The Horticulture Journal 89 (3): 319–327. 2020. e Japanese Society for doi: 10.2503/hortj.UTD-110 JSHS Horticultural Science http://www.jshs.jp/

Higher Attention Capacity After Improving by Indoor Plant Placement in Elementary School Classrooms

Ho-Hyun Kim1, In-Young Yeo2 and Jae-Young Lee3*

1Department of Information, Communication and Technology Convergence, ICT Environment Convergence, Pyeongtaek University, Pyeongtaek, 17869, Korea 2Department of Environmental Radiation & Radioactivity Assessment, Korea Institute of Nuclear Safety, Daejeon, 34142, Korea 3Institute of Life Science & Resources, Kyung Hee University, Yongin, 17104, Korea

This research evaluated the attention capacity of 70 pupils in the sixth grade with the intervention of indoor air quality regulated by indoor plant placement in the classrooms of two elementary schools in Seoul, South Korea. Two sets of three-week measurements were conducted with an interval of 12 weeks from 27th June to 7th October, 2016. We divided subjects into two groups (Group I and II): subjects in Group I occupied classrooms without indoor plants and those in Group II occupied classrooms with indoor plants. The classrooms with indoor plants had indoor levels with constant air temperature (approximately 26°C), relative −3 humidity (around 50%), and (CO2) (around 1100 mg·m ). Additionally, 12-week placement of indoor plants reduced the indoor concentrations of airborne contaminants. After 12 weeks of the experiments, the subjects’ attention capacity improved as demonstrated by a standard questionnaire (Frankfurt Aufmerksamkeits-Invertar, FAIR). Indoor plant placement showed little difference in terms of efficiency (FAIR-E) and continuity (FAIR-C) scores, but exhibited a significant improvement for performance (FAIR-P) (increasing from 0.964 to 0.989) and quality (FAIR-Q) scores (increasing from 0.945 to 0.973). Based on multiple regression, the current study suggested that indoor plant placement was one of the most important factors to improve the attention capacity of pupils in classrooms.

Key Words: airborne contaminant, FAIR (Frankfurt Aufmerksamkeits-Invertar), indoor environment, indoor occupant, volatile organic compound (VOC).

quent mechanical ventilation. However, the ventilation Introduction tends to be done without considering the contamination Spending more of our lives indoors is one of the most level in indoor spaces (Moya et al., 2018). Researchers widespread current trends. Earlier studies reported that have suggested that indoor plant placement could be an the general public nowadays spend approximately 80% alternative method for regulating indoor environments of their daily lives indoors (Orwell et al., 2004; United efficiently with the expectation of physical, as well as States Department of Labor, 2006; WHO, 2010). Con‐ psychological benefits (Adachi et al., 2000; sequently, it could be postulated that the health of in‐ Bringslimark et al., 2009; Dijkstra et al., 2008; Lohr door occupants is more greatly influenced by the indoor et al., 1996; Orwell et al., 2006; Wood et al., 2002). In environment quality than outdoor factors. addition to the visual attractiveness, indoor plant place‐ Indoor occupants have often tried to maintain their ment provides additional benefits to indoor environ‐ indoor environments at a comfortable level using fre‐ ments via plants’ metabolic actions (Bringslimark et al., 2009; Gary and Birrell, 2014; Ottele, 2011; Raanaas Received; June 9, 2019. Accepted; October 31, 2019. et al., 2011; Wolverton, 1997). First Published Online in J-STAGE on December 28, 2019. That is, the placement of indoor plants regulates air This work was carried out with the support of “Cooperative Research temperature and humidity through evapotranspiration Program for Agriculture Science and Technology Development (Davis and Hirmer, 2015; Mangone and van der (Project No. PJ014270032019)” by the Rural Development Administration, Republic of Korea. Linden, 2014; Perez-Urrestarazu et al., 2016). After the * Corresponding author (E-mail: [email protected]). National Aeronautics and Space Administration

© 2020 The Japanese Society for Horticultural Science (JSHS), All rights reserved. 320 H.-H. Kim, I.-Y. Yeo and J.-Y. Lee

