The Secret Lives of Filters

JEFFREY SIEGEL, University of Toronto

     Abstract Number: 341
     Working Group: Invited by Conference Chair

Abstract
Improving indoor air requires addressing source control, ventilation, and filtration. There is an implicit hierarchy in these measures and a long history surrounding the importance of source control and ventilation, even though source control is often not possible, and ventilation is limited by ambient air pollution. Filtration is a much newer approach that has received much less attention. Part of this arises from the fact that filters are often viewed as static with performance solely determined by efficiency as a function of particle size. However, filters are dynamic as the filter efficiency curve of the same filter will change depending on the application as well as over the filter lifetime. Further, filter performance is often largely a function of the context of how the filter is used as much as the filter itself. This presentation explores filter performance from both aerosol science and building science perspectives with a focus on how theoretical and laboratory-tested filtration efficiencies translate to filtration performance in real buildings. The removal of particulate matter is only part of the filtration story. Filters also have a variety of secondary consequences including emissions of gas-phase compounds and complicated impacts on energy use. These effects need to be considered in overall considerations about filter use. However, some of these secondary effects may have a positive impact, including the ability of filters to offer insight on air quality through filter forensics, the analysis of the particles that accumulate on the filter. Several examples of filter forensics for disease surveillance, exposure assessment, and ambient air quality are used to illustrate the hidden value in used filters. The COVID-19 pandemic has further increased the attention paid to central and portable filtration in buildings and this presentation assesses new challenges and opportunities that arise from this renewed focus.