Thomas Talhelm – Page 17

DIY Talk at the US Embassy’s Beijing American Center

2020-07-152014-04-24 by Thomas Talhelm

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.

Independent Tests

2020-07-152014-02-16 by Thomas Talhelm

Beijing-based Dr. Saint Cyr’s tests of air purifiers were one of my original inspirations for the whole DIY project, so I was happy to see that the DIY recently became a part of those tests: These are the first independent tests of the DIY, and the results parallel …

A New Way to Test Whether the DIY Works

2020-07-152014-02-10 by Thomas Talhelm

So far, I’ve been testing air purifiers by taking a baseline measurement of particulate pollution in a room, and then turning on the purifier and testing whether the counts drop. I’ve used that method to test the DIY and more expensive machines.

However, I recently bought a second laser particle counter, so my collaborator Gus suggested another method:

Run one particle counter in the bedroom that has the purifier
Run another particle counter in a different room that does NOT have a purifier.

Two Problems Solved

The benefit of this method is that the control room represents the counterfactual–what would have happened if we hadn’t turned on the air purifier. That can answer two types of “what if’s.”

1. Fluctuations in outdoor air pollution

If a northwest wind hits Beijing and makes the outdoor air a lot cleaner, we can separate the effect of the outdoor air fluctuations from the effect of the purifier. In that situation, my old method would artificially raise our estimates of effectiveness. Changes in outdoor air can also artificially lower our estimates of effectiveness if the outdoor air gets dirtier after we turn on the purifier.

In previous tests, I corrected for this by averaging over multiple tests. I also analyzed the data after removing days in which outdoor air pollution fluctuated a lot (for example, I do that sort of analysis in the extra nerd notes here).

But it’s always nice to use different types of tests to make sure an effect is real, so Gus did this experiment.

2. Particles settling in closed rooms

If you close a room, the particles–even really small particles–will slowly float down and settle out of the air.

Thus, if we’re testing in a closed room at night, how do we know the purifier is causing the reduction, and not particle settling?

The Control Room Purifier Test

Gus set up one particle counter in his room and one in his kitchen:

He let the particle counters run for several hours, and then a timer turned on the Original DIY in his room. (The kitchen had no air purifier.) Here’s what happened:

The difference between the bedroom and the kitchen air quality can approximate the effect of the air purifier. It looks like Gus would have been breathing 16,000 of these 0.5 micron particles in the air in his bedroom if he hadn’t turned on his DIY purifier.

And it’s pretty clear that the kitchen air quality (where we don’t have a purifier running) is following outdoor air quality:

(Be aware that I’m overlaying these two lines on the same graph, but the Y-axes are different. This is NOT saying that indoor air is as bad as outdoor air. Indoor air is usually cleaner than outdoor air.)

Conclusion

Similar to earlier tests, the double particle counter test shows that the DIY purifier is removing particulate pollution from the air.

As always, I’m including more details for fellow data nerds below.

Do Chinese New Year Fireworks Pollute Indoor Air?

2020-07-152014-01-31 by Thomas Talhelm

I’ve posted data before showing that outdoor air quality is strongly correlated with indoor particle counts (r = .71), but Chinese New Year gives nerds like me a great chance to see what happens when we get a momentary shock to air quality. The media made a big deal about people cutting …

The Dirtiest Filter I’ve Seen

2020-07-152014-01-03 by Thomas Talhelm

Matt Myers attended our workshop in September, and he used it straight through December. On December 7th, he sent me a picture of the blackest HEPA (and pre-filter) I’ve ever seen. Yikes! Time for a new filter! I’d be happy that black gunk is in the filter and not in …

Q&A

2020-07-152014-01-01 by Thomas Talhelm

joshuaw81 提问: Hi Thomas, just started one of your cannon kits earlier today and it’s already turning gray. Already a fan of your work! Two quick questions for you: 1- I received a foam/fiber square that is white on one side and light green on the other. I’m assuming this …

Measuring Air Purifier Noise

2020-07-152013-12-16 by Thomas Talhelm

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:

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. That’s the distance between my pillow and where I put the purifiers. Here are the results:

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

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

Conclusions:

Cannon-owners can use the lower settings without sacrificing much performance.
For people who are particularly sensitive to noise, the Original may be a better choice.
For people who are VERY sensitive to noise, the Philips AC4072 is 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.

DIY air purifier effectiveness blueair iqair philipps cheap god air purifier

Directly Comparable Tests: DIY vs Blue Air

2020-12-152013-12-09 by Thomas Talhelm

I’ve wanted to know for a long time whether DIY air purifiers are as effective as the Ferrari filters.

