Can Activated Carbon Remove Formaldehyde?

2021-03-102021-01-05 by Thomas Talhelm

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

Do Air Purifiers Dry Out the Air?

2020-12-312020-09-27 by Thomas Talhelm

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 Combination of Air Filters Do I Need to Protect Against Everything?

2020-07-152019-04-17 by Thomas Talhelm

What combination of air filters do I need to protect against everything? This will sound like a grand claim, but two filters are all you need. Here’s why (with data). Very Reasonable Reasons To Be Skeptical Why might you be skeptical? For one, big purifier companies are in an … Read more

The Best Way to Remove Formaldehyde and VOC Chemicals From Your Home

2021-03-112018-11-29 by Thomas Talhelm

There’s a lot of noise about how to remove formaldehyde and VOC chemical build up in homes. Here are three scientific, data-backed ways to reduce and filter formaldehyde in the home. Method 1: Open a window Researchers have found that even in developed urban areas, outdoor concentrations of formaldehyde are near … Read more

Ozone Pollution: Often Invisible, Always Dangerous

2020-11-122018-06-11 by Thomas Talhelm

When summer rolls around, enticing blue skies often draw people outside. Throw on top the fact that most cities in China have less PM2.5 pollution in the summer, what’s stopping us from heading outside? Ozone Pollution on Rise Across China Ozone has been on a steady increase across China in … Read more

Does Adding a Carbon Layer Reduce Particulate Effectiveness?

2020-07-152015-01-13 by Thomas Talhelm

I recently published tests showing that carbon actually removes VOCs. But adding that carbon layer raises a question: adding carbon means the fan has to power through yet another layer of resistance. Does that make purifier less effective at removing particulates?

Test Method

To test this question, I ran 10 room tests with the Cannon and 10 tests with the Original DIY in the same 15m2 Beijing apartment as my earlier tests without a carbon layer.

I measured how much particulate it removed with a Dylos particle counter and compared the particle counts (1) before I turned on the purifier at night and (2) the average of the last four hours before I woke up in the morning.

Carbon vs. HEPA Results

With the additional charcoal layer, the Cannon particulate effectiveness dropped 1-2%. Thus, charcoal has a very minor negative effect on the Cannon.

However, the Original DIY had a harder time powering through the extra layer. Its 0.5 micron effectiveness dropped 19%, and 2.5 micron effectiveness dropped 15%.

Conclusion: Carbon Tips

For people who need carbon (and that may not be everyone), I would recommend adding the carbon to the Cannon, but I would think twice about adding carbon to the Original. One workaround is to have one Original fan running with a HEPA and another running with a carbon filter.

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