An emission inventory is an accounting of the amount of pollutants discharged into the atmosphere. An emission inventory usually contains the total emissions for one or more specific greenhouse gases or air pollutants, originating from all source categories in a certain geographical area and within a specified time span, usually a specific year. An emission inventory is generally characterized by the following aspects:
* Why: The types of activities that cause emissions
* What: The chemical or physical identity of the pollutants included, and the quantity thereof
* Where: The geographic area covered
* When: The time period over which emissions are estimated
* How: The methodology to use Emission inventories are compiled for both scientific applications and for use in policy processes.