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Can Activated Carbon Remove Formaldehyde?

“Formaldehyde” (甲醛) is a surprisingly common word in China. I say surprising because I’m from the US, where only scientists and high schoolers dissecting frogs tend to be familiar with the chemical.

But it’s not because Chinese people are all nerds. At dinner with Chinese colleagues, my friend David once used the word “carbohydrate” (碳水化合物) and was instantly made fun of for using a “science word” in casual conversation. Why the double standard? Because in China, just like carbs in America, formaldehyde is an everyday health concern.

What’s the big deal?

Why are they so concerned? Formaldehyde 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 is so hard to remove

Formaldehyde is a tricky problem because it escapes from materials as a gas, and HEPA filters aren’t made to capture gases. I’ve heard companies claim that activated carbon can remove 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.

Since there’s a profit motivation for companies to claim they can get rid of formaldehyde, I wanted to empirically test whether carbon actually works.

Tests

In my quest for an answer, the first stumbling block was detecting formaldehyde. Many companies on Taobao will sell you a “formaldehyde detector”, but they’re actually general VOC detectors. (There are lots of volatile organic compounds; formaldehyde is one type.) 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.

Thus, to be absolutely sure we were detecting formaldehyde, my collaborator Anna bought bottles of liquid formaldehyde–risking our health for science!

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

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

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To attack the formaldehyde, Anna put a composite activated carbon filter on the Cannon.

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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

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

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But we need to be sure that’s the effect of the carbon, 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:

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The formaldehyde levels stayed higher for longer in the fan-only condition, but the levels dropped much quicker when we used carbon.

I averaged across all three carbon 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 and then down 0% by 25 minutes.

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Conclusion

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

Does everyone need carbon?

Studies have found that formaldehyde is much more common in new and recently remodeled homes, so people in new or remodeled homes probably need carbon. However, my MX6 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?

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.

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Data

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

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Methods

Check out my earlier VOC 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:

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

Limitations

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 because that would be a closer approximation of how most people would use it.

However, one difficulty of that sort of test is that the VOC detector wouldn’t be able to tell us if we’re detecting formaldehyde or other VOCs. In one sense, that’s not important–we want to get rid of all of them. 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 (although if anyone knows of an easier way to detect formaldehyde and only formaldehyde, let me know).

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Does Carbon Really Work?

I wrote early on that my number one concern in China is particulate pollution. It’s on so many people’s minds that nowadays even the guy I buy chuan’r from knows the word “PM 2.5.”

HEPAs do an amazing job at removing particulates, but particulates aren’t everything. Gases like volatile organic compounds (VOCs) are so small that they slip through HEPAs. “VOC” is a big category, including things like benzene and formaldehyde. VOCs can cause cancer, throat irritation, dizziness, and other not-fun side effects.

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And for homes that have VOCs problems, we’re supposed to use activated carbon filters. But do they actually work?

When I published the instructions for how to build your own purifier, I wasn’t comfortable recommending activated carbon because I hadn’t tested it, and I didn’t want to just trust what the big filter companies say. So this year, I set out on a journey to test whether carbon actually works.

Method

I soon learned that gas testing is not easy. First off, “harmful gases” is not a natural category. You can buy a particle counter that will detect all particles of a certain size, but there is no detector that will detect all gases. Instead, you need one for each type of gas, and that is not cheap.

In this case, my scientific curiosity cost me $3,542 for this Industrial Scientific Ibrid MX6. It detects VOCs, carbon monoxide, sulfur dioxide, hydrogen sulfide, and nitrogen dioxide. It uses a photo-ionization detector to measure VOCs from 0-2,000 parts per million with a resolution of .1.

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Next, I needed a source of gas pollution. Interestingly enough, my apartment didn’t have enough VOCs to register on the MX6–nor did 8 other Beijing apartments I tested. (That speaks to whether purifier companies should scare people into thinking that everyone needs carbon.)

Because I didn’t have detectable VOCs in my home, I had to go out and find VOCs to pump into my room. I chose cigarettes because they are known to emit VOCs like benzene and formaldehyde.

