Update January 2016: My data below speaks for itself, but people should be aware of possible quality problems reported here. I think I’m done testing air purifiers. Yes, I’ve said this before, and I admit I often enjoy crunching the numbers, but I think I mean it now. The only possible way I could be persuaded to test another model would be an amazing breakthrough in technology. But it would still have to be reasonably affordable, even under 1,000 RMB per machine. Actually, it’s not, because I sold all my IQAirs and my Blueair and switched to six air purifiers which cost me a total of 5,200 RMB. a total of 5,200 RMB, for six new machines. I hardly doubt I need to remind most of you that’s half the price of only one of the many popular machines on the market now. And as this article will show, I’ve proven that these new machines are keeping my family’s indoor PM2.5 under 10 ug/m3, which is the goal of the World Health Organization and thus should be everyone’s goal (read more about that here).

So why would I even want to test anything else? As to which machine, many readers probably already know my answer because I started to test them last year: the Xiaomi 小米空气净化器 at 899 RMB, covering 48 square meters (apparently there’s a newer, smaller model as well for only 699). I initially blogged about Xiaomi last year discussing my test results of indoor air purifiers under 1,000 RMB. After last year’s testing, I had replaced two imported models in bedrooms with the Xiaomi purifier, and my bedroom air has been just fine since the switch. Just a few weeks ago I made the really big leap, returning two large air purifiers in my front rooms with three Xiaomi purifiers (I needed one extra as the coverage was comparatively less). And for the record, I am getting no promotional money or free anything from Xiaomi. In our nine years in China we’ve always used well known imported air purifiers to cover our front rooms, which are essentially one large open space covering 83 square meters.

But the price gouging in China always galled me. So after last year’s testing of purifiers under 1,000 RMB, I was always thinking, why can’t I see if I can also replace these big machines in the front rooms with something of more value yet equally effective? The timing was perfect as we’ve had multiple December days way over 200, 300 — and the worst two days of pollution I’ve ever seen in Beijing in my nine years here, our 2015 Airpocalypse with readings over 600 and an eerily dark, yellow sky in the afternoon of December 1st.air duct cleaning anchorage ak Let’s jump right in to the only thing that matters: hard data. trane electronic air cleaner reviewsAnd maybe the most important test was Airpocalypse 2015. massey ferguson 65 air cleaner hose

So here’s the bottom line: data from our Laser Egg PM2.5 monitor showed an outdoor average PM2.5 concentration of 465 ug/m3 over those couple days, and inside the front rooms only 25 ug/m3. That’s an astonishing 95% steady improvement over the worst pollution you’ll pretty much ever see here, and although it’s not at my ideal of 10 ug/m3, it’s still far below the 35 that most Chinese environmental teams shoot for anyway, and the 95% reduction is certainly way below the usually recommended 80% goal. And the machine’s weren’t even on the top, super-noisy speed but the middle speed, which is still fine for general conversation and TV watching. Here’s the graph from the Laser Egg app, with the red line showing outdoor PM2.5 and the blue line showing my living room PM2.5 (the left side axis is PM2.5 concentration in ug/m3 and the bottom axis is just the number of data entry points): On more “normal” days the data was much closer to, and usually under, my aggressive goal of PM2.5 concentration under 10 ug/m3.

Here’s the data from earlier November: Even a quick glance at the graph above tells me everything I need to know: my living room air (the blue line) is generally exactly around 10, and always under 20 even as the outdoor air climbs up. And as Beijing’s annual average is 70-90 ug/m3, my three Xiaomi machines easily get me to my goal of 10 during those typical days — and at a nice auto setting with very comfortable sound level. For calculated averages over this week using the Excel spreadsheet data from the Laser Egg, my front room average was 6.1 ug/m3 when outdoor air was a relatively clean 61; 9.8 during heavier days averaging 136 outside; and a still respectful 14.4 when outdoor air tanked for a couple days at 220 (that’s an impressive 93% reduction). You notice there are a few spikes on the blue line, but all of those are easily explainable as with any other air purifier I’ve had: either the windows were open while we were using our laundry dryer, or we were cooking, or the machines were accidentally off for a while and no one had noticed.

Here’s one more graph from my bedroom, again demonstrating even more clearly than last year’s test that a Xiaomi on quiet setting is perfectly effective, and easily just as effective as any machine I’ve ever tested, including all the far more expensive models. The calculated average PM2.5 concentration was 8.0 ug/m3, again nicely below my goal of 10. It was 8.6 ug/m3 when the outdoor air was a horrible 224 over two days; and 7.4 ug/m3 on two clearer days, when the outdoor air average was 69: So let me be perfectly blunt to those in China who say that an indoor PM2.5 of 10 ug/m3 is impossible and too expensive: I say that’s nonsense, especially now, certainly on the money side. A goal of 35 ug/m3 still gives everyone a 15% increased mortality risk, as the . I do realize this is a sensitive concept for some readers, as many people have spent a lot of money on air purifiers, or even work for those companies. And it’s fair to point out that these don’t last as long as others (three months, although they’re only 179 RMB), and (rated H11) is not as efficient as most other higher-end machines’ filters, and maybe the machine’s solidity isn’t so great, and perhaps they may break down sooner than other machines. 

We simply don’t know yet, as these are new machines only a year on the market — which in itself should give people some pause. Also, the built-in sensor is quite inaccurate and pretty much useless to follow — but I’ve never found sensors ever reliable on any air purifier, and I always control all of them manually anyway (and none of the major brand machines ever had a sensor anyway). The sensor’s more concerning issue is that it thinks that a PM2.5 concentration of 75 ug/m3 and under is safe. That’s simply too high, and even the Chinese government rating of 35 would be more proper. I of course think 10 is best, but for a machine made in China I would think 35 is reasonable. So if people are using a Xiaomi and relying only on the sensor on auto speed, then indeed they still may be inhaling not great air. This again is why everyone, using any type of air purifier, should not be relying only on any machine’s auto setting ever (my personal opinion). You need to get a separate monitor and use that to test your air.)

And yes, Xiaomi is mostly a cell phone company first. But let’s be very clear here: I’ve mentioned many, many times that anyone living anywhere in polluted areas, whether China or India or Los Angeles, has an ultimate goal to get your indoor air pollution under the World Health Organization’s goal of PM2.5 under 10 ug/m3. The scientific data is very clear; any PM2.5 over 10 starts to have health effects. So people in polluted areas absolutely must have air purifiers indoors, where you spend 90% of your lives. At the very least, put one in your bedroom. And for heaven’s sake, make sure your children’s rooms are all protected. So you’re more than welcome to get any air purifier machine you want, as long as you’re reaching your goal of PM2.5 under 10 ug/m3, and routinely monitoring your air afterwards (perhaps with the new Laser Egg, only 499 RMB) to make sure all is working fine. In terms of which air purifier is best, again I’ve mentioned often that all that anyone needs for indoor protection is a good filter attached to a good fan.