1/ I have been getting a lot of requests from the media and others to comment on unproven indoor air pollution control technologies that make very bold claims. It happened again today. I refuse to comment on specific (unproven) technologies unless ....
2/ (a) I have tested the technology myself, or (b) another researcher I trust has done so and published the results. I thought, based on a lot of experience, I would write a thread on the kinds of misinformation I have observed in the past & provide some questions to ask.
3/ Beware of claims related to destruction of VOCs. If a company says that it can remove X% of VOCs, ask whether they have published proof that the VOC is completely mineralized to CO2 and H2O and under what conditions.
4/ My experience is that companies will not have this proof, or will say that they do but the data have not been published or are not available. The problem is that some technologies, e.g., photocatalytic oxidation and others, may indeed "remove" a target VOC.
5/ However, what they fail to say is that the removal of that target VOC leads to intermediate chemicals that might be worse for indoor air than the target. For example, generation of formaldehyde. Beware, this is very common.
Major red flags if a company makes highly dubious or incorrect claims for one pollutant and contend that it can also remove other pollutants.
6/ Beware of irrelevant claims made to sound important. In my courses on indoor air quality I often show an advertisement for a personal air purifier that shows a woman holding a baby. It states it can remove particles as small as 200 microns. Well, so does the floor.
7/ Beware of “technologies” that are tested in small, poorly ventilated (or non-ventilated chambers) and that show pollutant decay over time. This includes those magic houseplants. In most cases, I could put an old pair of socks in the chamber and get the same result.
8/ If one can actually obtain the actual data for these “technologies” (some have been published) and complete a mass balance on the chamber used it will be clear that the Clean Air Delivery Rate (CADR) is often 1,000 times (or more) smaller than a good portable air cleaner.
9/ Put another way, you’d need 1,000 of these devices or plants in a room the size of a bedroom to achieve what you can with a single portable air cleaner to remove particles or (with enough activated carbon) ozone and VOCs.
10/ There are so many more examples of unproven or proven ineffective (snake oil) sold to those not aware of what to look for – I have outlined an entire chapter in a book on this subject. Not enough time ....
11/ Stick to proven technology. During this pandemic aim to remove particles in air of a size of roughly 0.5 (or 1) micron to about 20 microns. A good portable air cleaner with a HEPA filter that has a CADR > 300 ft3/min will make an appreciable dent …
12/ in most rooms less than 1,000 ft2 and 8 to 10 ft ceiling height. To get an equivalent increase in air exchange rate, take the CADR, multiply it by 60, and then divide by (floor area x ceiling height)
13/ If the CADR = 300 ft3/min X 60 = 18,000 ft3/hr. If floor area is 800 ft2 & ceiling height = 8 ft, volume = 6,400 ft3. 18,000 ft3/hr divided by 6,400 ft3 = 2.8/hr.
14/ If the air exchange rate is 1.4.hr, the portable air cleaner just yielded an effective tripling to 4.2/hr.
15/ Avoid gimmicky add-ons to the portable HEPA filter. You do not need additional ionizers or ozone generation. I am often asked about the activated carbon added to the HEPA filter.
16/ The activated carbon is harmless, but does little to remove particles & is usually insufficient in mass to remove VOCs/odors. Not needed. Remember, basics! Aim for a portable air cleaner with a HEPA filter & CADR (for smoke) > 300 cfm (see above)