(NASA) Clean Air Study presented a study about the and measuring the indoor environment. Detailed de‐ metabolic actions of plants to remove toxic agents from scriptions of the current study were as follows. the air in the 1980s (Wolverton et al., 1984, 1989), re‐ searchers have reported similar results that indoor plant Arrangement of facilities and subjects placement helped reduce the indoor level of airborne The current study used two groups of classrooms contaminants (Kim et al., 2011; Lim et al., 2009; (Group I and II) at two elementary schools (Schools A Orwell et al., 2006; Wood et al., 2002). and B) which were established in 2011. Each school The health of indoor occupants is greatly influenced provided two classrooms: one classroom without indoor by the indoor environment quality and the accumulation plants (Group I) and the other classroom with indoor of carbon dioxide (CO2) (Shendell et al., 2004) and plant placement (Group II). The classrooms of both volatile organic compounds (VOCs) (Daisey et al., schools had two opposing walls with windows. The 2003; De Kluizenaar et al., 2016) are caused by insuffi‐ classrooms of both schools had the same rectangular cient ventilation. Based on previous studies, it is postu‐ dimensions of 9.0 m long and 7.7 m wide. To regulate lated that the indoor environment quality plays an the indoor environment at an air temperature of 26°C, important role in the health and work performance of individual systems of mechanical ventilation and air indoor occupants (Al Horr et al., 2016; Blueyssen et al., conditioning were used for two hours twice a day 2016; Frontczak et al., 2012; Kosonea and Tan, 2004; (from 10:00 a.m. to 12:00 p.m. and from 2:00 p.m. to Raanaas et al., 2011; Wyon, 2004). Other reports also 4:00 p.m.). pointed out that the interaction between indoor occu‐ We recruited 70 pupils in the sixth grade of elemen‐ pants and plants in indoor environments can alter the at‐ tary school who could attend school for the experimen‐ titudes, behavior, and physical responses of the indoor tal duration without absence. All the pupils participated occupants, improving their productivity and overall sat‐ in this experiment with the permission of their parents isfaction (Gary and Birrell, 2014; Lohr et al., 1996; after fully understanding the experimental procedure. Relf, 1990; Shoemaker et al., 1992). We enrolled 40 participants for each of two classrooms Young individuals in their growth phase are highly at School A and 30 participants for each of two class‐ sensitive to environmental factors (Faustman et al., rooms at School B, respectively (Table 1). 2000). They usually spend more than half of their daily lives in classrooms. Classrooms can be distinguished Indoor plant placement from other indoor environments by their overpopulation The current study followed the descriptions of certain and abundant pollution sources (Becker et al., 2007; previous reports regarding the types, quantity and meth‐ Fromme et al., 2008; Theodosiou and Ordoumpozanis, ods for indoor plant placement (Kil et al., 2008; 2008). Some researchers suggested that exposure to a Soreanu et al., 2013; WHO, 1986). We placed indoor cleaner natural environment could help people improve plants in the classrooms of Group II at both schools for attention capacity (Felsten, 2009; Kaplan, 1995; 12 weeks (from 6th March to 28th May) to acclimatize Tennessen and Cimprich, 1995; Wells, 2000). Others the pot plants to the indoor environment and removed also proposed that proper management of the indoor en‐ them for four weeks to reduce any environmental dam‐ vironment quality using plants could enhance the atten‐ age to them prior to the actual examination. Then, in‐ tion capacity of indoor occupants (Momovic et al., door plants were again placed in the classrooms for the 2009; Raanaas et al., 2011). entire experimental duration (12 + 3 weeks, 27th June Considering the points above, the current study tried to 7th October). to clarify the relationship between the attention capacity We classified pot plants into two categories (large of indoor occupants and their indoor environment quali‐ and small) based on a previous report by Lee and Kim ty when regulated by indoor plant placement. The aim (2005): a large pot plant was one with a leaf area of of this study is to propose an appropriate indoor envi‐ 3000 to 5000 cm2 and a small pot plant was one with a ronment quality for elementary school pupils during leaf area of less than 1000 cm2. Considering capacity their time indoors to improve attention capacity. for decomposition, earlier researchers recommended the suitable pot plants: lady palm, rubber Materials and Methods plant, areca palm, and heavenly bamboo as large plants This research evaluated the attention capacity of 70 and bird’s-nest fern, peace lily, golden pothos, and tiny pupils in the sixth grade with the intervention of indoor ardisia as small plants (Kil et al., 2008; Kim et al., air quality regulated by indoor plant placement in the 2009; Lee and Kim, 2005). A large pot plant was grown classrooms of two elementary schools in Seoul, South in a pot with a size of ø30 cm × 41 cm (h) (28.976 L) or Korea. Two sets of three-week measurements were con‐ ø24 cm × 23.5 cm (h) (10.626 L), and a small plant was ducted with an interval of 12 weeks from June 27 to grown in a pot with a size of ø18 cm × 15 cm (h) October 7, 2016. The authors followed the same pat‐ (3.815 L). Then, the researchers placed more than one terns as previous reports by Kim et al. (2013, 2016) in large pot plant and one small pot plant in an area of arranging facilities and subjects, placing indoor plants, 6 m2 by the window wall of each classroom, following Hort. J. 89 (3): 319–327. 2020. 321 the description of a previous report by Lee and Kim Measurement of indoor environment conditions (2005) (Table 2; Fig. 1). The current study assessed indoor air conditions by Table 1. General description of the subjects. recording the indoor levels of air temperature (°C), rela‐

