What are the steps in the national-scale assessment?
The national-scale assessment includes the following four major steps for assessing air toxics across the contiguous United States (also Puerto Rico and the Virgin Islands) for the 32 air toxics plus diesel particulate matter. • Compiling a 1996 national emissions inventory of air toxics emissions from outdoor sources. The types of emissions sources in the inventory include major stationary sources (e.g., large waste incinerators and factories), area and other sources (e.g., dry cleaners, small manufacturers, wildfires), and both onroad and nonroad mobile sources (e.g., cars, trucks, boats). EPA made some modifications to the 1996 National Toxics Inventory to prepare the emissions for computer modeling. See limitations in the emissions for more information about these modifications. • Estimating 1996 ambient air concentrations based on an air dispersion model (the ASPEN model) and 1996 emissions as input to the model. As part of this modeling exercise, EPA compared estimated ambient co
