Honeywell True HEPA air purifiers help remove microscopic airborne allergens as small as 0.3 microns, which are invisible to the naked eye (1). The activated carbon pre-filter helps reduce odours and VOCs. Honeywell air purifiers - delivering cleaner air for over 25 years.(1) From the air that passes through the filter, 0.3 microns and larger, results based on independent testing. Overall allergen reduction depends on many factors including the amount of air processed, the allergen type and the allergen introduction rate into the environment.(2) Based on March 2018 Cascade Survey Research results reporting 48 out of 70 (69%) surveyed U.S. Allergists that recommend a brand of portable air purifiers to their patients, recommend “Honeywell” air purifiers as their first choice.(3) When operated with the odour reducing pre-filter. It is recommended to always use the pre-filter when operating this air purifier. The pre-filter should be replaced every 3 months to effectively reduce common household odours and gases in a room. This product does not reduce or absorb carbon monoxide gas. Make sure gas appliances are well ventilated.