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Emissions Inventory

Definition Overview
How Do I Do an Emissions Inventory?

Definition

An emissions inventory is a database that lists, by source, the amount of air pollutants discharged into the atmosphere of a community during a given time period.

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AQ Modeling flowchart
Overview

The development of a complete emission inventory is an important step in an air quality management process. Emission inventories are used to help determine significant sources of air pollutants, establish emission trends over time, target regulatory actions, and estimate air quality through computer dispersion modeling. An emission inventory includes estimates of the emissions from various pollution sources in a specific geographical area. A complete inventory typically contains all regulated pollutants.

Different methods for calculating the emissions inventories are available, and the choice of method depends on the availability of data, time, staff and funding. The methods may include, but are not limited to: continuous monitoring to measure actual emissions; extrapolating the results from short-term source emissions tests; and combining published emission factors with known activity levels.

An emission factor may be used to estimate emissions when actual emission data is not available. In most cases, these factors are simply averages of all available data of acceptable quality, and are generally assumed to be representative of long-term averages for all facilities in the source category. General emission factors are available to the public, and may be accessed under the AP-42 link below. However, variations in the conditions at a given facility, such as the raw materials used, temperature of combustion, and emission controls, can significantly effect the emissions at an individual location. Whenever possible, the development of local emission factors is highly desirable.

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How Do I Do an Emissions Inventory?

In Europe, the third edition of the emission inventory guidebook (prepared by the United Nations European Environment Agency Task Force on Emissions Inventories and Projections) provides a comprehensive guide to state-of-the-art atmospheric emissions inventory methodology to support reporting under the UNECE Convention on Long-Range Transboundary Air Pollution and the EU directive on national emission ceilings.

New Zealand also has a Guide for Preparing Emissions Inventories, which is a step-by step guide to preparing emission inventories that contains information on the purpose, process, methodology and application of emission inventory investigations.

In the U.S., the EPA Clearinghouse for Inventories & Emission Factors contains information on emissions inventories, emissions factors, software and tools used for emissions inventories, and emissions modeling. For an overview of the mobile source category and specific methods to identify and inventory sources, estimate emissions, and establish and maintain a useful, current mobile source emissions inventory, you may access Procedures for Emission Inventory Preparation, Chapter IV: Mobile Sources that was prepared by the U.S. Department of Transportation and U.S. EPA. For information on the Compilation of Air Pollutant Emission Factors, you may access EPA's AP-42 documentation.

As with the other management activities related to the AQM process, it is critical to contact the regulated community and other affected parties, as the public should be consulted as part of the process.

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