See the context of this sign.

How's the View?

Look at the view of Grand Canyon today.
Is this good visibility or bad? The display on
the right side of this panel will tell you.
The display is linked to a transmissometer
which measures visibility conditions.

The transmissometer is just one example
of how the National Park Service monitors
pollution at Grand Canyon. Daily photographs,
samples of atmospheric particles, and
visibiity measurements provide scientists
with data about Grand Canyon's air quality.
This work is part of a nationwide program
by which researchers monitor the types and
amount of air pollutants in selected national
parks throughout the country.

Visibility Condition
The display on this panel indicates the current
visual range. Visibility--how far and how
clearly you can see--is affected by the amount
of pollution in the air. Air pollution also alters
your perception of the color and texture of
canyon features.

Other factors, such as the angle of the sun at
different times of the day, also affect the view.
The same scene may appear clearer or hazier
depending on the time of the day, even though
the concentration of pollutants is the same.

A transmissometer measures the amount of light
received from a distant light source. The more
pollution, the less light received. This light is
lost as fine particles of air pollution scatter or
absorb it. Sometimes visibility inside the canyon
is quite different from that above the rim.

Visual Range
One measure of visibility is visual
range--how far you can see.
Visual range at Grand Canyon
generally extends the farthest
during the winter when the park's
air is cleanest. The increase in
pollution haze during the summer
significantly reduces visual range.

The visual range depicted in this
photo is 130 miles (120 km), which
is the average visual range during
the winter. Some winter days have
excellent visibility, with a visual
range of 250 miles (400 km).

The visual range depicted in
this photo is 94 miles (152 km),
which is the average summer
visual range. During the summer,
visual range decreases because
south and southwest winds carry
air pollution from large cities and
other source. Only one-tenth of
the days are as clear as the average
winter visual range.

Grand Canyon's haziest days
still have much better visibility
than the humid, more polluted
air of the eastern United States.
In this photo visual range is less
than 68 miles (109 km), which
occurs only one-tenth of the time
in the summer. Can you see
Mt. Trumbull, 60 miles (100 km)
to the west of here?

Don't miss the rest of our virtual tour of Grand Canyon National Park in 10803 images.