I just saw an amazing video from TED conference in Feb'09 that is touching the subject of sustainable architecture project of an office building using plans for purifying the air: Mother-in-law's Tongue (Sansevieria trifasciata), Money Plant (Epipremum aureum) and Areca Palm (Chrysalidocarpus lutescens).
This is the speach of Kamal Meattle, who 17 years ago became allergic to Dehli's air and doctors said, that his lounge capacity went down by 70%.
They designed a healthy building and the study says that after staying 10 hours in this building there is 32% probability of 1% raise of oxygen in human's blood.
Ha! Sansevieria is the bedroom plant, because it converts CO2 to oxygen at night.
Just see this short, but very valuable speach here.