Evaluating the filtration efficiency of commercial facemasks’ materials against respiratory aerosol droplets

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Satya S. Patraa , Jyotishree Nathbc, Subhasmita Pandabc, Trupti Dasbc & Boopathy Ramasamybc* a Lyles School of Civil Engineering, Purdue University, West Lafayette, Indiana, USAb Environment & Sustainability Department, CSIR-Institute of Minerals and Materials Technology (CSIR-IMMT), Bhubaneswar, Indiac Academy of Scientific and Innovative Research (Acsir), CSIR-Institute of Minerals and Materials Technology (CSIR-IMMT), Bhubaneswar, IndiaSatya S. Patra is currently a Ph.D scholar in the Lyles school of Civil Engineering, Purdue University. His research interest lies in understanding the physical, chemical and biological aspects of airborne particles in indoor as well as outdoor environments. Additionally, he is passionate about development and evaluation of low cost sensors.Jyotishree Nath is pursuing Ph.D. in Environment and Sustainability Department at CSIR- Institute of Minerals and Materials Technology, Bhubaneswar, Odisha, India. Her research interest is studying the tropospheric microbiome and its emission and transportation sources in ambient aerosol and its impact on human health.Subhasmita Panda is a postgraduate in Chemistry and currently pursuing Ph.D. at CSIR-Institute of Minerals and Material Technology, Bhubaneswar, Odisha, India. Her major research focus is to understand the chemical characterstics of ambient aerosols and how they relate to atmospheric chemistry, climate, air quality and human health.Trupti Das is a microbiologist by training and has worked extensively on development of sustainable processes for biological treatment of industrial and municipal wastewater. A part of her research pursuit also includes the study of atmospheric aerosols and trace gases and their overall impact on the regional atmosphere. The recent focus is on monitoring and characterization of ambient aerosols to determine their composition, source and fate in the atmosphere, to understand the spatial temporal variation, transport pathways using measurement and remote sensing data. Impact of fine particulate matter and ozone on human health as well as on plant growth and productivity are some new initiatives.Boopathy Ramasamy is a Ph.D in Chemical Engineering-Environmental Technology, currently working as a Scientist in Environment & Sustainability Department, CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, Odisha, India. His major thirst area are advanced oxidation process for the removal of pollutants in water and wastewater, design and development of novel bioreactors and sustainable composite materials for the pollutants removal. Also having knowledge and interest on physical and chemical characterization of ambient aerosol (Indoor and outdoor) and trace gases.CONTACT Boopathy Ramasamy chemboopathy@gmail.com Environment & Sustainability Department, Council of Scientific and Industrial Research-Institute of Minerals and Materials Technology (CSIR-IMMT), Bhubaneswar-751 013, Odisha, India.ABSTRACTRespiratory droplets serve as a viable transmission mechanism for many viruses and other pathogens. Facemasks are commonly used to minimize the risk of this transmission. However, information on the size-resolved filtration efficiency of commonly available commercial facemasks is not readily available in the literature. To fill this gap, the current study performs aerosolized chamber experiments to evaluate the filtration efficiencies of commonly available commercial facemasks’ materials in a size range of 0.3–10 µm. Results rank the performance of filtration through commercial facemasks’ materials as follows (values in brackets indicate the average filtration efficiencies across 0.3–10 µm): 6-Layer N95 mask (0.918) > N95 mask – without valve (0.88) > KN95 mask (0.84) > N95 mask -with valve (0.834) > Heavy knitted cotton mask (0.808) > Surgical mask (0.778) > Cotton mask-2 layers (0.744) > Nylon fabric mask-2 layers (0.740) > T-shirt fabric mask-2 layers (0.708) > T-shirt fabric mask-1 layer (0.648). The size-resolved filtration efficiencies through the material across the evaluated commercial facemasks ranged from 38–83% in the size range of 0.3–0.5 µm, 55–88% in the size range of 0.5–1 µm, 69–93% in the size range of 1–2.5 µm, 76–96% in the size range of 2.5–5 µm, and 86–99% in the size range of 5–10 µm. Subsequently, the filtration efficiencies of materials post washing (with detergent in warm water and allowing to dry completely) were also evaluated. The average reduction in filtration efficiencies post washing are as follows: 6-Layer N95 mask: 3%, N95 mask – without valve: 2%, KN95 mask: 4%, N95 mask -with valve: 3%, Heavy knitted cotton mask: 4%, Surgical mask: 18%, Cotton mask-2 layers: 11%, Nylon fabric mask-2 layers: 6%, T-shirt fabric mask-2 layers: 6%, T-shirt fabric mask-1 layer: 8%. This decrease in the filtration efficiency was more pronounced for the sub-micron particles than the super-micron ones.Implications: Facemasks are commonly used to minimize the risk of pathogens through ambient air transmission. However, information on the size-resolved filtration efficiency of commonly available commercial facemasks materials is not readily available in the literature. To fill this gap, the current study performs aerosolized chamber experiments to evaluate the filtration efficiencies of commonly available commercial facemasks materials in a size range of 0.3–10 µm. The performance of the commercial facemasks materials as follows in the order of (values in brackets indicate the average filtration efficiencies across 0.3–10 µm): 6-Layer N95 mask (0.918) > N95 mask – without valve (0.88) > KN95 mask (0.84) > N95 mask -with valve (0.834) > Heavy knitted cotton mask (0.808) > Surgical mask (0.778) > Cotton mask-2 layers (0.744) > Nylon fabric mask-2 layers (0.740) > T-shirt fabric mask-2 layers (0.708) > T-shirt fabric mask-1 layer (0.648). The choice of facemask is greatly driven by the size of viable respiratory droplets that need to be eliminated. If droplets with particle size less than 0.5 µm are required to be filtered, N95 masks without the valve or more layers are preferred. If the primary objective is to filter particles between 0.5–1 µm, then N95 (both with or without valves) or KN95 masks are recommended. Surgical masks and heavy knitted cotton masks may also be used for this purpose, but with caution.