Method of sensing acidic/acid-forming and oxidizable gases for use as a residual filter life indicator

A process for determining residual capacity of an in-service filter/filtration system, comprising:

• depositing one or more metal oxyhydroxides on a swatch of material or locating one or more metal oxyhydroxides within a filter material;
• a) contacting an acidic/acid-forming and/or oxidizable gas with said metal oxyhydroxide for a sampling time;
• or
• b) contacting said metal hydroxide to heat for a sampling time;
• obtaining a post-exposure photoluminescence ratio of said metal oxyhydroxide between the photoluminescence at a first wavelength and a second wavelength;
• and determining said residual capacity by comparing said ratio to a pre-exposure ratio or control.

A process for manufacture of a metal oxyhydroxide material, comprising:

• obtaining a post-manufacture ratio of photoluminescence at a first wavelength and a second wavelength of a metal oxyhydroxide material;
• determining a difference between said post-manufacture ratio of photoluminescence and a control;
• and
• using or rejecting the use of a metal oxyhydroxide material based on said difference.