Table 1. General description of the subjects.

Classification Measurement item Total Withoutz With General feature Number of individuals 70 35 35 Gender, Male/Female 33/37 17/18 16/19 (male %) (47.1%) (48.6%) (45.7%) Age 11.9 ± 0.3 11.8 ± 0.3 12.0 ± 0.3 (range) (11.3 to 12.5) (11.1 to 12.3) (11.4 to 12.5) Indirect smoking 42.9% 48.6% 37.1% Pet 21.4% 25.7% 17.1% Housing form APTy, 97.1% APT, 97.1% APT, 97.1% Medical history of family (%) Atopic disease 20.0 17.1 22.9 Allergic rhinitis 28.6 31.4 25.7 Allergic conjunctivitis 1.4 — 2.9 Asthma 4.3 5.7 2.9 Atopic dermatitis 45.7 42.9 48.6 Medical history of individuals (%) Atopic disease 17.1 20.0 14.3 Allergic rhinitis 24.3 25.7 22.9 Allergic conjunctivitis — — — Asthma 2.9 2.9 2.9 Atopic dermatitis 38.6 42.9 34.3 Mean ± SD. z Without; subjects in classrooms without indoor plants: With; subjects in classrooms with indoor plant placement. Tabley APT: 2. apartment List of indoor house. plants placed in classrooms.

Table 2. List of indoor plants placed in classrooms.

Indoor plant Size Category Number of articles Common name Scientific name (Diameter × Height) Large plantz Lady palm Rhapis excelsa ø30 × 41 cm 3 Rubber plant Ficus robusta ø30 × 41 cm 3 Areca palm Chrysalidocarpus lutescene ø30 × 41 cm 2 Heavenly bamboo Nandina domestica ø24 × 23.5 cm 2 Small plant Bird’s-nest fern Asplenium nidus ø18 × 15 cm 3 Peace lily Spathiphyuuum spp. ø18 × 15 cm 3 Golden pothos ø18 × 15 cm 2 Tiny ardisia Ardisia pusilla ø18 × 15 cm 2 z Large plant; a plant with a leaf area of 3000 to 5000 cm2/plant: Small plant; a plant with a leaf area of less than 1000 cm2/plant.

Before indoor plant placement After indoor plant placement Fig. 1. Photographs of classrooms for attention capacity measurements according to indoor plant placement. 322 H.-H. Kim, I.-Y. Yeo and J.-Y. Lee

