Indoor-Outdoor Relationships and Infiltration Behavior of Elemental Components of Outdoor PM_2.5 for Boston-Area Homes

Abstract

In order to investigate the relationship between indoor and outdoor elemental concentrations and to characterize the infiltration behavior of elemental PM_2.5 constituents, we conducted an analysis of indoor and outdoor PM_2.5 elemental data collected during a comprehensive particle characterization study of nine nonsmoking homes in Boston, MA. Using data from nighttime periods when little or no particle-generating activity occurred, analyses focused on six elements that were consistently detected in both indoor and outdoor samples and that spanned a range of particle sizes: sulfur, nickel, zinc, iron, potassium, and silicon. Results showed that outdoor levels of all the elements were highly correlated with their corresponding indoor levels. Correlations remained high for different air exchange rate conditions, building characteristics, and seasons, suggesting that variability in ambient elemental infiltration into residences may not be a large source of variability affecting personal-ambient correlations for these elements. Elemental infiltration factors showed strong relationships with air exchange rate and season and were suggestive of an effect of particle size, which was likely obscured by remaining indoor source impacts. Analyses of this small dataset provided an indication that several elements—in particular nickel—could potentially serve as accurate tracers for infiltration of total PM_2.5 mass- and size-resolved particles into residential buildings. Similar to previously reported findings for sulfur, these elemental tracers showed the poorest performance for smaller and larger particle sizes.

Acknowledgments

This article is based upon a field study conducted as part of Christopher Long's doctoral thesis in the Department of Environmental Health at the Harvard School of Public Health. The authors would like to thank Petros Koutrakis and Helen Suh for their generous mentoring and sage guidance. The authors would also like to express their sincere gratitude to all of the study participants as well as to George Allen, Jim Sullivan, Mark Davey, Denise Belliveau, and Jessica Sekula for their invaluable assistance during field and laboratory work. The field component of this study was funded by the Center for Indoor Air Research (CIAR) under contract #96-08A, with support also from the U.S. EPA STAR Graduate Fellowship Program.

Notes

^a Indicates significance at the 0.05 level (p < 0.05).

^b As described in the text, I/O ratios > 1.15 have been removed.