In each test, I burned 3 Marlboro cigarettes in an enclosed 3.78 m2 porch. At the same time, I ran the Cannon on high for five tests with a composite carbon filter on the front:

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I ran four control tests with a fan but no filter. That way the room still has air flow, but no carbon. The cigarettes burned out after about 15 minutes, and I left the fans on for another 30 minutes.

Results

Looking at the Cannon + carbon alone after the cigarette extinguished, the VOCs dropped. Here is the data from one test:

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From there we can zoom out to include the time the cigarette was burning and the control fan-only condition. From there, it becomes clearer that the carbon was removing VOCs above and beyond just having a fan on.

Averaging across all of the tests, the VOCs reached a maximum of about 1 ppm while the carbon was on. Without the carbon, VOCs reached 1.5 ppm.

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After the cigarette burned out, the Cannon cleared the air of VOCs in 5 minutes to just over 15 minutes on average. Without carbon, the air still had VOCs after 30 minutes.

Averaging over all of the tests, the carbon removed 38% of VOCs by the time the cigarettes burned out compared to the fan-only condition. The Cannon removed 68% after another 5 minutes and 100% by 20 minutes after the cigarettes burned out.

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Conclusion

The results showed that carbon effectively removed VOCs. Thus, I’ve decided these filters are ready for game time. I’ve started shipping these tested carbon filters via Taobao and PayPal for 70 RMB.

Does everyone need carbon?

Purifier companies have a financial incentive to convince people to buy carbon filters. They make more money if they can scare people into buying carbon. But does everyone need carbon?

I don’t want to scare people into buying carbon. Why? In most homes, my MX6 detected zero VOCs. I only found VOCs in homes that had an obvious source of pollution such as remodeling or smoke. And in all of the places where the MX6 detected VOCs, I was able to notice a chemical smell. That makes sense, since lots of VOCs have noticeable smells, like benzenetoluene, and formaldehyde.

Now, I don’t want to say that VOCs are never a problem. Photo ionization detectors like the MX6 are not the most sensitive test type out there. I bet I’d pick up small amounts of VOCs if I sent air samples to a laboratory.

However, scientists have used fancier methods and found similar results. For example, scientists in Hong Kong tested homes and found that most non-smoking homes did not have un-safe levels of VOCs. We need more tests like this.

For now, I will not be using carbon in my home, but I think it is right for people whose homes have:

1. Recent remodeling

2. Recent painting

3. Smoking

4. Odors

5. Nearby sources of gas pollutants (such as living near a factory)

6. Symptoms such as inflammation and asthma

Do I still need the HEPA?

Yes. Carbon is designed to get organic compounds, not particulate in general. I wouldn’t have even tested this, but Anna accidentally forgot to attach the HEPA and unknowingly ran a regular particulate room test with carbon only.

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The results weren’t pretty–far below the 95% reduction with the added HEPA. Thus, I do not recommend using carbon only.

As always, I’m posting the raw data and more details on the methods for fellow nerds below.


Gas Test Methods

During the gas test, all of the doors and windows were closed. Because the test was in an enclosed porch, there were several windows, which means the room was less well sealed than an interior room.

During the test, I burned three Marlboro cigarettes pointing straight up in an ash tray on the floor. The gas detector was on a small ledge at just above waist height, only a few feet laterally away from the cigarettes. The purifier was placed a couple feet from the cigarettes in the center of the porch with the air stream pointing upward.

Limitations

Burning three cigarettes in a small room is extreme. With the exception of airport smoking lounges, few places will have this much smoke in one place. However, the test does demonstrate that carbon reduces VOCs.

Many people have asked me how long carbon filters last. Unfortunately I don’t have a good answer to that. The carbon filter I used was still effective after several of these powerful smoke tests, which should be far more VOCs than a normal person would face, but I cannot say more than that.

VOC Info: The PID lamp has an eV rating of 10.6. eV ratings determine what types of VOCs PID machines can detect. With a rating 10.6 eV, this machine was probably reliably detecting benzene, which has an ionization potential of 9.25 and perhaps toluene, which is at 8.82.

