Regional Haze

Haze is caused when sunlight is absorbed or scattered by airborne particles which, in turn, reduces the clarity and color of what we see.  Airborne particles are produced by a variety of natural and manmade sources.  Natural sources can include windblown dust, soot from wildfires, and even the evaporation of organics from plants. Manmade sources can include motor vehicles, electric utility and industrial fuel burning, incineration, mining, pulp mills, and other industrial sources.  For example, power plant emissions of sulfur dioxide (SO₂) lead to the formation of sulfate particles, which contribute to the formation of haze.

The Clean Air Act includes a goal to remedy any existing impairment of visibility – in national parks and wilderness areas– resulting from manmade sources of air pollution.  The Act also directs EPA to develop regulations that ensure the nation makes reasonable progress to attaining the goal.

In 1999, EPA issued the Regional Haze Rule, which requires the states, in coordination with EPA, the National Park Service, U.S. Fish and Wildlife Service, and the U.S. Forest Service, to develop and implement air quality protection plans to reduce the pollution that causes visibility impairment. Under the rule, states must compare the baseline visibility conditions in the years 2000–2004 to natural background conditions, and then determine the amount of progress needed to reach natural background conditions by the year 2064.  States will submit their first implementation plans under the Regional Haze Rule to EPA by January 2008.    These plans will outline various emission reductions programs, such as the Clean Air Interstate Rule (CAIR) and Clean Air Visibility Rule (CAVR), which the state will implement in order to achieve reasonable progress toward the goal.  These plans will be revised and resubmitted every 10 years.

The Clean Air Act also includes a requirement that certain existing stationary emission sources “which may reasonably be anticipated to cause or contribute to any impairment of visibility” must install “best available retrofit technology” (BART) in order to reduce emissions.   In July 2005, EPA published the CAVR which defines BART requirements for affected sources, including certain electric generating units (EGUs) that will be required to meet emission limits for SO₂ and nitrogen oxides (NOx), depending on their age, size, and configuration.  The requirements under CAVR are national in scope, but states can choose to determine that EGUs subject to the CAIR NOx and SO2 programs also satisfy the BART requirements for NOx and SO₂.  On October, 5, 2006, EPA finalized an alternative emissions trading program that gives flexibility for states to satisfy the BART requirements if the trading program meets or exceeds the visibility benefits resulting from CAVR’s source-by-source approach to BART.

© 2008 Edison Electric Institute