−3 tive humidity (%), and CO2 (mg·m ), and evaluated in‐ (Frankfurt Attention Inventory, FAIR) questionnaire for door air quality by measuring the indoor concentrations the assessment through the scores for performance (μg·m−3) of formaldehyde and additional VOCs includ‐ (FAIR-P), efficiency (FAIR-E), quality (FAIR-Q), and ing , , ethylene, and xylene (BTEX). continuity (FAIR-C), carefully following the guideline The measurements were conducted over two mea‐ to prevent the accidental errors from learning effects surement periods: the first and second measurement pe‐ (Fink et al., 2002; Moosbrugger and Oehlsclagel, 1995, riods. The first measurement was conducted just prior 1996; Schweizer et al., 2000). To analyze the factors af‐ to indoor plant placement (from 27th June to 15th July) fecting attention capacity, the authors used a model for and the second measurement was carried out just after multiple regression analysis based on the questionnaire. 12 weeks of observation (from 19th September to 7th Independent variables included the levels of indoor air October). Each measurement period consisted of nine compounds and the concentrations of indoor airborne measurement days over three weeks (every Monday, contaminants. Wednesday, and Friday). On every measurement day, we conducted the measurement at 9:00 a.m. and 1:00 Statistical analysis p.m. with the pupils in an active state after closing all A paired t-test was used to analyze the variations in the windows and doors and ceasing mechanical air ven‐ indoor air conditions and indoor air quality with the in‐ tilation to prevent possible contamination from the out‐ tervention of indoor plant placement. Factors affecting side environment. the attention capacity of subjects were analyzed using The indoor levels of air temperature and relative hu‐ multiple regression. midity were recorded at one site at a height 1.5 m above Results floor level in the mid-part of the classroom (less than 4.0 m from plants) using a digital recorder (Testo 950; Measurement of indoor air conditions and indoor air Testo SE & Co. KGaA, Lenzkirch, Germany). The in‐ quality door concentration of CO2 was measured at two sites After 12 weeks of observation, the classrooms with‐ (front and back sites, 3.0 to 6.0 m from plants) using a out indoor plants had increased air temperature (from −3 digital gas analyzer (Gas Analyzer OXYBABY M+; 25.1 to 29.4°C) and CO2 (from 1087 to 1277 mg·m ), Witt-Gasetetechnik, Witten, Germany). and decreased relative humidity (from 57 to 51%). The The current study measured the indoor concentra‐ placement of indoor plants did not alter the increasing tions of formaldehyde and BTEX at two sites in the tendency of air temperature or CO2, or the decreasing classrooms (front and back sites, 3.0 to 6.0 m from trend in relative humidity. However, the increases of air plants). We installed a personal air sampler (Minipump temperature and CO2 were reduced and the decreasing ΣMP-100H; SHIBATA SCIENTIFIC TECHNOLOGY trend of relative humidity was facilitated in the class‐ LTD., Saitama, Japan) in serial connection with an rooms with indoor plants (Fig. 2). ozone scrubber cartridge (Waters Corp., Milford, MA, The indoor concentration of formaldehyde signifi‐ USA), which was filled with 350 mg of DNPH-silica cantly decreased from 31.02 to 12.01 μg·m−3 over time (100 mg of DNPH). Then, indoor air was absorbed at a in the classrooms without indoor plants (P < 0.001). height of 1.5 m above floor level at a flow rate of The placement of indoor plants slightly facilitated a de‐ 0.5 L·min−1 for 30 min and the concentration of creasing tendency of formaldehyde. In the classrooms formaldehyde was measured using high-performance without indoor plants, benzene showed a lower concen‐ liquid chromatography system equipped with ultra- tration at the second measurement (5.50 μg·m−3) than at violet absorption (Alliance 2690 and 2487; Waters the first measurement (5.92 μg·m−3) (P < 0.01). Indoor Corp.). The indoor concentrations of BTEX using a plant placement significantly facilitated a decreasing solid thermal desorption method were also measured trend in benzene from 5.25 to 3.84 μg·m−3 (P < 0.001). (Kim et al., 2010, 2011; Lim et al., 2009). We collected After an interval of 12 weeks, we found the indoor con‐ indoor air using another personal air sampler centration of toluene slightly increased from 65.77 to (Minipump ΣMP-100H; SHIBATA SCIENTIFIC 68.51 μg·m−3 in the classrooms without indoor plants, TECHNOLOGY) equipped with a Tenax-TA tube but decreased from 75.42 to 39.10 μg·m−3 in the class‐ (1/4" × 10 cm stainless steel; Supelco, Bellefont, PA, rooms with indoor plants. The current study found little USA) at a flow rate of 10 L·min−1 for 30 min, and ana‐ difference in the indoor concentrations of ethylbenzene lyzed the indoor concentrations of BTEX. and xylene, with no significant differences over time. However, indoor plant placement led to clear decreas‐ Evaluation of attention capacity ing tendencies in the indoor concentrations of the two The attention capacity of all subjects was assessed contaminants with clear significance (decreasing from twice a day at 9:00 a.m. and 1:00 p.m. for the nine mea‐ 9.82 to 5.06 μg·m−3 and from 7.75 to 6.36 μg·m−3, re‐ surement days (every Monday, Wednesday, and Friday spectively) (Table 3). over three weeks) for each measurement period. We used the Frankfurt Aufmerksamkeits-Invertar Hort. J. 89 (3): 319–327. 2020. 323

