The NASA Clean Air Study has been led by the National Aeronautics and Space Administration (NASA) in association with the Associated Landscape Contractors of America (ALCA). Its results suggest that certain common indoor plants may provide a natural way of removing toxic agents such as benzene, formaldehyde and trichloroethylene from the air, helping neutralize the effects of sick building syndrome.

The first list of air-filtering plants was compiled by NASA as part of a clean air study published in 1989, which researched ways to clean air in space stations. As well as absorbing carbon dioxideand releasing oxygen, as all plants do, these plants also eliminate significant amounts of benzene, formaldehyde and trichloroethylene. The second and third list are from B. C. Wolverton's book  and paper and focus on removal of specific chemicals.

NASA researchers suggest efficient air cleaning is accomplished with at least one plant per 100 square feet of home or office space. Other research has shown that micro-organisms in the potting mix (soil) of a potted plant remove benzene from the air, and that some plant species also contribute to removing benzene.

http://goo.gl/FxLB4A