The universal carbon pre-filter helps capture large airborne particles before passing through the HEPA filter, therefore maximizing the HEPA filter life. The activated carbon pre-filter also helps reduce common household odors. Should be replaced every 3 months of use. For all Honeywell round QuietCare and Silent Comfort series air purifiers. Replaces pre-filters model No. 32002, 33002, 34002, 35002, and 38002.