Evaluation of attention capacity placement of indoor plants facilitated the increase in After an interval of 12 weeks in the classrooms with‐ some, but not all, FAIR scores. The variations in FAIR- out indoor plants, subjects’ FAIR scores increased. The P scores between the two measurement periods were 0.017 in the classrooms without indoor plants (0.970 for 1st period the first period and 0.986 for the second period) and 28 2nd period 0.025 in the classrooms with indoor plants (0.964 for ) C

° the first period and 0.989 for the second period). Based (

e r on the independent t-test with the intervention of indoor

tu 24 a r

e 29.4 plant placement, we found that the variation in FAIR-P p

m 26.3 scores between the two measurement periods was sig‐ te 25.6 25.1 ir 20 nificantly higher in the classrooms with indoor plants A than in those without them. 16 Regardless of indoor plant placement, subjects’ Without (*) With (NS) FAIR-E scores increased over the experimental period. The placement of indoor plants had a negligible impact on FAIR-E scores between the two measurement peri‐ 60 ods. The variations in FAIR-E scores between the two ) %

( measurement periods were 135 in the classrooms with‐

ity out indoor plants (433 for the first period and 568 for id 50 m the second period) and 135 in the classrooms with in‐ hu 61 e 57 door plants (439 for the first period and 574 for the sec‐ tiv

la 40 51

e 48 ond period). R The mean value of FAIR-Q scores increased for the 30 subjects of both groups over the experimental period, Without (NS) With (NS) and was significantly facilitated by indoor plant place‐ ment. The variations in FAIR-Q scores were 0.013 in 1500 the classrooms without indoor plants (0.938 for the first ) 3

- period and 0.945 for the second period) and 0.028 in the m ·

g 1200 classrooms with indoor plants (0.951 for the first period m (

n and 0.973 for the second period). FAIR-C scores in‐ tio

a 900 creased over the experimental period. The placement of tr n 1277 indoor plants did not cause a significant difference in ce

n 1087 1102 1125 o

c 600 FAIR-C scores, with scores of 136 in the classrooms 2

O without indoor plants (412 for the first period and 548 C 300 for the second period) and 139 in the classrooms with Without (NS) With (NS) indoor plants (421 for the first period and 560 for the

Fig. 2. Thermal conditions and CO2 concentrations in the class‐ second period) (Table 4). rooms. Vertical bar on top bar indicated standard error. 1st Peri‐ od; measurement before indoor plant placement (June 27 to Statistical analysis of the factors affecting attention July 15): 2nd Period; measurement after indoor plant placement capacity (September 19 to October 7). Without; classrooms without in‐ The authors found the scores for subjects’ attention Table 3.door Indoor plants: concentrations With; classrooms of airborne with indoor contaminants plant placement. in classrooms NS: (unit: μg·m−3). non-significance, * significant at P < 0.05. capacity had a highly positive correlation with indoor

Table 3. Indoor concentrations of airborne contaminants in classrooms (unit: μg·m−3).

