-emitting source was applied in an air quality monitoring experiment to mimic a non-ventilated workplace. The environmental conditions and the pollutant concentrations in the air were measured in real time, and the monitoring data was uploaded to cloud storage media by a wireless technique. Compared with natural dissipation, our results demonstrate a 70% decrease in the required time to achieve 1.0 ppm of gaseous formaldehyde using the biological purifier. In addition, the effect of photo-regulation was not significant in the use of potted plants to remove gaseous formaldehyde. Our study provides an accurate and available platform for the public to determine the health risks of VOCs in their buildings.
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Aerosol and Air Quality Research, 17: 2543–2554, 2017
Copyright © Taiwan Association for Aerosol Research
ISSN: 1680-8584 print / 2071-1409 online
doi: 10.4209/aaqr.2017.04.0145
Investigation of A Potted Plant (Hedera helix) with Photo-Regulation to Remove
Volatile Formaldehyde for Improving Indoor Air Quality
Ming-Wei Lin
1
, Liang-Yü Chen
2*
, Yew-Khoy Chuah
1*
1 Department of Energy and Refrigerating Air-Conditioning Engineering, National Taipei University of Technology, Taipei
10608, Taiwan
2 Department of Biotechnology, Ming-Chuan University, Taoyuan 33348, Taiwan
ABSTRACT
Formaldehyde is the most common volatile organic compound (VOC) emitted from household materials and is
associated with many health risks, including sick building syndrome. A potted Hedera helix was used as an air purifier to
remove the gaseous formaldehyde. Development of a test platform is necessary to evaluate the indoor performance of air
cleaning protocols. The box modulation with a novel volatile pollutant-emitting source was applied in an air quality
monitoring experiment to mimic a non-ventilated workplace. The environmental conditions and the pollutant concentrations
in the air were measured in real time, and the monitoring data was uploaded to cloud storage media by a wireless
technique. Compared with natural dissipation, our results demonstrate a 70% decrease in the required time to achieve 1.0
ppm of gaseous formaldehyde using the biological purifier. In addition, the effect of photo-regulation was not significant
in the use of potted plants to remove gaseous formaldehyde. Our study provides an accurate and available platform for the
public to determine the health risks of VOCs in their buildings.
Keywords: Phyto-degradation; Ornamental plant; Gas sensor; Air cleaning; Photoreaction.
INTRODUCTION
Air quality is a global problem causing economic loss
and human health threats (Seppänen and Fisk, 2006). Serious
health problems are related to sick building syndrome, which
is usually associated with the quality of indoor air (Mullen
et al., 2016; Mandin et al., 2017). In urban areas, most
citizens have long-term exposure to large amounts of harmful
chemicals indoors, whether it’s at home or working at the
office (Zheng et al., 2011; Shi et al., 2015; Lukcso et al.,
2016). People are usually exposed to a higher intake or
breathe in a greater concentration of air pollutants because
these pollutants are more prevalent in indoor than outdoor
environments (Zhang et al., 2017).
However, increased industrial development and urban
activities have brought about worsened outdoor air quality
(Alam et al., 2016). Air pollution in China and India has
received a lot of scientific attention, even affecting the lives of
people in neighboring countries in Asia (Venkatachalam,
2017). People spend more time indoors, while outdoor air
* Corresponding author.
Tel.: +886-3-3507001 ext. 3773; Fax: +886-3-3593878
E-mail address: loknath@mail.mcu.edu.tw (L.Y. Chen);
yhtsai@ntut.edu.tw (Y.K. Chuah)
pollution has caused serious hazards to health (Zhang et
al., 2017). Understanding and controlling indoor air
quality can help reduce the risk of indoor health concerns,
especially Legionnaires' disease (Sundell, 2017), respiratory
allergy (Guan et al., 2016; Lukcso et al., 2016) and children’s
asthma (Huang et al., 2016).
