How does dust effect the system?
Dust build up inside a smoke chamber can be as issue in smoke detectors. A chamber designed for a backscatter system tends to be more prone to this issue. The surface of the chamber facing the ADPD188BI is designed to reflect away from the part. If dust settles on this surface it will scatter some amount of the light back to the part, shifting the dc level. As long as the total dc level remains similar or less than the alarm threshold levels this can be removed with a long term averaging filter.