Research Projects

Project at a Glance

Project Status: complete

Report Published May 2002:


Title: Update and refinement of an indoor exposure assessment methodology.

Principal Investigator / Author(s): Arlene S. Rosenbaum

Contractor: ICF Consulting

Contract Number: 98-327


Research Program Area: Health & Exposure

Topic Areas: Indoor Air Quality


Abstract:

The primary mission of the ARB Indoor Program is to identify and reduce Californians' exposures to indoor pollutants. To fully consider indoor exposures in assessing risk, the ARB needs estimates of average and peak indoor exposures for the general California population as well as certain subgroups of that population such as individuals who may be highly sensitive to indoor pollutants. The model described in this document--California Population Indoor Exposure Model, Version 2 (CPIEM 2.0)--is a software product that has been designed to expedite the exposure-assessment process by providing a user interface and calculation tools for supplying and integrating all required information. It is an enhanced version of the original CPIEM 1.4F released by ARB in 1998.


Enhancements include greatly improved ease of use through a Windows interface, superior graphic outputs, an updated default database, as well as enhanced and new calculation capabilities, including uncertainty analysis. The CPIEM is a software tool that combines:

• Air pollutant concentration distributions for several microenvironments, including outdoors, and
• Population activity patterns that specify time spent in each microenvironment in a Monte Carlo framework to predict distributions of exposure concentrations for the California population. The default databases of microenvironment concentration distributions and activity patterns are specific to California, but the model allows the user to easily add his or her own data as well.

For many air pollutants, the indoor concentration data are either sparse or nonexistent. To address this limitation, and to provide a means of evaluating hypothetical exposure reduction activities, the CPIEM also includes a mass-balance algorithm so that the user can estimate indoor concentration distributions based on distributional information for parameters such as indoor source emission rates, building volumes, and air exchange rates.

The Windows platform of this new version of CPIEM greatly improves the software’s efficiency and ease of use with standard, easily understood drop-down menus and dialogue boxes. The graphic outputs are presentation quality. Scenarios are easily saved and edited to facilitate sensitivity analysis. The default databases have been updated with more recent data on indoor and outdoor pollutant concentrations, mass-balance parameters, and the demographic composition of California’s population.

The exposure distributions predicted by CPIEM reflect the variability of exposure concentrations across population groups, but not our uncertainty about them. A new supplementary software program, designed to be used in conjunction with the new CPIEM, facilitates the estimation of the uncertainty of these exposure distributions. The uncertainty supplement creates alternative distributions for the CPIEM input variables with Monte Carlo sampling to reflect our uncertainty about the parameters of the input distributions. The user provides each alternative to CPIEM for iterative simulations. At the conclusion of the simulations of the alternatives the uncertainty supplement combines the resulting exposure distributions to estimate uncertainty distributions for selected percentile values. Other enhancements to the CPIEM capabilities include refinement of the pollutant removal process calculation in the mass-balance algorithm, and additional output metrics.


 

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