How Does Infiltration Behavior Modify the Composition of Ambient PM 2.5 in Indoor Spaces? An Analysis of RIOPA Data (original) (raw)

2007, Environmental Science & Technology

The indoor environment is an important venue for exposure to fine particulate matter (PM 2.5 ) of ambient (outdoor) origin. In this work, paired indoor and outdoor PM 2.5 species concentrations from three geographically distinct cities (Houston, TX, Los Angeles County, CA, and Elizabeth, NJ) were analyzed using positive matrix factorization (PMF) and demonstrate that the composition and source contributions of ambient PM 2.5 are substantially modified by outdoor-to-indoor transport. Our results suggest that predictions of "indoor PM 2.5 of ambient origin" are improved when ambient PM 2.5 is treated as a combination of four distinct particle types with differing infiltration behavior (primary combustion, secondary sulfate and organics, secondary nitrate, and mechanically generated PM) rather than as a "single internally mixed entity." Studywide average infiltration factors (i.e., fraction of ambient PM 2.5 found indoors) for Relationship of Indoor, Outdoor, and Personal Air (RIOPA) study homes were 0.51, 0.78, and 0.04 (consistent with P ) 0.6, 0.9, and 0.09; k ) 0.2, 0.1, and 0.6 h -1 ) for PM 2.5 associated with primary combustion, secondary formation (excluding nitrate), and mechanical generation, respectively. Modification of the composition, properties, and source contributions of ambient PM 2.5 in indoor environments has important implications for exposure mitigation strategies, development of health hypotheses, and evaluation of exposure error in epidemiological studies that use ambient central-site PM 2.5 as a surrogate for PM 2.5 exposure.