Carbon filters can absorb VOC, which we can prove with the tests we have conducted. If there isn’t an obvious change in smell, this is due to the fact that there are more volatile sources of VOC. The absorption by the activated carbon is not enough to change the indoor VOC concentration. Furthermore, it is very sensitive, and the minimum odorable formaldehyde level is 0.05mg / m3 (mg / m3). So any smell of VOC beyond this concentration is easily picked up by us. As long as the concentration is not reduced to a safe level, we can all detect the smell.