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Types of FiltersTypes of Filters

Premise: This blog is for people concerned about air pollution. There are many valid reasons people want air purifiers: pet allergies, pollen, and asthma. However, these are not what I’m concerned about while living in China. So I assess purifiers solely based on whether they can help protect me from particulate air pollution.

With that in mind, here are the three most common types of filters in portable air purifiers:

  1. UV light filters are designed to kill bacteria. In China, I’m concerned about air pollution, not bacteria, so UV filters are unnecessary. But beyond that, Consumer Reports says that UV filters in most air purifiers don’t even kill bacteria:

The Environmental Protection Agency cautions that air cleaners outfitted with ultraviolet light are unlikely to kill bacteria and mold because they won’t be in contact with UV light long enough to have any effect.

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Conclusion: UV filters aren’t what I need.

  1. Activated carbon filters use charcoal screens to catch certain types of chemicals and organic matter that happen to interact with carbon. In other words, these filters catch some things, but not particulate in general. In sum, these will do a little bit, but they aren’t the whole solution.

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Activated charcoal is good at trapping other carbon-based impurities (“organic” chemicals), as well as things like chlorine. Many other chemicals are not attracted to carbon at all – sodium, nitrates, etc. – so they pass right through. Howstuffworks.

Conclusion: Carbon filters may help (particularly for certain types of gases that carbon can get), but they don’t target all particulate matter. It would be a mistake to use ONLY a carbon filter to get rid of particulate pollution.

  1. HEPA filters are the solution. “HEPA” sounds fancy, but it’s just a standard that means the filter catches 99% of particles .3 micrometers and above (they also get particles smaller than .3 micrometers–the .3 designation is based on the overlapping point of different types of filtering). That covers a lot of particulate pollution–the most-often cited figures are for 2.5 micrometers.

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HEPA filters aren’t rocket science. They work pretty simply: particles get stuck in the fiberglass fibers (using a few types of physical filtering processes). In fact, if you have a vacuum cleaner, it probably has a HEPA filter in it. You can get one for about $10.

Contrast that with the major purifier companies like IQ Air and Blue, which have proprietary HEPA filters with names like “HyperHEPA” that cost $200. These may have benefits, such as a longer lifetime or smaller pore size, but it’s not clear to me that’s necessary or worth 20 times the price.

Bottom line: If your concern is particulate air pollution, a HEPA filter is really all you need. And for that, you don’t need spend 8,000 RMB. You can make your own for 166 RMB.