Plants have raised an increased interest in research for their ability to improve indoor air quality by removing harmful volatile organic compounds (VOCs). In addition to removing these pollutants, plants also emit a diverse cross-section of VOCs of their own. They are used by plants for several kinds of biological functions: attraction of pollinators, protection against pathogens or herbivores, thermotolerance, scent, flavor, etc. The amount and quality and their possible effects to indoor air quality have however been studied very little. Some of the plant volatiles are known to have health properties, such as anti-inflammatory, antimicrobial and anti-tumor effects.

This study (2009) aimed to identify and quantify VOCs and their sources from four common indoor species: Spathiphyllum wallisii, Sansevieria trifasciata, Ficus benjamina and Chrysalidocarpus lutescens. These plants were acclimated for two weeks to indoor conditions, and then individually placed in glass containers with inlet and outlet ports. The inlet ports had a charcoal filter to supply purified air, and the outlet port was connected to a sorbent trap. VOCs emitted by the plants were then collected for 10 h by flowing purified air into the container, and samples were collected both during the day and night (12-h photoperiod). VOCs from the plastic pot with the media as well as the plastic pot alone were also assessed to determine the source of the individual compounds, i.e. plant, media/microbes, and pot.

VOCs were quantified and identified:

• Compounds varied between the plants, but certain compounds were found in all of them
• VOCs emitted by plants were comprised of terpenoids, alcohols, ketones, and esters:
  • S. wallisii: 61.5 ng·100 g−1 dw/hour of 23 different VOCs, dominated by 97.8% of terpenoids
    F. benjamina: 1.5 ng·100 g−1 dw/hour of 13 different VOCs, dominated by 79,0% of terpenoids
    C. lutescens: 1.2 ng·100 g−1 dw/hour of 16 different VOCs,  dominated by 66.9% of terpenoids
    S. trifasciata: 0.4 ng·100 g−1 dw/hour of 12 different VOCS, dominated by 34.6% esters
• VOCs were also emitted from the growth media or micro-organisms
• VOCs were also emitted by the plastic pots, some of which are known to have undesired effects on animals

Terpenoids emitted by plants were recognized as flavor and odour compounds, and some had been noted for their pharmacological properties (e.g. anticarsinogenic and antimicrobial) and ecological significance (pollinator attraction, defence against pathogens). I.e. santanol that was present in S. wallisii, has been reported to have a relaxing effects in humans.

The VOC profiles differed greatly among the species between day and night, night time rates being lower due to the plant stomata being closed. S. wallisii emitted significantly more VOCs because it was in flower, which represented 90.3% of the total pg of volatiles from it. Variation in the biosynthesis and emission of VOCs depends on the species and their developmental stage.

Authors make a note of the study in a later review (Kays 2011) that the levels of emitted VOCs were very low, and those emitted did not appear to represent a health concern. More studies are needed to assess how the removal and emission of VOCs act together in improving the indoor air quality.