As shown in Fig. 1, indoor air quality is dominated by
many dynamic processes, including air exchange, human
activities, and pollutants transferring within the building,
weather, and building occupants (Zheng et al., 2011). People
usually notice uncomfortable symptoms or illness after
working for several hours, and feel better after leaving the
building for some days. The amount of time they spend in
the building is associated with the health effects (Francisco
et al., 2017). However, specific pathogens or causes cannot
be identified in most cases. Therefore, a well-defined
experimental platform needs to characterize the major
components, distributions, boundaries, exchangeable rate,
and loading between the system and surroundings (Freijer
and Bloemen, 2000; Yang and Zhang, 2008; Demou et al.,
2009; Kim et al., 2010). The indoor air quality is significantly
influenced by infiltration into the building mainly through
the ventilation system and to a lesser extent, through
windows or cracks (Saraga et al., 2017).
Common indoor air pollutants can be categorized as
volatile organic compounds (VOCs), microbial contaminants,
gaseous contaminants, and particulate matter (PM). The air
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
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pollutants related to the sources of air pollution are listed
in Table 1. Thus, the pollution sources must be first identified
for the removal of indoor air pollutants. Formaldehyde
(HCHO) is one of the most common VOCs affecting indoor
air quality and the health of occupants in buildings (Brown
et al., 2015). Recent observation also demonstrated that the
HCHO is the most serious air pollutant in the decorated
residences and public places (Chang et al., 2017). Carbon
dioxide (CO2) levels can be used as an indicator of biotic
odors, and a health risk should be considered at very high
levels, greater than 5000 ppm (Rackes and Waring, 2013).
The chemical contaminants exist in the indoor environment
within the different dynamic behaviors and frequencies.
Ventilation is an effective way of ameliorating air quality
that works by diluting the concentrations of indoor pollutants,
but it increases energy use because the utilization of indoor
air handling systems must increase (Ciuzas et al., 2016;
Francisco et al., 2017). Besides, using effective means to
reduce indoor air pollution and improve air quality are
important issues for building occupants and users in non-
ventilated places, like hospitals and laboratories (Brown et
al., 2015; Lucas et al., 2016; Verriele et al., 2016; Bradman et
al., 2017). Indoor air handling systems with HEPA filters
control the ambient environmental conditions, including
the temperature, humidity, air flow and air cleaning (Russell
et al., 2014). However, filtration does not reduce the levels
of all indoor air pollutants, and some types can actually
exacerbate the problem (Yu et al., 2006). Chemicals or
particles can penetrate indoors through the building envelope,
affecting the indoor PM2.5 levels in real housing units with
a controlled indoor-outdoor pressure differences (Choi and
Kang, 2017). Therefore, a well-defined performance metrics
of air cleaner is need to developed for the indoor air quality
management (Hodgson et al., 2007; Yan et al., 2008).
The use of plants to improve indoor air quality was
investigated by the U.S. National Aeronautics and Space
Administration (NASA) to explore the possibilities of long-
term space habitation for closed environments in space
missions (Wolverton et al., 1989). The pioneering screening
studies by Wolverton and colleagues showed over 50 species
Fig. 1. Schematic assessment framework of indoor air quality, including a series of dynamic life cycles of chemicals,
biological activities, as well as the physical factors and exchange with the outdoor air (surroundings).
Tab l e 1 . Sources and types of pollutants in the indoor air.
