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NPS » Explore Nature » Air » Monitoring » Visibility 

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Additional Information 

z Introduction to Visibility 

z NPS WebCams 

z IMPROVE Web Site 

z IMPROVE Newsletters 

z VIEWS Web Site 

z Air Atlas 

z ARIS 

z Publications 

z Studies 

Visibility Monitoring 

Overview 

Our national parks and wilderness areas offer stunning mountain vistas and scenery full of unique landscapes 

and geologic features. The enjoyment and appreciation of these are linked to one's ability to see clearly through 

the atmosphere. Unfortunately, air pollution affects our ability to see clearly. Small particles suspended in the 

atmosphere, mostly as a result of human-caused air pollution, often create haze -- a grey or white veil over the 

scene that scrubs it of its colors, forms, and textures and the lessens the visitor's experience of seeing "forever". 

The National Park Service and the U.S. Environmental Protection Agency (EPA) first began long-term visibility 

monitoring at selected national parks in 1979. In 1985, a national visibility monitoring program was established 

One of the clearest days at 

Yosemite National Park, California 

photograph

One of the haziest days at 

Yosemite National Park, California 

photograph

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called Interagency Monitoring of Protected Visual Environments, or IMPROVE. IMPROVE is a cooperative 

effort led by a Steering Committee of representatives from the EPA, U.S. Forest Service, National Park Service, 

Fish and Wildlife Service, Bureau of Land Management, National Oceanic and Atmospheric Administration, 

and several interstate air quality management organizations. 

The goals of the IMPROVE program are to 

z measure current visibility and aerosol conditions in mandatory Class I areas 

z identify chemical species and emission sources responsible for existing human-caused visibility 

impairment 

z document long-term visibility trends 

z and with the enactment of the regional haze regulations, to provide visibility monitoring representative of 

all visibility-protected Class I areas. 

More information about IMPROVE is available on the IMPROVE web site. The publications, Introduction to 

Visibility and Air Quality in the National Parks, 2nd edition, also provide good general discussions of visibility 

and how it is affected by air pollution.

Three types of visibility measurements are undertaken in the IMPROVE network: particle, scene, and optical. 

The mass and chemical composition of the suspended fine particulate matter (PM-2.5) and the mass of coarse 

particulate matter (PM-10) is measured by the particle monitor. Every IMPROVE site has such a monitor. 

The appearance of a scene viewed through the atmosphere changes under different particle concentrations and 

lighting conditions. The visual appearance of a scene is qualitatively documented with 35mm color slides, digital 

images, or video images. 

Optical monitoring measures the ability of the atmosphere to scatter and/or absorb light as it passes through it. 

Optical monitoring instruments used in IMPROVE include transmissometers and nephelometers. 

Locations 

US Visibility Monitoring Site Map

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Procedures 

The IMPROVE particle monitor consists of four independent sampling modules. Three modules collect only 

fine particles (PM2.5), while the fourth collects both fine and coarse particles (PM10). The IMPROVE monitor 

measures mass, chemical elements, sulfate, nitrate, organics, and elemental carbon. The samplers run for 24 

hours every third day collecting the particulate matter on filters. These filters are retrieved once a week and sent 

to contracted laboratories for physical and chemical analyses. Particle data are available on the IMPROVE and 

VIEWS (Visibility Information Exchange Web System) web sites. 

Scenic conditions are monitored by automatic camera systems that include cameras that take still photographs 

three times a day, and web cameras that upload new photos to a web site every 15 minutes. Collections of color 

images taken at many national parks by these camera systems are available on the IMPROVE web site. 

Optical measurements (pdf, 338KB) are also made at a handful of parks. These measurements include the 

attenuation of light over a given distance by transmissometers and light scattering in a sampled volume of air by 

nephelometers. 

Visibility is monitored at 50 units of the National Park System. Transmissometers, nephelometers, 

and automatic camera systems are deployed at selected locations. For a larger map with additional 

information, and a detailed table, please visit our Visibility Monitoring Locations web page. 

Particle Sampler at Big Bend 

National Park, Texas 

photograph

35 mm camera located in 

Tonto National Monument 

photograph

Transmissometer at Grand 

Canyon National Park, 

Arizona 

photograph

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Data 

* The VIEWS website is sponsored by the Regional Planning Organizations for the exchange of information 

relevant to regional haze, and as such, the website includes many different databases on air quality, including 

IMPROVE data. The website also utilizes many sophisticated data analysis tools. 

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Results 

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DataType Details Access Data

Metadata what, where, and when monitors have 

operated in national parks

Monitoring History Database

Particle elements, sulfate, nitrate, organic carbon, and 

soil concentrations and extinction estimates

IMPROVE website

VIEWS website*

Real-time Scenic and Air 

Quality Conditions

current on-line scenic views, ozone, PM2.5, 

and/or meteorological data

Web Cameras

Scenic Conditions photographic archive IMPROVE website/photos

Visibility total light extinction and extinction due to 

scattering

IMPROVE Optical Data

2005-2007 Average Visual Range in Kilometers 

Visibility data collected at national parks and wilderness areas by 

the NPS and other IMPROVE program participants have helped 

define spatial and temporal variations in visibility throughout the 

United States. For a larger map and additional information, please 

visit our Visibility Monitoring Results web page. 

US Average Visual Range Map 2005-2007

NPS Visibility Monitoring Program 

Manager Bret Schichtel (970) 491-8581

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updated on 07/12/2007 I http://www.nature.nps.gov/air/monitoring/vismon.cfm I Email: Webmaster 

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