FILTRATION
IN-LINE FILTER HOLDER
An in-line filter holder holds either a 25 mm or 47 mm filter, depending on the model, in a fixed sample line. Filters are the primary standard used for determining aerosol concentration. Filters collect particulates by interception, inertial impaction, and diffusion as the aerosol is drawn through them. The sample flow rate is a calibrated flow. Filters are weighed before and after sample collection. The weight differential is determined: post sample weight – pre-sample weight. The volume of air sampled is calculated: sample flow rate x sample time. The quotient of differential weight and sample volume is the mass per unit volume aerosol concentration. Sample weight differential can also be determined by chemical analysis rather than gravimetrically.