Source Major Pollutions
Outdoor air exchange PM, Ozone, Nitrogen oxides, Dust, Pollen, Carbon oxides
Building materials, paint, glues, upholstery, wallpapers Benzene, Toluene, Insects, Formaldehyde, Alcohols
Furniture and decorative supplies, televisions,
refrigerators, carpets, heater
Formaldehyde, PM, Fungi, Insects, Benzene, Ethyl acetate,
Carbon oxides, Ammonia, Acetone, Fungi
Office equipment, printer, paper, photocopiers, inks,
computers, fax, cosmetics
PM, Ethanol, Formaldehyde, Carbon oxides, Ozone,
Nitrogen oxides, Ammonia, Acetone, Ester, Bio-aerosol
Activities of households, cooking, cleaning, smoking,
foods
Carbon dioxide, PM, Benzene, Ether, Acetate, Fungi,
Alcohols, Eater, Bio-aerosol
Pets and planting PM, Ammonia, Sulphur compounds, Carbon dioxide,
Methane, Ethyl acetate, Insects, Bio-aerosol
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
2545
of houseplants had air-cleaning capacity and reduced
VOCs levels in the air (Wolverton et al., 1989; Wolverton,
1996). English ivy (Hedera helix) is an evergreen climbing
plant that is well adapted to indoor conditions. Hedera helix
climbs by means of aerial rootlets with matted pads which
cling strongly to the substrate. The leaves are of two types,
with five-lobed juvenile leaves on creeping and climbing
stems, and unrobed adult leaves on fertile flowering stems
exposed to sun. Different varieties of Hedera helix are
widely cultivated as ornamental plants, preferring moist,
shady locations and avoiding direct exposure to sunlight.
Hedera helix is also usually listed as a top 10 houseplant
air cleaner for VOCs removal (Yang et al., 2009).
Thus, the potted Hedera helix and HCHO were used as
model plants and air pollutants to appraise the green
technique of improving indoor air quality in this study. Two
sources of air pollution in different emitting modes were
first utilized in a well-defined test box. The impacts of
biological factors on environmental conditions were also
evaluated by observations with quantitative data in real
time. A wireless air quality monitoring system was conducted
with field studies to verify the feasibility of prediction
models and estimate the exchange between the system and
its surroundings (Kang et al., 2016). The multiple boxes-
modeling was used in a laboratory-type test to describe the
performance of planting on the cleaning of indoor air.
Although the earlier laboratory studies have demonstrated
the ability of bioremediation technologies to remove VOCs
(Kim et al., 2008; Xu et al., 2010; Xu et al., 2011; Dela
Cruz et al., 2014; Gawronska and Bakera, 2015; Pandey et
al., 2016; Hong et al., 2017), no experimental field-study
has been made to investigate the potted-plant can bring
about significant reductions of VOC pollution in the real
environments. Our study might provide an accurate and
relatively accessible platform for the public, interior designers
and engineers to determine if the health risks of VOCs in
their building space. The phyto-remediation not only is
able to remove the VOCs from air but also stabilize the
temperature and humidity, to improve people's mental health.
EXPERIMENTAL METHODS
Plants Materials
Four potted plants (Hedera helix) were purchased from
the Jian-Kuo flower market in Taipei, Taiwan. All plants
were chosen to be free of insects and pathogens and cultured
in 8-cm-diameter pots with sterilized media. Before use in
experiments, clean water would be poured into the pot,
which was covered by aluminum foil to avoid withered
planting and infiltration of gaseous pollutants.
Setup of Experimental Box for Air Quality Monitoring
As shown in Fig. 2(A), the experimental platform of air
quality monitoring was designed as a controlled box to
mimic the indoor space and operations in this study. A
quasi-closed box was made of acrylic polymer in 90(L) ×
50(W) × 50(H) cm and equipped with two recirculating
fans; one illumination unit; and two exchangeable ports. The
recirculating fans were used to promote the composition
uniform of air quality in the experimental box. Two
fluorescent tubes (T5/2FT 14W, daylight, Wellypower
Optronics Corporation, Taiwan) were used to meet a
specification of 16(D) × 549(L) mm, with 1200 lm and
color temperature of 6500K, and were placed on the upper
layer of the box to meet the illumination requirement. The
spectrum of the fluorescent tube was measured by a
UV/visible/infrared micro-spectrometer (GREEN-Wave
UVNb-25, StellarNet Inc., USA) and characterized as shown
in Fig. 2(B). The irradiation intensity was also validated
using a multi-sense optical radiometer (MS-100, Ultra-Violet
Products Ltd., UK).
