The National Park Service, Air Quality Division, is responsible for preserving, 

protecting, and enhancing air quality and "air quality related values" in the National 

Park System by ensuring compliance with the requirements of the Clean Air Act and 

the National Park Service Organic Act. Air quality related values include visibility, 

flora, fauna, cultural and historical resources, soil, water quality, and virtually all 

resources that are dependent upon and affected by air quality. The Air Quality 

Division monitors air quality; reviews proposed major emitting sources, air quality 

legislative and regulatory proposals, and NPS and other federal or state air quality 

plans; develops data on sensitive park resources; researches acid precipitation; and 

develops meteorology and atmospheric dispersion modeling. 

The National Park Service disseminates the results of biological, physical, and social 

science research and monitoring through the Natural Resources Technical Report 

Series. Natural resources inventories, scientific literature reviews, bibliographies, and 

proceedings of technical workshops and conferences are also disseminated through 

this series. 

The purpose of this report is to present the final, validated gaseous pollutant and 

meteorological monitoring data collected at a unit of the National Park System. All data 

presented in this report have been collected using continuous monitoring methods 

designated by the U.S. Environmental Protection Agency (USEPA) as Reference or 

Equivalent Methods. Further, the data generally meet the USEPA monitoring and 

quality assurance requirements specified in 40 CFR Part 58, and the data have been 

entered into the USEPA's Aerometric Information Retrieval System (AIRS). All data 

contained in this report are accessible through AIRS. The ambient air quality data 

processing, validation and analysis was performed by AeroVironment Inc. of 

Lakewood, Colorado under National Park Service contract number CX-0001-9-0004, 

and the staff of the Monitoring and Data Analysis Branch of the Air Quality Division. 

Mention of trade names or commercial products does not constitute endorsement or 

recommendation for use by the National Park Service. 

Copies are available from the following: 

Chief, Monitoring and Data Analysis Branch (303) 969-2072 

Air Quality Division 

National Park Service 

P.O. Box 25287 

Denver, CO 80225-0287 

Or 

Technical Information Center (303) 969-2130 

Denver Service Center 

P.O. Box 25287 

Denver, CO 80225-0287 
AIR QUALITY IN THE NATIONAL PARKS 

A Summary of Findings from the National Park Service 

Air Quality Research and Monitoring Program 

Prepared by Energy and Resource Consultants, Inc. 

NPS Contract No. CX-0001-4-0054 

Christine Shaver, Chief 

Policy, Planning, and Implementation Branch 

Air Quality Division 

Darwin (Dee) Morse, Environmental Protection Specialist 

Policy, Planning and Implementation Branch 

Air Quality Division 

Donna O'Leary, Editor 

July 1988 

U.S. Department of the Interior 

National Park Service 

Air Quality Division 
ACKNOWLEDGEMENT 

Without the help and efforts of Mark Scruggs. Bill Malm, Miguel Flores, Jim 

Bennett, Ken Stolte. and Dave Ross this report would not have been possible. 

Special thanks also to Bob Rowe and Laurie Chestnut at Energy and Resource 

Consultants, Inc., for their help in drafting this report, to Rita Brasz for 

designing the illustrations, and to Christine Schumacher for text-processing 

support. 
CONTENTS 

 1.0 AIR QUALITY RESEARCH PROGRAM RESPONSIBILITIES AND ACTIVITIES / 1-1

Legislative Mandates / 1-1 

Schematic Of The Air Pollution Problem / 1-1 

NPS Air Quality Research and Monitoring Program / 1-3 

 2.0 VISIBILITY / 2-1 

What is Visibility? / 2-1 

NPS Visibility Monitoring Network / 2-6 

Visibility Conditions At Monitored NPS Units / 2-9 

Causes of Visibility Impairment At NPS Units / 2-20 

Points Raised By NPS Visibility Research / 2-26 

 3.0 EFFECTS Of VISUAL AIR QUALITY ON VISITOR EXPERIENCE / 3-1 

Human Perception of Visual Air Quality / 3-1 

Importance Of Visual Air Quality To Visitor Experience / 3-8 

Points Raised By NPS Visitor Experience Research / 3-13 

 4.0 CRITERIA POLLUTANTS IN NPS UNITS / 4-1 

NPS Criteria Pollutant Monitoring Program / 4-1 

Criteria Air Pollutant levels In NPS Units / 4-2 

 5.0 AIR POLLUTION EFFECTS ON BIOLOGICAL RESOURCES / 5-1 

Effects Of Air Pollution On Plants / 5-1 

NPS Biological Effects Studies / 5-5 

Findings Of NPS Biological Effects Research Program / 5-9 

Points Raised By NPS Biological Effects Research Program / 5-19 

 6.0 NPS PARTICIPATION IN PROTECTION OF AIR QUALITY RESOURCES / 6-1 

Review of Permit Applications and Environmental Assessments / 6-1 

Development Of Procedures for Protection Of NPS Resources / 6-6 

Effects On Air Quality From Activities Within MPS Units / 6-8 

Incorporation; of Air Quality Concerns Into Planning and Interpretive 

 Activities / 6-9 

 7.0 SELECTED REFERENCES / 7-1 

iii 
FIGURES 

1-1 Schematic of the Air Pollution Problem / 1-2 

 2-1 Examples of the Effects of Uniform Haze on Visual Range and Contrast in a 

 Vista at Big Bend National Park / 2-4 

 2-2 Examples of Layered Haze and Plume / 2-5 

 2-3A NPS Visibility Monitoring Network / 2-7 

 2-3B NPS Camera-Only Monitoring Sites / 2-8 

 2-4 Isopleths of Median Visual Range over the Western United States for Summer 

 1983 / 2-10 

 2-5 Median Summer Visual Range and Isopleths for Suburban/Nonurban Areas, 

 1974-1976 / 2-12 

 2-6 Seasonal Average Standard Visual Range, Fine Sulfur, and Fine and Coarse Mass 

 Concentrations, at Grand Canyon from 1979 to 1983 / 2-16 

 2-7 Year-to-Year Variation in Median Visual Range for Summer and Fall / 2-17 

 2-8 Spacial Distribution of Average Airport Visual Range in the Eastern United States 

