Although a tier must be run before preceding to later tiers, the system allows the models to be rerun at the user's discretion. For example, users may run the National model using either BLS or WEFA forecasts before performing regional modeling on the last national model run. E-GAS is designed such that growth factor projection scenarios for each nonattainment area and attainment portion of States can be made using a common assumption about future U.S. economic activity. The National economic forecasts in E-GAS can provide a common forecast with which to forecast regional economic growth. The nature of ozone formation requires attention to be paid to the location as well as the level of economic activity.
National forecasts provide estimates of total economic activity.
The regional model will distribute this activity among U.S. urban areas, States, and regions. The spatial characteristics of the regional forecasts are designed to meet the needs of the photochemical models used by ozone nonattainment areas.