About the County Emissions Report - Hazardous Air Pollutants

What does the report tell me?

The County Emissions Report summarizes hazardous air pollutant (HAP) emissions from all sources by county. The report lists county total estimated annual emissions of up to six HAPs you select, and subtotals for each of four types of sources: major, nonpoint, onroad mobile, and nonroad mobile. (See report column descriptions, below, for explanations of these source types.) Emission totals by state or EPA region also are available, as described in the Detail or Summary section below.

Each row of the County Emissions Report displays estimated annual HAP emissions for the geographic entity it represents -- a county, a state, or an EPA Region. The Grand Total line at the bottom of each report page shows the total HAP emissions of the entire geographic area included in the report.

The National Emissions Inventory (NEI) is an emission inventory developed every three years (1999, 2002, etc.) by EPA. The NEI is a national inventory of stationary and mobile sources that emit hazardous air pollutants (HAPs). HAPs are generally defined as those pollutants that are known or suspected to cause serious health problems. Section 112(b) of the Clean Air Act currently identifies a list of 188 pollutants as HAPs. The NEI contains emission estimates for major sources, nonpoint sources, mobile sources, and other sources which do not readily fall into these categories. Point sources in the NEI are sources for which the specific location is known; they may be either major or area sources. As best as possible, point sources in the NEI have each been identified as either major or area, but this identification may not correspond to the official regulatory classification of some sources. Nonpoint sources in the NEI include area sources that are not identified as point sources because their specific locations are not known. Nonpoint sources also include other sources such as wildfires and prescribed burning whose emissions are estimated at the county level.

What does the report look like?

This example lists county by county emissions of the hazardous air pollutant acrolein. The emissions column gives the total acrolein emissions from all types of sources in each county. Subsequent columns give subtotals for four types of sources: major, nonpoint, onroad mobile, and nonroad mobile. Report rows are in descending order of county total acrolein emissions, as indicated by the red down-arrow button in that column.

How can I customize the report?

Sort Order

You can use the SORT buttons in each report column to change the order of rows in the report. The default sort order is descending total HAP emissions, which puts counties (or states or EPA Regions) with the most emissions at the beginning of the report.

Detail or Summary

This is always a summary report. Omitting optional report columns can change the level of summarization. The default report summarizes emissions and number of point sources by county. Omitting the County and County Code columns produces a state-level summary, and omitting the State column produces an EPA region summary.

Individual Pollutants or Total Emissions

You may have the report display the emissions of one to six separate HAPs, the total emissions of urban HAPs (Sum of 33 urban HAPs), or the total emissions of all HAPs (Sum of 188 HAPs). If you select specific HAPs, the report includes sources emitting at least one of those HAPs. If you select Sum of 33 urban HAPs, the report includes sources that emit one or more of the 33 urban HAPs. If you select Sum of 188 HAPs, the report includes sources that emit any of the 188 HAPs.

If you choose Sum of 188 HAPs in combination with individual HAPs, the report includes sources that emit any of the 188 HAPs. If you choose Sum of 33 urban HAPs in combination with individual HAPs, the report includes sources that emit any urban HAP and sources that emit any individual HAP selected.

Format of Emissions Values

Depending on the Pollutant Emissions Format option that you choose for the report, emission values are displayed as decimal numbers (0.0351) or in scientific notation (3.51E-02). With the decimal option in effect, values smaller than 0.0001 are displayed as "< 0.0001" in an html report and displayed in scientific notation when exporting to a text file.

What do the report columns mean?

