How far can you see?
Every year there are over 280 million visitors to our nation's
most treasured parks and wilderness areas. Unfortunately, many
visitors aren't able to see the spectacular vistas they expect.
During much of the year a veil of white or brown haze hangs
in the air blurring the view. Most of this haze is not natural.
It is air pollution, carried by the wind often many hundreds
of miles from where it originated.
In our nation's scenic areas, the visual range has been substantially
reduced by air pollution. In eastern parks, average visual
range has decreased from 90 miles to 15-25 miles. In the West,
visual range has decreased from 140 miles to 35-90 miles.
What is haze?
Haze is caused when sunlight encounters tiny pollution particles
in the air. Some light is absorbed by particles. Other light
is scattered away before it reaches an observer. More pollutants
mean more absorption and scattering of light, which reduce
the clarity and color of what we see. Some types of particles
such as sulfates, scatter more light, particularly during
Where does haze-forming pollution come from?
Air pollutants come from a variety of natural and manmade
sources. Natural sources can include windblown dust, and
from wildfires. Manmade sources can include motor vehicles,
electric utility and industrial fuel burning, and manufacturing
operations. Particulate matter pollution is the major cause
of reduced visibility (haze) in parts of the United States,
including many of our national parks. Find out more about
Some haze-causing particles are directly emitted to the air.
Others are formed when gases emitted to the air form particles
as they are carried many miles from the source of the pollutants.
What else can these pollutants do to you and the
Some of the pollutants which form haze have also been linked
to serious health problems and environmental damage. Exposure
to very small particles in the air have been linked with increased
respiratory illness, decreased lung function, and even premature
death. In addition, particles such as nitrates and sulfates
contribute to acid rain formation which makes lakes, rivers,
and streams unsuitable for many fish, and erodes buildings,
historical monuments, and paint on cars.
You will need Adobe Acrobat Reader to
view the Adobe PDF files on this page. See EPA's
PDF page for more information about getting and using
the free Acrobat Reader.
How can I learn more about visibility?
How Air Pollution
Affects the View (PDF) (2 pp, 793 KB) -
EPA brochure describing the health and environmental effects
to Visibility (PDF) (79 pp.,
3.3 MB) - Report by William Malm, National Park Service
State Institute for Research on the Atmosphere
What other Federal agencies address visibility?
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