The monitoring instruments were installed for air quality
and environmental conditions in real time. An illuminometer
(TENMARS YF-1065, TECPEL Co., Taipei, Taiwan) and
combo air quality sensors (AQM-100 and APM-200, AIGO
TECH Co., Taipei, Taiwan) were used in the study. Each of
the major sensors used in this work was characterized and
listed in Table 2.
Exposure to Gaseous HCHO with Different Emission
Modes
Two types of emission source of gaseous HCHO were
used to examine the removal efficiency of HCHO pollution
in indoor environments. One was the spraying of 2 ml of
14% HCHO liquid into the experimental box and using an
atomizing nozzle to make the molecules vaporize and
rapidly disperse. The emission mode of the volatile pollutant
was termed the “fast discharge”. The other emission mode
was termed “slow release”, whereby 1 ml of 14% HCHO
liquid was poured in a glass dish with a porous material. In
the slow release mode, the HCHO molecules were vaporized
and diffused into the box space.
The 14% HCHO liquid was purchased from First-
Chemical Works (Taipei, Taiwan). Ultrapure water produced
by a Milli-Q system (Millipore, USA) was used as a solvent.
Experimental Design and Observation
Several preliminary studies were carried out for
observation requirements, such as the maximum detectable
level, the background level, and the time required for natural
decay under the experimental conditions. The air quality of
the experimental box was conditioned to the background
standards before every treatment. For the target pollutant,
the HCHO concentration should be less than the 0.1 ppm
of DNEL in the air (Johansson et al., 2016). Therefore, the
active ventilation would make the HCHO level decrease to
0.03 ppm for 1 hour.
Every six hours, the illumination system was toggled
automatically between light and dark environments. The
observations without a planting were considered a control
for the system under an indicated emission mode of air
pollutant. The eight parameters listed in Table 2 were
measured and collected in real time. Once the HCHO level
in the air was attenuated to 0.05 ppm as the low removal
efficacy, the observations were ended. The time series of
experimental data per minute were recorded on a computer
and uploaded to a cloud storage media by Wi-Fi router.
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
2546
Fig. 2. Illustration of an experimental system for air quality monitoring. (A) The modeling box was used with a potted
Hedera helix, an illumination unit and the data acquired network in this study. (B) The emission spectrum of fluorescent
lamps used in this study was measured at a wavelength range of 190–1050 nm.
Tab l e 2 . Sensors and their specifications.
Parameters Measurement Response Range Sensitivity Symbol (Unit)
1. Illumination Si Photodiode
0.120000 ± 0.1 Luminance (Lux)
2. Temperature e-Resistivity
30100 ± 0.1 Temp. (°C)
3. Relative Humidity e-Conductivity 090 ± 3% RH% (%)
4. Formaldehyde Electrochemistry
05.000 ± 0.001 [HCHO]air (ppm)
5. Carbon Dioxide NDIR 05000 ± 5% [CO2]air (ppm)
6. Carbon Oxide n
d
Electrochemistry
0100 ± 5% [CO]air (ppm)
7. Total Volatile Organic Chemicals n
d
Semiconductor 0.1250.6 ± 5% TVOC (ppm)
8. Ultrafine Particles n
d
Photometer
0999 ± 10% PM2.5 (ppb)
The superscript of “nd” is indicated the non-detectable data monitored by the sensor, which was used in this study.
Statistical Analysis
All data represent the mean with a standard deviation of
independent experiments. Only the control experiment of
slow release mode was executed once, because the
observation was time-consuming. The results were analyzed
using the unpaired, two-tailed Student’s t-test.
