air pollutant; asthma; chronic obstructive lung disease; coronavirus disease 2019/pc [Prevention]; coughing; droplet transmission; hand washing; health care facility; health care personnel; human; letter; nonhuman; PM2.5 exposure; public health; sneezing; social distancing; virus load; virus transmission; cloth mask; face mask; HEPA filter; minimally 80 percent efficient filtering facepiece respirator; minimally 94 percent efficient filtering facepiece respirator; protective equipment; surgical mask