Air sampling filtration media: Collection efficiency for respirable size-selective sampling

The collection efficiencies of commonly used membrane air sampling filters in the ultrafine particle size range were investigated. Mixed cellulose ester (MCE; 0.45, 0.8, 1.2, and 5m pore sizes), polycarbonate (0.4, 0.8, 2, and 5m pore sizes), polytetrafluoroethylene (PTFE; 0.45, 1, 2, and 5m pore sizes), polyvinyl chloride (PVC; 0.8 and 5m pore sizes), and silver membrane (0.45, 0.8, 1.2, and 5m pore sizes) filters were exposed to polydisperse sodium chloride (NaCl) particles in the size range of 10-400nm. Test aerosols were nebulized and introduced into a calm air chamber through a diffusion dryer and aerosol neutralizer. The testing filters (37mm diameter) were mounted in a conductive polypropylene filter-holder (cassette) within a metal testing tube. The experiments were conducted at flow rates between 1.7 and 11.2l min(-1). The particle size distributions of NaCl challenge aerosol were measured upstream and downstream of the test filters by a scanning mobility particle sizer (SMPS). Three different filters of each type with at least three repetitions for each pore size were tested. In general, the collection efficiency varied with airflow, pore size, and sampling duration. In addition, both collection efficiency and pressure drop increased with decreased pore size and increased sampling flow rate, but they differed among filter types and manufacturer. The present study confirmed that the MCE, PTFE, and PVC filters have a relatively high collection efficiency for challenge particles much smaller than their nominal pore size and are considerably more efficient than polycarbonate and silver membrane filters, especially at larger nominal pore sizes.