Can Activated Carbon Remove Formaldehyde?

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 testing it against carbon filters.  How did the carbon filter do with formaldehyde removal?

Activated carbon granules

Formaldehyde is a big deal for many people. In China, I’ve found most of my Chinese friends know the word “formaldehyde.” But this is not because Chinese people are all science nerds. It’s because in China, formaldehyde is an everyday health concern. I’ve also seen people in India bring up formaldehyde as a health concern.  In reality, formaldehyde is a problem in every country in the world.  Therefore, finding a solution for formaldehyde removal is crucial.

What’s the Big Deal with Formaldehyde?

Why are they so concerned with formaldehyde? Formaldehyde is a volatile organic compound (VOC) that causes scary health problems like ulcers and cancer. Yet it’s common in construction materials and new furniture. The people who should worry the most are people in new or recently renovated homes. Tests of new and renovated homes routinely find high levels of formaldehyde.

Why Formaldehyde Removal Is So Hard

Formaldehyde removal is a tricky problem because – just like all VOCs – it escapes from materials as a gas. That’s tricky because the most common filters are HEPA filters. But HEPA filters aren’t made to capture gases. I’ve heard companies claim that activated carbon are the best for removing formaldehyde. But I’ve also seen companies selling sprays that claim to clear formaldehyde from your home. That sounds a lot like snake oil to me.

Formaldehyde spray China

Since there’s a profit motivation for companies to claim they have the best solution for getting rid of formaldehyde, I wanted to empirically test whether activated carbon filters actually work.

Formaldehyde Tests

In my quest for an answer, the first stumbling block was detecting formaldehyde. Many companies will sell you a “formaldehyde detector”, but they’re actually general VOC detectors. They measure what’s called TVOCs or ‘total VOCs’. So even if the machine tells you it’s detecting formaldehyde, you have no way of knowing whether it’s formaldehyde or some other VOC. These “formaldehyde” detectors even react to oranges.

Thus, to be absolutely sure we were detecting formaldehyde, Smart Air co-founder Anna bought bottles of liquid formaldehyde. We’re risking our health for science!

Formaldehyde solution China

To spread the formaldehyde in the room, we put it in a rice cooker along with 250 ml of water. When the rice cooker heats up, it releases formaldehyde as a gas into the air.We ran the cooker in a 4.14m2 porch (volume 10.35m3).

Formaldehyde activated carbon charcoal filter test

The Industrial Scientific MX6 detects different types of VOCs (TVOC), not formaldehyde specifically. But because we released formaldehyde in the room, we can be sure that that VOC is formaldehyde.

Ibrid MX6 Industrial Scientific Review Test VOCs

To attack the formaldehyde, Anna put a composite activated carbon filter on the Smart Air Cannon air purifier. Carbon filters – sometimes called activated charcoal filters – absorb formaldehyde and other VOCs.

Smart Air Cannon purifier DIY carbon

Anna turned the cooker and the fan on at the same time and let them run until the VOC level fell back to zero. We also ran a control test with a fan only. We ran a total of three carbon tests and two fan-only tests.

Results – Activated Carbon Filters vs. Formaldehyde

Here’s what one of the carbon tests looked like, starting from the peak formaldehyde level:

Formaldehyde activated carbon charcoal filter test

Great, it looks like activated carbon can remove formaldehyde! But we need to be sure that’s the effect of the carbon filter, not just the formaldehyde dispersing over time. To do that, we need to compare those results to the fan-only condition. Here’s what the two tests look like side by side:

Formaldehyde activated carbon charcoal filter test

The formaldehyde levels remained high in the fan-only condition. But with the activated carbon filter, formaldehyde dropped much quicker.

I averaged across all three carbon filter tests and compared the average reduction compared to the fan-only condition. On average, the carbon reduced formaldehyde levels to 50% within 15 minutes of the peak formaldehyde levels. By 25 minutes, formaldehyde was down to 0%.

Formaldehyde activated carbon charcoal filter test


These composite activated carbon filters removed formaldehyde from the air. Earlier tests show that these carbon filters remove other types of VOCs too.

Does Everyone Need a Carbon Filter?

Studies have found that formaldehyde is much more common in new and recently remodeled homes. That means people in new or remodeled homes probably need carbon. However, my Ibrid MX6 detector found zero VOCs in ALL apartments I tested, except for places that had recent renovation or smoking,

Now, there could be VOCs at levels lower than the MX6 can detect, so I’m not confident to say there are ZERO VOCs in most houses. But I think it’s reasonable to say that carbon filters are not mandatory for homes without obvious sources of formaldehyde or other VOCs.

Do I still need a HEPA Filter?

Activated carbon is made to get smells and gases like VOCs. It is not designed to get particulate in general. In fact, activated carbon is made to be as porous as possible to get as much air into contact with the carbon. And my tests with a carbon filter alone show that it is does not remove high amounts of small particles. Thus, we still need a HEPA.

As always, I’m including the raw data and more details on the testing for fellow nerds.


The raw data is a large file, so I’m making it available as a download. Here is the summary data:



Check out my earlier VOC and carbon tests for more details on the MX6 detector, placement of the detector, and the fan-only control condition. Conditions were identical except for the pollution source.

How do we know the detector was actually detecting formaldehyde?

I wanted to test whether the MX6 was detecting the formaldehyde and not the heat and humidity coming from the electric cooker. To test that, I also ran a condition where I filled the rice cooker with water, but no formaldehyde. In that condition, the MX6 read zero:


That tells us that the MX6 wasn’t mistaking heat or water for formaldehyde.


Similar to my earlier VOC tests, one limitation is that the formaldehyde here was not naturally occurring. It would be ideal to find a house that was recently remodeled and already has formaldehyde in it. That setup would more closely approximate how most people face formaldehyde.

However, one difficulty of that sort of test is that the VOC detector can’t tell us if we’re detecting formaldehyde or other VOCs. Thus, we can’t be 100% sure whether the carbon is actually removing formaldehyde or other VOCs. In one sense, that’s not important–we want to get rid of all VOCs. But it would also be interesting to know if we’re getting formaldehyde specifically. To do that, we would need to take gas samples and have them sent to a lab.

BONUS: Want Smart Air Professionals to Help You Remove Formaldehyde?

Smart Air can help you with formaldehyde removal and air quality testing. Smart Air is a certified B Corp started by University of Chicago Professor Thomas Talhelm to combat the myths big companies use to inflate the price of clean air.

How I Protect Myself

I set up Smart Air because I realised big companies were charging crazy amounts of money for clean air.

Smart Air is a certified B Corp committed to combating the myths big companies use to inflate the price of clean air. Smart Air provides empirically backedno-nonsense purifiers and masks, that remove the same particles as the big companies for a fraction of the cost. Only corporations benefit when clean air is a luxury.

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