 During the Summer from 1948 to 1983 / 2-19 

 2-9 Average Composition of Fine Particles at Several Sites, June 1982 to November 

 1983 / 2-24 

 2-10 Isopleths of Fine Sulfate to Fine Mass Ratio in the Western United States, June 

 1982 to November 1983 / 2-27 

 2-11 Origins of "Clean" and High Sulfur Content Air in the Colorado Plateau 

 Area / 2-28 

 3-1 Relationship Between Perceived Visual Air Quality and the Amount of 

 Particulates in the Air / 3-5 

 3-2 Examples of Contrast Measures of Brown Plumes at Navajo National Monument 

 /3-6 

 3-3 Percentage of Observers Who Could Detect a Nitrogen Dioxide Plume as a 

 Function of Plume Contrast / 3-7 

 3-4 Average Visitor-Rated Importance of Park Features / 3-10 

 4-1 NPS Gaseous Pollutant Monitoring Network / 4-3 

 5-1 Ozone Injury to Ponderosa Pine in Sequoia/Kings Canyon National Parks / 5-4 

 5-2 Ozone-Injured Common Milkweed in Catoctin Mountain Park / 5-4 

iv 
FIGURES (continued) 

 5-3 National Parks Where Studies of the Effects of Air Pollution on Biological 

 Resources Have Been Conducted as of Summer 1985 / 5-6 

 5-4 National Parks Where Effects of Air Pollution on Biological 

 Resources Have Been Found as of Summer 1985 / 5-10 

 6-1 Locations of Proposed Projects Reviewed by National Park Service Since 

 1979 / 6-2 

TABLES 

 2-1 Highlights of Findings of NPS Visibility Research / 2-2 

 2-2 Visual Range at NPS Visibility Monitoring Sites, Summer 1978-Fall 1984 / 2-13 

 2-3 Average Particulate Mass at NPS Monitoring Sites, June 1982 to November 1983 

 / 2-22 

 2-4 Categories of Fine Particulates / 2-23 

 3-1 Highlights of NPS Visitor Experience Research / 3-2 

 4-1 Ozone Monitoring Levels in NPS Units / 4-5 

 4-2 Sulfur Dioxide Concentrations at NPS Units / 4-7 

 5-1 Studies, Methods, and Determinations of NPS Biological Effects 

 Program / 5-8 

 5-2 NPS Units Where Foliar Injury to Vascular Plants Has Been 

 Documented / 5-12 

 5-3 NPS 1984 Milkweed Study Findings / 5-14 

 5-4 Ecological Effects Being Investigated at NPS Units / 5-15 

5-5 NPS Areas Where Elevated Levels of Toxic Trace Elements Have Been 

 Documented / 5-17 

v
SUMMARY 

The units of the National Park System contain some of the world's most spectacular 

scenery, unique cultural and historic resources, and diverse wildlife and vegetative 

communities. Millions of people visit the parks each year in search of rest, recreation, and 

physical and spiritual renewal. Visitors continue to be astounded and inspired by these 

national treasures and place a high value on knowing these resources are being protected 

and preserved for future generations. 

Air pollution can damage and destroy the very resources and values that units of the 

National Park System have been created to protect and preserve. Data collected through 

the National Park Service (NPS) air quality research and monitoring program show that 

the units of the National Park System are not islands isolated from the by-products of an 

urban and industrial society. Manmade air pollutants are transported long distances and 

have been detected at all NPS monitoring sites. Air pollution effects are often subtle and 

insidious. Therefore, it is important that air quality and air pollution effects on park 

resources and values be monitored so that even slight changes can be detected. 

The purpose of this report is to summarize findings from the NPS air quality research and 

monitoring program based on data collected through 1987. This information helps the 

National Park Service to remedy and prevent resource degradation so that future 

generations can enjoy the parks in as natural a condition as possible. 

Visibility monitoring has shown that, in addition to natural sources of visibility 

impairment, there are varying degrees of visibility impairment from manmade pollution in 

virtually all monitored parks. NPS research findings suggest that fine sulfate particles are 

the single most important contributor to visibility impairment in most NPS units. Fine 

sulfate particles, which can be transported long distances in the atmosphere, are 

primarily the result of sulfur oxide emissions from energy and industrial sources. In the 

Colorado Plateau area, where Grand Canyon National Park and several other NPS units 

are located, fine sulfate particles are responsible for 40 to 60 percent of the visibility 

impairment. In eastern areas of the country, fine sulfates play an even larger role in 

visibility impairment. In the Pacific Northwest, sulfates are not the primary cause of 

visibility impairment; instead, fine carbon from controlled burning of timber and 

agricultural land and natural forest fires plays a prominent role. 

Research on effects of visibility on the visitor experience in five NPS units indicates that 

clean, clear air is one of the most important features of these parks. It appears that 

visitors value an environment undisturbed by man above all other features of the parks. 

Research findings on the effects of changes in visual air quality suggest that a small 

increase in air pollution is more easily noticed and more disturbing to the human 

observer when the atmosphere is initially relatively clean. 

Ambient air quality monitoring has found that ozone concentrations are high in some NPS 

units and even exceed National Ambient Air Quality Standards in several of these areas. 

These high concentrations occur not only in NPS units located near urban areas, but also 

in areas that are relatively remote such as 

vii 
Acadia National Park. Some ozone occurs naturally, but most of the ozone in the lower 

atmosphere results from the photochemical reaction of manmade hydrocarbons, nitrogen 

oxides, and sunlight. Levels of sulfur dioxide as high as 40 percent of the short-term 

National Ambient Air Quality Standards are also found in some parks. It is especially 

significant that some injury to sensitive plant species has been documented at ozone and 

sulfur dioxide concentrations below the National Ambient Air Quality Standards. 

Biological effects research has found ozone effects, which appear as characteristic foliar 

injury, on one or more species of plants and trees in virtually every park surveyed. This 

suggests that ozone injury is a widespread problem that even occurs at NPS units remote 

from urban areas. There is also evidence suggesting that reduced growth and increased 

mortality of some sensitive species are occurring in some of the more heavily affected 

areas. Research has found an apparent loss of lichens in two urban parks and effects on 

these sensitive plants in many parks located near sources of sulfur dioxide. Elevated 

levels of sulfur and heavy metals have been found in vegetation in several parks. 