Group Period Formaldehyde Benzene Toluene Ethylbenzene Xylene Withoutz 1st Periody 31.02 ± 12.02 5.92 ± 2.68 65.77 ± 26.97 10.36 ± 6.67 7.46 ± 5.56 2nd Period 12.01 ± 2.57 5.50 ± 1.42 68.51 ± 56.31 9.31 ± 5.94 7.53 ± 2.42 t-testx *** ** * NS NS With 1st Period 32.12 ± 15.20 5.25 ± 2.71 75.42 ± 32.34 9.82 ± 6.03 7.75 ± 5.16 2nd Period 11.37 ± 2.87 3.84 ± 1.35 39.10 ± 35.06 5.06 ± 5.26 6.36 ± 2.41 t-test *** *** *** *** * Mean ± SD (n = 18). z Without; classrooms without indoor plants: With; classrooms with indoor plant placement. y 1st Period; measurement before indoor plant placement (27th June to 15th July): 2nd Period; measurement after indoor plant placement (19th September to 7th October). x Paired t-test at the level of 0.001 (***), 0.01 (**), 0.05 (*), and non-significance (NS). Table 4. Changes in attention capacity scores according to indoor plant placement. 324 H.-H. Kim, I.-Y. Yeo and J.-Y. Lee

Table 4. Changes in attention capacity scores according to indoor plant placement.

Group Period FAIR-Pz FAIR-E FAIR-Q FAIR-C Withouty 1st Periodx 0.970 ± 0.015 433 ± 49 0.938 ± 0.023 412 ± 62 2nd Period 0.986 ± 0.028 568 ± 85 0.951 ± 0.087 548 ± 82 t-testw * ** ** * With 1st Period 0.964 ± 0.085 439 ± 66 0.945 ± 0.016 421 ± 63 2nd Period 0.989 ± 0.042 574 ± 86 0.973 ± 0.035 560 ± 81 t-test *** ** *** * Mean ± SD (n = 18). z FAIR (Frankfurt Aufmerksamkeits-Invertar) scores: P (performance), E (efficiency), Q (quality), and C (continuity). y Without; classrooms without indoor plants: With; classrooms with indoor plant placement. x 1st Period; measurement before indoor plant placement (June 27 to July 15): 2nd Period; measurement after indoor plant placement (September 19 to October 7). Tablew Independent 5. Multiple t-test regression at the level analysis of 0.001 of attention(***), 0.01 capacity. (**), 0.05 (*), and non-significance (NS).

Table 5. Multiple regression analysis of attention capacity.

FAIR-P FAIR-E FAIR-Q FAIR-C Variable β t β t β t β t Indoor plant 0.131 −3.144** 0.385 −9.882** 0.250 −6.044** 0.394 10.094** Air conditions Temperature −0.032 −0.822 0.013 −0.363 0.046 −1.191 0.020 −0.558 Relative humidity −0.032 −0.803 −0.090 −2.390* −0.007 −0.173 −0.092 −2.450* Carbon dioxide 0.089 −2.745** 0.139 −4.547** −0.021 −0.657 0.017 −4.169** Ventilation frequency −0.064 −2.088* −0.165 −5.692** −0.027 −0.878 −0.153 −5.277** Air contaminants Formaldehyde −0.152 −3.481** −0.050 −1.235 0.070 −1.610 −0.042 −1.036 Benzene 0.093 −2.696** 0.079 −2.427* 0.056 −1.625 0.080 −2.466* Ethylbenzene −0.103 −3.009** −0.086 −2.074** 0.031 −0.909 −0.071 −2.205* F value 5.886 16.185 6.241 15.662 Adjusted R2 0.065 0.178 0.069 0.173 FAIR (Frankfurt Aufmerksamkeits-Invertar) scores: P (performance), E (efficiency), Q (quality), and C (continuity). * significant atP < 0.05, ** significant atP < 0.01.

