Filtration of airborne microorganisms: Modeling and prediction

The filtration of airborne particulates has been studied extensively and removal efficiencies can be adequately predicted from theory or from catalog data. The filtration of airborne microorganisms, however, has not been specifically addressed by theory and has seen limited empirical study. This paper addresses the variety of factors that may cause microbial filtration efficiency to deviate from predicted values based on particulate size alone. A model is developed to incorporate those factors likely to have significant impact, namely, aspect ratios and lognormal size distributions. This model is then challenged with a database of known airborne pathogens and allergens for which these parameters have been established. Results suggest existing filtration models are accurate within reason for the prediction of filtration efficiencies of airborne bacteria and spores, provided logmean diameters are used. Implications for the use of filtration in health care facilities are discussed.