Nanoparticle collection efficiency of capillary pore membrane filters

Area of Science:

• Environmental Science
• Materials Science
• Aerosol Science

Background:

• Capillary pore membrane filters are used for air sampling.
• Accurate measurement of airborne particles relies on filter collection efficiency.
• Understanding particle deposition is crucial for air quality monitoring.

Purpose of the Study:

• To quantify the surface and overall collection efficiencies of capillary pore membrane filters for sub-micrometer particles.
• To investigate the influence of particle size and filter face velocity on collection efficiency.
• To determine the primary deposition location of nanoparticles within the filters.

Main Methods:

• Utilized scanning electron microscopy (SEM) to measure particle loadings on filter surfaces.
• Employed scanning mobility particle sizer (SMPS) to determine airborne particle concentrations.
• Tested filters with 0.4 μm and 0.8 μm pore sizes at face velocities of 3.7 cm/s and 18.4 cm/s.

Main Results:

• Surface collection efficiency was <100% for particles <316 nm and <55% for particles <100 nm.
• Overall collection efficiencies dropped to 45% for 70 nm particles.
• Nanoparticle collection efficiencies were significantly higher overall than surface efficiencies, indicating internal pore deposition.

Conclusions:

• Surface collection efficiency is insufficient for accurate nanoparticle concentration assessment from filter analysis.
• Deposition of nanoparticles predominantly occurs within the filter pores, not solely on the surface.
• Accurate derivation of airborne nanoparticle concentrations requires considering internal filter deposition mechanisms.