The National Emissions Inventory

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. The NEI is prepared every 

three years by the USEPA based primarily upon emission estimates and emission model inputs 

provided by State, Local, and Tribal air agencies for sources in their jurisdictions, and supplemented 

by data developed by the USEPA. The 2008 NEI was built from emissions data in the Emissions 

Inventory System (EIS).

Version History: (For a detailed list of caveats and changes from 

version one, please see the Version 1.5 issues file. 

 Version 1.5 (released May 16, 2011): Key updates are to include 

the nonpoint data and major updates to point sources in Indiana, 

Maryland, Nebraska, and Lincoln/Lancaster air agencies. 

 Version 1 (released April 4, 2011) 

Detailed documentation for each of the five data categories Point, NonPoint, OnRoad, NonRoad, and 

Event are available below.

2008 National Emissions Inventory Data

NEI Browser. Note that a public NEI Browser is available that currently retrieves NEI data for only the 

Criteria air pollutants.

Sector Summaries - Criteria and 

Hazardous Air Pollutants by 59 

emission sectors

*To use the multiple selection boxes hold CTRL 

and click on options you would like to include in 

your query. To select multiples in order click your 

first option then hold SHIFT + click the last 

selection to highlight everything in between. To 

unselect options use the same method as with 

selecting.

*Sector selections are limited to 12 states to 

avoid any timeout issues. 

This site uses pop-up windows, click here for help on 

allowing pop-ups from this site

State / County

Geographic Aggregation
State County 

Region 1 - Connecticut

Region 1 - Massachusetts

Region 1 - Maine

Region 1 - New Hampshire

Region 1 - Rhode Island

Region 1 - Vermont

Pollutant Sector

CAP - Ammonia

CAP - Carbon Monoxide

CAP - Nitrogen Oxides

CAP - PM Condensible

CAP - PM10 Filterable

CAP - PM10 Primary (Filt + Cond)

Agriculture - Livestock Waste

Bulk Gasoline Terminals

Dust - Construction Dust

Fuel Comb - Comm/Institutional - Biomass

Fuel Comb - Comm/Institutional - Coal

Fuel Comb - Comm/Institutional - Natural Gas

Create CSV File

Tier 1 Summaries - Criteria Air 

Pollutants only by 13 majors tiers

State / County

Geographic Aggregation

State County 

Region 1 - Connecticut

Region 1 - Massachusetts

Region 1 - Maine

Region 1 - New Hampshire

Region 1 - Rhode Island

Region 1 - Vermont

Pollutant Tier 1 Category

CAP - Ammonia

CAP - Carbon Monoxide

CAP - Nitrogen Oxides

CAP - PM Condensible

CAP - PM10 Filterable

CAP - PM10 Primary (Filt + Cond)

Fuel Combustion - Electric Utility

Fuel Combustion - Industrial

Fuel Combustion - Other

Chemical & Allied Product Manufacturing

Metals Processing

Petroleum & Related Industries

Create CSV File

The full detail data files for the Point, Onroad and Nonroad data categories and a Facilitylevel by Pollutant summary file can be downloaded from the following drop-down menu. A 

README file is available here.

Facility
Additional Summary Data

 Tribal Lands Emissions Summaries

Sector (Includes both criteria and hazardous air pollutants) 

Tier 1 (Includes criteria pollutants only)

 Facility Emissions Summaries

Lead (Pb) by facility by data source emissions summary 

Lead (Pb) Version 1.5 by facility by data source emissions summary 

Sulfur Dioxide (SO2) by facility by data source emissions summary 

Sulfur Dioxide (SO2) Version 1.5 by facility by data source emissions summary

2008 National Emissions Inventory Documentation

The 2008 NEI is based primarily upon emission estimates and emission model inputs provided by 

State, Local, and Tribal air agencies (S/L/Ts), supplemented by data developed by the USEPA. In 

general, the USEPA used State, Local, or Tribal air agency data whenever it was reported and was not 

flagged as an obvious outlier. A summary of the data submitted by each S/L/T for version 1.5 is 

provided here.

USEPA datasets were developed and used to fill gaps where pollutants or entire source types were not 

reported by S/L/Ts. The main gap-filling by USEPA datasets were for certain NonPoint emissions 

sectors that could be estimated adequately by USEPA using nationally-available data; for Point sources 

for some hazardous air pollutants where not reported by S/L/Ts; for OnRoad and NonRoad sources 

where emission model inputs were available to USEPA; and for Aircraft, Locomotive, and Commercial 

Marine Vessel sources. The dataset selection order that was used for each of the four data categories 

included in version 1.5 (Point, NonPoint, OnRoad, and NonRoad) is available here.

In addition to the above-described USEPA developed datasets, the USEPA also created and used three 

types of datasets based upon the 2008 data submitted by S/L/Ts. The first dataset type was used to 

split S/L/T reported emissions of total chromium into the Chromium III and Chromium VI valences 

that are preferred. Any S/L/T reported values for Chromium III and Chromium VI were used. The 

second dataset type was used to gap-fill the various Particulate Matter size ranges and filterable or 

condensable components when not all were reported by the S/L/Ts. In a small number of cases this 

dataset has values to be used in lieu of S/L/T values where the S/L/T values were internally 

inconsistent, such as where a PM2.5 value was greater than a PM10 value. The third type of dataset 

are the USEPA Overwrite datasets, which are used to select EPA emissions values (usually zeros) over 

individual S/L/T values which have been flagged as obvious outliers or are for pollutants and SCC 

combinations that are inconsistent with EPA’s expectations. At this time the inconsistent pollutant-SCC 

combinations overwrites are limited to the OnRoad and NonRoad data categories, where emission 
models are used to develop emission estimates.

Description of NEI Data Categories 

The NEI Point data category contains emissions estimates for sources that are individually 

inventoried and usually located at a fixed, stationary location, although portable sources such as some 

asphalt or rock crushing operations are also included. Point sources include large industrial facilities 

and electric power plants, but also increasingly include many smaller industrial and commercial 

facilities, such as dry cleaners and gas stations, which had traditionally been included in Nonpoint 

sources. The choice of whether these smaller sources are estimated individually and included as point 

sources or inventoried as a NonPoint source County or Tribal area aggregate is determined by the 

separate State, Local, or Tribal air agency.

The NEI NonPoint data category contains emissions estimates for sources which individually are too 

small in magnitude or too numerous to inventory as individual point sources, and which can often be 

estimated more accurately as a single aggregate source for a County or Tribal area. Examples are 

residential heating and consumer solvent use.

The NEI OnRoad and NonRoad data categories contain mobile sources which are estimated for 

version 1.5 of the 2008 NEI via the MOBILE6 and NONROAD models, respectively, run within the 

National Mobile Inventory Model (NMIM). Note that emissions data for aircraft, locomotives, and 

commercial marine vessels is NOT included in the NonRoad data category starting with the 2008 NEI. 

Aircraft engine emissions occurring during Landing and Takeoff operations and the Ground Support 

Equipment and Auxiliary Power Units associated with the aircraft are now included in the point data 

category at individual airports in the 2008 NEI. Emissions from locomotives that occur at rail yards are 

also included in the point data category. In-flight aircraft emissions, locomotive emissions outside of 

the rail yards, and commercial marine vessel emissions (both underway and port emissions) are 

included in the NonPoint data category.

The Events data category includes wildfires and prescribed burns. This data category is not included 

in version 1.5 of the 2008 NEI.