Impact of indoor plant-induced relative humidity on PM concentration in indoor urban environment

Abstract

The study investigates the influence of indoor plants on relative humidity (RH) and the subsequent reduction in particulate matter (PM) in a naturally ventilated office room at CSIR- NPL, Delhi. PM concentrations were compared under two conditions: control (without plants) and experimental (with eight potted Epipremnum aureum plants). The comparison was conducted under two distinct cases: background PM, and induced PM from incense burning.

The presence of plants resulted in an average RH increase of 13.55% and a temperature decrease of 4.1%. Plant-induced RH elevation led to a sixfold reduction in PM I/O ratios. RH values (>60%) were negatively correlated with ultrafine, fine, and coarse particles. Plant-induced RH accelerates the deposition loss rate of all sized particles by ∼44% and reduces the infiltration rate by ∼78%. During pre-emission, in addition to PM dry deposition, plant-induced RH contributed to a substantial reduction of fine PM by 6.53% and coarse PM by 26.45% respectively. During incense burning, in the presence of plants, ultrafine PM concentrations dropped by 23.41%, fine PM by 72.39%, and coarse PM by 71.49%. It demonstrates that PM chemical composition significantly influences PM reduction, as it alters particle hygroscopicity. There was a decrease in the mass percentage of elements like Na, Mg, Al, Si, Cl, and K by 1.87, 1.23, 2.26, 5.48, 0.66, and 0.91 percent respectively. It can be inferred that to achieve a 13% increase in the average RH, plants with a leaf area size equivalent to ∼6% of the room surface would be required.