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?
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.