What are the Results of the Variability Analysis?
The national-scale assessment produced hundreds of millions of estimates of ambient air concentration, exposure and risk. There were estimates of all three of these quantities for each of the air toxics compounds and for each of more than 61,000 census tracts. This can be an overwhelming amount of information, and so it has been organized here to address some of the most important questions that might be asked about variability of these quantities across geographic regions. This organization is into three levels of detail: County level. The results from separate census tracts in a county have been combined to provide estimates of ambient air concentration and exposure in each county (risks are considered only at the national scale discussed below). This was done by taking the median ambient air concentration and average exposure for all census tracts in a county. This provides an understanding of how these average quantities vary between counties. The maps that have been produced allow
