The United States made the first major effort in limiting air pollutants, including sulfur dioxide (SO₂), nitrogen oxides (NOx), carbon monoxide, ozone, lead, and particulate matter with the 1970 Clean Air Act and the amendments to that act in 1977. Since then, industry has developed new technologies to reduce pollutants from power plants and automobiles. With the initiation of the Energy Department’s Clean Coal Technology Program in the 1980s, the United States was on its way to proving electrical power could be made from coal more efficiently with lower pollution.

Although we’ve worried about air pollution for a long time, it wasn’t until 1995 that we developed emission standards for NOx - aimed first at electric utilities in an effort to reduce acid rain.

Power plants in the United States emit significant amounts of air pollution in the form of sulfur dioxide (SO₂), nitrogen oxide (NOx), and mercury. These are some of the constituents of acid rain and smog and all are known to contribute to health problems. However, efforts to date have proved that we can, and are, reducing these pollutants while improving the efficiency of energy production. The Clean Air Act further reduces pollution with the following goals:

• Cutting current SO₂ emissions of 11 million tons to a cap of 4.5 million tons in 2010 and 3 million tons in 2018; a reduction of about 73 percent.
• Cutting current NOx emissions of 5 million tons to a cap of 2.1 million tons in 2008, and to 1.7 million tons in 2018; a reduction of 66 percent.
• Cutting current mercury emissions of 48 tons to a cap of 26 tons in 2010 and 15 tons in 2018; a reduction of about 69 percent.

Government Agencies Working Together to Reduce NOx Emissions
Innovations in pollution control for existing power generating facilities support the President’s Clear Skies Initiatives and EPA’s Clean Air Interstate Rule with a goal to develop technologies that substantially reduce emissions.

In continued efforts to reduce NOx and other emissions from existing coal fired power plants, new technology projects have been initiated throughout the United States. The process becomes complicated due to the different methods of burning coal to make steam.

Department of Energy Reducing NOx
The Department of Energy (DOE) continues the efforts to cut acid rain and other effects of NOx by working with industry to develop new control technologies. Present day efforts include using low- NOx burners and selective catalytic reduction (SCR) to meet future goals of NOx reduction. The DOE leads the effort to develop advanced technologies that achieve environmental compliance for the nation's coal-fired power plants. By developing new processes to produce energy, the DOE can help industry comply with future emission standards and improve the quality of the environment. One example of successful technology is used at the Ameren Sioux Unit 1 plant in the figure below.

Ameren’s Sioux Unit 1 has demonstrated the first in-furnace control technology that achieves NOx emissions below 0.15 pounds per million Btu on a coal-fired cyclone boiler—a 90% reduction over the unit’s baseline NOx emissions at half the cost of current technologies. Ameren is now reconsidering its plans to install standard NOx-control technology in favor of ALTA (Advanced Layered Technology Approach).

NETL Reducing NOx
The National Energy Technology Laboratory (NETL) is addressing the problem by initiating projects with technologies aimed at reducing NOx that can be used in existing power plants (see map below).

Source: NETL NOx Control Technologies

EPA Reducing NOx
Emissions Standards For Motor Vehicles
The U.S. Environmental Protection Agency (EPA) and state and local governments are working together to reduce NOx emissions. Reducing NOx is an important part of the EPA’s strategy for cleaner air. Initially, the effort began in the 1970s when the EPA created emission standards for motor vehicles. Manufacturers were required to design vehicles that emitted lower NOx emissions from vehicles. As a result of EPA’s program, all cars, pickups, SUVs, and vans will be as much as 95% cleaner by 2009.

Emission standards for electric utilities
Coal-fired power plants were tasked to reduce NOx emissions by 400,000 tons per year from 1996 to 1999. A second phase began in 2000 with a goal to reduce NOx by more than 2,000,000 tons per year. With the help of state-initiated reductions in the northeastern part of the country, the phase-II goal has been surpassed.

NOx Transport Rule for Midwest and Eastern States
NOx is also one of the main ingredients involved in the formation of ground-level ozone. The Clean Air Act not only requires states to reduce ground-level ozone, it also requires “upwind” states to implement programs to protect the “downwind” states. This means each state must account for its NOx emissions being carried by winds to another state. Also, the EPA has directed many states in the eastern half of the country to make further reductions in NOx by taking advantage of cleaner control strategies. Refer to the map below.

The Transport Rule makes states accountable for NOx emissions, which may affect another state because of prevailing winds.

Making Progress
Since implementation of the Clear Skies Initiative and continuing air quality programs, we expect to see very positive environmental improvements. Nitrogen deposition (one component of acid deposition) could be dramatically reduced by the year 2020 (see the map below).

Developing cleaner coal fired power generation is also an ongoing process. Initiation of the Clear Skies Initiative has motivated the government and industry to push the envelope on new power generating systems, including coal-fired power plants. We are developing new technologies that use coal to generate electricity that will reduce, and even eliminate, NOx emissions from the process.