Seattle Urban Visibility Study

Here you will find information about:

• Why are we studying visibility?
• What does the visibility study involve?
• What questions will the visibility study attempt to answer?
• What does the difference between good and poor visibility look like?

Why are we studying visibility?

On a clear day you can see far from Kerry Park, located on the south side of Queen Anne Hill (altitude 320 feet). The Space Needle, downtown Seattle, the Duwamish industrial area and Mount Rainier are all visible. Unfortunately, long-term trends measured from Sea-Tac Airport showed that the number of clear days in the summer months has been decreasing since 1986. This information led to a wintertime visibility study 1991-1992. The purpose of that short-term study was to judge the feasibility and need of a larger, long-term visibility study. The results of this initial study led to the development of the year-round Seattle Urban Visibility Study.

Visibility is an integral part of air quality. The purpose of the Seattle Urban Visibility Study is to find out what kind of pollution is obscuring our view and what we can do to reverse the trend of decreasing visibility.

What does the visibility study involve?

The study is designed to document and track long-term visibility trends, determine what is causing decreased visibility, possibly set a visibility goal, develop and implement control methods to reduce emissions that decrease visibility, and evaluate the effectiveness of the emission reduction strategies.

For this study, an automatic camera located in Kerry Park takes pictures three times a day, recording visual images of visibility conditions. Concurrently, real-time measurements of scattering and absorption are taken at Beacon Hill. In addition, air samples are taken twice a week and the pollutants extracted from these samples are analyzed for chemical constituents.

What questions will the visibility study attempt to answer?

With the data that we collect, the study will attempt to answer the following questions:

• What is causing the problem?
  The study will analyze aerosol measurements to determine the chemicals responsible for visibility degradation.
  
• Where did it come from?
  The sources of the visibility degradation in our airshed will be determined using the constituents of the aerosol measurements and the known chemical fingerprints of major pollution contributors. Other urban visibility studies have shown that major contributors to visibility degradation include diesel and other mobile sources, wood burning, and industrial sources of sulfur dioxide and nitrogen oxides.
  
• What can we do about it?
  We will consider a visibility goal and possible control strategies. The public will also be surveyed to determine their willingness to improve visibility, either by payment or changing behavior, such as driving less.  The last stage of the visibility study will be to evaluate the effectiveness of the emission reduction measures that may be implemented.

  By increasing the visibility in the Puget Sound region, we will also be increasing the general health quality. Pollutants that diminish visibility also diminish the air quality causing breathing difficulties, eye irritation and reduced resistance to lung infections and colds.
  

What does the difference between good and poor visibility look like?

This picture of the view from Queen Anne toward Mt. Rainer was taken on a sunny day in May 1995.



This picture of the same view was taken on a sunny day in May 1996.

If you would like more information about the visibility study, please contact Naydene Maykut at (206) 689-4062 or 1-800-552-3565 ext. 4062. Or send an e-mail message to us.

Updated December 1996

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