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Purification Effect of Areca Palm for Continuously Emitting Formaldehyde in a Real Office Environment
Abstract
Plant air-purification effect to reduce formaldehyde in a real office
environment was examined. A potted Areca palm (height: about 2m) was
adopted as a subjective plant. Plant purification effect was evaluated
using a tin oxide gas sensor and a commercial tool for formaldehyde
measurement was also used. The effect became higher as the atmospheric
formaldehyde concentration was higher. The concentration became lower as
the plants were installed. The effect did not greatly increase when the
number of the installed pots was increased to seven from four.
Concentration of carbon dioxide increased up to 450ppm by placing the
pots at night. It is, however, below the regulated value (1000ppm) of
Japan building managing law. Light intensity in the room fluctuated
periodically and the carbon dioxide concentration changed periodically
according to the fluctuation of light intensity from outside. There was
a negative correlation between their characteristics. When the
characteristic of carbon dioxide concentration was shifted forward by 1
hour with respect to the light intensity characteristic, the maximum
value of correlation coefficient was obtained to be about -0.9. An
integration value of a sensor output curve with time after the setting
of potted plants could be regarded as a measure of an exposure volume of
the plants to formaldehyde. The exposure value was found to become
smaller as the number of the plants increased. In the experiment,
formaldehyde was emitted continuously and the atmospheric concentration
was kept at about 0.3ppm and the value was decreased to about 0.1ppm by
the potted plants. This is close to the regulated value of 0.08ppm by
WHO.
... However, the bioelectric potential of a plant is affected by the surrounding environment; for example, it varies with the concentration of formaldehyde in the air [5,6], air humidity, air temperature, and the soil moisture content [7]. Moreover, the bioelectric potentials of plants have been found to change with growing conditions, such as light levels and wind [8][9][10][11]. ...
Some animals and plants function as bioantennas in that changes in their surrounding environment produce variations in their bioelectric potentials. While the bioelectric potential is affected by living activities of the plant, it has been observed that the bioelectric potential can be reduced using plants. Thus, the influence of the life activity of a plant on the reception signal must be accounted for when a plant is used as a sensor. In this study, we produced an environmental change near a foliage plant growing in an indoor environment and examined the directivity of the plant's sensing ability. The sensitivity of the plant was a roughly circular area centered on the location of the plant. We also investigated the influence of the number of leaves on the plant on its sensing ability and found that it decreased with a reduction in the number of leaves.
In addition, we monitored the effect of a person walking on the spot near the plant on the bioelectric potential of the plant. Six subjects stepped on the spot 50 cm from a rubber tree and we measured the variation in the bioelectric potential of the tree produced by this stepping motion. The results confirmed that stepping motion produces a measurable response in the bioelectric potential of a plant and that this response varies in synchrony with the subject's stepping rate. Moreover, by conducting principal component analysis using the peak value of the spectrum characteristics of the measured bioelectric potential, cumulative proportion was found to reach nearly 97% at low-frequency components up to the fifth peak.
Phoenix roebelenii (commonly called Roebelenii palm or dwarf date palm) is a wellknown potted plant, which is endemic to Hachijyo Island in Japan. It is commonly called "Roebe." Roebe production is an important industry on the island. Most products of this industry are exported to Europe. The export volume has been decreasing since 2001 and the producers of Roebe are badly affected by this decrease. The reason for the decrease is that cheap Roebes from South America are now exported to Europe. Roebe is placed in indoor spaces, namely, offices and homes, because it has a healing effect and an air-purifying function. It is necessary to revitalize the agricultural industry in Hachijyo by characterizing the positive features of the Hachijyo Roebe. In this study, the air purification capability (Pa) considering environmental factors (temperature and light intensity) and the healing effect of Roebe were examined with the goal of increasing the export volume of this plant. Results showed that Pa increased with an increase in room temperature from 21 to 26°C, reaching a range of 15-35. It became clear that Roebe has a substantial purification function. It also became clear that it has a healing effect to some degree. The effect was evaluated using an instrument that measures the amylase activity in the saliva of subjects. The relationship between Pa and the molecular weight of a polluting chemical was also examined. Results showed that Pa decreased as the weight increased.
In this study, we monitored electromagnetic waves generated by human activity and investigated a method for individual identification by looking at the bioelectric potential of a rubber tree. Four subjects were asked to walk in place at a distance of 60 cm from a rubber tree while we measured variations in the bioelectric potential of the tree as produced by the stepping. The results confirmed that electromagnetic waves generated by a human subject walking in place produce a measurable response in the bioelectric potential of a plant. It was also found that this variation in bioelectric potential varies in synchrony with each subject's walking pace. The spectral envelope of the observed signal was approximated using a straight line and the distribution of the coefficients of this line was plotted. Even for a simple straight-line approximation, we demonstrated that this coefficient distribution varies considerably among individual subjects.
Houses are gradually becoming airtight due to heat insulating structures. Thus, air exchange is decreasing in an indoor environment. Indoor air-quality is also worsening by generation of VOCs (Volatile Organic Compounds) from building materials, and it causes sick-house syndrome. On the other hand, it is known that plants and microorganisms inhabiting the rhizosphere purifies indoor air-pollutants. The empirical model, however, involves some problems such as the long interval needed for the measuring of the purification process, and the process is modeled by a simple straight line approximation. In this paper, we find the purification process of plants in detail for the basic study of a design that suitably arranges plants in a room. As an example of a typical foliage plant, a purification process of Epipremnum aureum for formaldehyde is measured continuously using a tin oxide gas sensor. As a result, it is found that the purification rate is fixed at about 40%/h when the formaldehyde concentration range is less than 50ppm in the experimental chamber. Therefore, the purification process could be approximated using an exponential function. Furthermore, the purification rate rose with the increasing intensity of illumination.