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 FEmin at 300 nm was used to calculate the mask Quality Factor (QF). The N95 masks showed the highest FE60-300, 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 FE60-300 of 0.89, with a good QF of 15.9 KPa−1. Nonwoven masks showed an average FE60-300 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 FE60-300, 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为减缓新型冠状病毒肺炎（COVID-19）大流行的传播速度，全球多国已要求公共场所强制佩戴口罩。在发展中国家，街头普遍使用工艺与面料各异的自制织物口罩。此类织物口罩对严重急性呼吸综合征冠状病毒2（SARS-CoV-2）的防护效果差异显著。当前主流口罩类型包括N95口罩、医用外科口罩，以及自制非织造布口罩与棉质口罩。 本研究对巴西境内使用的227款不同口罩展开性能评估，以量化其透气性与空气颗粒物过滤效率（Filtration Efficiency, FE）。测试采用粒径范围为60~300nm的氯化钠（NaCl）气溶胶颗粒，其中300nm粒径下的过滤效率被定为最低过滤效率（FEmin）。通过口罩两侧的压差与300nm粒径下的FEmin，可计算出口罩质量因子（Quality Factor, QF）。 实验结果显示：N95口罩的FE60-300最高，约为0.98，质量因子为13.2 KPa⁻¹，被作为评估自制口罩性能的参照标准；医用外科口罩的FE60-300为0.89，质量因子达15.9 KPa⁻¹，性能优异；非织造布口罩的平均FE60-300为0.78，质量因子高达24.9 KPa⁻¹，可视为自制口罩的最优面料选择。而自制口罩最常用的棉质面料，其FE60-300波动显著，区间为0.20~0.60，对应的质量因子仅为1.4 KPa⁻¹，防护性能偏低。 口罩可有效减少新冠病毒有症状与无症状感染者喷出的飞沫和气溶胶，从而降低SARS-CoV-2的传播污染。本研究版权归2021年美国气溶胶研究协会（American Association for Aerosol Research）所有。