Thanks for your contact and purchase.
The air purifier aims to clean air by removing 2 kinds of objects:
1) particles （ Ultra HEPA Filter )
large particles: pet danger, pollen, hair, asbestos, etc
Micro particles: dust mites, mold, germs, virus, etc
2) gases ( Carbon Filter )
terrible odors: household odor, animal smell, wildfire smoke, etc
toxic gases: formaldehyde, benzene, toluene, TVOC, etc.
We can easily see those large particles are blocked by Pre-filter; but towards those micro particles, we highly appreciate your kind understanding that we're unable to see except they're accumulated to a certain extent.
When large amount of micro particles are absorbed by the HEPA Filter, the color of the filter will be changed from white to gray; and the performance of Carbon Filter will be decreased gradually after the terrible odors and gases are absorbed.