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Grantee Research Project Results

Grantee Research Project Results

Refined Ambient PM2.5 Exposure Surrogates That Account for Outdoor-to-Indoor Transport and Their Application in Epidemiology Studies

EPA Grant Number: FP917336
Title: Refined Ambient PM2.5 Exposure Surrogates That Account for Outdoor-to-Indoor Transport and Their Application in Epidemiology Studies
Investigators: Hodas, Natasha
Institution: Rutgers University - Camden
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: September 1, 2011 through August 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011)
Research Category: Academic Fellowships , Fellowship - Human Health: Public Health Sciences



Because people spend most of their time indoors, exposure to ambient fine particulate matter (PM2.5) mostly occurs in the indoor environment. Exposure estimates that take into account the modification of the chemical and physical properties of PM2.5 with indoor transport are important for understanding and mitigating health effects associated with PM2.5 exposure. This research aims to improve models of outdoor-to-indoor transport of PM2.5 to reduce exposure error in air pollution epidemiology studies.


The Aerosol Penetration and Persistence (APP) Model describes the indoor concentrations of the major chemical components of ambient PM2.5 as functions of their outdoor concentrations, residential air exchange rates, particle losses indoors due to deposition, and in the case of nitrate, indoor losses resulting from evaporation. Particle composition is taken into account in the APP model through the use of chemical-speciesspecific deposition rates and by accounting for the semivolatile nature of particulate nitrate. Deposition rates are functions of particle size and can be predicted from chemically resolved PM2.5 size distribution data. In this work, geographicregionspecific deposition rates will be determined from chemically resolved size distribution data from geographically diverse locations across the United States. The treatment of particulate organic carbon (OC) in the APP model also will be addressed in this research. Currently, particulate organic carbon (OC) is treated as nonvolatile. However, there is evidence that phase changes of organics following indoor transport have a large impact on the fraction of ambient OC that penetrates and persists indoors. A substantial database exists characterizing the volatility distribution of ambient organic particulate matter. This, in combination with gas-particle partitioning theory, will be used to simulate the gas-particle partitioning behavior of particulate OC in indoor air.

Expected Results:

The research tool developed in this project can be used to identify geographic locations, seasons and temporal and spatial scales for which outdoor-to-indoor transport of ambient PM2.5 is (or is not) a substantial source of exposure error in air pollution epidemiology. It also will provide a method to predict the indoor concentrations and characteristics of ambient PM2.5 in indoor air from readily available data. The development of modeling tools to accomplish this will enable such refined exposure surrogates to be used in large epidemiological studies.

Potential to Further Environmental / Human Health Protection

This research advances existing models of PM2.5 exposure, develops and evaluates a new method for estimating organic PM2.5 exposure, and seeks to address disparities in exposure error for vulnerable populations. Because the fraction of outdoor-generated PM2.5 that penetrates and persists indoors differs for homes above and below the poverty line, as well as with source proximity, this work especially is important for reducing exposure error for populations in urban areas and with low socio-economic status. The refined exposure surrogates developed in this work have the potential to improve understanding of the health effects associated with PM2.5 exposure and will aid in the development of successful exposure mitigation strategies.

Supplemental Keywords:

indoor air quality, particulate matter, exposure

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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