Just thought I’d drop by one of the best discussion board on the net and mention a thread I started on Slashdot on indoor air quality (and air purifier):
Does anyone here have an opinion on a good (or bad) air purifier out there?
trees
Yes, of course, trees. But kind of impractical in an appartment downtown… Will green plants do? 
I have a several pets and live in a large city that is warm and humid half the year so we have dander, mold, pollens, and urban air polution. Perhaps as a result, several of my family members have chronic allergic rhinitis. Consequently, I have been interested for some time in techniques to purify indoor air. I read reports on allergies and the means to prevent them in Consumer Reports, selected magazines and newspapers, and in scientific journals. (I generally don’t look for such information in Omni, the National Enquirer, or publications from the EPA.)
In general, all the reliable sources seem to say that HEPA filters may (repeat, may) help. Certainly they do take particles out of the air (making lots of noise and a big dent in your pocketbook in the process). However, there seems to be very little evidence that filters reduce allergy symptoms. The reliable reports should probably be taken as “damning with faint praise” and a sensible person would not waste her money but I, nevertheless, ended up with two expensive HEPA filter units. I should have saved some money and bought copper bracelets; they probably would have worked just as well.
Here is what Reisman RE, Mauriello PM, Davis GB, Georgitis JW, DeMasi JM concluded from “A double-blind study of the effectiveness of a high-efficiency particulate air (HEPA) filter in the treatment of patients with perennial allergic rhinitis and asthma” (published in J Allergy Clin Immunol 1990 Jun;85(6):1050-7): "For the total study, there was
no difference in the total symptom/medication scores or individual symptom scores during the placebo and active-filter periods. Analysis of the last 2 weeks of each filter period in which respiratory infection was absent demonstrated definite differences in total and individual symptoms, suggesting active-filter benefit. Patients’ subjective responses also suggested benefit from the filter. The overall impression is that the HEPA filter can reduce allergic respiratory symptoms.
On the other hand, here is what Wood RA, Johnson EF, Van Natta ML, Chen PH, Eggleston PA concluded from “A placebo-controlled trial of a HEPA air cleaner in the treatment of cat allergy” (published in Am J Respir Crit Care Med 1998 Jul;158(1):115-20): “Although the combination of a HEPA room air cleaner, mattress and pillow covers, and cat exclusion from the bedroom did reduce airborne cat-allergen levels, no effect on disease activity was detected for any parameter studied.” It is worth reading at least the whole abstract which can be found at http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9655716&dopt=Abstract.
As for taking things out of the air other than allergens, the activated carbon prefilters should work. However, the only non-allergen indoor air “contaminant” I know of that actually causes any health problems is radon and the filters won’t remove radon.
I’m just a little unclear as to what you are looking for here? Are you soliciting people to answer you query on Slashdot? That’s against our forum rules. Are you looking for opinions? That belongs in the forum “In My Humble Opinion.”
Either way, I’m closing this thread.