In an earlier post, I compared my data to the tests of Dr. Saint Cyr (whose excellent posts inspired me to look into filters in the first place). But I noted that the comparisons were far from perfect because:

The rooms were different.
The Cyr post did not specify how long the tests were (and that can make a big difference if you’re looking at times under an hour–see this time comparison).
The Cyr post did not describe the particle counter or particle size.

How We Tested The Air Purifiers

But now I finally have directly comparable data! That’s because two kind souls donated a Blue Air 203/270E (3,600 RMB) and a Philips AC4072 (3, 000 RMB). That means I could finally 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 Blue Air and 9 tests with the Philips. As always, I 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 a Dylos DC1700 laser particle counter to take hourly measurements of the air in her 15m2 room.

Anna used the highest setting on each purifier. (I’m putting the original data and more details about the methods for fellow nerds at the end of this post.)

And (drumroll!) here are the results:

The Cannon removed as much particulate as the expensive machines. Not bad for 450 RMB!

Yet all four filters were making the room air significantly cleaner. For particles 2.5 microns and above, all four removed over 90%. For particles 0.5 microns and bigger, all four removed over 80%. I’m not the first person to say: All you need to significantly reduce the particulate pollution in your home is a simple HEPA filter.

Based on the data, here’s how much you’re paying for each percentage reduction in 0.5 micron particles:

(And that’s not counting the cost of the exorbitantly priced replacement filters.)

Recently, a Chinese news article claimed air filter companies are making “falsely inflated profits.” That fits with this data showing that the Cannon removes as much particulate as the Blueair, yet costs about 10% per percentage of 0.5 micron reduction. Similarly, the Original DIY removes 4% less 2.5 micron particulate and 6% less 0.5 micron particulate than the Blueair on average, yet the Blue Air costs more than 16 times as much.

Bottom Line

Bottom Line: Air Purifier Test

You can remove particulate pollution from the air in your home and pay far less than a Blueair or Philips

Smart Air

What About Gas Pollution?

Now, as I’ve said before, particulates are not everything. There are also gases like ozone and nitrogen dioxide (although I’m less concerned about those). Here’s how to know whether your home has serious gas pollution. If it does, tests show that activated carbon removes gases like formaldehyde and benzene.

Open Data and Methods

As always, I’m posting the original data and detailed methods for fellow nerds. Don’t believe me. Check out the data and decide for yourself.

DIY Cannon: Better, Faster, Stronger

2026-03-092013-11-19 by Thomas Talhelm

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: …

How Much Does Outside Air Pollution Affect Indoor Air?

2025-01-022013-10-28 by Thomas Talhelm

I’ve always wondered: how much does outdoor air pollution affect the air in my home? Even if I keep my windows closed, if the air outside gets really polluted, does air in my home get a lot worse?

To answer that question, my Smart Air collaborator Anna has been taking particle counts in her Beijing apartment everyday for the last two months and comparing the counts to outside pollution. Here’s how she does it:

When she gets home from work (and before she turns on her DIY filter), she uses a particle counter to measure how much particulate matter is in her room and compares it to outside air pollution from the US Embassy Twitter feed. Her windows are always closed, and her home is near Chaoyangmen, which is in central Beijing.

Here’s the data from 41 days:

Inside and outside pollution correlate at r = .71, which is quite strong. Compare that to the r = .89 correlation between air outside my home and the US Embassy numbers.

With this data, we can actually start to predict how polluted the air is inside based on how polluted it is outside. To do that, I removed a few outlying datapoints and plotted a regression line:

So when does indoor air pollution get dangerous?

To answer that question, we first have to define “dangerous.” I use the WHO limit of concentration of 25 micrograms per meter cubed.

Then we need to convert the 0.5 micron measurements from my Dylos machine into official concentration numbers. That’s tough, but we can get a rough estimate based on my prior tests and from a formula Dylos published to convert to micrograms (0.5 microns – 2.5 microns)/100. My data shows that the WHO limit of 25 micrograms is equivalent to about 4,000 on the Dylos; according to the Dylos formula, that’s around 2,500. Using either standard, the graph above shows that the air in Anna’s home is frequently over the WHO pollution limit.

If we round those numbers up to a very conservative 5,000, we can reach a rough conclusion:

Rough rule: If outside concentration is above 40 (AQI 112), the indoor counts are very likely to be above the 5,000 limit.

Conclusion: Outdoor air pollution strongly affects indoor air pollution, and indoor air is often more polluted than the WHO limit–even with the windows closed.

Now, remember this data is from one apartment in Beijing. The numbers probably vary a lot between apartments that have better or worse seals around the windows. The numbers probably also vary between downtown and farther out in the suburbs. That said, this data convinces me that indoor air in China frequently has dangerous levels of particulate.

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