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Emissions Modeling Clearinghouse

Emission projections refers to extrapolating baseline emission estimates to predict future emissions based upon expected future activity levels and emissions controls. Projected emissions estimates are often used for planning, evaluation of potential control measures, analysis of new source impacts, modeling of future air quality, and assessment of the effectiveness of air pollution control strategies. A baseline emissions inventory is important because it represents a snapshot of emissions for a given baseline year. However, because sources and their associated air emissions are not static over time, baseline emissions may not accurately represent emissions for a future year. Emission projections are an attempt to account for the effects of future growth and emissions controls. Because projections attempt to quantify the unknown future, there will always be some uncertainty associated with any estimate of projected emissions. This uncertainty can be minimized by using source-specific growth factors and control factors that most nearly approximate future year emissions.

Projections are usually not considered to be a modeling inventory development step. Modeling inventory development steps are typically considered to be limited to temporal allocation, spatial allocation, and speciation. In fact, modeling inventory emissions that have been temporally allocated, gridded, and speciated are usually not projected into the future. Instead the annual baseline emissions data are projected. These projected emissions can then be temporally allocated, spatially allocated, and speciated to create modeling inventories of the projected emissions.

Related Tools and Documents

Growth factor and emission reduction ancillary files for use with the EMS-HAP (version 3.0) model May 2005.
We are providing, for your review and comment, a set of emissions reduction and growth factor ancillary files for use with EMS-HAP version 3.0 for hazardous air pollutant (HAP) emission projections. We also descibe (in the README files) how we developed these files and how EMS-HAP used them for projecting future year emissions from a baseline emission inventory. EMS-HAP version 3.0 is an emissions model that prepares annual toxics emission inventory data, such as the 1999 National Emission Inventory for HAPs for subsequent air qualtiy modeling using either the ASPEN of ISCST3 model. EMS-HAP can also project emissions to a future year, if you provide the emission reduction and growth factor ancillary files.

Comments on these files and the projection methodology may be emailed to Madeleine Strum at strum.madeleine@epa.gov.
Emission reduction ancillary files for use with the EMS-HAP (version 2.0) model December 2002.
The purpose of this information is to serve as a reference for the reduction files we have posted for use with EMS-HAP version 3.0. This reference information consists of a “Readme” file that explains how we developed the emission reduction information for EMS-HAP Version 2.0, and two Excel files showing the information in spreadsheet format. This information was developed for projecting the 1996 National Toxics Inventory (NTI) which is no longer available. However, because this information was the starting point for the reduction information we use for EMS-HAP version 3.0, we provide it here as a reference.

Economic Growth Analysis System - EGAS
For more information contact Larry Sorrels at sorrels.larry@epa.gov or Linda Chappell at chappell.linda@epa.gov.
Economic Growth Analysis System (EGAS) v 5.0
EGAS Version 5.0 is a tool that can generate emissions growth factors by sector. Growth factors from EGAS 5.0 can be used to project emissions inventories for multiple pollutants.

EIIP Document Series - Volume 10 Emission Projections
The focus of this report is to provide information and procedures to State and local agencies for projecting future air pollution emissions for the following emitting sectors: point, area, onroad and nonroad mobile.

| Office of Air Quality Planning & Standards | Technology Transfer Network |
| Clearinghouse for Inventories & Emissions Factors |

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