The Hazardous Air Pollutant Exposure Model, Version 5 (HAPEM5)

The HAPEM5 model has been designed to predict the "apparent" inhalation exposure for specified population groups and air toxics. Through a series of calculation routines, the model makes use of census data, human activity patterns, ambient air quality levels, climate data, and indoor/outdoor concentration relationships to estimate an expected range of "apparent" inhalation exposure concentrations for groups of individuals. Further technical details about the HAPEM model please refer to the 1996 NATA section on HAPEM4. Other exposure and risk models can be found at the FERA (Fate, Exposure, and Risk Analysis) Web site.

The Hazardous Air Pollutant Exposure Model, Version 5 (HAPEM5) includes a number of new features. Some of these new features are designed to provide exposure estimates that better characterize the variability across the population. Others provide more recent data for improved accuracy in exposure estimates. Several aspects of HAPEM5 have also been modified to make it easier to apply. These new features are summarized here, and detailed in other portions of this User's Guide.

• Microenvironment factors are now characterized with probability distributions instead of point estimates, to better reflect the variability found in measurement studies. Default files are provided for each of three categories of HAPs: gaseous, particulate, and semi-volatile.
• New algorithms have been added for creating annual average activity patterns from daily activity pattern data, using cluster analysis and a Markov chain selection process. These new algorithms require two new input files. Default files are provided.
• The default population file has been updated with 2000 US Census data.
• The final output file now lists many of the parameter settings used for the simulation to help with file tracking.
• The number of replicates to be simulated for each demographic group in each census tract is no longer hard-coded into the HAPEM module, but is specified by the user in the parameter file. This means the user no longer has to modify the HAPEM source code and re-compile it in order to change the number of replicates.
• The name of the parameter file is no longer hard-coded, but is specified by the user on the command line when a HAPEM5 module is run. This means the user no longer has to modify the source code and re-compile it in order to change the name of the parameter file.

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