Human Exposure Modeling - Databases to Support Exposure Modeling

Human Activity Pattern Data

Most human exposure models require human activity pattern data as an input. An activity pattern is a series of discrete events of varying time intervals describing an individual's lifestyle and routine when moving through different microenvironments. EPA ORD's National Exposure Research Laboratory (NERL) maintains the Consolidated Human Activity Database (CHAD). CHAD contains data obtained from pre-existing human activity studies that were collected at city, state, and national levels (currently about 22,000 days of human activity are included in CHAD). CHAD is intended to be an input file for exposure/intake dose modeling and/or statistical analysis. To access CHAD go to: /healthresearch/consolidated-human-activity-database-chad-use-human-exposure-and-health-studies-and-predictive-models

Microenvironmental Factors

Microenvironments (ME) are generally described as a small space in which human contact with a pollutant takes place, and which can be treated as a well-characterized, relatively homogenous location with respect to pollutant concentrations for a specified time period. ME include indoors at home, school, work, inside an automobile or bus, outdoors, etc. For some of EPA's exposure models (e.g., HAPEM4, APEX), the approach to estimating concentrations wthin various ME is to use a "factors" approach. Detailed information on the ME factor approach and estimated values for 33 air toxics can be found at:

Commuting Database for Workers

Several of EPA's exposure models account for commuting between home and work. A national database containing commuting pattern data was derived from a special U.S. 1990 census database that specifies for each census tract the number of residents that work in each tract (i.e., the population associated with each home tract/work tract pair). This database has been adjusted to reflect 2000 Census tract definitions.

Population and Demographic Databases

The U.S. Census Bureau is the primary source of most population demographic data used in EPA's exposure models. The Census collects information on where people live, their demographic makeup (e.g., age, gender, ethnic group), and employment. Most of EPA's exposure models use U.S. Census data reported at the spatial resolution of census tracts, which are small, relatively permanent statistical subdivisions of a county. Census tracts usually contain between 2,500 and 8,000 residents. The current population/demographic file containing the year 2000 tract-level Census counts, tract locations, national \ employment probabilities by age are available on the TRIM.ExpoInhalation APEX Download Page.

Air Exchange Rate Databases for residential, motor vehicles and other indoor microenvironments

The most extensive air exchange rate database for U.S. residences is based on data collected by Brookhaven National Laboratory (BNL) for four seasons in four regions of the U.S. Lognormal distributions by season and region are presented in "Residential Air Exchange Rates in the United States: Empirical and Estimated Parametric Distributions by Season and Climatic Region" Murray, D.M. and D.E. Burmaster, 1995 Risk Analysis, Vol. 15, No. 4, 459-465. Currently, there are no national databases for air exchange rate data for motor vehicles or other indoor microenvironments. Information on distributions of air exchange rates used by OAQPS in its past exposure modeling efforts for residential, non-residential, and vehicle microenvironments can be found in Sections 6.3 and 6.4 of "A Guide to Selected Algorithms, Distributions, and Databases Used in Exposure Models Developed By the Office of Air Quality Planning and Standards"

Ambient Air Quality Data

EPA's Air Quality System (AQS) contains ambient air pollution data collected by EPA, state, local, and tribal air pollution control agencies from thousands of monitoring stations. AQS also contains meteorological data, descriptive information about each monitoring station (including its geographic location and its operator), and data quality assurance/quality control information. To obtain ambient air quality data and related meteorological data maintained in EPA's AQS that can be used as an input to human exposure models, go to: /aqs

Air Quality Modeling

To obtain air quality models and related information which can be used to estimate ambient air quality concentrations based on emissions data and meteorological information that can be used as an input to human exposure models, go to the EPA Support Center for Regulatory Atmospheric Modeling (SCRAM) website.

Human Exposure Measurements

EPA ORD's National Exposure Research Laboratory (NERL) maintains a Human Exposure Database System (HEDS). HEDS is an integrated database system that contains chemical measurements, questionnaire responses, documents, and other information related to EPA research studies of the exposure of people to environmental contaminants. To access HEDS, go to: