Air Purifier Filter Leve1 Pre-Filter: Capture initial dust and allergen particles. It helps extend the life of the HEPA filter by removing large particles before they can get to the HEPA Filter. Level 2: Hepa Filter: HEPA stands for High-Efficiency Particulate Air. It removes at least 99.97% of all particles as small as 0.3 microns. Level 3: Active Carbon Filter: absorbs common household odors caused by tobacco, pets, garbage, and cooking.