Short answer: Yes! Long answer: Keep reading
Let’s break down this question into three smaller questions:
- Is the air coming out of the Smart Air DIY air purifier clean?
- Is the Smart Air DIY air purifier able to actually clean the air in the entire room?
- How well does the Smart Air DIY air purifier perform compared to expensive air purifiers?
1. Is the air coming out of the Smart Air DIY air purifier clean?
This is the easiest question to answer, and we do it by holding a Dylos DC1100 Pro particle counter in front of the purifier and watching the numbers drop. Here’s a video of Thomas doing just that:
Conclusion: Yes, air coming out of the purifier is clean.
2. Is the Smart Air DIY air purifier able to actually clean the air in the entire room?
Answering this question is more difficult because you need a controlled environment (for example, you don’t want to walk in and out of the room during the test), and you need to test the air for a longer period of time. But fortunately for you, Thomas is a huge nerd and does this kind of thing for fun.
To answer this, Thomas set up the particle counter on one side of his 13.5 m2 bedroom and put the DIY filter on the opposite side of the room. Here’s what our filter did in one hour:
And over the course of eight hours:
The particle counter also gives data on .5 micron particles — even smaller than the 2.5 micron reading. Here’s what that looks like over eight hours:
Conclusion: Yes, the clean air from the DIY filter is cleaning the entire room.
For fellow nerds, here are some more details on how the tests were conducted:
The test above was done starting at 11:30 pm on 6/16/2013, when the outside AQI in Beijing was 230 according to the US embassy’s AQI Twitter feed. (The outside air improved the next day, but results were similar on a later test where AQI actually went up slightly from 195 to 202 during the test.)
According to comparisons of our particle counter’s tests of outside to US embassy AQIs, an AQI of 230 would convert to about 2,650 on the PM 2.5 count on the reader. (Remember, the particle counter gives the raw number of particles 2.5 micrometers and above per .01 cubic feet. The US embassy takes mg/m3 and converts that to an AQI. Therefore, the raw numbers are different, but they correlate highly. You can think of this as the difference between measuring attendance at a basketball game by the number of people in the stadium versus the total weight of those people. The two numbers are highly correlated, but not identical.)
Thomas did the test in his bedroom with the doors and windows closed. The room is 13.5 m2, with two windows.
The particle counter tends to take 5-10 minutes to get stable readings, so to be conservative, Thomas gave it about an hour:
The spike at the top was when Thomas entered the room to turn the air purifier on and reset the machine, so it may be the dust he kicked up by walking around. A more stable reading for that time would probably be about 230.
The uptrend prior to turning the filter on may have been because Thomas was running a dehumidifier (which itself has some small filters) in the room before the tests.
Regardless, this data suggests that the effect of the filter was not a confound of calibration.
3. How well does the Smart Air DIY air purifier perform compared to expensive air purifiers?
Thanks to kind souls who donated a BlueAir 203/270E(3,600 RMB), a Philips AC4072 (3,000 RMB), and anIQAir Health Pro (8,000 RMB) we’ve finally been able to test the DIY against expensive brands in the same room, for the same amount of time, with the same particle counter.
To do that, Anna ran 11 overnight tests with the BlueAir, 9 tests with the Philips, and 11 tests with the IQAir. Thomas calculated effectiveness as percent reduction in particulates from the room air. Anna tested the air before she turned on the air filter, and then set the particle counter to take hourly measurements of the air in her 15 m2 Beijing bedroom. Anna used the highest setting on each filter.
All of the filters significantly reduced particulates, but the 470 RMB Cannon removed as many particles as the highest-performing big brand. Even the 200 RMBOriginal was only 6% behind the Blue Air on the .5 micron particles and 4% behind on the 2.5 micron particles.
Among the different brands, there seems to be no relationship between price and particulate removal:
Conclusion: You can remove particulate pollution from the air in your home and pay far less than the cost of a Blue Air, Philips, or IQAir.
For fellow nerds, here are more details on our data and methods:
Methods: Anna turned the purifier on the highest setting before she went to bed at night and turned it off after she woke up. To measure particulates, she used a Dylos particle counter, which measures particles .5 microns and above and 2.5 microns and above per .01 cubic foot. The particle counter took one measurement each hour.
Calculating Effectiveness: Thomas calculated effectiveness as the percentage of particles the purifier removed from the room air. The baseline was the particle count before turning on the purifier. The final count was the average number of particles over the last four hours before Anna woke up. We prefer this over comparisons to outside air because:
2. The baseline room number takes into account how dirty the outdoor air is because indoor particulates go up and down with outside air.
However, the drawback is that outdoor particulates sometimes go up after the test starts (lowering estimates of effectiveness) and sometimes go down (raising estimates). However, these average out over multiple tests, and the results are similar if you look only at days where outdoor particulates were relatively stable.
Room: Anna’s bedroom is 15 m2, located in Chaoyangmen, Beijing. The doors and windows were closed while Anna slept, but she opened the door at various times in the very beginning of the test before she went to sleep. Although the doors and windows were closed, the apartment isn’t new, and the seal isn’t great.
For more details on the methods, see the end of Thomas’s earlier post. All methods were identical to those earlier tests.
Filter Life: After all the tests were done, the IQ Air said the pre-filter had 1,931 hours of use left, the carbon filter had 3,077 hours, and the HEPA had 1,910 hours. Thus, the filter was in its prime.
Outlier: Of the 11 tests, one day was a strong outlier. On May 22nd, the IQ Air got only 68% of the .5 micron particles. Normally when we see poor results, it’s because the outdoor air got a lot dirtier during the night. But on May 22nd, the outdoor concentration fluctuated between 74 and 110 micrograms, which isn’t out of the ordinary.
Because we couldn’t see any reason the results were poor that night, we left the data in. If we redo the analysis with that day included, the results are only slightly better: 93.0% of .5 micron particles and 96.5% of the 2.5 micron particles. That would put the IQ Air about equal with the Philips and still 4% below the Cannon.
Have any questions about testing? Send us an email!
We’re not PhDs in fluid dynamics, but we love to talk shop about clean air.