The types of exposure of interest are the instantaneous exposure and the cumulative exposure. The instantaneous exposure is the exposure at any time, t, and the cumulative exposure is the total or integrated exposure over the time of interest. The nature of the pollutant and the effects of the pollutant determine which type of exposure is more important.
Individual exposure is determined by the time spent at a given pollutant concentration. Therefore, it is a function of both the building concentration time history and the individual activity pattern--that is, where the individual is located at what time. Different activity patterns, for example, entering and leaving a building at different times or moving from one room to another, result in different exposures to the same building pollutant concentration time history. Sparks (12) discusses exposure modeling.
Calculation of exposure requires the pollutant concentration, the time exposed to the concentration, and (for inhalation exposure) the breathing rate and the volume per breath. The time exposed to the concentration depends on the individual activity pattern.
An activity pattern, in the context of the model, is defined by providing the time a person enters and leaves the various rooms of the building, or leaves the building for the outdoors. The model allows up to 10 room changes per day. The model is based on a 24-hour day. The activity patterns in the model repeat from day to day.
The model provides instantaneous exposure time plots and cumulative exposure time plots for individual activity patterns. The instantaneous exposure allows identification of high exposure situations and of the peak exposure.
While the model was designed to allow assessment of the impact of indoor air pollution sources and sinks and IAQ control options on individual exposure from specific activities, it can also be used to help estimate population exposures if data on population activity patterns are available. The model can be run for each activity pattern and then the results can be weighted according to the population statistics.