plant placement through multiple regression analysis. concentration of benzene exhibited a positive correla‐ The t-values of indoor plant placement showed highly tion with the scores of FAIR-P, FAIR-E, and FAIR-C, significant values with all the factors of attention capac‐ having t-values of 2.696**, 2.427**, and 2.466*, re‐ ity as follows: 3.144**, 9.883**, 6.044**, and spectively (Table 5). 10.094** for FAIR-P, FAIR-E, FAIR-Q, and FAIR-C, Discussion respectively. We also found that the scores for subjects’ attention In addition to being visually pleasant, indoor plant capacity had a weak relationship with indoor air condi‐ placement provides psychological benefits as well as tions and air airborne contaminant concentrations. The physical benefits to indoor occupants (Bringslimark scores of FAIR-P, FAIR-E, and FAIR-C exhibited a pos‐ et al., 2009; Gary and Birrell, 2014; Mangone and van itive correlation with the indoor concentration of CO2 der Linden, 2014; Raanaas et al., 2011; Wolverton, with t-values of 2.745**, 4.547**, and 4.169**, respec‐ 1997). We studied 70 individuals in two elementary tively, but showed a negative correlation with ventila‐ schools to examine their attention capacity with the in‐ tion frequency with t-values of −2.088*, −5.692**, and tervention of indoor environment quality regulated by −5.277**, respectively. indoor plant placement. The scores for subjects’ attention capacity were neg‐ In the present study, the indoor environment quality atively correlated with the indoor concentrations of of each classroom was properly managed through indi‐ formaldehyde and ethylbenzene: a t-value of −3.481** vidual systems of mechanical ventilation and air condi‐ between formaldehyde concentration and FAIR-P score, tioning. Therefore, we only found slight differences in and t-values of −3.009**, −2.074**, and −2.205* be‐ the indoor air temperature, levels of relative humidity, tween ethylbenzene concentration and FAIR-P, FAIR-E, and CO2 between the two groups of classrooms. An ob‐ and FAIR-C scores, respectively. In contrast, the indoor servation period of 12 weeks revealed variations to Hort. J. 89 (3): 319–327. 2020. 325 some degree in the indoor air temperature, levels of rel‐ improvement in the FAIR-P and FAIR-Q scores. This ative humidity and CO2 in the classrooms without in‐ investigation using the FAIR-questionnaire had a high door plants. The indoor level of relative humidity possibility of accidental errors such as a bias caused decreased (48%) and the air temperature (26.3°C) and from repeated testing and the natural improvement in −3 CO2 concentration (1125 mg·m ) were constant in the attention capacity over time. classrooms with indoor plants. Previous researchers Therefore, the appropriate guidelines (Moosbrugger have reported that indoor plant placement can regulate and Oehlsclagel, 1995, 1996) were followed to reduce air temperature and relative humidity in indoor spaces the experimental errors. We believe the results of this through evapotranspiration (Davis and Hirmer, 2015; investigation are significant based upon previous re‐ Mangone and van der Linden, 2014; Moya et al., 2018; ports on the reliability of the questionnaire (Fink et al., Qin et al., 2014). Other previous studies pointed out 2002; Schweizer et al., 2000). that a classroom is a unique space because of its over‐ In previous reports, occupying a natural environment population of students (Becker et al., 2007) and the in‐ enabled people to increase their attention capacity creased indoor level of CO2 mainly by the metabolic (Adachi et al., 2000; Dijkstra et al., 2008; Felsten, processes of indoor occupants (Cetin and Sevik, 2016). 2009; Kaplan, 1995; Tennessen and Cimprich, 1995;

