Smart Air Filters featured on CNN Money

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

Charles Riley, a journalist with CNN Money, recently published a long-form article on Delhi’s air quality and its impact on individuals—particularly children and those with asthma. Smart Air Filters was thrilled to be featured as one of the groups making Delhi’s air cleaner through our low-cost, DIY air filters. The article also featured Saurabh Bhasin, a lawyer taking up legislative battles with the Supreme Court and Dr. Naresh Trehan, who has called for government reforms to promote cleaner air.

Check out the full article on CNN Money’s website.

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常见的净化器有几种?

我写这个博客是给关心空气污染的人。买净化器的人有不同的原因,比如说,有的人对花粉、宠物毛发过敏,或者有哮喘症。但就我在中国生活的时候,我最担心的是空气污染。所以,这篇博文对空气净化器的评估只关注它们去除空气中可吸入颗粒物的能力。

1. UV紫外线

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这类净化器的主要功能是除菌。而我更担心的问题是空气中的颗粒污染。所以这类净化器并不对我胃口。然而,客观第三方结构《消费者报告》说,许多UV紫外线空气净化器其实连空气中的细菌都不能有效去除:

美国环保局调查显示,内置UV紫外线的空气净化器并不能有效去除空气中的细菌与霉菌。原因在于,紫外线光照通常不能与空气中的细菌、霉菌接触足够长的时间,以达到灭菌效果。

结论:UV紫外线不是我需要的。

2. 活性炭

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活性炭的确有过滤功效:空气中某些含“碳”的化学物质、有机物能与活性炭相互作用,从而被去除。颗粒污染当中,活性炭能消除一部分,但是很多颗粒跟活性炭没有反应。所以这类滤网也不能解决我的问题。

活性炭能很好地过滤含碳杂质(也就是有机物)以及氯化物。而对比如含钠、氮这类杂质,活性炭就不那么有效了。这类杂质可以畅通无阻地穿过活性炭滤网,丝毫不会减少。(Howstuffworks

结论:活性炭净化器虽然能消除一部分空气污染(还有一部分能与碳发生作用的有害气体),但对颗粒污染并不那么有效。所以,如果只靠活性炭来去除空气中的颗粒污染并不可行。

3. 静电

静电的净化器用正负电荷吸引空中的颗粒。静电能够使颗粒物吸附在一个金属板子上。好处是可以清洗滤板,延长滤网使用寿命,长期下来就节省了更换滤网的成本。

有的净化器里面用静电,但也有很多知名品牌(比如Blue Air,IQ Air)不用静电。我猜是因为静电还会产生臭氧而臭氧对人体有害,会刺激呼吸道和减少抵抗力。同时,静电滤网还需要花更多的时间维修和清洗,所以美国的《消费者报告》(Consumer Reports)建议不要买带静电的净化器

4. HEPA滤网过滤器

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HEPA能解决我担心的问题。“HEPA”这个名字听上去高大上,但它其实只是一个业界标准。HEPA表示这个滤网能去除99%直径0.3微米及以上的可吸入颗粒物(HEPA也能去除直径小于0.3微米的颗粒;0.3微米只是测试HEPA的标准大小)。所以,HEPA净化器能去除绝大部分颗粒污染,包括大家熟悉的PM2.5。

其实,HEPA净化器并非什么高科技,它的工作原理非常简单:空气中的颗粒通过滤网时,会被卡在滤网的“玻璃纤维”间。其实,如果你家里有吸尘器,里面八成也有HEPA滤网。超市的吸尘器要几千块吗?在美国亚马逊网上,十几美金就能买一个。

像市面上常见的IQ Air和Blue Air这些空气净化器,里面都有HEPA滤网。不过他们给自己的HEPA取了一些高大上的名字(比如“Hyper HEPA”),然后要价上千块。相比DIY,那些净化器或许寿命更长一点、可能能过滤更细小的颗粒,但我觉得,不至于在它们身上“一掷千金”。

结论:如果你担心空气中颗粒污染对健康的危害,那HEPA净化器就能满足需求。而且我们完全不用花七八千块钱买空气净化器。DIY自己的净化器只要166块。

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Noise

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

The new Cannon kicks butt (scientific definition of kicking butt), but it’s noisier than the Original DIY. How noisy is it? As is my habit, I wanted to answer this question scientifically.

So I bought a decibel meter:

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And I tested the Cannon, Original DIY, Blue Air 203/270E, and IQ Health Pro Plus on their highest settings from 1.95 meters away. Here are the results:

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The cannon is noisier than I’d like, but it’s similar to the Blue Air on the high setting. To give you an idea of how loud that is, this decibel chart says that’s between “conversation at home” and “conversation in restaurant.”

It’s still louder than I’d like, but fortunately I’ve found that the Cannon is still very effective on the lower settings:

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So I recommend running the cannon on a lower setting if you find it noisy.

