Emissions

Emission Density Maps
These maps allow you to view 1996 emission density values (in tons per square mile per year) on a county average basis for any State in the United States (except Alaska and Hawaii) plus Puerto Rico and the Virgin Islands.

Data Tables
There are two types of tables you will be able to view: one type is organized so you can see data specific to an individual pollutant, and the other is organized so you can see the data for each county in a State. All of these tables are available as either a downloadable file in Excel Spreadsheet format or as an Adobe Acrobat pdf file. Both types of tables contain information about annual emissions and emission densities and a breakdown of emissions into major, area and other, onroad mobile and nonroad mobile sources.

Data Summaries:
The 1996 National Toxics Inventory (NTI) is the underlying basis for the 1996 emissions used in the national-scale assessment. For details about how the 1996 NTI was modified to prepare the emissions for computer modeling, see the discussion of the limitations in the emissions. The NTI contains air toxics emission estimates for four overarching source types: major, area and other, onroad mobile, and nonroad mobile.

For additional information about 1996 emissions of air toxics, including sources of emissions, visit AIRData.

For summary information on air toxics trends, see the air toxics section (pdf)(1290KB) of the 1999 National Air Quality and Emissions Trends Report.

Data Sources:
EPA compiled the 1996 National Toxics Inventory (NTI) using five primary sources of data:

• State and local toxic air pollutant inventories (developed by State and local air pollution control agencies),
• Existing databases related to EPA's air toxics regulatory program,
• EPA's Toxic Release Inventory (TRI) database,
• Estimates developed using mobile source methodology (developed by EPA's Office of Transportation and Air Quality), and
• Emission estimates generated from emission factors and activity data.

In compiling stationary source emissions information for the NTI, preference is given to State- and locally-generated information where available. Where such data are not available, existing data from EPA's regulatory development databases are utilized. If neither of these data sources contains information for a known stationary source, EPA uses data from the TRI. EPA also gives preference in inventory development to emissions data resulting from direct measurements over those generated from emissions factors and activity data.

For more information on emission inventories, see the National Emission Inventory Data web page.