Those early experiments claiming that plants can clean indoor air had significant methodological problems, and the results have not been reproducible in realistic building environments:
Does anyone know what is special about the pollutants addressed by these plants? Are there other pollutants that are helpful to filter, and why did NASA focus on this set?
Not entirely sure, but a lot of these VOCs come from stuff in your house (carpet, paint, plastics).
When I lived in Augusta, GA the air around the city would occasionally reek due to a nearby paper mill. The smell would blow over the city after an hour, but anything that slipped into drafty homes would remain for hours; I'd only notice after returning from walking the dogs.
I started to wonder what I was breathing and found a list of possibile offenders: formaldehyde, acetaldehyde, benzene, chloroform, tetrachloroethylene, and trichloroethylene [1]
I was hoping my plants would help (the link nate_meurer posted casts some doubt).
http://www.buildingecology.com/articles/critical-review-how-...
The fact that NASA's name is associated with this study has led it to be widely accepted uncritically.