Information collected through the NPS air quality research and monitoring program has 

been used in a variety of decision-making arenas. The NPS Air Quality Division has 

reviewed permit applications for over 200 major industrial and energy facilities proposing 

to locate near NPS units to ensure that no adverse impacts to air quality related values 

would occur. Information regarding visibility impairment and ozone injury to vegetation in 

NPS units has been shared with the Congress and transmitted to the U.S. Environmental 

Protection Agency and state air quality control agencies to promote the development of 

national air pollution control programs and standards that will protect park resources. 

Air 

resource information is also shared with the public through interpretive programs and 

exhibits. 

viii 
1.0 AIR QUALITY RESEARCH PROGRAM RESPONSIBILITIES AND ACTIVITIES 

LEGISLATIVE MANDATES 

In 1916, Congress enacted the National Park Service Organic Act--a law which 

established the National Park Service (NPS) and directed the new agency "to conserve the 

scenery and natural and historic objects and the wildlife therein and to provide for the 

enjoyment of the same in such manner and by such means as will leave them unimpaired 

for the enjoyment of future generations" (16 U.S.C. 1). This mandate has two major 

objectives: (1) to protect park resources and (2) to ensure visitor enjoyment. The value of 

preserving scenic and natural settings has long been recognized as important for 

maintaining national parks, monuments, and recreation areas. 

The Clean Air Act, as amended in August 1977, provides one of the most important 

mandates for protecting air resources in NPS areas. In section 160 of the act, Congress 

states that one of the purposes of the act is "to preserve, protect, and enhance the air 

quality in national parks, national wilderness areas, national monuments, national 

seashores, and other areas of special national or regional natural, recreation, scenic, or 

historic value." 

The Clean Air Act also establishes stringent requirements for "class I" areas, national 

parks over 6,000 acres and national wilderness areas over 5,000 acres that were in 

existence on August 7, 1977. Federal land managers (defined as the Secretaries of the 

Interior and Agriculture) and the federal official charged with direct responsibility for each 

area have been given an affirmative responsibility to protect air quality related values in 

these areas from adverse impacts. Air quality related values are defined by the National 

Park Service as "visibility and those scenic, cultural, biological, and recreation resources 

of an area that are affected by air quality" (43 Federal Register 15016). 

Determination of an adverse impact on air quality related values requires identification of 

a current or potential impact and consideration of how it might affect park resources and 

visitor experiences. This determination combines information gathered from NPS 

research, information provided by a proposed new source applicant, and the federal land 

manager's judgment and experience about whether allowing this effect would be 

consistent with the National Park Service Organic Act. 

The Clean Air Act also defines a national goal of remedying existing and preventing future 

visibility impairment in class I areas. The act requires that states incorporate measures in 

their state implementation plans that will ensure reasonable progress toward this goal. 

SCHEMATIC OF THE AIR POLLUTION PROBLEM 

In order to carry out these responsibilities, the National Park Service must understand 

the cause and effects of air pollution. Figure 1-1 illustrates an air pollution problem from 

a resource management perspective. The NPS air quality research and monitoring 

program addresses the following questions that are illustrated in Figure 1-1. 

1-1 

1. Is There an Identifiable Effect? 

Can park personnel, visitors, or researchers identify an effect that might be related 

to air pollution? The right-hand side of Figure 1-1 represents a park area where 

effects on resources may be noticed. Such an effect might be impaired visibility, 

visible injury or stunted growth of plants, or an accumulation of potentially toxic 

substances in the ecosystem. 

2. What Might Be Causing The Effect? 

If an effect is identified, is it being caused by air pollution? This involves 

conducting studies in the park or in the laboratory, collecting and analyzing data 

on pollution levels in the air, examining plant tissue, and investigating other 

conditions that might be causing the observed effect. 

3. Where Are the Pollutants Coming From? 

If an identified effect is being caused by air pollution, what is the source of the 

pollution? This includes a determination of whether or not the pollution is 

manmade or natural. If it is manmade, the emissions sources need to be identified 

and the transport and transformation of the emissions in the atmosphere need to 

be understood in order for the pollution effects to be reduced or eliminated. 

NPS AIR QUALITY RESEARCH AND MONITORING PROGRAM 

This document summarizes the findings of the NPS air quality research program which 

was established in 1979. Air quality research is conducted to determine the current 

status of air quality in the NPS units and to identify any effects air pollution is having or 

may have on NPS resources or visitor experiences. Air quality research is also conducted 

to determine sources of air pollution in the parks and the sensitivity of park resources to 

air pollution. The NPS air quality research program provides information needed to 

participate effectively in decisions that can affect the air quality in and near NPS units, 

and helps the National Park Service to manage air quality resources as a part of its 

resource protection mandate. 

The NPS air quality research program involves an extensive network of monitoring for 

pollution, visibility conditions, and biological effects in NPS units. The monitoring 

program has included the following: 

• Teleradiometers for measuring visibility at over 30 parks. 

• Cameras for measuring visibility at over 50 parks. 

• Fine particulate monitors for identifying the causes and sources of visibility 

impairment at over 40 parks. 

• The use of biomonitors (species of plants known to be sensitive to air pollution) 

to identify the presence of air pollutants in several parks. 

1-3 
• Ozone monitors at over 30 parks for establishing baseline conditions, assisting 

the ozone effects research, and evaluating new pollution sources. 

• Sulfur dioxide monitors at over 25 parks for establishing baseline conditions, 

assisting the sulfur dioxide effects research, and evaluating new pollution 

sources. 

Air quality modeling is developed and used to study the transport and transformation of 

pollutants in the atmosphere. Information from the visibility monitoring network along 

with air quality models is used to determine the effect of manmade air pollutants on 

visibility at NPS units. The Park Service uses the information obtained from the air quality 

research and monitoring program to guide its participation in the following: 

• Resource management planning within the National Park Service. 

• Permit reviews concerning potential effects from increased emissions from 

proposed new major industrial and energy facilities outside park boundaries. 

• Participation with state and local officials and industry in reaching decisions to 

minimize or eliminate potential impacts to the park resources and to the visitor 

experience. 

• Reviews of environmental impact statements developed by other federal agencies 

concerning activities that might affect NPS units. 