RESULTS AND DISCUSSION
Characterization of Indoor Air Quality Changes
The air quality of the experimental box to mimic indoors
is a constantly changing interaction of complex factors
affecting the types, levels and importance of pollutants in a
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
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controlled environment. Indoor temperature, relative
humidity, and illumination are the environmental factors
affected and controlled by the ambient surroundings and
the observer’s activities. As shown in Fig. 3, only five
environmental and air quality parameters were available
and detectable for this observation on March 4, 2017. In
addition, illumination was an operating factor for photo-
regulation. Luminance, carbon dioxide, temperature and
relative humidity were immediately affected by opening
the box with the air exchange at Event (1). The box air was
rapidly cooled and humidified while the spraying of HCHO
liquid atomized the water molecules and absorbed heat
Fig. 3. Example of the time courses of environmental and air quality parameters in the box by the monitoring data in
March 4, 2017. The blue-lined area represents a period of data loss. The numbered events indicate the effects of the
processes, the box opening and plant setting were carried at Event (1); the 2 ml HCHO liquid was injected into box at
Event (2); the illumination unit was turned off at Event (3); the illumination unit was restarted at Event (4).
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
2548
from the air at Event (2). The raised level of carbon dioxide
was caused by the breathing of the observer. With the
molecular diffusion and heat exchange between the system
and surroundings, these parameters gradually returned to a
stable range. The alterations in illumination at Event (3)
and Event (4) made subtle changes in the relative humidity
and carbon dioxide.
The harmful gaseous pollutants, such as carbon monoxide,
total volatile organic chemicals and fine particles were non-
detectable and less than the toxic levels in these observations.
A good indoor environment establishes the range of
environmental conditions acceptable to achieve healthy
and thermal comfort for human occupancy (Xiong et al.,
2015; Sundell, 2017). For thermal comfort purposes, the
air temperature and the relative humidity should be held in
the range of 22–26°C and 40–60%, respectively. After
spraying pollutants into the box, the gaseous HCHO level
in the air was raised over the upper limit level of sensor
measurement (5 ppm) and was then reduced with time.
In this observation, the removal of gaseous HCHO presents
an exponential decay curve with complicated regulations and
multiple mechanisms via illumination and plants. Note, a
slightly increased signal was present in the attenuated curve
after the occurrence of Event (3) while the illumination
was turned to dark. The phenomenon reveals an emitting
source contributes gaseous pollutants into the box air more
than the removal amount from the box air. We believe the
plants play an important role in the removal of gaseous
HCHO and were regulated by illumination.
Effects of Pollutant Emitting Modes on Indoor Air
Quality
HCHO occurs naturally and is an important industrial
chemical. Workplaces in health care facilities, research
institutes, and mortuaries may present the high exposure
risks due to the use of chemicals (Demou et al., 2009).
However, many studies have investigated the removal
kinetics of VOCs with a short-term exposure in a controlled
space. Studies based on long-term exposure are rare in the
literature review (Hun et al., 2010; Nielsen et al., 2017).
Thus, we presume different types of emission sources of
VOCs and their degradation patterns in Fig. 4(A) from the
life experiences. A combination of slow discharge and
cyclical release modes mimicked the long-term emission
source of indoor VOCs in this study. The performance of
the emission sources should be validated and characterized
for different experimental requirements. The emission source
in the fast discharge mode was applied in this short-term
study (less than ten hours), and one of the slow release
modes was used for the long-term study, such as the
botanic filter application and health risk assessment. Urea-
formaldehyde (UF) is a non-transparent thermosetting
resin or plastic used in adhesives, finishes, particle board,
and molded objects (Broder et al., 1991). These UF resins
are a class of thermosetting resins of which resins make up
80% produced globally for improving tear strength, in
molding electrical devices. Thus, the emission source with
porous material could mimetic the dynamics of indoor
VOCs production (Hun et al., 2010).
In Fig. 4(B), the gaseous HCHO level in the air was
rapidly reduced to a safe level in the fast discharge mode;
but the other observation needed more time to achieve a
similar level in the slow release mode. Our previous study
demonstrated the temperature and relative humidity of
indoor air are not sensitive to HCHO removal via natural
dissipation and photo-degradation (Lin et al., 2017).
