*3.3. Results of Using Sansevieria trifasciata for IAQ Improvement*

Table 3 presents the results of monitoring the parameters that are relevant to IAQ during the experimental placement of mother-in-law's tongue plants in the poorly ventilated room.


**Table 3.** Results of indoor air quality improvement using *Sansevieria trifasciata*.

Table 3 shows that the average concentration of CO2 was decreased by placing 2, 3, 4, 5, and 6 mother-in-law's tongue plants in the office as compared to there being no plants in the room, as can be visually observed in Figure 9. The concentration of CO2 in the room was not varied by the number of plants, but influenced by temperature of the room. This means if the door is opened, the temperature will be high and the CO2 concentration will be reduced. Closed chamber is required to control infiltration and ventilation to only consider the influence of plant on indoor CO2.

**Figure 9.** The trend of 24-hour CO2 concentration and number of *Sansevieria trifasciata*.

From Figure 9, it can be seen that there was an increasing trend in CO2 concentrations from 9:00 to 15:00, after which they declined to an ambient air concentration at 473.23 ± 8.66 ppm. The reductions in the percentage CO2 concentrations with 2, 3, 4, 5, and 6 of *S. trifasciata* when compared to no plants being placed in the office were 19.29%, 21.99%, 14.36%, 13.66%, and 10.47%, respectively. The overall average CO2 decreased by 15.95 ± 4.13%, which was slightly (±4%) lower than the reduction that was achieved in Case 2 by turning off the AC during lunchtime. The statistical analysis by One-Way ANOVA results was significant at *p* = 0.009132 (*p*<0.05) and *f*-ratio value is 3.53877. The results are different among treatments. However, the result of statistical analysis to compare between Case 2 (turned off AC at noon) and 3–6 indoor plants found *p* = 0.061, so it is not significant at the 95% confidence level. Therefore, reducing indoor CO2 could be done by turning off air conditioner and opening the door during lunch hour, or by planting *S. trifasciata* in offices because there was no difference from statistical analysis results.

These results were consistent with those of other studies, which have found that plants could reduce indoor CO2 concentrations [44,45]. Therefore, during the daytime, human respiration is clearly the key factor in increasing the CO2 concentration, while ventilation is the main factor in decreasing the level of CO2 in a room. Hence, the number of people in the room and their activities are the main drivers of the CO2 concentration. Thus, the concentration of CO2 is not directly related to the number of plants that are placed in the room. It was found that the respiration of plants during the night had no effect on the CO2 concentration when compared with no plants in the room with a declining trend in CO2 to the same level among different options from 0–6 mother-in-law's tongue plants being apparent.

The envelope air permeability of the room was the air passing through 2–3 millimeters around the door, which was caused by damage of the sealed material. The infiltration rate of the room was considered from the CO2 concentration when there was no plant in the room to avoid the effect from photosynthesis or respiration of plant and microorganism in soil. The maximum rate was found at around 17:00–18:00 when people went back after finish working. The average maximum value of ventilation rate was 0.0152±0.0006 m3/s. The maximum infiltration was found at 0.0162 m3/s.
