Clean Air Markets
Annual NOₓ Trends
Last updated: 05/2016
Annual NOₓ Trends
- ARP: Units in the ARP NOₓ program emitted 1.6 million tons of NOₓ in 2014, indicating that ARP sources reduced emissions by 6.5 million tons from the projected level in 2000 without the ARP, and over three times the Title IV NOₓ emission reduction objective.
- CAIR and ARP: In 2014, the sixth year of operation of the CAIR NOₓ annual program, sources in both the CAIR NOₓ annual program and the ARP together emitted 1.7 million tons, a reduction of 4.7 million tons (73 percent reduction) from 1990 levels, 3.5 million tons (67 percent reduction) from 2000, and 2.0 million tons (54 percent reduction) from 2005 levels.
- CAIR: Emissions from CAIR NOₓ annual program sources alone were about 1.2 million tons in 2014. This is about 1.5 million tons (56 percent) lower than in 2005 and 340,000 tons (23 percent) below the CAIR NOₓ annual program's 2014 regional budget of 1,504,871 tons.
Annual NOₓ State-by-State Emissions
- CAIR and ARP: All states participating in the ARP and CAIR NOₓ annual programs decreased their NOₓ emissions from 1990 to 2014.
- CAIR: Seventeen states (16 states plus Washington, D.C.) had emissions below their CAIR 2014 allowance budgets, collectively by about 380,000 tons. Another six states exceeded their 2014 budgets by a combined total of about 53,000 tons. This indicates that, on an aggregate basis, sources within those states covered a portion of their emissions with allowances banked from earlier years, transferred from an out-of-state account, or purchased from the market. Overall, in 2014 the total NOₓ emissions from participating sources were about 330,000 tons below the CAIR regional emission budget of 1,504,871 tons.
Annual NOₓ Emission Rates
- In 2014, the CAIR and ARP average annual NOₓ emission rate was 0.13 lb/mmBtu, a 50 percent reduction from 2005.
- Although heat input has remained relatively steady over the past 14 years, emissions have decreased dramatically since 2000, indicating an improvement in NOₓ emission rates (see Figure 4, below). 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 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 health effects.
Overall, NOₓ emissions have declined dramatically under the ARP, former NOₓ Budget Trading Program (NBP), and CAIR programs, with the majority of reductions coming from coal-fired units. Other programs—such as regional and state NOₓ emission control programs—also contributed significantly to the annual NOₓ emission reductions achieved by sources in 2014.