Study of Surface Morphology and Effectiveness of Common Nasopharyngeal Masks: A Case of Kathmandu, Nepal

Facemasks are widely used worldwide to prevent inhaling airborneparticles and viruses, especially after the outbreak of COVID-19. To assess theeffectiveness of various facemasks against PM₁₀ and PM_2.5,experiments with a mannequin head were conducted at 10 and 55 LPM airflowrates. A total of 38 masks, including 26 CMs, 7 SMs, and 5 N95 masks, weretested against PM₁₀ and PM_2.5 at 55 LPM airflow rate,while 18 masks, including 10 CMs, 6 SMs, and 2 N95 masks, were tested at 10 LPMairflow rate. The surface morphology of these facemasks was examined using asimple digital microscope of 0.3 M image sensor. SMs and N95 masks had smallerpore sizes and higher porosity, resulting in higher filtering efficiency. Incontrast, CMs had larger pore sizes and lower porosity, leading to poor filtering efficiency. Theaverage pore sizes of SMs and CMs were 70 μm and 160 μm, respectively, whiletheir porosities were 99 pores/mm² and 20 pores/mm², respectively. N95FFRshad an average pore size of 49 μm with a porosity of 88 pores/mm². The averagefiltering efficiency of facemasks followed the order N95 FFRs > SMs >CMs. The Prototype Cloth Masks (PTCMs) were stitched using cottonfabrics with adjustable ear straps, nose pins, and polypropylene (PP) fabric asthe filter. Their filtering efficiency was found to be nearlyequivalent to N95 masks and their performance did not deteriorate even afterfive washing and drying cycles. This facemask can help reduce particulateexposure, particularly in developing countries with high air pollution, such asthe Kathmandu Valley.