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.
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