• Regulatory and legislative analyses. 

• Development of interpretive programs for park visitors and training courses for 

NPS employees. 

1-4
2.0 VISIBILITY 

Most people have had the experience of visiting a beautiful park only to find fog, haze, or 

rain obscuring the scenery. In the mid-1970s Congress was made aware of the possibility 

that manmade pollution was affecting visibility even in remote areas of the country. In the 

1977 Clean Air Act Amendments, Congress responded to this concern by establishing a 

national goal of remedying any existing and preventing any future manmade visibility 

impairment in major national parks and wilderness areas and specifically requiring 

consideration of visibility in efforts to prevent deterioration of air quality in clean air areas. 

The preservation of unique scenic resources is very important to the National Park Service and 

specific vistas are often mentioned in legislation or congressional reports concerning the 

establishment of an NPS unit. For example, in a House report recommending establishment 

of Shenandoah National Park, the Southern Appalachian National Park Committee spoke 

of being able to see the Capitol and the Washington Monument on a clear day. Yet today, 

Washington, D.C. is rarely visible from Shenandoah, and there is evidence that the cause 

is manmade air pollution. In fact, NPS visibility monitoring has shown that in excess of 90 

percent of the time scenic vistas are affected by manmade pollution at all monitoring 

locations within the lower 48 states. Even at Grand Canyon National Park, the color and 

textural detail of the canyon are nearly always impaired to some extent by manmade haze. 

The NPS visibility research program was established, in part, in response to the concern 

that important scenic resources are being affected by air pollution or might be affected in 

the future. The program was also designed to provide decision makers with the tools, 

methods, and data needed to manage and protect visibility in the parks. 

An important part of the NPS visibility research program is a visibility monitoring network 

which gathers information about current visibility conditions at the parks. The monitoring 

network also provides information about the composition of the particles in the air 

associated with visibility impairment. This information can be used to determine how 

much of the observed visibility impairment is manmade, and what types of sources emit 

the identified particles. Analysis of the monitoring data and research on the transport and 

transformation of pollutants in the air help to identify the region and sources of the 

manmade pollutants that cause visibility impairment. Information from the visibility 

research program is applied to NPS resource management decisions, and conveyed to 

visitors through interpretive activities. Since the Clean Air Act requires NPS involvement 

in certain regulatory and permitting decisions, the information is also used to promote 

development of programs needed to protect NPS resources. The findings of the NPS 

visibility research program to date are summarized in Table 2-1. 

WHAT IS VISIBILITY? 

Atmospheric conditions, including particles and gases in the air, determine visibility 

conditions which influence how easily a person can see through the air. There are several 

different quantitative measures of visibility conditions that characterize different aspects 

of these conditions. 

2-1 
Table 2-1. Highlights of Findings of NPS Visibility Research 

CURRENT STATUS OF VISIBILITY AT NPS UNITS 

• In excess of 90% of the time, scenic vistas are affected by manmade pollution at all 

NPS monitoring locations. 

• The best visibility at monitored NPS units is in eastern Nevada, western Utah, and 

southern Idaho. The next best area is the Colorado Plateau region where the Grand 

Canyon and several other NPS units are located. 

• The worst visibility at monitored NPS units is in Shenandoah and Great Smoky 

Mountains National Parks. 

• Visual range at NPS units is typically best in winter and worst in summer when 

meteorological conditions are such that more pollution is transported from urban 

areas and industrial developments to remote areas, causing more uniform haze to 

occur than in the winter months. 

CAUSES OF VISIBILITY IMPAIRMENT AT NPS UNITS 

• Fine particles (diameter less than 2.5 microns) are generally responsible for a major 

share of visibility impairment at monitored NPS units. 

• Fine sulfate particles are the single most important contributor to visibility 

impairment in NPS units except in the northwestern United States where fine carbon 

from manmade and natural burning plays a more prominent role. Sulfate particles 

are primarily the result of manmade sulfur oxide emissions. 

• In the Colorado Plateau area, fine sulfate particles are responsible for 40% to 60% of 

the visibility impairment. In Shenandoah, fine sulfate particles appear to be 

responsible for over 70% of visibility impairment. 

• On the average, soil-related ("crustal") material is responsible for 10% to 30% of the 

visibility impairment. 

• Air masses containing the highest levels of sulfate particles at Grand Canyon appear 

to have previously passed over southern California. Air masses lowest in sulfate 

particles arrive at Grand Canyon from north of the park (Nevada and Utah). 

2-2 
Air pollution can be visible in three forms: uniform haze, layered haze, and plumes. The 

three photographs in Figure 2-1 illustrate uniform haze, which is a homogeneous haze 

that reduces visibility in every direction from the observer. The two photographs in Figure 

2-2 illustrate a layered haze and a plume, respectively. Layered haze is seen as a band or 

bands of discoloration, with a noticeable boundary between the more polluted and the 

cleaner air. A plume is a band of discoloration that can typically be seen to be coming 

from a nearby source. 

Which of these conditions might occur when pollutants are present will depend in large 

part on atmospheric conditions. Uniform haze occurs when the air is well mixed and 

pollutants are evenly distributed. A plume is formed when there is a surface wind to carry 

visible pollutants horizontally from an emission source into a stable atmosphere. 

The difference between layered haze and uniform haze is a matter of perspective. If the 

observer is positioned high enough to be looking over the top of the haze, it will appear to 

be layered. Layered hazes are usually seen from viewpoints overlooking a valley or canyon. 

Layered hazes are typically associated with stable air masses where there is little mixing of 

the air. This occurs more often in the winter than in the summer. Layered haze can be 

seen some of the time at almost all parks. Recent NPS studies have found that layered 

hazes can be seen at Mesa Verde and Bryce Canyon National Parks on about 80 percent of 

the winter mornings. The condition usually does not occur in the summer, but does 

periodically occur in the spring and fall. 

The most common measures of visibility as related to uniform haze are standard visual 

range, apparent contrast, light extinction, and contrast transmittance. Standard visual 

range, probably the most familiar measure, is the distance from an observer at which a 

black object just disappears against the horizon. This is a measure of how far a person 

can see and is one indication of how clear the air is. Apparent contrast is a measure of the 

contrast between the brightness of a large feature in the vista and the background sky. 

