Aerosol filtration efficiency of household materials for homemade face masks: Influence of material properties, particle size, particle electrical charge, face velocity, and leaks

As a consequence of the COVID-19 pandemic caused by the SARS-CoV-2 virus, the widespread daily use of face masks is promoted worldwide. Particle-size dependent filtration efficiencies (FE;d(p) = 30 nm-10 mu m), applying a particle counting approach, and additionally pressure drops (Delta p) were determined for 44 samples of household materials and several medical masks. HugeFEdifferences were found between sample materials and for different particle sizes, spanning from FEwere determined ford(p)= 50-500 nm particles with significantly larger values ford(p) = 30 nm particles and especially for those withd(p)> 2.5 mu m. Measurements at different numbers of layers showed that stacks of textiles can be treated as separate filters and totalFEand Delta pcan readily be estimated from the features of the individual layers, leaving laborious measurements of individual combinations obsolete. For many materials, electrostatic attraction contributes strongly to overallFEfor particles up to 100 nm diameter. Measurements with defined leaks showed that already a small fractional leak area of 1-2% can strongly deteriorate totalFE. This is especially the case for particles smaller than 5 mu m diameter, whereFEdropped by 50% or even two thirds. Our measurements show that by stacking an adequate number of layers of many fabrics, decent filtration efficiencies can be reached for homemade face masks over large particle size ranges with acceptable pressure drop across the material. Very important, however, is good fit of the masks to minimize leak flows and selection of non-hazardous mask material.

Automated summary

The COVID-19 pandemic has led to widespread use of face masks worldwide. Testing 44 samples of household materials and medical masks for filtration efficiencies and pressure drops across different particle sizes revealed significant variations between materials and particle sizes. Electrostatic attraction plays a strong role in overall filtration efficiency for particles up to 100 nm in diameter.