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INDOOR-OUTDOOR-PERSONAL RELATIONSHIPS OF SELECTED FINE PARTICLE TRACE ELEMENTS IN SEATTLE, WA
Citation:
Larson, T. V., L. S. Liu, R. Allen, AND J Lewtas. INDOOR-OUTDOOR-PERSONAL RELATIONSHIPS OF SELECTED FINE PARTICLE TRACE ELEMENTS IN SEATTLE, WA. Presented at International Society of Exposure Analysis 2002 Conference, Vancouver, Canada, August 11-15, 2002.
Impact/Purpose:
The primary study objectives are:
1.To quantify personal exposures and indoor air concentrations for PM/gases for potentially sensitive individuals (cross sectional, inter- and intrapersonal).
2.To describe (magnitude and variability) the relationships between personal exposure, and indoor, outdoor and ambient air concentrations for PM/gases for different sensitive cohorts. These cohorts represent subjects of opportunity and relationships established will not be used to extrapolate to the general population.
3.To examine the inter- and intrapersonal variability in the relationship between personal exposures, and indoor, outdoor, and ambient air concentrations for PM/gases for sensitive individuals.
4.To identify and model the factors that contribute to the inter- and intrapersonal variability in the relationships between personal exposures and indoor, outdoor, and ambient air concentrations for PM/gases.
5.To determine the contribution of ambient concentrations to indoor air/personal exposures for PM/gases.
6.To examine the effects of air shed (location, season), population demographics, and residential setting (apartment vs stand-alone homes) on the relationship between personal exposure and indoor, outdoor, and ambient air concentrations for PM/gases.
Description:
The overall goal of this work is to better understand not only the sources of outdoor PM but also the sources that contribute to personal PM exposures. This paper summarizes the results of x-ray fluorenscence (XRF) analysis on 24-hr PM2.5 samples collected both inside and outside the homes of subjects participating in a larger study characterizing PM exposures and examining the health consequences of PM2.5 exposures. Here we report the results for 238 indoor/outdoor pairs taken between Autumn 2000 and Autumn 2001. Of the 33 elements examined via XRF, 18 had median values above their detection limits (Al, Si, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, As, Br, Sn, Ba and Pb). Of these latter species, only five had 75th percentile indoor-outdoor ratios less than one (S, K, V, Fe, and Pb); in contrast, six had corresponding ratios above 1.5 (Al, Si, Cl, Ca, Cr, Cu) indicating significant contributions from indoor sources for most elements. The correlations between indoor and outdoor levels were examined by performing a factor analysis on each of the 238 indoor samples and comparing these factor scores with those obtained from a similar analysis of the corresponding 238 outdoor samples. Three features with eigenvalues >1 were extracted from the outdoor samples. These included: 1) a soil-like feature exhibiting high correlations between Al, Si, Ca, Fe, and Ti; 2) a feature driven by high correlations between S, K, Cu, Zn, As and Se; and 3) a separate Mn/Br/Pb feature. Interestingly, three similar features were extracted independently from the corresponding indoor samples. Feature #2 was most strongly associated with PM2.5 mass in both indoor and outdoor samples (R2=0.88). It is premature at this time to attribute feature #2 and #3 to specific source categories. However, in an effort to uncover more correlated features, we are currently extending these analyses to encompass additional analytes, including temperature resolved particulate carbon measurements that are available for all these indoor-outdoor pairs. In addition, XRF results from personal samples will be included in the analysis for identifying sources attributed to personal PM2.5 exposures. We also plan to compare the above results with those obtained using two alternative multivariate models, partial least squares and 3-D positive matrix factorization.
This work has been funded wholly by the United States Environmental Protection Agency under EPA Cooperative Agreement number (#R82717701) and the EPA/UW Northwest Center for Particulate Matter and Health (R-827355-01-0). It has been subjected to Agency review and approved for publication