HEPA and ULPA are intended for particle removal and are not efficient for removing molecular contamination. The presence of air-borne molecular contamination (AMC) has been shown to play an increasing critical role in yield process for integrated circuits, disk drives, and liquid critical displays. Chemical and activated carbon filters are typically used to remove AMC when a problem is known to exist. The inlet air quality is dynamic based on environment contamination levels around the facility and level and type of process occurring within the facility and the challenge on chemical filter changes every moment.

Chemical filters have a finite holding capacity and a designed capture limit on the amount of AMC they can remove during a unit of time and as such the outlet air quality will be vary depending the challenge rate. Chemical filters by design are not absolute filters but are a demand percentage removal filters.

When chemical filter performance fail they tend to deteriorates in terms of lost capture efficiency and the AMC released on the outlet will increase...  Effect on the product being processes will show gradual degradation until a critical limit is reached. It is critical to have on-line AMC monitoring to prevent any product lost. Because of the dynamic challenge on AMC filters, Time scheduled replacement does not insure performance and risk of product lost.