Smart Air on PRI/NPR

As a nerd who grew up listening to NPR, I was psyched to see Smart Air on NPR/PRI’s The World today! PRI journalist Rebecca Kanthor visited our Shanghai workshop and took audio with Henry and Gus.

DIY Talk at the US Embassy’s Beijing American Center

In celebration of Earth Day, the US Embassy’s Beijing American Center hosted a Smart Air DIY talk and live test. According to Brian from the Center, “Gus brought down the house!” Thanks to our hosts for helping us get the word out about affordable clean air.  

DIY Cannon: Better, Faster, Stronger

Ever since I started my DIY filter experiments, I’ve been wondering whether I could create a super DIY by using a stronger fan. In the past three months, my collaborator Anna has helped me test a half dozen different fans. She now has a home full of fans:     …

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More Data!

A while back, I posted data comparing how effective the DIY purifier was compared to a 6,000 RMB Blue Air and 11,000 RMB IQ Air. In that test, I calculated effectiveness as percent difference from outside air. At the time, I said I didn’t like that way of calculating effectiveness, but I did it that way so I could compare my results with the results of Dr. Saint Cyr.

Now I’m posting data from new tests that improve on the old tests in three ways:

  1. The new tests calculate effectiveness as the percentage reduction from indoor air. This gives smaller percentages because outside air is dirtier than inside air. In my opinion, this is a more rigorous way to test air purifier effectiveness.
  2. The new tests were conducted by my Smart Air collaborator Anna Guo in her apartment. This helps test whether the results are generalizable. In other words, this way we can know that my original results were not a fluke just based on the layout of my room or how well my windows are sealed. Anna’s room (15 m2) is also slightly larger than mine (13.5 m2).
  3. Finally, the new tests are with the Meidi fan I’m now shipping to people from my Smart Air site. Thus, these results are more relevant for people using our DIY filter kits. (However, the Meidi fans are very similar to the blue Kadeer fans I was using before. I haven’t seen a noticeable difference in the results with the two fans.)

Methods: Anna used my particle counter to take a baseline 2.5 micron reading before turning on the filter. Then she turned on the filter, put the particle counter on the other side of the room from the DIY purifier, set it to take hourly measurements, and went to bed.

To calculate effectiveness, we took the average 2.5 micron reading of the four hours prior to waking up and calculated the percent reduction from the baseline reading before turning the filter on.

Filter: We used the same DIY kit with the Meidi fan that we’re shipping from Smart Air:


Results: Here’s what the data looks like. This data is from September 9th:


In these real-world tests, we need to be careful to check that outdoor particulate didn’t go down during the test. If it did, we would think the decrease is due to the purifier when really it’s due to outdoor air changes. To test that, we can overlay the outdoor PM 2.5 readings from the US Embassy:


Outdoor air actually got slightly worse during the test, so the reduction inside is not because outdoor air got cleaner.

And here’s the average reduction in 2.5 micron particles over the three test nights:


Conclusion: The DIY filter removed an average of 92%. That’s similar to the earlier result of 94%. I suspect the new result is 2% lower than before because this new calculation uses reduction from inside air rather than outside air.

Again, the effectiveness ratings are similar to Dr. Saint Cyr’s tests with the Blue Air and IQ Air, although remember that his room is larger (20 m2), and the post does not specify the length of testing time or the particle counter used. Ideally we’d have tests with the same particle counter in the same room.

As always, I’m posting more details on the methods for fellow nerds here:

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Particle Counting in the Atlantic

Particle Counting and the DIY workshop made it into the Atlantic. Hooray for getting the word out about how to protect your health in China without shelling out big money.     More workshops are in the planning stages. Stay tuned.

Q&A: How Long Can HEPA Filters Last?

passport4adragon 提问: Hi, I’m in Shanghai and recently put together your DIY purifier and bought the same fan and filter you suggested – I think it’s working! A couple of questions – I bought the exact same filter you did on Taobao – how often should it be replaced if …

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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.