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Basic Information

Under the Clean Air Act, EPA establishes air quality standards to protect public health, including the health of "sensitive" populations such as people with asthma, children, and older adults. EPA also sets limits to protect public welfare. This includes protecting ecosystems, including plants and animals, from harm, as well as protecting against decreased visibility and damage to crops, vegetation, and buildings. View more information regarding the national standards for these pollutants.

EPA has set national air quality standards for six common air pollutants (also called the criteria pollutants):

Four of these pollutants (CO, Pb, NO2, and SO2) are emitted directly from a variety of sources. Ozone is not directly emitted, but is formed when oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. PM can be directly emitted, or it can be formed when emissions of NOx, sulfur oxides (SOx), ammonia, organic compounds, and other gases react in the atmosphere.

To achieve these standards, EPA has in place regulatory and voluntary programs to reduce the amount of air pollutants emitted from a wide range of emission sources. To keep track of these emissions, the EPA maintains the National Emission Inventory (NEI), the national database of air pollutant emissions information. EPA conducts a comprehensive emissions inventory every three years. EPA also modifies the NEI at least annually to correct and augment its inventory data. Developing and updating the inventory is time-consuming, and EPA is working to reduce the amount of time it takes. While the data provided in this site are several years old, they do reflect the most recent inventory. For additional technical information about the NEI, visit the National Emission Inventory website.

Emissions Data Source

This site groups emissions into 8 major source sectors. The table below provides more detail about which sources are included in each sector.

Major Source Sectors Detailed Category Names
Agriculture Crops & Livestock Dust
Fertilizer Application
Livestock Waste
Dust Construction Dust
Paved Road Dust
Unpaved Road Dust
Fires Agricultural Field Burning
Prescribed Fires
Fuel Combustion Comm/Institutional - Biomass
Comm/Institutional - Coal
Comm/Institutional - Natural Gas
Comm/Institutional - Oil
Comm/Institutional - Other
Electric Generation - Biomass
Electric Generation - Coal
Electric Generation - Natural Gas
Electric Generation - Oil
Electric Generation - Other
Industrial Boilers, ICEs - Biomass
Industrial Boilers, ICEs - Coal
Industrial Boilers, ICEs - Natural Gas
Industrial Boilers, ICEs - Oil
Industrial Boilers, ICEs - Other
Residential - Natural Gas
Residential - Oil
Residential - Other
Residential - Wood
Industrial Processes Cement Manufacturing
Chemical Manufacturing
Ferrous Metals
Non-ferrous Metals
Oil & Gas Production
Petroleum Refineries
Pulp & Paper
Storage and Transfer
Miscellaneous Bulk Gasoline Terminals
Commercial Cooking
Gas Stations
Miscellaneous Non-Industrial NEC
Waste Disposal
Mobile Aircraft
Commercial Marine Vessels
Non-Road Equipment - Diesel
Non-Road Equipment - Gasoline
Non-Road Equipment - Other
On-Road Diesel Heavy Duty Vehicles
On-Road Diesel Light Duty Vehicles
On-Road Gasoline Heavy Duty Vehicles
On-Road Gasoline Light Duty Vehicles
Solvent Consumer & Commercial Solvent Use
Dry Cleaning
Graphic arts
Industrial Surface Coating & Solvent Use
Non-Industrial Surface Coating


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