Advancing Approaches to Estimate Deposition Loss Rate Constants and Penetration Factors for Fine and Ultrafine Particles into Residences

SAEED FARHOODI, Haoran Zhao, Mohammad Heidarinejad, Brent Stephens, Illinois Institute of Technology

     Abstract Number: 123
     Working Group: Indoor Aerosols

Abstract
Much of human exposure to fine and ultrafine particulate matter of outdoor origin occurs inside buildings, particularly in residences. The penetration factor of those pollutants through leaks in a building’s exterior enclosure assembly is a key parameter that governs their infiltration and persistence. However, experimental data for particle penetration factors in real buildings remain limited. In previous studies, we have sought to improve methods to measure envelope penetration factors for PM2.5 and ultrafine particles (UFPs) in residences under infiltration conditions, but have been constrained by challenges in accurately estimating indoor deposition loss rate constants, which are key to informing estimates of penetration factors. Here we revisit data collected from 22 existing homes in Chicago, IL USA in which an instrumentation system that combined a scanning mobility particle sizer and optical particle sizer connected to an automatic switching system was deployed alongside a procedure to naturally elevate indoor concentrations near ambient levels and allow concentrations to decay towards background levels to allow for estimating loss rate constants and penetration factors from the resulting time-resolved data. The method was originally deployed in a variety of both single-family and multi-family homes with a range of vintages and building envelope characteristics (e.g., airtightness), as well as in a subset of homes before and after energy efficiency retrofits (e.g., air sealing and insulation). In revisiting this dataset, we have developed an algorithmic searching method to systematically scan potential values for initial and background (i.e., peak and valley) concentrations and identify likely values and ranges for deposition loss rate constants, which are then used in estimation of penetration factors using a regression approach with a discretized mass/number balance on indoor particles of outdoor origin. When applied to a total of 34 home visits with a mean (SD) estimated air change rate of 0.47 (0.40) per hour, preliminary estimates of mean (SD) total indoor loss rate constants (deposition + air change rate) were 0.65 (0.25) per hour for PM2.5 and 1.03 (0.40) per hour for total UFPs, and mean (SD) penetration factors were 0.75 (0.52) for PM2.5 and 0.68 (0.36) for total UFPs. Failure rates to resolve both parameters were on the order of approximately 20%.