Here is a little paper I wrote many years ago showing that plants are not effective at cleaning the indoor air.

Formaldehyde is a toxic substance with adverse health effects detectable at low concentrations. Formaldehyde causes irritation of the eyes, skin and respiratory tract, wheezing, nausea, coughing, diarrhoea, vomiting, dizziness and lethargy at levels as low as 50 parts per billion (ppb) (0.05 ppm). Formaldehyde has also been associated with aggravation of asthma, emphysema, hayfever and allergy problems at low levels (EPA, 1987). Formaldehyde is currently considered a potential carcinogen to humans (EPA, 1987). Formaldehyde is a ubiquitous gas found in elevated concentrations in indoor environments. Concentrations of formaldehyde are typically an order of magnitude greater inside buildings compared to outdoor air. Formaldehyde concentrations are particularly high in portable buildings due to the presence of more formaldehyde emitting materials and the relatively smaller interior volumes of air. Major sources of formaldehyde indoors are pressed wood products, such as particle board and plywood, and urea formaldehyde foam insulation. Other sources include carpets, curtains, floor linings, paper products, cosmetics and soaps, tobacco smoke and gas combustion. Methods to reduce indoor formaldehyde include source removal or use of non- polluting materials, emission reduction through physical or chemical treatments and dilution through ventilation and air purification. While most solutions involve dilution through ventilation, increased interest in the scientific literature as well as in the popular media has been given to the use of plants to purify air in buildings . Most studies however, have been conducted in the laboratory and are difficult to extrapolate to real life situations.

Reducing Formaldehyde Exposure in Office Environments Using Plants