Field measurements of fine and ultrafine particle penetration factors in Chicago residences

Abstract

Much of human exposure to fine and ultrafine particulate matter of outdoor origin occurs inside buildings, particularly in residences. The penetration factor of particles through leaks in a building’s exterior enclosure assembly is a key parameter that governs their infiltration and persistence (i.e., infiltration factor). Yet, experimental data for particle penetration factors in real buildings remain limited. Here we describe targeted field experiments to measure fine (PM_2.5) and ultrafine particle (UFP) deposition loss rate constants (k) and penetration factors (P) from time-resolved data in a variety of single-family and multi-family homes in Chicago, IL USA with a range of vintages and building envelope characteristics. A grid-search-based algorithmic method was developed to estimate k and associated uncertainty; a discretized linear regression was used to estimate P. Mean (SD) estimates of P in 18 housing units from the Chicago building stock with doors and windows closed were 0.63 (0.16) for PM_2.5 (ranging 0.34–0.90; mean ± SD uncertainty: 19±10%) and 0.62 (0.20) for UFP (ranging 0.24–0.94; mean ± SD uncertainty: 9±6%). In a subset of experiments conducted in 9 homes both before and after receiving energy efficiency retrofits (e.g., air sealing and insulation, with mean envelope leakage decreasing only ∼16%), there were no significant differences in estimates of P for either PM_2.5 or UFP. Parameter estimates were robust and not sensitive to several potential sources of bias. Estimates of P were not strongly associated with any building leakage characteristics, suggesting that P may not be easily predicted from simpler measures.