ARB Research Seminar

This page updated June 19, 2013

Rethinking Exposure Assessment Using Dose Fractions

William W Nazaroff Ph.D., Department of Civil and Environmental Engineering, University of California, Berkeley

May 23, 2001
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA



A key step in assessing human health risks from air pollutant emissions is evaluating pollutant transport from sources to receptors. Conventionally, this step employs modeling techniques with substantial data requirements. This presentation will discuss the concept of dose fractions for describing source-to-receptor relationships. The concept facilitates comparing the exposures to pollutant emissions released from different sources or under different circumstances. Using dose fractions, preliminary health risk assessments for air pollutant sources can be more easily conducted. Further advances could assist in the development of control strategies that more efficiently reduce human exposure to air pollutants.

In the context of this presentation, dose fraction is defined as pollutant mass inhaled by an exposed individual per unit pollutant mass emitted from a source. A cumulative population dose fraction is also defined to describe the total fraction of an emitted pollutant inhaled by all members of the exposed population. Typical population dose fractions for an urban area from emissions outdoors are ~10 to the 6th to ~10 to the 3rd. Population dose fractions associated with emissions in buildings or in moving vehicles are typically much higher, ~10 to the 3rd to ~10 to the 1st .

As an illustration of the concept, magnitude estimates are developed of the exposure in the South Coast Air Quality Management District to 14 pollutants from motor vehicles and environmental tobacco smoke (ETS). For acetaldehyde and PM2.5, population doses from ETS exceed those from cars by about an order of magnitude. These two source classes cause comparable population doses for acrolein, benzo(a)pyrene, 1,3-butadiene, formaldehyde, and styrene. Motor vehicles dominate ETS as a source of exposure to BTEX compounds (benzene, ethylbenzene, toluene, and xylenes) and carbon monoxide. Ongoing work aims to refine our estimates of dose fractions from motor vehicles. We will begin work in the fall on applying the dose fraction to explore the environmental health impact of distributed electricity generation.

Speaker Biography

William W Nazaroff - is the Roy W. Carlson Distinguished Professor of Civil and Environmental Engineering at the University of California, Berkeley. His research group addresses two main themes: (a) physics and chemistry of indoor air pollutants; and (b) understanding and controlling air pollutant exposures. He serves as associate editor of Journal of the Air & Waste Management Association and on the editorial board of Indoor Air. Other current activities include serving on the National Research Council's Committee on Air Quality in Passenger Cabins of Commercial Aircraft and as co-chair of a US delegation for a bilateral US-Italy workshop on New Technologies and Cultural Heritage. He is coauthor of a recently published textbook (Environmental Engineering Science, Wiley, 2001). Professor Nazaroff has been a member of theResearch Screening Committee of CARB since January 2000.

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