Skip to main content
U.S. flag

An official website of the United States government

Here’s how you know

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

HTTPS

Secure .gov websites use HTTPS
A lock (LockA locked padlock) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

    • Environmental Topics
    • Air
    • Bed Bugs
    • Cancer
    • Chemicals, Toxics, and Pesticide
    • Emergency Response
    • Environmental Information by Location
    • Health
    • Land, Waste, and Cleanup
    • Lead
    • Mold
    • Radon
    • Research
    • Science Topics
    • Water Topics
    • A-Z Topic Index
    • Laws & Regulations
    • By Business Sector
    • By Topic
    • Compliance
    • Enforcement
    • Laws and Executive Orders
    • Regulations
    • Report a Violation
    • Environmental Violations
    • Fraud, Waste or Abuse
    • About EPA
    • Our Mission and What We Do
    • Headquarters Offices
    • Regional Offices
    • Labs and Research Centers
    • Planning, Budget, and Results
    • Organization Chart
    • EPA History

Breadcrumb

  1. Home
  2. Air Quality Management Process

Managing Air Quality - Emissions Inventories

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

On this page:

  • How Does an Emissions Inventory Contribute to the Air Quality Management Process?
  • How are Emissions Inventories Developed?
  • Where Can I Find Information About Emissions Inventories in the United States?

How Does an Emissions Inventory Contribute to the Air Quality Management Process?

Governments use emission inventories to help determine significant sources of air pollutants and to target regulatory actions. Emissions inventories are an essential input to mathematical models that estimate air quality. The effect on air quality of potential regulatory actions can be predicted by applying estimated emissions reductions to emissions inventory data in air quality models.

Emission trends over time can be established with periodic updates of the emissions inventory. Inventories also can be used to raise public awareness regarding sources of pollution.

An emissions inventory includes estimates of the emissions from various pollution sources in a geographical area. It should include all pollutants associated with the air quality problems in the area. For example, an emissions inventory to support the management of ground-level ozone should include sources of nitrogen oxides (NOx) and of volatile organic compounds (VOC).

How are Emissions Inventories Developed?

Methods to determine emissions include, but are not limited to: continuous monitoring of emissions from a source; short-term emission measurements that are extrapolated to a longer time period, and use of emissions factors. The choice of method depends on the availability of data, time, staff and funding.

An emissions factor is a representative value that attempts to relate the quantity of a pollutant emitted with an activity level associated with the emission of that pollutant. An example format of an emissions factor is kilograms of particulate matter emitted per megagram of coal burned.

Emissions factors in the published literature typically are averages of available data of acceptable quality, and are assumed to represent long-term averages for similar facilities. However, variations among facilities, such as the raw materials used, operational conditions and emission controls, can significantly affect the emissions. Whenever possible, the development of local, source-specific emission factors is highly desirable.

EPA’s Clearinghouse for Inventories & Emission Factors contains information on emissions inventories, emissions factors and tools used for emissions inventories to support air quality management. EPA uses models to estimate emissions related to mobile sources.

Where Can I Find Information About Emissions Inventories in the United States?

The National Emissions Inventory (NEI) is a comprehensive and detailed estimate of air emissions of both criteria and hazardous air pollutants from all air emissions sources. EPA prepares the NEI every three years. It is based primarily upon information provided by state, local, and tribal air agencies for sources in their jurisdictions, and supplemented by data developed by EPA.

 Emissions trends and summaries, charts and maps of emissions from the NEI are available.

The Toxics Release Inventory (TRI) program tracks the management of certain toxic chemicals that may pose a threat to human health and the environment. Learn more about the TRI. Learn how the TRI Program works with other countries related to Pollutant Release and Transfer Registers (PRTRs)

EPA also develops and maintains an inventory of U.S. greenhouse gas emissions and sinks.

Air Quality Management Process

  • Air Quality Management Process Home
  • Overview of Air Quality Management
  • Assessment and Implementation
  • Tools and Resources
Contact Us About the Air Quality Management Process
Contact Us to ask a question, provide feedback, or report a problem.
Last updated on November 26, 2024
  • Assistance
  • Spanish
  • Arabic
  • Chinese (simplified)
  • Chinese (traditional)
  • French
  • Haitian Creole
  • Korean
  • Portuguese
  • Russian
  • Tagalog
  • Vietnamese
United States Environmental Protection Agency

Discover.

  • Accessibility Statement
  • Budget & Performance
  • Contracting
  • EPA www Web Snapshot
  • Grants
  • No FEAR Act Data
  • Plain Writing
  • Privacy
  • Privacy and Security Notice

Connect.

  • Data
  • Inspector General
  • Jobs
  • Newsroom
  • Regulations.gov
  • Subscribe
  • USA.gov
  • White House

Ask.

  • Contact EPA
  • EPA Disclaimers
  • Hotlines
  • FOIA Requests
  • Frequent Questions
  • Site Feedback

Follow.