Multipurpose filtering material

A multipurpose filtering material particularly for use in electrostatographic reproducing apparatus has a foraminous support matrix having a plurality of interconnecting voids to permit low impedance to the flow of gaseous material but sufficient to trap particulate material entrained in the gaseous material which is coated with a thin dehydrated alkaline film of an alkali metal silicate to neutralize nitrogen oxide species in the gaseous material and has adhesively bound thereto a particulate neutralizer for another noxious gas the surface of which is substantially exposed to the flow of gaseous material. A filter may be placed in electrostatographic reproducing apparatus at the inlet or outlet of an air stream passing therethrough to neutralize nitrogen oxide species and ozone generated by the corona discharge device, and ammonia from the incoming air.