Therefore, it is thought that the CO2 level in the class‐ Wells, 2000). Furthermore, green areas with plants in rooms was increased by the metabolic processes of indoor spaces could alter the attitude and behavior of pupils and regulated by the metabolic processes of in‐ indoor occupants (Moya et al., 2018) and improve their door plants (Fig. 2). perception (Mangone and van der Linden, 2014; Qin An overall observation of the indoor concentrations et al., 2014). A similar result was also found in an earli‐ of airborne contaminants during the experimental peri‐ er report of Lohr et al. (1996) in which the placement of od revealed that some of the contaminants decreased, indoor plants in a computer lab at a university improved while others increased. The placement of indoor plants the attention capacity of students. Considering all the facilitated the tendency to decrease contaminants and results above, we conclude that the interaction of indoor reversed the increasing trend to a decreasing one. Previ‐ plants could partly enhance the attention capacity of in‐ ous researchers defined this phenomenon as phytoreme‐ door occupants (Table 4). diation, by which plants remove contaminants from the Through statistical analysis using multiple regres‐ air, water and soil (Moya et al., 2018). This phe‐ sion, we revealed a relationship between the attention nomenon has been consistently reported by many re‐ capacity of subjects and the indoor contaminant levels searchers in various studies (Kim et al., 2009, 2010; in their environments and identify the most significant Lim et al., 2009; Orwell et al., 2006; Wood et al., environmental factors affecting subjects’ attention ca‐ 2002). However, a closer observation of the indoor con‐ pacity. The multiple regression showed that indoor centration of formaldehyde revealed that indoor plant plant placement was the most significant factor affect‐ placement had little effect on the decreasing tendency. ing subjects’ attention capacity. According to earlier reports, the decomposition degree It is clear that the indoor environment quality can of airborne contaminants varied depending on the kinds play an important role in the work performance and of plants placed, the growing media used (Salt et al., productivity of indoor occupants (Al Horr et al., 2016; 1998) and the chemical properties of the contaminants Blueyssen, 2016; Frontczak et al., 2012; Perez- (Bacci et al., 1990; Trapp, 2007). Based on all the ob‐ Urrestarazu et al., 2016). Other researchers also report‐ servations above, we postulate that indoor plant place‐ ed that appropriate management of the indoor ment facilitated the decomposition of airborne environment could improve the learning ability of stu‐ contaminants to various degrees via the interaction of dents indoors (Mendell and Heath, 2005; Momovic indoor plants and airborne contaminants (Table 3). et al., 2009). We also found that indoor plant placement We also conducted three weeks of indoor plant place‐ resulted in airborne contaminant level reductions and ment for plant acclimation, followed by four weeks of enhanced psychological stability, which improved the indoor plant removal for a balanced comparison in the attention capacity of indoor occupants (Table 5). actual study. As a result, the numeric values of indoor While a great number of studies have been conducted conditions and indoor air quality exhibited little differ‐ to investigate the effects of indoor plant placement on ence in the first observation period as shown in Figure 2 indoor environment quality, most of them did not and Table 3. Based on the hypothesis above, it is achieve consistent results (Kim and Mattson, 2002; thought that the current study produced a fair compari‐ Park and Mattson, 2008, 2009; Shibata and Suzuki, son of attention capacity for the pupils of in the two 2001, 2002). The inconsistency could result from the groups. differences in measurement methods, indoor environ‐ After 12 weeks, all the subjects perceived that their ment, and plant conditions (Bringslimark et al., 2009; attention capacity had increased. The placement of in‐ Kim and Mattson, 2002; Shibata and Suzuki, 2004). door plants made little difference to the scores of FAIR- This study tried to generate consistent results by E and FAIR-C, but brought about significant using the FAIR questionnaire and applying multiple re‐ 326 H.-H. Kim, I.-Y. Yeo and J.-Y. Lee gression analysis; these factors improve the limitation pus: An attention restoration theory perspective. J. Environ. of conventional tests for attention capacity evaluation Psychol. 29: 160–167. which measure only a single function at a time. How‐ Fink, A., D. G. Schrausser and A. C. Neubauer. 2002. The mod‐ erating influence of extraversion on the relationship between ever, the present study also had certain limitations such IQ and cortical activation. Pers. Individ. Dif. 33: 311–326. as a lack of control of some individual conditions that Fromme, H., J. Diemer, S. Dietrich, J. Cyrys, J. Heinrich, W. could influence indoor environment quality and occu‐ Lang, M. Kiranoglu and D. Twardell. 2008. Chemical and pants’ attention capacity. From the results above, the morphological properties of particulate matter (PM10, authors found that indoor occupants were greatly influ‐ PM2.5) in school classrooms and outdoor air. Atmos. Envi‐ enced by indoor airborne contaminants. Especially, in‐ ron. 42: 6597–6605. dividuals in the growing phase are highly sensitive to Frontczak, M., S. Schiavon, J. Goins, E. Arens, H. Zhang and P. Wargocki. 2012. Quantitative relationship between occupant environmental factors (Faustman et al., 2000). For that satisfaction and satisfaction aspects of indoor environment reason, appropriate management should be established quality and building design. Indoor Air 22: 119–131. for indoor environment quality for individuals in the Gary, T. and C. Birrell. 2014. 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