However, the time course of gaseous HCHO removal
presented a photo-regulated phenomenon by switching the
illumination environment. The lighting would increase the
air temperature and indirectly enhance the vaporized rate
of HCHO from the supported material into the air. Real
absorbents have pores of various sizes; the diffusion plays
an increasingly important role to decrease the observed
activation energy, and the reaction order approaches unity
(Lin et al., 2017).
Otherwise, the positive effect of illumination would also
contribute to the removal of gaseous HCHO through
photo-degradation. Due to the exponential decay curve of
gaseous HCHO removal, the apparent kinetic equation was
proposed as follows: [HCHO]air (t) = [HCHO]air (0)·e–K+(t–0),
and the removal rate of gaseous HCHO was derived from the
logarithmic plot in Fig. 4(C). The slope of the logarithmic
curve with time presents an apparent rate constant, K+.
With Arrhenius temperature dependencies for the reaction
and diffusion, the observed activation energy would be
approximately one-half the true activation energy by
strong pore resistance, Eobs E
true/2. The results of the
kinetic observations clearly demonstrate an approximated
one-stage matter in the slow release pollution and a two-
stage mechanism depended on the concentration for the
fast discharge pollution.
Performance Evaluation of Plants on Volatile HCHO
Removal
Current performance assessment of the air cleaning
primarily has been occurred in laboratories, often using
high challenge concentrations of chemicals, low airflow rates,
and single contaminant species in a controlled environment
(Yu et al., 2015). In generation, a performance of air
cleaning was determined by two ways including a direct
upstream versus downstream measurement and empirical
determination with a single zone mass balance model
(Thunyasirinon et al., 2015; Ciuzas et al., 2016). The air
purification performance could be assessed by the removal
amount, the removal rate, and the required time to achieve
the acceptable values of air quality. For short-term
assessments, the removal of contaminants is the most used
indicator in quantitation.
However, the World Health Organization (WHO)
established an exposure limit of gaseous HCHO of 0.08 ppm
for 30-minute periods (Salthammer et al., 2010; Nielsen et
al., 2017). The main human exposure pathways of HCHO
are inhalation of gaseous HCHO from the air or
transdermal absorption of aqueous HCHO (Gelbke et al.,
2014). Therefore, the required time is more available as the
indicator to evaluate the performance of a biological method
for indoor HCHO removal (Darlington et al., 1998; Xu et
al., 2011; Dela Cruz et al., 2014).
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
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Fig. 4. The effect of emitting sources with different modes on gaseous pollutants removal without plants. (A) Patterns of
gaseous pollutant concentration are proposed with the three types of emission sources. (B) The time courses of HCHO
concentration were recorded with the fast discharge mode and the slow release mode. (C) Plotting of the logarithmic
concentration of gaseous HCHO versus the time was used to characterize the removal rate of HCHO. The grey block
means the experiments were performed without illumination (in dark).
For comparison, the control experiments were performed
in the box system without household plants. As shown in
Fig. 5(A), treatment with potted Hedera helix could slightly
accelerate the removal of gaseous HCHO from the air
under the fast discharge mode of the emission source. The
efficiency of potted Hedera helix was greater at lower levels
of gaseous HCHO, at less than 1 ppm. This result shows
the botanic filters are not suitable to treat acute exposure to
VOCs. However, the efficiencies of potted Hedera helix
were significantly improved for gaseous HCHO removal
under the slow release mode of the emission source, as
shown in Fig. 5(B). The required times to achieve 1.0 ppm
HCHO were 58.5 hours and 17.1 hours using natural
dissipation and the biological purifier, respectively. The
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
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Fig. 5. The time efficacies of gaseous HCHO removal with a potted Hedera helix. Evaluation was based on the time
required to achieve the indicated concentration (1.0 or 0.5 ppm) of gaseous HCHO under the emission source of (A) fast
discharge mode, or (B) slow release mode. For comparison, the control experiments were performed in a box system
without household plants. The difference was designated as the level of significance with * (P < 0.5), with ** (P < 0.05) or
with *** (P < 0.01).
required times to achieve 0.5 ppm HCHO were 67.6 hours
and 20.9 hours using natural dissipation and the biological
purifier, respectively.