Conclusions: 

  1. Cannon-owners can use the lower settings without sacrificing much performance.
  2. For people who are particularly sensitive to noise, the Original may be a better choice.
  3. For people who are VERY sensitive to noise, the Philips AC4072is expensive (2,700 RMB), but it’s quite quiet on the low setting.

As always, I’m posting the data and methods below for fellow nerds.

(更多…)

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More Comparisons

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

Dr. Saint Cyr recently pointed me to great tests of air purifiers from the Shanghai Consumer Protection Bureau:

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The reason this type of research is so badly needed is that Western research (like this report from Consumer Reports) focuses on allergens, not general industrial air pollution. Allergens are probably more relevant for most Americans, but for those of us living in China, particulate air pollution is the real problem. And a lot of smog is smaller than pollen:

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Thus, I was excited to see research that focused on PM 2.5 here in China (results here, in Chinese). In removing PM 2.5, 17 out of 22 models removed more than 90% of PM 2.5 in just 20 minutes in a 30-square-meter room. Pretty good!

Yet even the cheapest of the “non-famous” brands cost about 1,500 RMB. For that price, you could make 9 of my DIY filters, and that’s before eating the cost of proprietary replacement filters (US$200 a piece at IQ Air). Even with these cheaper brands, I still think consumers lack a truly affordable way to get clean air. Using the consumer bureau’s results, I calculated how much you’re paying for each percent reduction in PM 2.5.

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Now, their tests weren’t perfect. The biggest downside I see is that they used cigarette smoke as the PM 2.5 source, rather than outside air. It’s not clear to me if cigarette smoke behaves the same as smog in filters. Also, many filters were less effective at removing the formaldehyde that they released in the room. That said, I don’t know how much formaldehyde is in the air normally.

But these results from Dr. Saint Cyr do use ambient air pollution in China (as do mine 1, 2). In tests with doors closed and the filters at their highest settings, Dr. Saint Cyr’s two Alen Air filters, Blueair, and IQ Air all got rid of at least 95% of PM .3. But the Alen Air A375 will set you back US$500 or RMB 5,000 imported in China. Here’s how to get the same results for 166 RMB.

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DIY Compared to Expensive Filters

对不起,此内容只适用于美式英文。 For the sake of viewer convenience, the content is shown below in the alternative language. You may click the link to switch the active language.

UPDATE:

I now have directly comparable data with the DIYs, Blue Air, and Philips: Direct comparison tests.

In earlier posts (1, 2), I showed that you can make an effective DIY air purifier to clean Chinese air pollution out of your home air. But just because the DIY filter is effective doesn’t mean it’s as effective as the Ferrari filters. How effective is the DIY filter compared to the expensive filters?

I’ll attempt to answer this question from several angles in different posts. Here’s one method: comparisons with the published data from the blog of the Beijing doctor Dr. Saint Cyr (which was an original inspiration for me that air purifiers could actually reduce air pollution). He ran tests of an 11,000 RMB IQ Air and a 6,000 RMB Blue Air. I used the same calculation of effectiveness and compared his results for the pricey machines with tests of my DIY purifier. Here are the results:

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To make the comparisons more precise, I compared my filter results only to the tests he reports from the IQ Air and Blue Air on max power in his smaller room.

Dr. Saint Cyr calculated reductions based on outside air quality, which I do not think is the best method. I think it makes more sense to calculate reductions based on the room air before and after using the filter because my room air is significantly cleaner than outside air, even before using the filter (more on that later). But to make the data comparable, I calculated effectiveness using Dr. Saint Cyr’s method.

Now, the comparisons aren’t perfect. Dr. Saint Cyr’s smaller room is still 6.5 meters larger than mine. He also doesn’t say how long he ran his filters and whether the doors were closed. My tests were with the doors closed and overnight, so the filter had several hours to run.

(Update: via email Dr. Saint Cyr said his tests were with doors closed and testing times of 1 hour+.)

But even if the difference in room size bumps mine down 5% and the others up 5%, that would mean 11,000 RMB and 166 RMB get you similar results. To illustrate that, I calculated a graph of how much you’re paying for each percentage reduction in air pollution:

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Of course, the ideal test would use all three filters in the same room with the same particle counter. To that end, I will hopefully get the chance to borrow a friend’s Panasonic filter and test it in my home. I’ll post those results when I get them.

Conclusion: Although the comparisons are imperfect, they show that a DIY filter is at least roughly comparable to expensive filters at a far lower cost. This illustrates my larger point: all you really need to combat particulate air pollution is a HEPA filter. In fact, Dr. Saint Cyr found the same thing in his tests of a much simpler Hunter brand HEPA filter. In a room with the doors closed, his HEPA got 91% of the pollution–similar to what I found.

For data nerds like me, I’m posting more details on my data and methods here:

Test Details:

(更多…)