Citation:

OZKAYNAK, H. A., T. PALMA, J. TOUMA, AND J. THURMAN. MODELING POPULATION EXPOSURES TO OUTDOOR SOURCES OF HAZARDOUS AIR POLLUTANTS. Journal of Exposure Science and Environmental Epidemiology . Nature Publishing Group, London, Uk, 18(1):45-58, (2008).

Impact/Purpose:

The primary objectives for this task are:

to assess the contribution of outdoor sources to total personal exposures for high priority air toxics and components of particulate matter (PM),

to identify the important microenvironments and human activities contributing to high exposures for these pollutants, and

to evaluate and refine model algorithms and inputs by incorporating new approaches and data, and modularizing model algorithms for application to multiple air pollutants (particles/gases).

Description:

Accurate assessment of human exposures is an important part of environmental health effects research. However, most air pollution epidemiology studies rely upon imperfect surrogates of personal exposures, such as information based on available central-site outdoor concentration monitoring or modeling data. This study evaluates the limitations of this conventional approach by examining the differences between modeled personal exposures and outdoor concentrations of over 30 gaseous and particulate hazardous air pollutants (HAPs) in the US. The analysis uses the results from an air quality dispersion model, ASPEN (Assessment System for Population Exposure Nationwide), and an inhalation exposure model, HAPEM (Hazardous Air Pollutant Exposure Model, Version 5), applied by the U.S. Environmental Protection Agency (EPA) during its 1999 National Air Toxic Assessment (NATA) for the US. Our results show that the total predicted chronic exposure concentrations of outdoor HAPs from all sources are lower than the modeled ambient concentrations, by about 20% on average for most gaseous HAPs, and by about 60% on average for most particulate HAPs (mainly, due to the exclusion of indoor sources from our modeling analysis and lower infiltration of particles indoors). On the other hand, the HAPEM/ASPEN concentration ratio averages for onroad mobile source exposures were found to be greater than 1 (around 1.20) for most mobile-source related HAPs reflecting the importance of near-roadway and commuting environments on personal exposures to air toxics. We conclude that the increase in personal exposures from the corresponding ambient levels tends to occur near locations where there are either major emission sources of HAPs or when individuals are exposed to either on- or non-road sources of HAPs during their daily activities. These findings have important implications for both the design and interpretation of results from air pollution health effects studies.

Record Details: