The COVID-19 pandemic has made face masks essential personal protective equipment to prevent in- and exhalation of virus containing droplets and thus limit the spread of the air borne virus. A wide array of filter materials and mask designs have been studied and used from homemade, cloth type masks to commercial high efficiency N95 and KN95 masks. Still the importance of the specific capture mechanism, in particular for the smallest (sub 200 nm) particles, remains poorly characterized in particular the impact of surface charge on particle capture. The latter is surprising as many engineered mask materials use a substantially charged layer to enhance particle capture efficiency. In this project, we have used an electrostatic voltmeter to measure the surface potential of different types of mask materials before studying their capture efficiency for a variety of charged model aerosols and under different humidity conditions. A scanning mobility particle sizer was used to obtain size-resolved particle number concentrations up and downstream of the test material and hence obtain number-based capture efficiencies. In this project, we have investigated 2 different types of N95 masks and three different types of surgical masks. All these masks are challenged by 3 different types of 150 nm functionalized particles, in different charge states (positive/negative/neutral). Results show the capture efficiency is improved with higher electrostatic charge for most types of challenge aerosol. Humidity has a strong impact on capture efficiency while the surface charge on the mask material evolved over time because of the captured particles. We will present a complete discussion of our results.

Particle capture efficiency studies on face mask

ACS Fall 2021

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