## 1 Introduction  
### Background Problems in Indoor CO\({}_{2}\) Mitigation  
Indoor air quality (IAQ) can be 3-100 times worse than the outdoor air, due to the concentration of assorted gaseous pollutants [1; 2]. In IAQ indication of building space, carbon dioxide (CO\({}_{2}\)), which represents 60-85% of greenhouse gas (GHG), is considered among the most significant air constituents that impact occupant safety, work productivity, and well-being in the spatial environment [3]. Therefore, it is needed to find active, lower-risk, and economically more sustainable building solutions to dilute indoor CO\({}_{2}\) and improve air sterility.  
Technical methods to reduce CO\({}_{2}\) largely include (i) pollutant source control, (ii) increased ventilation, and (iii) indoor air purification. Regarding (i) and (ii), it is straightforward to manage indoor CO\({}_{2}\) levels adequately by developing monitoring systems and refreshing the air readily at exact source positions. However, it becomes suboptimal in practice because CO\({}_{2}\) is emitted with random living activities and metabolic respiration. Especially in densely occupied buildings, it is almost impossible to prevent CO\({}_{2}\) concentration through direct source management due to the complex spatial air streaming. In effect, natural/ forced-air ventilation performance highly depends on outdoor atmospheric composition [4] and often becomes very expensive due to the extra energy demand for air conditioning. The recent energy-oriented building system operation tends to risk IAQdeterioration, as recirculated indoor air may convey an excessive level of CO\({}_{2}\)[5]. Poor building design and improper system planning may have indoor space vulnerable to air contamination. Meanwhile, non-ventilation decarbonizing technologies [6; 7; 8] such as the ionized absorber-based indoor air cleaning by means of physical/chemical scrubbing can be considered [9; 10; 11]. Nevertheless, it is not always more effective than mechanical air filtering, since its efficiency depends on the CO\({}_{2}\) concentration, size, and type of ionizer, and the ventilation rate of the area being treated. Most oxidation technologies are tailored to remove volatile organic compounds (VOCs) because CO\({}_{2}\) is a stable compound that does not readily react with oxygen in air streams. It is also important to note that those methods are affected by degradation of the absorbents, corrosion, and high pressure drop [12; 13]. Many existing air cleaning systems based on the traditional physicochemical remediation often significantly suffer from drawbacks of a high installation/maintenance expense and generation of secondary gas pollutants [14; 15; 16].  
To overcome the above limitations, biological air remediation using plants and microorganisms (phytoremediation) has drawn attention recently [17; 18; 19]. For example, in the phytoremediation that uses the metabolic ability of living plants to catabolize and detoxy contaminated compounds [20], Sangeveria (Snake plant) can absorb CO\({}_{2}\) at -0.49 ppm/m\({}^{3}\)[21], and, in a closed chamber (1 m\({}^{3}\)), house plants can reduce CO\({}_{2}\) to 17-24% [22], up to 51-77% by combining ventilation [23]. Nevertheless, there still exist unavoidable obstacles in actual implementation: large planting areas, constant fertilization and irrigation, potential generation of toxic byproducts, daytime CO\({}_{2}\) accumulation from the soil substrate, etc. [PERSON] et al. [24] report that a leaf area of 57 m\({}^{2}\) absorbs only 13% of CO\({}_{2}\) generated per person.