I was recently asked my thoughts on air purifiers so it is perfect timing with the arrival of allergy season. There are a variety of reasons to use air purifiers and if you go to this link it will give a whole listing http://en.wikipedia.org/wiki/Air_purifier.
I personally use the AirSource 3000 air purifier. The company selling this has a great track record for quality products and has a whole line of green non-toxic cleaners that have been promoted by Oprah on her show.
The AirSource 3000 helps reduce all three of the major forms of air pollution: particles such as pollen, pet dander, dust, and cigarette smoke; microbes such as mold and bacteria; and gases and odors. That’s especially critical since the Environmental Protection Agency consistently ranks indoor air pollution among the top five environmental risks to public health. You can purchase at http://www.shaklee.net/greenlifebasics/product/55102
For More information see my page entitiled Air Purifiers.
Clinical tests
New AirSource 3000 Usage Recommendations When the AirSource 3000 was first introduced, based upon testing verified by an independent engineer, a minimum square footage of 120 square feet was recommended. Later, resulting largely from distributor and customer feedback rather than from additional testing, the minimum recommendation was increased to 1,000 square feet. This was intended to deter usage in small or unventilated spaces. More advanced testing recently conducted at a prestigious university test facility showed that for ventilated spaces occupied by people and/or pets with average air quality, a minimum of 500 square feet is acceptable. Spot cleaning by temporarily placing the unit in an unoccupied area with the door closed (as in basements) also is acceptable.