People are exposed to localized and accumulated doses
of VOCs due to staying indoors for a long time (Wolkoff et
al., 1998). Usually, the most effective way to improve indoor
air quality is to eliminate individual sources of pollution or
reduce their emissions. However, most emission sources of
indoor VOCs are continuous and slow release (Manoukian
et al., 2016). Gaseous HCHO can be removed by many
pathways, including diffusion, adsorption, polymerization,
photolysis and photocatalytic oxidation decomposition (Li et
al., 2014). Our results demonstrate plants have an advantage
in treating chronic pollution and the residual pollutants in
ambient air.
Photo-Regulated Effects of Hedera Helix on Gaseous
HCHO Removal
Under proper light irradiation, the photosynthesis of
green plants utilizes the carbon dioxide in air to provide
carbohydrates and energy source for growth. The volatile
chemicals are absorbed and metabolized by the physiological
pathways of the plants, and the efficiency of pollutant
removal depends on the plant species, time, light intensity
and pollutant species (Kim et al., 2008; Wang et al., 2014).
The data set of long-term monitoring was chosen to
investigate the photo-regulated effect on improving indoor
air quality with plants. Thus, the emission source of gaseous
HCHO was used as the slow release mode to provide a
detectable level in the air. In Fig. 6(A), the gaseous HCHO
level was decreased and the removal rate tended to slow
after exposure of 8 hours. For high level region, the time
course of gaseous HCHO is changed significantly in the
removal rate. In addition, the system illumination was
periodic switched every six hours. The time-lag effects
were also observed in these irradiation events. The Fig. 6(B)
shows illumination could assist the Hedera helix in removing
gaseous HCHO at lower levels, at less than 1 ppm. Thus,
gaseous HCHO removal by Hedera helix was again validated
as a concentration dependent matter.
The carbon dioxide levels in the box air could be an
indicator of respiration and were shown in Fig. 6(C).
Lower levels of carbon dioxide were observed in the light
environment, compared with the dark environment. The
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
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Fig. 6. Effects of illumination on HCHO removal, kinetic rate and carbon dioxide level in air. (A) The time courses of
HCHO concentration were recorded in the slow release mode from March 12 to 15. (B) The kinetic rate of gaseous HCHO
removal was evaluated for less harmful concentrations of HCHO on March 13. Plotting of the logarithmic scale versus the
time was used to display the removal rate with Hedera helix. (C) The time courses of carbon dioxide concentration were
recorded and compared to the HCHO removal at March 13. The grey block means the experiment was carried without
illumination. The symbols of D L and L D show the experimental environments changed from dark to light and from
light to dark, respectively.
effectiveness of photosynthesis was inhibited by the high
level of carbon dioxide in the air. The post-illumination
CO2 burst was observed after the illumination turned off
(LD). For C3 plants, light respiration will counteract
about 30% of the photosynthesis. Oxygen is consumed during
the process and generates carbon dioxide. Therefore, reducing
light respiration is considered one way to improve the
effectiveness of photosynthesis.
Biological regulation is a complex, adaptive and dynamic
process, and the illumination and planting has a strong
Lin et al., Aerosol and Air Quality Research, 17: 2543–2554, 2017
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impact on the ecological stability of human life. Some
studies reported the biogenic VOC has an indirect impact
on the lifetime of greenhouse gases and the secondary
organic aerosol formation in the atmosphere (de Oliveira
and Moraes, 2017). However, the benefit outweighs of
planting for improving the indoor air quality is larger than
the hazard risk from biogenic toxins.
