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Exposure Research

Additional Information on EMI

Background
The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to public health - known as primary standards - including the health of sensitive populations such as asthmatics and children. According to the Clean Air Act, primary standards for the six principal pollutants - known as criteria pollutants - must be based on sound science that often uses air pollution health studies to understand the relationship between individual exposures and health outcomes. According to the National Research Council report on epidemiology and air pollution, discrepancies in data collection from health study participants can result in uncertainty and bias to risk estimates.

The Exposure Model for Individuals (EMI) is expected to:

  • Provide better understanding of linkages between ambient concentrations and individual exposures;
  • Identify key exposure factors to optimize the design of health studies;
  • Characterize and reduce uncertainty of individual exposure predictions for air pollutants associated with adverse cardiovascular and respiratory effects in sensitive individuals; and
  • Demonstrate how individual exposure estimates can help develop more accurate, cost-effective, and less burdensome exposure metrics for epidemiologic analysis in cohort health studies.

EMI is being developed, evaluated, and applied by EPA, the University of Michigan, Harvard University, Applied Research Associates, the German Research Center for Environmental Health, and the National Children’s Study.

Plans for EMI development
Development and evaluation of EMI is ongoing. To support various health studies, initial development of EMI is focusing on estimating exposure to PM2.5, as summarized in an EMI presentation. To support future health studies, EMI will be expanded for multiple pollutants - including nitrous oxides, carbon monoxide, and black carbon which support a near roadway asthmatic health study in Detroit.

Exposure Metrics for Individuals in Health Studies
EMI provides multiple tiers of individual-level exposure metrics with different levels of complexity and information needs.

EMI tiers high resol

The four primary metrics listed from least to most complex are: (1) building air exchange rates, (2) indoor concentrations, (3) personal exposures, and (4) dose. Alternative metrics include time spent and activity level in specific microenvironments, and concentration during high activity levels. These exposure metrics are used for epidemiological analysis in health studies with individual health outcomes.

EMI & Microenvironment Tracker (MicroTrac)
EMI uses a microenvironment tracker (MicroTrac) for its time-location-activity module. MicroTrac utilizes personal GPS data loggers and novel algorithms to determine time spent in microenvironments as specified by EMI. MicroTrac will provide time-location data with improved spatial and temporal resolution, and accuracy with reduced participant burden, as compared to time location diaries.

Development of MicroTrac is ongoing. Technical capabilities of the GPS data loggers are being characterized to make recommendations to health studies. MicroTrac initiated the use of GPS data loggers into the design of a near roadway asthmatic health study in Detroit. The algorithms needed to map GPS-derived locations into the specific microenvironments used by EMI are also being developed and evaluated with time-location diaries before MicroTrac is applied to health studies. More on MicroTrac

Model Evaluation
EMI estimates will be evaluated using questionnaires and measurements from data-rich exposure field studies. Data from these studies - including criteria air pollutants and air exchange rates - will be tested against data collected with EMI. Field studies include:

Related Publications

  • Breen M.S., Schultz B., Sohn M., Long T., Langstaff J., Williams R., Isaacs K., Meng Q., Stallings C., Smith L. A Review of Air Exchange Rate Models for Air Pollution Exposure Assessments. J Expo Sci Environ Epidemiol. 2013 doi:10.1038/jes.2013.30.
  • Vette A., Burke J., Norris G., Landis M., Batterman S., Breen M., Isakov V., Lewis T., Gilmour M., Kamal A., Hammond D., Vedantham R., Bereznicki S., Tian N., Croghan C. The Near-Road Exposures and Effects of Urban Air Pollutants Study (NEXUS): Study Design and Methods. Sci Total Environ. 2012.
  • Breen M. S., Breen M., Williams, R. W., Schultz, B. D. (2010). Predicting residential air exchange rates from questionnaires and meteorology: model evaluation in central North Carolina. Environ. Sci. Technol., 44, 9349-9356. publication and supporting information.
  • Burke, J., M. Zufall, H. Özkaynak (2001) A population exposure model for particulate matter: Case study results for PM2.5 in Philadelphia, PA. J Exp Anal Environ Epidemiol., 11, 470-489.

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