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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):
- nitrogen dioxide (NO2),
- ozone (O3),
- sulfur dioxide (SO2),
- particulate matter (PM),
- carbon monoxide (CO), and
- lead (Pb)
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.
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 | |
| Wildfires | |
| 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 | |
| Mining | |
| NEC | |
| 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 | |
| Locomotives | |
| 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 |
| Degreasing | |
| Dry Cleaning | |
| Graphic arts | |
| Industrial Surface Coating & Solvent Use | |
| Non-Industrial Surface Coating |