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 QuietCare and Silent Comfort series air purifiers. Replaces pre-filters Model No. 32002， 33002， 34002， 35002， and 38002.