This PID lamp is not designed to detect formaldehyde, which has an ionization potential of 10.88. However, I later conducted tests with formaldehyde samples and found that the MX6 could detect it, and an engineer at Industrial Scientific told me he thought it was plausible that the machine would pick up on formaldehyde, although not 100% reliably.

Detector Info: The MX6 came with a pump to draw in air (as opposed to versions that passively sample air). During the test, it was outfitted with the filter designed to prevent particles from entering the machine. I zeroed the machine if necessary before the test.

Early Tests: As I started doing the tests, I was still figuring out how to do the tests–it seems simple when you look at the results, but tests like this are not easy! For the first three control tests, I had not yet decided to let the MX6 run for 30 minutes after the cigarettes burned out, so data is limited for those three occasions. However, the conclusions are similar with those three tests excluded.

Control Condition: In the control condition, I used a Honeywell fan on the low setting to approximate the air flow of a Cannon on high with a filter on it. In other words, a filter lowers the air flow, so the Honeywell may be a better approximation of the amount of air flow during the experimental condition.

In addition, I ran tests with an IQ Air Health Pro Plus (1) with the filters removed and (2) with the pre-filter only as additional control tests. The results were similar to the Honeywell fan-only tests. I’ll use the IQ Air tests as the control condition in tests of the IQ Air’s ability to remove VOCs in the future.

Gas Test Data

Below is a summary of the gas tests. Because the raw data file is large, I’m making it available as a download here.

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Data: Carbon-only test

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Anna only ran the carbon-only test for one day because it was an accident. More tests would give a more reliable estimate of the effectiveness of using carbon only, but because carbon isn’t designed to get particulates in general, I’m hesitant to subject anyone to that much dirty air. On the upside, the outdoor PM 2.5 was quite stable that day, only moving up 4 micrograms from start to finish.

 

 

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Types of FiltersTypes of Filters

Premise: This blog is for people concerned about air pollution. There are many valid reasons people want air purifiers: pet allergies, pollen, and asthma. However, these are not what I’m concerned about while living in China. So I assess purifiers solely based on whether they can help protect me from particulate air pollution.

With that in mind, here are the three most common types of filters in portable air purifiers:

  1. UV light filters are designed to kill bacteria. In China, I’m concerned about air pollution, not bacteria, so UV filters are unnecessary. But beyond that, Consumer Reports says that UV filters in most air purifiers don’t even kill bacteria:

The Environmental Protection Agency cautions that air cleaners outfitted with ultraviolet light are unlikely to kill bacteria and mold because they won’t be in contact with UV light long enough to have any effect.

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Conclusion: UV filters aren’t what I need.

  1. Activated carbon filters use charcoal screens to catch certain types of chemicals and organic matter that happen to interact with carbon. In other words, these filters catch some things, but not particulate in general. In sum, these will do a little bit, but they aren’t the whole solution.

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Activated charcoal is good at trapping other carbon-based impurities (“organic” chemicals), as well as things like chlorine. Many other chemicals are not attracted to carbon at all – sodium, nitrates, etc. – so they pass right through. Howstuffworks.

Conclusion: Carbon filters may help (particularly for certain types of gases that carbon can get), but they don’t target all particulate matter. It would be a mistake to use ONLY a carbon filter to get rid of particulate pollution.

  1. HEPA filters are the solution. “HEPA” sounds fancy, but it’s just a standard that means the filter catches 99% of particles .3 micrometers and above (they also get particles smaller than .3 micrometers–the .3 designation is based on the overlapping point of different types of filtering). That covers a lot of particulate pollution–the most-often cited figures are for 2.5 micrometers.

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HEPA filters aren’t rocket science. They work pretty simply: particles get stuck in the fiberglass fibers (using a few types of physical filtering processes). In fact, if you have a vacuum cleaner, it probably has a HEPA filter in it. You can get one for about $10.

Contrast that with the major purifier companies like IQ Air and Blue, which have proprietary HEPA filters with names like “HyperHEPA” that cost $200. These may have benefits, such as a longer lifetime or smaller pore size, but it’s not clear to me that’s necessary or worth 20 times the price.

Bottom line: If your concern is particulate air pollution, a HEPA filter is really all you need. And for that, you don’t need spend 8,000 RMB. You can make your own for 166 RMB.