Using Time- and Size-Resolved Particulate Data To Quantify Indoor Penetration and Deposition Behavior

Abstract

Because people spend approximately 85-90% of their time indoors, it is widely recognized that a significant portion of total personal exposures to ambient particles occurs in indoor environments. Although penetration efficiencies and deposition rates regulate indoor exposures to ambient particles, few data exist on the levels or variability of these infiltration parameters, in particular for time- and size-resolved data. To investigate ambient particle infiltration, a comprehensive particle characterization study was conducted in nine nonsmoking homes in the metropolitan Boston area. Continuous indoor and outdoor PM2.5 and size distribution measurements were made in each of the study homes over weeklong periods. Data for nighttime, nonsource periods were used to quantify infiltration factors for PM2.5 as well as for 17 discrete particle size intervals between 0.02 and 10 microns. Infiltration factors for PM2.5 exhibited large intra- and interhome variability, which was attributed to seasonal effects and home dynamics. As expected, minimum infiltration factors were observed for ultrafine and coarse particles. A physical-statistical model was used to estimate size-specific penetration efficiencies and deposition rates for these study homes. Our data show that the penetration efficiency depends on particle size as well as home characteristics. These results provide new insight on the protective role of the building shell in reducing indoor exposures to ambient particles, especially for tighter (e.g., winterized) homes and for particles with diameters greater than 1 micron.

Particulate matter and polycyclic aromatic hydrocarbon concentrations in indoor and outdoor microenvironments in Boston, Massachusetts

“…For ultrafine particulate matter, indoor concentrations were generally lower than outdoor levels if indoor sources were not present, but cooking activities led to substantial increases in concentrations. The lower indoor -outdoor ratios for ultrafine particles, when compared with PM 2.5 , are supported by past studies ( Long et al, 2001 ) and can be related to greater depositional losses from diffusion and lower penetration rates (Mosley et al, 2001 ). Specific cooking activities have been implicated in elevated ultrafine concentrations in residential settings (e.g., Abt et al, 2000b;Wallace, 2000 ), the effect of which is magnified in a food court with numerous grills.…”

Relationship between indoor and outdoor levels of fine particle mass, particle number concentrations and black smoke under different ventilation conditions

“…As shown by , the particle NC is dominated by the ultrafine fraction (with diameter smaller than 100 nm). Since particles smaller than 100 nm were found to have higher deposition rates, more likely coarse-mode particles than accumulation-mode particles (Lai and Nazaroff, 2000;Long et al, 2001), we expect lower I/O ratios for BS and NC in comparison with PM 2.5 . Moreover, the penetration factors for all particles sizes o500 nm were determined to be less than unity (Vette et al, 2001).…”

Variability in the fraction of ambient fine particulate matter found indoors and observed heterogeneity in health effect estimates

“…13 As a result, exposure to ambient PM 2.5 mostly occurs in the indoor environment and, specifically, within the residence. Importantly, the fraction of ambient PM 2.5 that penetrates and persists indoors (F) varies temporally 14 and spatially, 15 and is different for different components of the PM 2.5 mixture. 16 Exposure metrics that rely on central site concentrations do not account for this variability, nor do they account for changes in PM 2.5 properties (i.e., composition and size distribution) that result from outdoor-toindoor transport.…”