Air Purifiers – breath of fresh air or a whole lot of smoke?

The hazy conditions in Singapore over the last few days have prompted a scramble for portable air filters. These devices can cost any where between $100+ to about $600. Are they worth the money? Do they actually help?

According to NEA, “several models of air cleaners have been found to be able to reduce the level of fine particles in a typical bedroom to an acceptable level during a smoke haze, such as that experienced by Singapore in 1997.” However, there is a caveat. The doors and windows of your room need to be closed, only to be opened occasionally for ventilation. And what does occasionally mean? NEA says “at least once a day”.

This makes sense. Because portable air purifiers are only useful if they are able to clean the air at a rate that is at least as fast, if not faster, than polluted air enters the room. In other words, one of the important question to ask if the portable air purifier you intend to buy is useful is: What is its CADR?

CADR stands for Clean Air Delivery Rate. Each portable air purifier will probably have CADRs for different sizes of pollutants. Roughly speaking, this measures the volume of air that the device can clean in a given unit of time. For example, if the CADR is 250 cubic feet per minute for dust, it means that the device can, in one minute, reduce dust particle levels to the same concentrations as would be achieved by adding 250 cubic feet of clean air in that one minute.

If you are comfortable with having all your doors and windows closed AND not having your air-con on, then you may not need something with a very high CADR. Yes. You heard me. Turning on your air-con works against your portable air purifier. Because your air-con causes air from outside to flow into your room. And if the air outside is hazy, well, then the air flowing into your room through your air-con will have dust and haze particles too. Unless your air-con has fantastic HEPA filters, otherwise, turning your air-con on may essentially mean that your portable air purifier is essentially useless.

But if you insist on having the air-con on, and still want to have clean air, your best option is to get an air purifier with high CADR. Then you would want to place the inlet of your air purifier as near to the air-con vent. Why? Because in a room that is otherwise sealed, the air-con vent becomes the source of “polluted” (or not so clean) air of your room. You also want to ensure that the outlet of your air purifier is not blocked by any furniture or any obstructions. Even then, with the air-con on, according to the US Environmental Protection Agency, you may not be able to significantly reduce the dust concentration of the air as much as you would like.

So. Are portable air purifiers worth the money? Perhaps for their placebo effect. But do they really make a significant difference when used in the ways that most Singaporeans use them? Questionable.


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