Air-Filtering Masks for Respiratory Protection from PM_2.5 and Pandemic Pathogens

Air-filtering masks, also known as respirators, protect wearers from inhaling fine particulate matter (PM_2.5) in polluted air, as well as airborne pathogens during a pandemic, such as the ongoing COVID-19 pandemic. Fibrous medium, used as the filtration layer, is the most essential component of an air-filtering mask. This article presents an overview of the development of fibrous media for air filtration. We first synthesize the literature on several key factors that affect the filtration performance of fibrous media. We then concentrate on two major techniques for fabricating fibrous media, namely, meltblown and electrospinning. In addition, we underscore the importance of electret filters by reviewing various methods for imparting electrostatic charge on fibrous media. Finally, this article concludes with a perspective on the emerging research opportunities amid the COVID-19 crisis. Considering that air pollution will continue to be a major health concern in newly industrialized countries and the ongoing COVID-19 pandemic may create lasting cultural shifts around the world to increase mask usages, the pursuit of more efficient and cost-effective masks will be a cornerstone to maintaining public health. This review provides a comprehensive picture of the historic development of air-filtering masks, identifies remaining knowledge gaps, and envisions emerging research opportunities amid the pressing challenges of air pollution and COVID-19.