Why does the flow rate of the RDS drop as the sample progresses ?
As the sample progresses fine particles (PM 10 fraction) of dust get deposited in the pores of the filter paper. This increases the resistance offered by the filter to the passage of air. In APM 460 RDS the Blower causing air flow is operating at a fixed RPM so increased pressure drop across the filter causes a drop in flow rate through the system.
