how to measure the efficiency of carbon filter [or of activated carbon/charcoal]?
1/ The iodine method:



I found the answer on this video (from Cody's lab youtube channel). Cody's show how to make activated carbon/charcoal and how to test its efficiency. 

It's quite an easy task. The test below measures the absorption's efficiency of your charcoal filter (activated or not).

● Take a gram of your active charcoal (from your filter)
● Put it in a test tube
● Add 2ml hydrochloric acid (to make sure the charcoal is acidified, because otherwise, the alkaline ash in the charcoal will react with the iodine)
● just warm it a little to help the reaction.
● Add 25ml of iodine (iodine with alcohol).
● Wait for 24h, look at the color of your solution: the lighter the color the more effective is the charcoal (the lighter, the more it has absorbed iodine which is dark). You could compare it with some active carbon you bought, or normal charcoal


To measure more precisely the efficiency of your charcoal:
● Take 10ml of the solution you made above.
● Add some thiosulfate to it (drop after drop) until your solution becomes clear.
● Measure the quantity of thiosulfate that was needed.

See Cody's video for more details.



2/ The Formaldehyde (or VOIC) method:



If you want to know if your activated carbon filters works, you can also test it using Thomas Talhelm method (he is the most famous air pollution DIY expert). But this technique require a solution of formaldehyde, and a device to mesure the quantity of formaldehyde in the air.


Buy a formaldehyde solution.
warm it (eg. using a rice cooker) in a closed room.
measure the level of formaldehyde
turn ON your activated carbon filters, and keep measuring.


If your filter is working you should see that:



  With a fan only (red line), formaldehyde levels stayed high. But with
  a carbon filter on the fan (blue line), formaldehyde levels went down.