Air Purifier Spares - AOS - Active carbon filter To be changed every 6 months Price: £26.43 incVAT The active carbon filter eliminates harmful fumes like ozone and formaldehyde and odours from tobacco smoke, animals and cooking. For use with the AOS Air Purifier and the AOS Combi Humidifier/Air Purifier. IN STOCK NOW. FREE MAINLAND UK DELIVERY IN 2-3 WORKING DAYS.