ARB Research Seminar

This page updated July 26, 2013

Applying New Exposure Tools to ARB Efforts: Mobility-Based Exposure Modeling and Intake Fraction

Julian Marshall, Ph.D., School of Occupational and Environmental Hygiene, University of British Columbia

January 30, 2006
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA



This presentation will explore two recently developed tools for estimating population exposure to air pollution and their relevance to ARB efforts.

  1. Intake fraction, a metric that summarizes the emission-to-inhalation relationship, facilitates comparisons among sources in terms of their exposure potential. Intake fraction may be useful in prioritizing emission reductions, and in estimating the health benefit attributable to emission reductions. For a given emission source and pollutant, intake fraction is the fraction of emissions that are inhaled (i.e., the cumulative mass inhaled by the exposed population divided by the cumulative emissions). One way to estimate the environmental health impact of a pollution source or source class is as the product of three terms: emission rate (mass per time), intake fraction (mass inhaled per mass emitted), and toxicity (health impact per mass inhaled). I will present intake fraction results for motor vehicle emissions in urban environments. Urban-scale intake fraction values determined using several methods are consistent with each other, and values are approximately constant over time, suggesting that intake fraction is a robust and reliable exposure assessment metric.
  2. Air pollution exposures are estimated for ~25,000 individuals in Los Angeles based on their activities and location (latitude and longitude) throughout the day. Exposure concentrations are modeled as individuals change microenvironment (outdoors, in a residence, in a non-residential building, and in-vehicle) and location throughout the urban area (for work, shopping, etc.). Use of Census data in an exposure assessment implicitly assumes that people stay at home all day. For most individuals, the impact of this assumption on model-estimated exposures is less than a factor of 2. The mobility-based approach provides improved exposure estimates, which can be used in environmental epidemiological studies.

Both tools - intake fraction and the mobility-based exposure model - are useful for understanding how exposure levels vary with demographic attributes such as income and ethnicity.

Speaker Biography

Julian Marshall is a researcher in the School of Occupational and Environmental Hygiene at University of British Columbia. Dr. Marshall's research focuses on population exposure to air pollution, especially transportation emissions. Specific investigations have explored the role of urban planning in reducing exposures, environmental impacts of transportation in developing versus developed countries, and use of exposure analyses in setting environmental policy. His current air pollution exposure research is part of an epidemiological study on adverse birth outcomes in Vancouver, British Columbia. His graduate degrees (MS, PhD) are from the Energy and Resources Group at UC Berkeley, and his undergraduate degree (BSE) is in Chemical Engineering from Princeton University. He has professional experience in air quality modeling and health risk assessment in the Bay Area, as a chemical engineering lecturer in Singapore, and in environmental development work in India.

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