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Emission Reductions

Annual Nitrogen Oxides (NOₓ) Figures

Source: EPA, 2017
Last updated: 05/2017

Related Figures

Annual NOₓ Emissions from CSAPR and ARP Sources, 1990–2015
State-by-State Annual NOₓ Emissions from CSAPR and ARP Sources, 1990–2015
Comparison of Annual NOₓ Emissions and Heat Input for CSAPR and ARP Sources, 2000–2015
CSAPR and ARP Annual NOₓ Emissions Trends

Key Points

Overall Results

  • Annual NOₓ emissions have declined dramatically under the ARP, NOₓ Budget Trading Program (NBP), CAIR, and CSAPR programs, with the majority of reductions coming from coal-fired units.
  • These reductions have occurred while electricity demand (measured as heat input) remained relatively stable, indicating that the emission reductions were not driven by decreased electric generation.
  • These emission reductions are a result of an overall increase in the environmental efficiency at affected sources as power generators installed controls, ran their controls year-round, switched to lower emitting fuels, or otherwise reduced their NOₓ emissions while meeting relatively steady electricity demand.
  • Other programs—such as regional and state NOₓ emission control programs—also contributed significantly to the annual NOₓ emission reductions achieved by sources in 2015.

Annual NOₓ Emissions Trends

  • ARP: Units in the ARP NOₓ program emitted 1.3 million tons of NOₓ emissions in 2015, indicating that ARP sources reduced emissions by 6.8 million tons from the projected level in 2000 without the ARP, and over three times the Title IV NOₓ emission reduction objective.
  • CSAPR and ARP: In 2015, the first year of operation of the CSAPR NOₓ annual program, sources in both the CSAPR NOₓ annual program and the ARP together emitted 1.4 million tons, a reduction of 5.0 million tons (79 percent reduction) from 1990 levels, 3.8 million tons (73 percent reduction) from 2000, and 2.3 million tons (63 percent reduction) from 2005 levels.
  • CSAPR: Emissions from the CSAPR NOₓ annual program sources alone were about 905,000 tons in 2015. This is about 1.4 million tons (61 percent) lower than in 2005 and 360,000 tons (29 percent) below the CSAPR NOₓ annual program's 2015 regional budget of 1,269,837 tons.

Annual NOₓ State-by-State Emissions

  • CSAPR and ARP: From 1990 to 2015, annual NOₓ emissions in the ARP and CSAPR NOₓ program dropped in 46 states plus Washington, D.C. by a total of approximately 5.0 million tons. In contrast, annual emissions increased in two states (Idaho and Oregon) by a combined total of only 720 tons from 1990 to 2015.
  • CSAPR: Twenty two states had emissions below their CSAPR 2015 allowance budgets, collectively by about 370,000 tons. A single state (West Virginia) exceeded its 2015 budget by about 1,700 tons through use of excess allowances from EGUs in other states.

Annual NOₓ Emission Rates

  • In 2015, the CSAPR and ARP average annual NOₓ emission rate was 0.11 lb/mmBtu, a 58 percent reduction from 2005.
  • Although heat input has decreased slightly over the past 10 years, emissions have decreased dramatically since 2005, indicating an improvement in NOₓ emission rates. This is due in large part to greater use of control technology on coal-fired units and increased heat input at natural gas-fired units that emit less NOₓ emissions than coal-fired units.

Analysis and Background Information

Nitrogen oxides, or NOₓ, are made up of a group of highly reactive gases that are emitted from power plants and motor vehicles, as well as other sources. NOₓ emissions contribute to the formation of ground-level ozone and fine particle pollution, which cause a variety of adverse health effects. NO₂, one form of NOₓ, is specifically linked to adverse health effects on the human respiratory system.

More Information

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