Row #: Sequence number of report rows (lines). Sequence numbers are not associated with particular rows; they simply enumerate the rows of a report from first to last. Thus, choosing an alternate sort order for a report would change the sequence numbers associated with particular rows.
EPA Region: EPA region number in which a source is located. There are ten EPA regions. [ Details ]
State: Postal abbreviation for the state or territory in which a source is located. [ Details ]
County: Name of the county (or equivalent jurisdiction) in which a source is located.
County Code: Code for the county (or equivalent jurisdiction) in which a source is located, consisting of 2-digit FIPS state code and 3-digit FIPS county code. FIPS is the acronym for Federal Information Processing Standards, which defines codes used in most U.S. government information systems.
Urban/Rural Designation: (This column is included in the report only if County or County Code also is included.) For purposes of developing EPA's Integrated Urban Air Toxics Strategy, a county was considered "urban" if either:
1) it includes a metropolitan statistical area with a population greater than 250,000; or
2) the U.S. Census Bureau designates more than fifty percent of the population as "urban."
The Integrated Urban Air Toxics Strategy is an important part of EPA's national air toxics program. Please note that the definition of "urban" does not necessarily apply for regulatory or implementation purposes. (www.epa.gov/ttn/atw/urban/urbanpg.html)
Emissions: The total estimated annual HAP emissions, in pounds, in the geographic area represented by a row of the report. This quantity is a sum of the major, nonpoint, onroad mobile, and nonroad mobile source emissions, described below. The report includes an emissions column for each HAP you selected. See the NEI HAP Names table for alternative pollutant names and identification codes.
% of Emissions Total: Fraction (percentage) of the report's Grand Total emissions attributable to the geographic area represented by a row of the report. The report includes a percentage column for each HAP you selected.
Major Emissions: Total estimated annual HAP emissions, in pounds, from major sources in the geographic area represented by a row of the report. The report includes an emissions column for each HAP you selected.

Major sources are stationary sources (point sources, facilities) that emit or have the potential to emit at least 10 tons per year of any one HAP, or at least 25 tons per year of a combination of HAPs. Examples of major sources are electric utility plants, chemical plants, steel mills, oil refineries, and hazardous waste incinerators. These sources may release air toxics from equipment leaks, when materials are transferred from one location to another, or during discharge through emissions stacks or vents. The NEI database has HAP emission estimates for each major source. The NEI designation as major source corresponds to the official regulatory classification for most sources, but there may be exceptions.
% of Major Total: Fraction (percentage) of the report's Grand Total major source emissions attributable to the geographic area represented by a row of the report. The report includes a percentage column for each HAP you selected.
Nonpoint Emissions: Total estimated annual HAP emissions, in pounds, from nonpoint sources in the geographic area represented by a row of the report. The report includes an emissions column for each HAP you selected.

Nonpoint sources, sometimes called "area" sources, are stationary sources that each emit less than major-source threshold amount, 10 tons per year of a single HAP or 25 tons per year of all HAPs combined. Examples of nonpoint sources are neighborhood dry cleaners and gas stations. Though emissions from an individual source may be relatively small, the collective emissions from many sources can be of concern, particularly where they are located in heavily populated areas. The NEI database has HAP emission estimates for some individual nonpoint sources and county aggregate emissions for others.

Nonpoint sources also include diffuse processes, such as wildfires and prescribed burning. The NEI database has county aggregate emissions for these sources.
% of Nonpoint Total: Fraction (percentage) of the report's Grand Total nonpoint source emissions attributable to the geographic area represented by a row of the report. The report includes a percentage column for each HAP you selected.
Onroad Emissions: Total estimated annual HAP emissions, in pounds, from onroad mobile sources in the geographic area represented by a row of the report. The report includes an emissions column for each HAP you selected.

Onroad mobile sources consist of licensed motor vehicles, including automobiles, trucks, buses, and motorcycles. The NEI database has county aggregate emissions for these sources.
% of Onroad Total: Fraction (percentage) of the report's Grand Total onroad source emissions attributable to the geographic area represented by a row of the report. The report includes a percentage column for each HAP you selected.
Nonroad Emissions: Total estimated annual HAP emissions, in pounds, from nonroad mobile sources in the geographic area represented by a row of the report. The report includes an emissions column for each HAP you selected.

Nonroad mobile sources consist of 2- or 4-stroke and diesel engines, nonroad vehicles, aircraft, commercial marine vessels, and locomotives. The NEI database has county aggregate emissions for these sources.
% of Nonroad Total: Fraction (percentage) of the report's Grand Total nonroad source emissions attributable to the geographic area represented by a row of the report. The report includes a percentage column for each HAP you selected.