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Cross-State Air Pollution Rule (CSAPR)

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You will need Microsoft Excel to view the Excel spreadsheet files on this page. Microsoft offers a Free Excel Viewer exit EPA if you don't own Excel.

The Cross-State Air Pollution Rule (CSAPR) is one step the federal government is taking to fulfill its responsibilities to reduce interstate air pollution transport, helping to achieve healthy air quality on a regional scale. For more information on the CSAPR, visit the Basic Information Page. For more information on other EPA programs to improve air quality, visit EPA's Air and Radiation page.

Helping Power Plants be Better Neighbors

How to use this map | View this map as an Excel Spreadsheet (62Kb)

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The map above shows the Cross-State Air Pollution Rule "linkages" between states where pollution from upwind states is linked to one or more areas in downwind states that have problems attaining or maintaining the 1997 ozone National Ambient Air Quality Standards (NAAQS), 1997 annual PM2.5 NAAQS, and the 2006 24-hour PM2.5 NAAQS. For states to be "linked" on this map, two things must occur:

  1. The downwind state must have at least one nonattainment or maintenance area for these NAAQS; and,
  2. Sources in the upwind state must emit enough SO2 or NOX pollution to affect air quality in that area at or above the threshold level set by EPA.

To use the map, place your cursor on any state in the CSAPR region - the highlighted arrows entering the state show upwind states who contribute pollution (i.e., are "linked") to one or more areas in a downwind state that do not attain the ozone, annual fine particle, or 24-hour fine particle standards. The highlighted arrows exiting the state show the reverse: the downwind state(s) whose attainment or maintenance of those standards is affected by emissions in the highlighted state. To see a closer view of a region of the map, right click and select "zoom in"; to return the map to its original size, right click again and select "show all". The linkages shown in the map are also available in an Excel spreadsheet. (62Kb)

For example, the map shows that ozone pollution sources in Florida are "linked" to one or more nonattainment or maintenance areas in Texas. This means that emissions from Florida affect ozone concentrations in these areas at or above the threshold. EPA's air quality modeling shows that emissions from Florida also affect the states in between - Alabama, Mississippi, and Louisiana. However, the map does not show a linkage to any of those states because:

  • Mississippi does not have any nonattainment or maintenance areas for Florida to be linked to;
  • The effects of emissions from Florida on air quality in the nonattainment and maintenance areas in Alabama and Louisiana are so small that in both cases they fail our threshold criteria for identifying linked states.

As noted above, the linkages shown in this map are unique to the 1997 ozone, 1997 fine particle, and 2006 fine particle standards; the modeling done for this final Cross-State Air Pollution Rule; and the framework of the CSAPR, including the threshold used for determining contribution.

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Sources Covered by the CSAPR

The map below shows the individual sources in the CSAPR states affected by the rule, including states that are in the supplemental rulemaking. Clicking on any source provides basic information about the facility, recent historical emissions data, and information on the CSAPR control programs affecting that source, as well as state-level historical and current emissions levels and state level budgets under the CSAPR. Double-clicking on the source provides a close-up, aerial view of the source. The points on this map are also available in an Excel spreadsheet. (282Kb)

More information on what pollution control technologies are installed at these facilities as of December 31, 2010 is available in this Excel spreadsheet. (648Kb)

Green Circle LegendFacilities controlled for both fine particles (annual SO2 and NOX) and ozone (ozone season NOX) (20 States)
Blue Circle LegendFacilities controlled for fine particles only (annual SO2 and NOX) (3 States)
Yellow Circle LegendFacilities controlled for ozone only (ozone season NOX) (5 States)
American Indian Reservations / Federally Recognized Tribal Entities shown were provided by the US DOI, BIA, and GDSC; they are not a legal representation of reservation boundaries.

Interstate Air Pollution Transport

Sulfur dioxide (SO2) and nitrogen oxide (NOX) emissions are pollutants that react in the atmosphere and contribute to formation of fine particle (PM2.5) pollution; NOX also forms ground-level ozone. These emissions and the PM2.5 and ozone they form can affect air quality and public health locally, regionally, and in states hundreds of miles downwind. The air quality in a particular location - even close to a source like a power plant - is due to a combination of local emissions and emissions from upwind sources hundreds of miles away. This long-distance transport of pollution across state lines makes it difficult for downwind states to achieve PM2.5 and ozone levels required by the NAAQS.

The NAAQS are national air quality standards that Congress requires EPA to set (and periodically revise) that protect our health and the environment by limiting the concentration of pollutants in the atmosphere. EPA, states, and local governments all play important roles in reaching these clean air goals. While most states have made great progress in improving their air quality in the last few years, many counties in the central and eastern United States are still violating the 1997 ozone and the 1997 annual and 2006 24-hour PM2.5 NAAQS. The emission reductions from the CSAPR will allow some additional areas to attain the NAAQS. For the rest, attaining these standards will require a combination of emission reductions from sources located within or near a nonattainment area (i.e., local pollution) and sources located further from the nonattainment area (i.e., transported pollution).

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