Light extinction is a measure of the light that is scattered and absorbed as it passes 

through the atmosphere and therefore does not reach an observer. More pollution in the 

atmosphere will cause more scattering and absorption and therefore increase the light 

extinction. Contrast transmittance is a measure of the ease with which the atmosphere 

transfers the image of the vista to the observer. 

Figure 2-1 shows three forms of visibility impairment in a view at Big Bend National Park. 

Each photograph shows the estimated level of standard visual range, apparent contrast of 

the dominant distant feature, and light extinction. Note the change in color, texture, and 

form that accompanies the change in the visibility conditions. The ability to see color, 

texture, and form is what has the most effect on the observer's enjoyment of the view. 

It is important to evaluate visibility conditions from the point of view of what the human 

observer sees. NPS research has made important contributions toward developing a 

measure of visibility that is appropriate for evaluating conditions in the parks. Standard 

visual range is a useful measure because it is easy to understand and is widely used, but 

it is not directly related to human visual perception and does not always reflect changes in 

how well an observer can see specific vista features. The results of NPS visibility

2-3 


perception research indicate that understanding the visual effects of a change in air 

quality requires consideration of the features of the vista as well as what is in the air, and 

that the most appropriate measure of visibility is one that reflects the change in color, 

texture, and form in a scene that is associated with a change in air quality. Contrast 

transmittance is a measure that meets these goals, but it has not been widely used 

because it is difficult to measure and is not as easy to understand as visual range. 

NPS VISIBILITY MONITORING NETWORK 

Visibility conditions are monitored by the National Park Service at over 50 park units 

throughout the United States. Figures 2-3 A and B show the locations of these NPS 

monitoring sites. The NPS visibility monitoring network has been growing and evolving 

since it was established in 1978. Most of the selected sites are at class I areas, which the 

Clean Air Act Amendments of 1977 singled out for special visibility protection. Some 

other sites were included in response to a particular visibility problem, or because visual 

air quality was an especially important value at those parks, or because they were 

situated along an important pollution transport pathway. In parks where sufficient data 

were collected, monitoring stations have been transferred to other NPS areas. 

Special congressional appropriations in 1986 and 1987 allowed for the addition of 17 new 

class I sites to the network, including Arches, Badlands, Carlsbad Caverns, Haleakala, 

Hawaii Volcanoes, Isle Royale, Lassen Volcanic, Petrified Forest, Redwood, Virgin Islands, 

Voyageurs, and Yellowstone National Parks; Denali National Park and Preserve; 

Bandelier, Great Sand Dunes, and Pinnacles National Monuments; and Point Reyes 

National Seashore. Also, in 1986, 14 existing NPS class I area monitoring sites, as well as 

Denali National Park and Preserve, became part of the Interagency Monitoring of 

Protected Visual Environments (IMPROVE) program. The IMPROVE program was 

established to meet regulatory requirements and is managed by a committee composed of 

the U.S. Environmental Protection Agency, the National Park Service, and other federal 

land managers. In 1988, Tonto National Monument was added to the IMPROVE network 

as a surrogate for a class I wilderness area managed by the U.S. Forest Service. 

Figures 2-3 A and B also show, that most of the monitoring is conducted in western 

parks. This is primarily because the weather conditions, open panoramas, and the 

relatively clean air typical in western parks result in long-distance views that are sensitive 

to small changes in air pollution. 

Before 1986, the NPS visibility monitoring effort consisted of cameras which produced a 

photographic record of how the view changes under different weather, sunlight, and air 

pollution conditions; the use of teleradiometer equipment to measure visibility levels in 

terms of contrast; and a measurement of the particles in the air using particulate 

samplers and laboratory analysis. A "fully complemented" site included a camera, 

teleradiometer, and particulate sampler. Some sites had automatic equipment, while 

others required a park staff person to take photographs and/or measurements manually 

each day. Most of the NPS monitoring sites were fully complemented, but some had only 

one or two of the monitoring components, usually a camera or a camera and a particulate 

sampler. 

2-6 


Standard visual range estimates were derived from photographs and from the information 

recorded by the use of teleradiometers. Teleradiometers measured the contrast of a 

landscape feature against the background sky. The target was typically a dark dominant 

distant feature in the vista, such as a mountain, and the same target was used for each 

reading. Because teleradiometers needed a dark target, accurate readings were not 

possible if the target was covered by snow or clouds. Teleradiometers have been phased 

out, since techniques have been developed for determining standard visual range and 

contrast values directly from photographic slides. In addition the camera network has 

been fully automated. 

Particulate samplers, which capture particles up to 15 microns in diameter are still being 

used at about 30 parks. However, since 1986, most particle monitors have been upgraded 

to allow measurement of additional visibility reducing aerosols, such as carbonaceous 

materials and nitrates. Particles are analyzed for elemental composition which suggests 

potential sources. Further analysis of visual range and particulate data helps determine 

the effect each pollutant has on visibility. 

In 1986, the National Park Service also began deploying instruments called 

transmissometers that are capable of directly measuring light extinction. A fully 

complemented site now consists of an automatic camera, an upgraded particle monitor, 

and a transmissometer. The 17 new monitoring sites added in 1986 and 1987, as well as 

all sites in the IMPROVE network, are expected to be fully complemented. 

VISIBILITY CONDITIONS AT MONITORED NPS UNITS 

Although weather conditions certainly affect visibility, results from the NPS visibility 

monitoring network show that reduced visibility is almost always associated with the 

presence of particles in the air that are known to be manmade. 

Differences in Visibility Levels Among NPS Units 

The visual range levels described in this section are the result of a combination of 

manmade and natural conditions. Teleradiometer readings taken when the target is 

covered with snow or completely obscured by clouds are not used in the median visual 

range calculations, because dark-colored targets are necessary for accurate contrast 

measurements, but the figures reflect the effects of fog, rain, and naturally produced 

particles, as well as manmade pollution. 

Figure 2-4 shows median standard visual range for the western United States for the 

summer of 1983 from June through August. The median value means that 50 percent of 

the time visual range is at this level or above. Summer of 1983 is used as an illustration of 

the typical geographical variation in visual range during the peak visitor season. Other 

summers generally show a similar pattern. Median visual range is approximately the same 

within the like-colored areas, each of which represents an increment of 20 kilometers 

visual range. For example, within the noncolored areas, median visual range is more than 

190 and less than 210 kilometers. 

