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EVALUATION OF A PERSONAL NEPHELOMETER FOR HUMAN EXPOSURE MONITORING
Citation:
Rea, A W., F. Martin III, AND W J. Mitchell. EVALUATION OF A PERSONAL NEPHELOMETER FOR HUMAN EXPOSURE MONITORING. Presented at EPA/AWMA Symposium, Research Triangle Park, NC, September 12-14, 2000.
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:
Current particulate matter (PM) exposure studies are using continuous personal nephelometers (pDR-1000, MIE, Inc.) to measure human exposure to PM. The personal nephelometer is a passive sampler which uses light scattering technology to measure particles ranging in size from 0.1-10 um using a light scattering technique, however, it is more responsive to particles in the fine particle size range (0.3 - 2 um). While the data from the nephelometer remain semi-quantitative, the instrument is very useful for identifying activities and microenvironments that may significantly enhance human exposure to PM. Based on the use of this instrument in the field, we recognize that it is important to identify activities or environments that may have an adverse effect on the instrument's response and subsequent data quality. We have tested the nephelometers response to sample vest fabric (cotton/polyester or nylon), sampler location on an individual (shoulder vs. waist), and relative humidity. Repeated scripted activities while wearing a 50-50 cotton/polyester or a nylon vest indicated that significantly more particles (p < 0.01) were introduced by the cotton/polyester vest than the nylon vest. The location of the monitor was weakly significantly different (p < 0.1) for many common activities, and significantly higher particle readings were observed at the waist (p < 0.02) while sweeping. After being exposed to relative humidity levels ranging from 40% to 90% at 21o C and from 40% to 60% relative humidity at 32o C, monitors equilibrated with stationary monitors within 2 to 3 minutes. Recovery took 5 to 15 minutes at relative humidity ranging from 80% to 85% at 32o C. Some monitors had problems recovering after being exposed to 90% relative humidity (32o C). Although some activities appeared to affect the response of the nephelometer, they were easily identified and the overall data quality was not likely to be compromised.
This paper has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and administrative review policies and approved for presentation and publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.