A High end: is Means a person living at the centroid (center of the population mass) of a census tract and engaging in a range of activities (indoors and outdoors) that tend to produce higher exposures and risks than is typical. These activities were chosen to represent the 90th percentile of individuals, meaning 90\% of individuals are expected to engage in activities that put them at lower risk. It is important to bear in mind, however, that the full variation in exposures between individuals is not reflected in the current assessment, since all individuals are placed at the centroid of a census tract.