2-9 

Figure 2-4 indicates that the area with the best visibility is in Nevada, Utah, and Idaho, 

with a median summer visual range between 190 and 210 kilometers. The second best 

visibility is in the area including most of the Colorado Plateau region where several wellknown NPS units (including the Grand Canyon National Park) are located. The next best 

visibility occurs in southern Arizona, most of New Mexico, and the Front Range area of 

the Rocky Mountains. The worst visibility in the western United States occurs along the 

coastal areas of California and Washington. 

NPS research indicates that at least 50 percent of the visibility impairing particles in the 

air at NPS units in the Southwest, Rocky Mountain Front Range, and Great Plains areas 

is manmade. This is discussed in more detail in the section on causes of visibility 

impairment, but it is important to note that manmade pollution is a significant influence 

on the levels of visual range illustrated in Figure 2-4. 

There are not enough NPS monitors in the East to extend this map across the entire 

country, but average median visual range for the same time period in Shenandoah 

National Park was 19 kilometers as opposed to over 100 kilometers in most western 

parks. 

Figure 2-5 shows median visual range during the summer for the East, based on 1974-

1976 data from suburban and nonurban airports. This figure is taken from a 1978 U.S. 

Environmental Protection Agency (EPA) report based on analysis of airport visual range 

data. This is not necessarily representative of visibility at NPS units but gives an idea of 

typical visual range levels outside of urban areas in the region. The worst visibility in the 

East occurs along the Mid-Atlantic Coast, the Gulf Coast, and the Ohio River Valley. The 

best is in northern New England. Comparing Figure 2-5 to Figure 2-4 shows that visual 

range in the summer months in the East is typically an order of magnitude lower than in 

the West. 

Table 2-2 gives the median visual range for all monitored sites in the NPS network since 

the start of monitoring in 1978. To put these visual range figures in perspective, the 

theoretically best possible visual range that can be measured using a teleradiometer is 

about 390 kilometers. A dash indicates insufficient data and the median visual range for 

the season was not calculated. This occurs more often in the winter when targets are 

more likely to be snow-covered. The data in this table show that visual range is typically 

much lower in the eastern parks than in the western parks throughout the year. 

Also included in Table 2-2 are the average 10th percentile and 19th percentile visual 

range levels for the summer season in each park over the monitored period to give an 

indication of the range of values typical for each park during the peak visitor season. The 

10th percentile means that visual range is at that level or below 10 percent of the time. 

The 19th percentile means that visual range is at that level or above 10 percent of the 

time. 

Seasonal Variation in Visual Range at NPS Units 

Figure 2-6 A illustrates the typical seasonal variation (averaged over 1979-1983) in visual 

range at Grand Canyon National Park. Visual range is best in winter, averaging about 

250 kilometers, and is worst in summer, averaging about 

2-11 


150 kilometers. A similar pattern of best visual range in winter and worst in summer can 

be observed at most parks listed in Table 2-2. 

The reason for this seasonal pattern is believed to be that the air is typically more stable 

in the winter allowing for less transport of air pollution from areas of high emissions, 

such as cities and industrial sites, to remote areas where parks are located. In winter 

there is a more frequent occurrence of temperature inversions, and stable air masses 

tend to trap emissions in urban and industrial areas. (A temperature inversion occurs 

when the air closest to the ground is colder than the air above it. The warmer air acts as 

a lid keeping the colder air and the emissions in it close to the ground.) In summer there 

is more mixing and transport of air masses and pollution emissions so that urban and 

industrial areas are typically more clear and remote areas are less clear than in the 

winter. Exceptions to the pattern of high winter and low summer visual range at a park 

occur more often if an urban or industrial pollution source is located nearby. 

Figures 2-6 B and C provide supporting evidence that seasonal differences in longdistance transport of pollutants are partially responsible for the seasonal variation in 

visual range. Figure 2-6 C shows the seasonal average amount of fine particles in the air 

at Grand Canyon National Park. These are manmade and naturally emitted particles that 

can be transported long distances in the atmosphere. Fine sulfur is one type of fine 

particle that is known to be the result of manmade emissions. Seasonal averages for fine 

sulfur at Grand Canyon are shown in Figure 2-6 B. The total fine mass and fine sulfur 

mass are highest in the summer and lowest in the winter, suggesting that these particles 

are contributing to the seasonal pattern of visual range. 

Figure 2-6 D shows that coarse mass is also highest in summer and lowest in winter. 

Coarse mass is made up of large particles such as wind-blown dust that are not 

transported long distances due to their size. They are the result of natural and manmade 

activity and are highest in summer probably because there is less moisture in the soil 

allowing particles to be more easily entrained by surface winds. Figure 2-6 D suggests that 

seasonal differences in coarse mass also contribute to the seasonal pattern of visual range 

observed at Grand Canyon. 

Although coarse and fine mass have the same seasonal variation at Grand Canyon, this 

trend does not hold at all monitoring sites. Coarse mass tends to be dependent on local 

terrain and meteorological conditions. For instance, at Big Bend National Park coarse mass 

is highest during spring and fall and lowest during summer months. Since Big Bend is 

quite dry year-round, coarse mass concentrations reflect seasonal wind conditions. 

Year-to-Year Variation in Visual Range in NPS Units 

The year-to-year variation in median summer and median fall visual range is illustrated in 

Figure 2-7 for nine parks in eight different geographical areas. Two seasons are shown 

because the year-to-year variation is somewhat different for each season. Summer and fall 

were selected because more complete data are available for these seasons than for winter 

and spring when snow cover is more common. A park with the most available years of 

data was selected for each of the geographical groupings that were used in Table 2-2. 

2-15 


Two parks from the Colorado Plateau area were included to show that the same pattern 

applied to both. Canyonlands and Grand Canyon National Parks show a similar pattern 

in summertime visual range with a decline to 1981 and an increase to 1983 and 1984. 

Fall visual range levels at both parks show a somewhat different pattern from the 

summertime variation. In the Southwest Desert area, visual range at Big Bend National 

Park shows little variation in summer or fall levels. Little variation is apparent in the 

Great Plains area at Wind Cave National Park. 

