Filtration efficiency of a large set of COVID-19 face masks commonly used in Brazil

The use of face masks is mandatory in public places in many countries to slow the spread of the COVID-19 pandemic. In developing countries, homemade masks with varying techniques and fabrics are used on the streets. On these fabric masks, the protection against SARS-CoV-2 varies significantly. The most common mask types are N95, surgical masks, and homemade nonwoven and cotton masks. The performance of 227 different face masks used in Brazil was evaluated to quantify their breathability and filtration efficiency (FE) for airborne particles. FE values were measured using NaCl aerosol particles sized from 60 to 300 nm and at 300 nm, minimum efficiency. The differential pressure drop over the mask and the FE_min at 300 nm was used to calculate the mask Quality Factor (QF). The N95 masks showed the highest FE_60-300, around 0.98, and a QF of 13.2 KPa⁻¹, and were considered the reference for evaluating homemade masks performance. Surgical masks have an FE_60-300 of 0.89, with a good QF of 15.9 KPa⁻¹. Nonwoven masks showed an average FE_60-300 of 0.78, with an excellent QF of 24.9 KPa⁻¹, and can be regarded as the best material for homemade masks. The most commonly used material for homemade masks, cotton fabrics, showed significant variability in FE_60-300, ranging from a low 0.20–0.60, with a low QF of 1.4 KPa⁻¹. Masks always reduce droplets and aerosols emitted by COVID-19 symptomatic and asymptomatic persons, reducing SARS-CoV-2 contamination. Copyright © 2021 American Association for Aerosol Research