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Air Quality Program

Regional Haze

Have you ever looked out expecting to see a breathtaking view of Mount Rainier or the North Cascades, and been disappointed to see an ugly brown or white haze ruining the view? It's called "regional haze," and it's air pollution. Regional haze has reduced scenic views in national parks and wilderness areas from an average of 140 miles down to 35-90 miles in the western U.S.; and from an average of 90 miles down to 15-25 miles in the eastern U.S.


Causes of regional haze

Haze is caused when tiny particles in the air absorb and scatter sunlight between the object we are looking at (such as Mt. Rainier) and our eyes. More particles means more light is either absorbed or scattered, reducing the clarity and color of what we see.

Sources of fine particles

The particles that cause haze come from both natural and human-caused sources. Natural sources include windblown dust and soot from wildfires or other burning. Human-caused sources include motor vehicles, electric utility and industrial fuel burning, and manufacturing operations. Some of the particles that cause haze are emitted directly to the air.  Others are formed from gases that are carried many miles from their source. This is why we often see haze in areas that don't usually have other kinds of air pollution.

Fine particles have also been linked to serious health problems and environmental damage. Learn more about fine particle pollution.

Measuring visibility

We measure visibility by collecting and analyzing particles in the air as part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network. In Washington, there are 10 IMPROVE monitoring sites. One 24-hour air sample is collected at each site every three days, providing a total of 121 samples each year from each site.

Once the samples are collected, we analyze them for substances such as sulfate, nitrate, carbon-containing particles, and dirt and sand, all of which affect visibility. We calculate visibility based on the types and amounts of substances in the particles.

We show visibility in one of two ways:

  • Visual range (the number of miles or kilometers the naked eye can see) or
  • Deciviews (the number on a visibility index where the higher the number, the worse the visibility). A change in visibility of one deciview can be noticed by the human eye.

The photos below show the same view, looking west from the slopes of Mt. Rainier, with and without regional haze.

Another way to measure visibility is by using an instrument such as a nephelometer.

Improving visibility

The federal Clean Air Act requires states to protect and improve visibility in national parks and wilderness area.  The Clean Air Act has set a goal of returning visibility in these areas to natural conditions by the year 2064. Congress designated 156 national parks and wilderness areas as "mandatory federal Class 1 areas" where visibility is especially important.  All states must submit plans to EPA to reduce air pollutants that affect visibility in their mandatory Class 1 areas. 

Washington has eight Class 1 areas, totaling more than 3.3 million acres of land. They are:

  • Alpine Lakes Wilderness Area
  • Glacier Peak Wilderness Area
  • Goat Rocks Wilderness Area
  • Mt. Adams Wilderness Area
  • Mt. Rainier National Park
  • North Cascades National Park
  • Olympic National Park
  • Pasayten Wilderness Area

Ecology wrote a regional haze State Implementation Plan (SIP. This plan documents current conditions at our Class 1 areas. It also defines a strategy for returning visibility in these areas to natural conditions, as required by the Clean Air Act. Ecology worked closely with other states and organizations to write this plan, mostly through the Western Regional Air Partnership (WRAP).

Regional Haze State Implementation Plan

In the fall of 2010, Ecology held a public hearing and took public comments on the draft State Implementation Plan for regional haze. See Ecology's response to comments on the draft plan.

2011 Regional Haze State Implementation Plan Updates

In April 2011, Governor Gregoire signed into law an agreement between the TransAlta power plant in Centralia, environmental groups, the Governor's Office, and the local community. It requires the two coal boilers in Washington to meet specific greenhouse gas emission standards by a certain time. It also requires TransAlta to install "selective non-catalytic reduction" (SNCR) technology for reducing nitrogen oxides. See the law.

In the fall of 2011, Ecology held a public hearing and took public comments on draft revisions of the TransAlta BART compliance order, TransAlta BART technical support document - (TSD), and related parts of the Regional Haze SIP to comply with the new law. See Ecology’s response to comments on the 2011 draft revisions.

The final revised TransAlta BART documents are:

Updated Regional Haze SIP documents:

Links to more information

You can find more information at the following web sites:

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