None of these parks shows a clear improvement or deterioration in visual range over this 

time period, but 3 to 7 years of data are considered insufficient to average out the effects 

of year-to-year meteorological variation. A few more years of data and more analysis of 

emissions and transport will be needed to determine if the contributions of manmade air 

pollution to visibility impairment in the NPS units are changing or remaining the same 

over the long term. 

Historical Trends in Visual Range Outside the National Park System 

Airport visual range data from the 1940s through the 1970s provide some information 

about long-term visibility trends throughout the country. Airports are typically located 

close to populated areas so visibility there may not be representative of visual range in 

national parks, but these data do provide relevant information. Studies using these data 

to analyze historical trends in visual range are summarized in the 1979 U.S. 

Environmental Protection Agency report to Congress, "Protecting Visibility," and in the 

1985 U.S. Environmental Protection Agency Visibility Task Force report "Developing LongTerm Strategies for Regional Haze." The historical trends in visibility presented in these 

studies indicate that manmade pollution has contributed to a general decline in visual 

range in many parts of the country over the last several decades, especially in nonurban 

areas and in the summer, suggesting that NPS units may have been affected. Summer 

trends are especially important because the summer is the peak visitation period for most 

national parks. 

The airport visual range studies show that summer visibility conditions in the East have 

deteriorated dramatically from the 1940s to the 1970s. Figure 2-8 shows the decline in 

average summer visual range in the East over the period 1948 to 1983. The authors note 

that the scales chosen for this figure mask a modest improvement in visibility in some 

areas of the southeastern United States since 1972. Visual range during the cool seasons 

showed some improvement in the northeastern region and significant deterioration in the 

Gulf Coast region over this period. The overall result was that by the early 1970s summer 

became and has remained the season with the poorest visibility in the East. 

This decline in summer visibility has been correlated with a change in the seasonal 

pattern of electricity production. In the 1950s there was a clear peak in production during 

the winter with lower levels throughout the rest of the year. By the 1970s electricity 

production showed two peaks in the year, one in the winter and one in the summer. 

While this does not prove that the deterioration in the summer visibility is a result of 

manmade pollution, it is strong circumstantial evidence. 

Studies that have examined differences between airport visual range trends in urban 

areas and in suburban/nonurban areas have found a significant decline in 

2-18 

visual range in suburban/nonurban areas, while visual range in urban areas has stayed 

about the same or improved slightly. This has been found in the East and in California 

and suggests that reduced visual range has changed from a local to a regional 

phenomenon. 

Analysis of airport visual range data in the Rocky Mountain Southwest shows a 

deterioration of about 10 to 30 percent from the mid-1950s to the early 1970s and a 

slight improvement (5 to 10 percent) into the mid-1970s. This improvement occurred 

especially at sites in or near Arizona and coincided with a reduction in emissions from 

Arizona copper smelters which occurred during that period due to a shut down in their 

operations. 

CAUSES OF VISIBILITY IMPAIRMENT AT NPS UNITS 

Understanding what causes changes in visibility conditions is essential if the National 

Park Service is to protect visibility in the parks now and in the future. Analysis of the 

particulate data from the NPS visibility monitoring network suggests possible sources of 

air pollution associated with visibility impairment. 

In the absence of manmade pollution, visibility is limited by the light scattering of air 

molecules and naturally occurring aerosols such as water droplets and wind-blown dust. 

Aerosols are small solid or liquid particles suspended in the air. Some are emitted 

directly and many are formed by the atmospheric reaction of natural and/or manmade 

gaseous emissions. 

Relative Effects of Different Particles on Visibility 

Aerosols scatter light to different degrees, depending on their size, and are the primary cause of haze 

in the atmosphere. Because different size particles reduce visibility with varying degrees of 

efficiency, it does not necessarily follow that an aerosol species making up a certain fraction of the 

total mass of aerosols in the atmosphere will be responsible for that same fraction of visibility 

reduction. In fact, fine aerosols, particularly those with diameters between 0.2 and 1.0 micron (less 

than one-tenth the diameter of a fine human hair), are the most efficient at scattering light and 

therefore cause a larger fraction of visibility reduction than their fraction of total mass. Coarse 

particles, with diameters of 2.5 to 15 microns, also contribute to visibility impairment, but not in 

proportion to their fraction of total mass. For example, coarse particles typically make up about 60 

percent of total particulate mass at the Grand Canyon National Park and other parks in the 

southwestern United States, but typically cause only about 20 percent of the visibility reduction, 

because they do not reduce visibility as much as smaller particles. 

Special attention has been given to fine sulfate particulates, which almost entirely come 

from manmade emissions of sulfur oxides. Fine sulfate particles most commonly occur in 

the form of ammonium sulfate particles that are particularly efficient at scattering light 

due to their size. 

Preliminary research suggests that fine particles at Grand Canyon are typically about 

one-third sulfate, but sulfates usually cause about two-thirds of all the 

2-20 
visibility impairment. The amount of fine sulfate particles present in the atmosphere may 

therefore be an important indication of the extent of manmade visibility impairment. 

Composition of Particulates at NPS Units 

Table 2-3 shows the average coarse, fine, and total particulate mass measured at NPS 

monitoring sites for June 1982 to November 1983. One-half to two-thirds of the total 

particulate mass is made up of coarse particles at most of the NPS sites. An exception is 

Shenandoah National Park where a higher percentage of total mass is made up of fine 

particles. Because NPS studies have shown that fine particles are responsible for more 

visibility impairment than coarse particles, even though coarse particles make up more of 

the total particulate mass in the air, NPS research has emphasized analysis of the 

composition of the fine particles measured at NPS monitoring sites. 

Table 2-4 gives the five categories of fine particles used in the analysis and lists the 

sources of each type of particle. In this analysis, all the sulfate particles are presumed to 

be ammonium sulfate. Since this is the most common form, this provides an acceptable 

approximation. Nitrates are another aerosol that results from manmade emissions, in 

this case emissions of nitrogen oxides. These are included in the "other" category. 

Figure 2-9 shows the average composition of fine particles at four NPS monitoring sites for June 

1982 through November 1983. Each site is in a different geographical region and the differences 

between them are indicative of the differences between these regions. The diameter of each circle is 

proportional to the total mass of fine particles typical for each park. 

