The Influences of Ambient Particle Composition and Size on Particle Infiltration in Los Angeles, CA, Residences

Abstract

Particle infiltration is a key determinant of the indoor concentrations of ambient particles. Few studies have examined the influence of particle composition on infiltration, particularly in areas with high concentrations of volatile particles, such as ammonium nitrate (NH 4 NO 3 ). A comprehensive indoor monitoring study was conducted in 17 Los Angeles-area homes. As part of this study, indoor/outdoor concentration ratios during overnight (nonindoor source) periods were used to estimate the fraction of ambient particles remaining airborne indoors, or the particle infiltration factor (F INF ), for fine particles (PM 2.5 ), its nonvolatile (i.e., black carbon [BC]) and volatile (i.e., nitrate [NO 3 Ϫ ]) components, and particle sizes ranging between 0.02 and 10 m. F INF was highest for BC (median ϭ 0.84) and lowest for NO 3 Ϫ (median ϭ 0.18). The low F INF for NO 3 Ϫ was likely because of volatilization of NO 3 Ϫ particles once indoors, in addition to depositional losses upon building entry. The F INF for PM 2.5 (median ϭ 0.48) fell between those for BC and NO 3 Ϫ , reflecting the contributions of both particle components to PM 2.5 . F INF varied with particle size, air-exchange rate, and outdoor NO 3 Ϫ concentrations. The F INF for particles between 0.7 and 2 m in size was considerably lower during periods of high as compared with low outdoor NO 3 Ϫ concentrations, suggesting that outdoor NO 3 Ϫ particles were of this size. This study demonstrates that infiltration of PM 2.5 varies by particle component and is lowest for volatile species, such as NH 4 NO 3 . Our results suggest that volatile particle components may influence the ability for outdoor PM concentrations to represent indoor and, thus, personal exposures to particles of ambient origin, because volatilization of these particles causes the composition of PM 2.5 to differ indoors and outdoors. Consequently, particle composition likely influences observed epidemiologic relationships based on outdoor PM concentrations, especially in areas with high concentrations of NH 4 NO 3 and other volatile particles. INTRODUCTIONBecause individuals spend Ͼ85% of their time indoors, 1 accurate assessment of the risks posed by particle exposures is dependent on our ability to characterize indoor concentrations of ambient particles. Key to this characterization is the assessment of particle infiltration indoors. Recent studies conducted under controlled conditions suggest that building design and operation, particle size, and particle composition are important factors influencing infiltration. 2,3 Studies of occupied homes, which allow for better generalization to real-world conditions than experimental studies, also indicate a strong influence of ventilation conditions and particle size on infiltration. 4 -6 However, relatively little data from occupied homes are available to examine the effect of particle composition on infiltration. 7-9 Moreover, these data are limited, lacking repeated sampling within each home, 7,9 particle size measurements, and, in partic...

Indoor/Outdoor Relationships, Trends, and Carbonaceous Content of Fine Particulate Matter in Retirement Homes of the Los Angeles Basin

“…F inf is typically highest for nonvolatile species such as EC. 27,28 To estimate F inf for OC, EC, PM 2.5 , and PN, two different techniques were used: an analysis of the indoor/outdoor concentration ratios and the recursive model (RM) developed by Allen et al 29 In the first approach, hourly indoor/outdoor ratios (I/O) for each particulate species were determined at times when no indoor particle sources, such as cooking or cleaning, were likely to be present (i.e., only I/O ratios Յ1 were considered). Daily F inf estimates were then obtained by averaging these segregated hourly I/O ratios.…”

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

“…At an AER of 0.45 h À1 , ambient particulate nitrate indoors was only 12% of its outdoor concentration; in contrast, F was 0.67 Outdoor and indoor concentrations of ambient PM 2.5 and the fraction of outdoor PM 2.5 that penetrates and persists indoors (F) for the scenarios described in Figure 1 and (Figure 3) are in agreement with the range of F values reported by several studies (F ¼ 0.32--0.8). 36 Sarnat et al 42 and Lunden et al 43 The model showed little sensitivity to changes in k dep with variations in species-specific size distributions across season and location; it was more sensitive to changes in P filter . The overall F value for scenario (a: NE composition) did not change when k dep values fit based on the Fresno species-specific size distributions were used rather than the New York City size distributions.…”

Application of a Diffusion Charger for the Measurement of Particle Surface Concentration in Different Environments

“…In general, d S increases both indoors and outdoors in the evening as the temperature drops, which, as argued earlier, is probably due to condensational growth of the particles at that time. However, the mean indoor diameter is always slightly lower than the outdoor (except between 3:00-5:00), which may be due to some particle evaporation as the aerosol is transported in the warmer indoor environment (Kuhn et al 2005;Lunden et al 2003;Sarnat et al 2006). For example, particulate compounds such as ammonium nitrate and organic species, which may account for 35-60% of outdoor PM 2.5 mass in the Los Angeles basin (Kim et al 2000;Tolocka et al 2001), volatilize as they entrain indoors (Lunden et al 2003).…”