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Emission Reductions

CAIR Ozone Season NOₓ Trends

Last updated: 05/2016

Related Figures

Ozone Season NOₓ Emissions from CAIR and NBP Sources, 2000-2014
State-by-State Ozone Season NOₓ Emission Levels from CAIR Sources, 2000–2014
Comparison of Emissions and Heat Input for CAIR NOₓ Ozone Season Source, 2000-2014
CAIR Ozone Season NOₓ Trends

Key Points

Ozone Season NOₓ Trends

  • CAIR: Units in the CAIR NOₓ ozone season program emitted 450,000 tons in 2014, a reduction of 1.6 million tons (78 percent) from 1990, 1.0 million tons lower (69 percent reduction) than in 2000 (before implementation of the NBP), 350,000 tons lower (44 percent reduction) than in 2005 (before implementation of CAIR), and about 25,000 tons lower (5 percent reduction) than in 2013. In 2014, CAIR NOₓ ozone season program emissions were 21 percent below the regional emission budget of 567,744 tons.
  • CAIR and NBP: In 2014, sources from both CAIR and the former NBP, together with a small number of sources that were previously in the NBP but did not enter CAIR, reduced their overall NOₓ emissions from 820,000 tons in 2005 (before implementation of CAIR) to 450,000 tons in 2014 (45 percent reduction).

Ozone Season NOₓ State-by-State Emissions

  • CAIR and NBP: Between 2005 and 2014, ozone season NOₓ emissions from CAIR and former NBP sources fell in every state participating in the CAIR NOₓ ozone season program except Arkansas, Rhode Island, and West Virginia, where emissions increased by a combined total of 3,000 tons.
  • CAIR: In 2014, every state and Washington, D.C. had emissions below their CAIR allowance budgets, collectively by about 250,000 tons.

Ozone Season NOₓ Emission Rates

  • In 2014, the average NOₓ ozone season emission rate fell to 0.13 lb/mmBtu. This indicates a 68 percent reduction from 2000 emission rates, with the majority of reductions coming from coal-fired units.
  • Although heat input has remained relatively constant over the past 14 years, emissions have decreased dramatically since 2000, indicating an improvement in NOₓ emission rate. 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, which emit less NOₓ than coal-fired units.

Analysis and Background Information

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 contributes to the formation of ground-level ozone and fine particle pollution, which cause a variety of adverse human health effects.

The CAIR NOₓ ozone season program was established to reduce interstate transport during the ozone season (May 1 – September 30), the warm summer months when ozone formation is highest, and to help eastern U.S. counties attain the 1997 ozone standard.

In general, the states with the highest emitting sources of ozone season NOₓ in 2000 have seen the greatest reductions under the CAIR NOₓ ozone season program. Most of these states are in the Ohio River Valley and are upwind of the areas CAIR was designed to protect. Reductions by sources in these states have resulted in important environmental and human health benefits over a large region.

In addition to the CAIR and ARP NOₓ programs and the former NBP, current regional and state NOₓ emission control programs have also contributed significantly to the ozone season NOₓ emission reductions achieved by sources.

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