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ESTIMATED HOURLY PERSONAL EXPOSURES TO AMBIENT AND NON-AMBIENT PARTICULATE MATTER AMONG SENSITIVE POPULATIONS IN SEATTLE, WASHINGTON
Citation:
Allen, R., L A. Wallace, T. Larson, L. Sheppard, AND L. S. Liu. ESTIMATED HOURLY PERSONAL EXPOSURES TO AMBIENT AND NON-AMBIENT PARTICULATE MATTER AMONG SENSITIVE POPULATIONS IN SEATTLE, WASHINGTON. JOURNAL OF AIR & WASTE MANAGEMENT ASSOCIATION 54(9):1197-1211, (2004).
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:
Epidemiological studies of particulate matter (PM) routinely use concentrations measured with stationary outdoor monitors as surrogates for personal exposure. Despite the frequently reported poor correlations between ambient concentrations and total personal exposure, the epidemiologic associations between ambient concentrations and health effects depend on the correlation between ambient concentrations and personal exposure to ambient-generated PM. This paper separates personal PM exposure into ambient and non-ambient components and estimates the outdoor contribution to personal PM exposures using continuous light scattering data collected from 38 subjects in Seattle, WA. Across all subjects, the average exposure encountered indoors at home was lower than in all other microenvironments. Cooking and being at school were associated with elevated levels of exposure. Previously published estimates of particle infiltration (Finf) were combined with time-location data to estimate an ambient contribution fraction ( 'a', mean = 0.66 +/- 0.21) for each subject. The mean 'a' was significantly lower for subjects monitored during the heating season (0.55 +/- 0.16) than during the non-heating season (0.80 +/- 0.17). Our modeled 'a' estimates agreed well with those estimated using the sulfur-tracer method (slope = 1.08; R2 = 0.67). We modeled exposure to ambient and non-ambient PM using both continuous light scattering and 24-hr gravimetric data and found good agreement between the two methods. On average, ambient particles accounted for 48% of the total personal exposure (range: 21-80%). The personal activity exposure was highly influenced by time spent away from monitored microenvironments. The median hourly longitudinal correlation between central-site concentrations and personal exposures was 0.30. Although both 'a' and the non-ambient sources influence the personal-central relationship, the latter seems to dominate. Thus, total personal exposure may be poorly predicted by stationary outdoor monitors, particularly among persons whose PM exposure is dominated by non-ambient exposures, e.g. those living in tightly sealed homes, those who cook, and children.
This work was funded by a cooperative agreement between the University of Washington and the U.S. EPA (#CR82717701)and by the Northwest Research Center for Particulate Air Pollution and Health (U.S. EPA grant #CR827355). It has been subjected to Agency review and approved for publication