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Visibility Monitoring |
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| The spectacular vistas that Glacier is famous for are protected by Congress through the Clean Air Act of 1977. Clear visibility is an extremely important part of the experience of visiting Glacier National Park. Glacier’s visual landscape is often affected by weather but it is also affected by air pollution. Protection of the park’s visibility through the Clean Air Act recognized this relatively pollution free visibility. Maintenance and protection of this quality must be given the highest priority. | ||
 Grinnell Lake |
 Chief Mountain |
 View from Mt. Brown |
| What
is Visibility?
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Visual quality is often judged by how far one can see on a given day, and how distant or clear the objects being viewed appear compared to how they look on other days. Visibility may be impaired by both natural and human influences. The most common sources of natural visibility impairment in the region of Glacier National Park are organic carbon from forest fires, atmospheric moisture (humidity, mist, fog, rain and snow) and wind blown dust. The primary man-made condition affecting the park’s visibility quality is organic carbon from agricultural, slash, prescribed and wood stove burning. Other sources of man-made visibility reduction include local industry and road dust.
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| Current
Program
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Glacier
has been monitoring visibility since 1982 with the objectives of: 1)
developing a visibility data base, and 2) determining the impact of
existing conditions affecting visibility. The monitoring program at
Glacier is part of a continuous nationwide monitoring program network
called IMPROVE (Interagency
Monitoring of PROtected
Visual Environments).
Visibility is monitored in two different ways by two separate instruments at Glacier. These two monitoring instruments, working in concert, demonstrate the connection between particulates in the air and visibility reduction. A transmissometer monitors Glacier’s visibility by measuring visual range, temperature and relative humidity hourly. The transmissometer emits a chopped beam of light toward a receiver station 5.28 km away. The receiver gathers the light and outputs visual range (distance of visibility). At the receiver station visibility data is sent via satellite for compiling. A fine particulate sampler measures the particles in the air which influence visibility. The sampler measures the concentration and composition of these fine air particles that can impair Glacier’s visibility. Filters are changed weekly and sent to a laboratory for analysis. |
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 Clean vs Dirty Filter |
 Changing Filters |
 Air Filter Instrument |
| Glacier National Park Visibility Photographs | These six photographs represent a range of visibility conditions at Glacier National Park. The view is of the Garden Wall from Apgar Village showing a distance of 18.3 miles looking northeast. | |
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Visibility
greater than 220 miles Occurs less than 1% of the time |
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Visibility
135-220 miles Occurs 10-25% of the time |
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Visibility
80-105 miles Occurs 40-60% of the time |
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Visibility
40-60 miles Occurs 10-25% of the time |
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Visibility
less than 10 miles Occurs less than 1% of the time |
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Current
visibility from the webcam at the foot of Lake McDonald. Use it to compare
to the photos above.
Click photo to go to the Glacier National Park Webcam page. |
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| For more information on visibility monitoring in the National Parks, visit: http://www.epa.gov/air/visibility | ||
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Air Quality Monitoring Introduction
Website Visitor Center |
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