CONCLUSION
Air cleaning techniques with low-energy consumption and
green properties are modern trends (Lu et al., 2010). To
gauge the potential benefits of these devices and techniques,
metric tools based on indoor air quality modeling and
performance data from field testing must first be applied
(Ozturk, 2015). A well-defined experimental platform with
an emission source of volatile organic chemicals was
investigated to evaluate the performance of a potted plant
in removing gaseous HCHO. The slow-release mode of
emitted pollution was first utilized to fulfill the requirement of
mimicking an indoor environment in a long-term monitoring
experiment. The contributions of natural dissipation,
photo-degradation and the botanic filter were assessed
quantitatively. Volatile HCHO levels can be reduced using
potted plants, which provide additional ornamental features.
The experimental results show that potted Hedera helix
can reduce 70% of the required time to reach 0.5 ppm of
gaseous HCHO when compared with natural dissipation.
Potted Hedera helix can also remove residual HCHO from
the environment, thus improving indoor air quality.
ACKNOWLEDGMENTS
The authors thank the assistances from the Lecturer Lin,
Liang-Tse in the Department of Civil and Construction
Engineering at National Taiwan University of Science and
Technology in the works of electronics and data acquirement.
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Received for review, April 21, 2017
Revised, June 16, 2017
Accepted, August 25, 2017
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The scientific articles and Indoor Air conference publications of the indoor air sciences (IAS) during the last 50 years are summarized. In total 7524 presentations, from 79 countries, have been made at Indoor Air conferences held between 1978 (49 presentations) and 2014 (1049 presentations). In the Web of Science 26,992 articles on indoor air research (with the word "indoor" as a search term) have been found (as of 1 Jan 2016) of which 70% were published during the last 10 years. The modern scientific history started in the 1970s with a question: "did indoor air pose a threat to health as did outdoor air?" Soon it was recognized that indoor air is more important, from a health point of view, than outdoor air. Topics of concern were first radon, environmental tobacco smoke and lung cancer, followed by volatile organic compounds, formaldehyde and sick building syndrome, house dust mites, asthma and allergies, Legionnaires disease and other airborne infections. Later emerged dampness/mold-associated allergies and today's concern with "modern exposures-modern diseases." Ventilation, thermal comfort, indoor air chemistry, semi volatile organic compounds, building simulation by computational fluid dynamics, and fine particulate matter are common topics today. From their beginning in Denmark and Sweden, then in the USA, the indoor air sciences now show increasing activity in East and Southeast Asia. This article is protected by copyright. All rights reserved.
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To identify the sources of PM2.5 pollutants in work environments and determine whether the air quality inside an office was affected by a change in outdoor pollution status, concurrent indoor and outdoor measurements of PM2.5 were conducted at five different office spaces in the urban center of Guangzhou on low pollution days (non-episode days, NEDs), and high pollution days (haze episode days, EDs). Indoor-outdoor relationships between the PM2.5 mass and its chemical constituents, which included water-soluble ions, carbonaceous species, and metal elements, were investigated. A principle component analysis (PCA) was performed to further confirm the relationship between the indoor and outdoor PM2.5 pollution. The results reveal that (1) Printing and ETS (Environmental tobacco smoking) were found to be important office PM2.5 sources and associated with the enrichment of SO4²⁻, OC, EC and some toxic metals indoors; (2) On EDs, serious outdoor pollution and higher air exchange rate greatly affected all studied office environments, masking the original differences of the indoor characteristics (3) Fresh air system could efficiently filter out most of the outside pollutants on both NEDs and EDs. Overall, the results of our study suggest that improper human behavior is associated with the day-to-day generation of indoor PM2.5 levels and sporadic outdoor pollution events can lead to poor indoor air quality in urban office environments. Moreover, fresh air system has been experimentally proved with data as an effective way to improve the air quality in office.