People have been intrigued by the use of potted plants indoors for air cleaning since a 1984 publication of NASA research claiming that certain plants can remove formaldehyde from indoor air. A study was conducted in a 7-story, 4600 M2 office building in a highly polluted Asian city. The building, housing 500 workers, contains about 900 plants from 5 carefully selected species. The plants are integrated into the building ventilation strategy, with the expectation that they remove a wide range of Volatile Organic Compounds (VOCs). The aim of this work was to ascertain whether VOCs are effectively removed by the indoor plants.
Measurements of a range of 29 VOCs commonly found in office buildings (carbonyls; cleaning solvents, bathroom products; office products and supplies; building materials; plant materials and wood; plasticizers; outdoor air) were made outdoors, in the rooftop greenhouse, on 2 floors, and in the building exhaust air, following the sequential flow of ventilation air through the building. An air washer is installed between the ventilation air inlet and the greenhouse to clean outdoor air. Particulate matter (PM2.5) was also measured indoors and outdoors.
Indoor formaldehyde levels in the building increased by almost 5-fold from ambient levels to 30 μg/m3 (chronic 8 hours reference exposure level = 9 μg/m3) on floor 3, doubling during transit through the greenhouse containing 160 plants. Hexanal, nonanal, and octanal, odorous VOCs, were measured on floors 3 and 5 at roughly 10 times documented odor thresholds. Methylene chloride increased about 30-fold in the indoor air. 1,4-dichlorobenzene, bathroom deodorizer, was measured throughout the building, increasing by a factor of 10 between the greenhouse and floor 5. PM2.5 indoors was reduced to 7% (30 μg/m3) of the outdoor 380 μg/m3 due to efficient HVAC filters.
Overall, VOC and aldehyde concentrations increased despite the use of selected potted plants, suggesting low overall effectiveness for VOC air cleaning.