Thomas Talhelm

Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people across the world breathe clean air without shelling out thousands of dollars for expensive purifiers.

Can Activated Carbon Remove Formaldehyde?

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Can activated carbon filters remove formaldehyde and VOCs? Earlier tests from Smart Air found that carbon can reduce VOCs from cigarette smoke. But formaldehyde and VOCs in general are particular concern for many people. We put activated carbon filters to the test by ordering formaldehyde straight from the factory and … Read more

$70 DIY Purifier Effectiveness Better than $1,000 IQAir

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New head-to-head test data from a citizen scientist finds that a simple, taped-together DIY purifier effectiveness is higher than a market-leading Swiss purifier. This data adds to an accumulation of data suggesting that the effective air purifiers need not be expensive. The Setup The underlying science of purifiers is simple: … Read more

Should I Run My Air Purifier All Day?

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Some purifier companies recommend running your air purifier all day. But is that really necessary? If so, isn’t running the purifier all the time a big waste of your filters and energy?

Test Method

To get to the bottom of it, I set a Smart Air Cannon on a timer to turn on for two hours everyday in a 13.5m2 Beijing bedroom:

Smart Air Cannon DIY Air Purifier Filter

I put a particle counter in the room to take measurements every minute. I did the test while I was on vacation, so there was no influence of me opening and closing doors.

Results

After six days, I came back and saw how long it took to the Cannon to clean the air each time it came on. Here’s what six days of data looked like for the small .5 micron particles:

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Over the six test days, the air in Beijing became progressively worse. But on each day, it was clear when the Cannon turned on and off. The dropoffs were sharp, showing the Cannon was working quickly.

I averaged over the six test days to find out how long it took the Cannon to clean the air on average.

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Conclusion

On average, the Cannon cut 0.5 micron particulate in half in 10 minutes. By 20 minutes, it removed 80%.

Bottom line: Should I Run My Air Purifier All Day?Powerful purifiers like the Cannon clean the air very quickly, so I see no need to run the purifier while I’m not at home.

Can I turn it off while I sleep?

The data can also answer another question a few people have asked me: “I don’t want to hear the fan while I sleep, so can I run it for an hour and then turn it off while I sleep?

In the tests, the air got dirty very quickly after the Cannon turned off (even though the windows and doors were closed). Dirty air is entering our homes constantly, even though we can’t see it.

 

Purifier closed room air dirty again

 

Bottom line: I do NOT recommend turning the purifier off while you sleep.

Open Data

As always, I’m publishing the raw data and more details on the methods below. I’ll also be publishing data from similar tests in a much larger room (30.5m2) and for tests when I’m at home and moving in the room.

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Why are air purifiers so expensive

Why are Air Purifiers so Expensive?

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I thought about why air purifiers cost a lot because I was living in Beijing when the (first) “airpocalypse” struck. Here’s what it looked like: The High Price of Air Purifiers I went out to buy an air purifier, and found that the one I wanted cost $2,000! I worked … Read more

HEPA Lifespan Test Filter Air Purifier

HEPA Longevity Test: Day 200

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One of the biggest questions when I started doing the DIY was HEPA lifespan–how long do the HEPAs last? Rather than just give people a nice-sounding answer, I wanted to see what the data says, so Gus has been dutifully turning on his Original DIY every day in his 12.3m2 Beijing … Read more

how to choose best air filter air purifier guide

Four Steps To Choosing The Best Air Purifier

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“What’s the best air purifier on the market?” It’s a question that many of us might ask. There are thousands of air purifier models to choose from, so how can you find the best air purifier that’s right for you? This article covers those steps in a slightly unorthodox way. What’s … Read more

Do Air Purifiers Dry Out the Air?

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Empirical data shows that air purifiers are great at cleaning air, but do they dry out the air and lead to other health problems? For me, dry air is mostly just a comfort issue. But for some people, dry air can exacerbate health problems like allergies and bronchitis. Do HEPA … Read more

What Are Ionizer Air Purifiers and Do They Work?

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The other day, someone on Quora asked whether ionizer air purifiers work and actually purify the air. This is an important question because ionizers are all over the place.  Ionizer air purifiers are often marketed with a variety of names.  These names include  “ion air purifiers”, “negative ion air purifiers”, … Read more

Smart Air is a social enterprise that creates simple, no-nonsense air purifier 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.