Indoor air quality (IAQ) is determined by the interactions of sources, sinks, and air movement between rooms and between the building and the outdoors. Sources may be located in rooms, in the heating, ventilation, and air-conditioning (HVAC) system, or outdoors. There may be sinks (i.e., materials that adsorb indoor pollutants) in the same locations. Sinks may also act as sources by re-emitting the pollutants collected in them. Individual exposure to pollutants from indoor sources is determined by the combination of indoor pollutant concentrations and individual activity patterns. Several models have been developed to analyze the IAQ impacts of all these factors.
RISK (1) is the third in a series of indoor air quality (IAQ) models developed by the Indoor Environment Management Branch of U. S. EPA's National Risk Management Research Laboratory. The first model, INDOOR (2), was designed to calculate the indoor pollutant concentrations from indoor sources. The second model, EXPOSURE (3), extended INDOOR to allow calculation of individual exposure. RISK extends EXPOSURE to allow analysis of individual risk to indoor pollutant sources. The three models were all developed as tools to carry out the mission of the engineering portion of the EPA's indoor air research program "To provide tools necessary to reduce individual exposure and risk to indoor air pollutants."
The three models reflect the status of EPA source and sink characterization research at the time the models were written. RISK includes new empirical source models and mass-transfer-based source models in addition to the common first order decay source models used in previous models. The mass-transfer-based source models are particularly useful for gas-phase-limited mass-transfer situations. RISK is the first version of the IAQ model designed for the Windows operating environment
RELATIONSHIP BETWEEN MODELING AND SOURCE CHARACTERIZATION
The role of the model relative to source characterization can be in Figure 1. Data related to source characterization are developed as part of EPA's indoor air source characterization program. These data are used to develop source emission models that are used in this IAQ model. The source models are updated whenever new information is developed by the source characterization research program.