HAPEM5 calculates microenvironmental concentrations of HAPs in 37 indoor, outdoor, and invehicle microenvironments (MEs). HAPEM5 uses HAP-specific ME factors (MEFs) to account for the contribution of indoor sources and ambient HAP concentrations to pollutant levels in the MEs.

The memorandum describes the development of MEF distributions for the two factors relating to ambient concentrations: the penetration factor (PEN) and the proximity factor (PROX).

• Memorandum: Development of Penetration and Proximity Microenvironment Factor Distributions for the HAPEM5 in Support of the 1999 National-Scale Air Toxics Assessment (NATA) April 5, 2004 (PDF)(22 pp, 70 K)