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Basic Information 

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 

humid conditions. 

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 soot 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 particulate pollution.

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 environment?

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, available as a free download, to view the following file. See EPA's PDF page 

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Visibility

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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 of haze. 

Introduction to Visibility (PDF, 79 pp., 3.3 MB) - Report by William Malm, National Park 

Service and Colorodo State Institute for Research on the Atmosphere 

What other Federal agencies address visibility?

National Park Service 

U.S. Forest Service 

U.S. Fish and Wildlife Service 

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