Can houseplants improve indoor air quality by removing CO2 and increasing relative humidity?

Abstract

High indoor CO 2 concentrations and low relative humidity (RH) create an array of well-documented human health issues. Therefore, assessing houseplants' potential as a low-cost approach to CO 2 removal and increasing RH is important. We investigated how environmental factors such as 'dry' (< 0.20 m 3 of water per m 3 of substrate, m 3 m-3) or 'wet' (> 0.30 m 3 m-3) growing substrates, and indoor light levels ('low' 10 µmol m-2 s-1 , 'high' 50 µmol m-2 s-1 and 'very high' 300 µmol m-2 s-1), influence the plants' net CO 2 assimilation ('A') and water-vapour loss. Seven common houseplant taxa-representing a variety of leaf types and sizes-were studied for their ability to assimilate CO 2 across a range of indoor light levels. Additionally, to assess the plants' potential contribution to RH increase, the plants' evapotranspiration (ET) was measured. At typical 'low' indoor light levels 'A' rates were generally low (< 3.9 mg hr-1). Differences between 'dry' and 'wet' plants at typical indoor light levels were negligible in terms of room-level impact. Light compensation points (i.e. the light level where the CO 2 assimilation equals zero) were in the typical indoor light range (1-50 µmol m-2 s-1) only for two studied Spathiphyllum wallisii cultivars and Hedera helix; these plants would thus provide the best CO 2 removal indoors. Additionally, increasing indoor light levels to 300 µmol m-2 s-1 would, in most species, significantly increase their potential to assimilate CO 2. Species which assimilated the most CO 2 also contributed most to increasing RH.

Interaction between plant species and substrate type in the removal of CO2 indoors

“…Indoor plants can act as a simple low-cost form of ventilation, reducing indoor ventilation requirements (by ~ 6%) with CO2 removal and consequently providing a reduction in building energy consumption, but only under certain environmental conditions i.e. a very high light level (~ 22000 lux) -as confirmed by several previous studies (Torpy et al, 2014;Torpy et al, 2017;Gubb et al, 2018).…”

“…Several studies have shown that light levels significantly influence a plants ability to remove CO2 via their impact on stomata as a main pathway for CO2 uptake (Pennisi and van Iersel, 2012;Torpy et al, 2014;Torpy et al, 2017;Gubb et al, 2018). Indoors, the light level is typically between 0 -500 lux, but can be as high as 3000 lux in certain workplace environments (Boyce and Raynham, 2009;Lai et al, 2009;Hawkins, 2011;Huang et al, 2012).…”

“…Often, supplementary lighting is required to support specific plant installations such as a green wall, where higher light levels are utilised above the installation and not throughout the entire room -this supplementary light can be engineered at least as high as 22200 lux (Gubb et al, 2018). Plants' under-or over-watering also affects a plant's ability to remove CO2 (Sailsbury and Ross, 1991) but our previous work showed that indoor light level was the primary driver of CO2 uptake and the soil drying had smaller impact (Gubb et al, 2018).…”

“…substrate moisture content -SMC). A few studies have investigated these issues in part, testing various plants potted in different peat-free substrates (Irga et al, 2013;Torpy et al, 2014;Torpy et al, 2017;Gubb et al, 2018) Torpy et al, 2014 determined the light response curves of eight common plants potted a peat-free substrate consisting of composted hardwood, sawdust, composted bark fines, and coarse river sand (2:2:1). These authors suggested that in typical 'low' indoor light some CO2 removal could be expected but, moderately increasing light levels would mean the studied plants could be effectively utilised in a built environment setting.…”

Indoor Air Quality Improvement by Simple Ventilated Practice and Sansevieria Trifasciata

“…where, Q is infiltration rate of air entering the room, V is volume of air in the office (m 3 ), t is time interval (s), C t is indoor concentration of CO 2 at time t (ppm), C ext is concentration of CO 2 in the ambient air (ppm), and C 0 is indoor CO 2 concentration at time 0 (ppm) [29,30]. The volume of air in the office (V) was calculated from the size of the room (4 m x 10 m x 3 m), Interval (t) was 3600 seconds from hourly average data, C ext was average monitoring outdoor CO 2 concentration at 430 ppm, C t was the monitored CO 2 concentration at time t (i.e., 18:00), and C 0 was the monitored CO 2 concentration at one hour before t (i.e., 17:00).…”