In the East, fine particles at Shenandoah National Park are almost 60 percent 

ammonium sulfates. This means that more than half of the fine particles in this area are 

the result of manmade emissions. Soil and smoke make up a fairly small percentage of 

all fine particles at Shenandoah. The total amount of fine particles is highest at 

Shenandoah relative to the other three parks shown. 

In the Great Plains, about one-third of the fine particles at Theodore Roosevelt National 

Park are ammonium sulfates. Soil and smoke make up a higher percentage of fine mass 

than at Shenandoah, but less than at the other western sites. 

In the Colorado Plateau area, fine particles at Grand Canyon National Park are also 

about one-third ammonium sulfate. Smoke and soil combined make up about another 

one-third, which is a higher percentage than at Shenandoah and Theodore Roosevelt. 

The total amount of fine particles is smallest at Grand Canyon relative to the other three 

parks shown. 

In the Southwest Desert area, fine particles at Big Bend National Park are more than 

one-third ammonium sulfate. Soil is a large component relative to the other sites, making 

up about one-fourth of all fine particles. Smoke is about 6 percent of fine particles, 

similar to the percentage at Theodore Roosevelt National Park. 

2-21 
Table 2-3. Average Particulate Mass at NPS Monitoring Sites 

June 1982 to November 1983 

 Coarse Fine Total 

 Mass % of Total Mass % of Total Mass 

 (microgram per cubic meter) 

6.4 63% 3.7 37% 10.1 

4.3 62% 2.6 38% 6.9 

Arches 

Bandelier Bryce 

Canyon 

Canyonlands 

Chaco Culture 

Dinosaur 

Grand Canyon 

Mesa Verde 

 9.7 68% 4.6 32% 14.3 

 5.8 57% 4.4 43% 10.2 

 4.7 62% 2.9 38% 7.6 

 8.0 70% 3.5 30% 11.5 

 7.1 65% 3.8 35% 10.9 

 8.4 68% 4.0 32% 12.4 

 4.9 60% 3.2 40% 8.1 

 3.9 53% 3.5 47% 7.4 

Big Bend 

Chiricahua 

Guadalupe Mountains 

Joshua Tree 

Tonto 

 9.2 61% 6.0 39% 15.2 

 6.6 58% 4.8 42% 11.4 

 8.7 65% 4.7 35% 13.4 

 7.3 62% 4.5 38% 11.8 

 8.7 62% 5.3 38% 14.0 

Capulin Volcano 

Glacier 

Grand Teton 

Rocky Mountain 

 5.6 62% 3.5 38% 9.1 

 5.0 49% 5.3 51% 10.3 

 3.2 37% 5.5 63% 8.7 

 4.6 57% 3.5 43% 8.1 

Theodore Roosevelt 

Wind Cave 

 8.6 65% 4.6 35% 13.2 

 6.4 60% 4.3 40% 10.7 

Death Valley 

Lassen Volcanic 

Yosemite 

 9.6 65% 5.2 35% 14.8 

 4.2 56% 3.3 44% 7.5 

 5.1 49% 5.4 51% 10.5 

Crater Lake 

Lava Beds 

Mount Rainier 

 3.4 51% 3.3 49% 6.7 

 3.5 51% 3.4 49% 6.9 

 7.2 56% 5.7 44% 12.9 

Shenandoah 5.7 36% 10.1 64% 15.8 

Craters of the Moon 

Lehman Caves 
Table 2-4. Categories of Fine Particulates 

Fine Particulate 

Category Definition Common Sources 

Aerosols formed in the • Power plants 

atmosphere as a result • Smelters 

of sulfur oxide emissions • Oil and gas fields 

• Refineries 

• Industrial boilers 

Soot and organic material • Prescribed forest 

emitted from open burning burning 

• Natural forest fires. 

• Agricultural burning 

• Wood stoves and 

 fireplaces 

Fine particles of wind- • Wind/ground 

blown dust • Surface mining 

• Construction 

• Traffic on dirt 

roads 

Fine metal particles such • Industrial processing 

as copper, lead, and zinc • Mining 

• Soil 

• Smelter operations 

• Motor vehicles 

Other Nitrates and organic * Power plants 

 aerosols and undefined • Motor vehicles 

 fine aerosols • Refineries 

• Vegetation 

• Combustion processes 

2-23 

Ammonium sulfates 

Smoke 

Soil 

Metal 

Figure 2-10 shows the average percentages of fine particulate mass made up of fine 

sulfate (ammonium) for June 1982 through November 1983 at the monitored NPS units 

throughout the western United States. Sufficient NPS data were not available to extend 

this to the entire country, but the sulfate component of fine particles is about 60 percent 

at Shenandoah National Park, which is higher than any of the monitored parks in the 

western United States. The sulfate content of fine particles sampled at NPS sites is the 

lowest at sites in the Pacific Northwest and northern Rocky Mountains. Smoke is typically 

the largest component of fine particles in the Pacific Northwest due to the extensive use of 

agricultural and prescribed forest burning. 

Locations of Sulfate Aerosol Sources 

The National Park Service has conducted analyses to determine the origins of sulfate 

aerosols found at NPS monitoring sites. The origins of sulfate aerosols have been studied 

through back trajectory residence time analyses, which use particulate monitoring data 

and meteorological data to model the path that the particles may have taken. Back 

trajectory analyses have been used to identify the major source regions from which 

"extreme" sulfur concentrations arrive at the Colorado Plateau. 

The results are illustrated in Figure 2-11. Air masses carrying high sulfur concentrations 

apparently come most often from southern California, a heavily populated urban area. 

Under some meteorological conditions, air masses carry high sulfur concentrations to the 

Colorado Plateau from southern Arizona, an area with several copper smelters. 

Similar analysis for low sulfur days shows that "clean air" is more likely to come from the 

areas to the north of Grand Canyon National Park. Under some meteorological conditions, 

air masses come to the Colorado Plateau from the north and this air is typically 1 ow in 

sulfur content. One important implication of these findings is that an increase in 

emissions of sulfur dioxide to the north of the Grand Canyon (which could be expected 

from major new development of energy resources and urban growth in the region) could 

reduce the frequency of clear air days at the Grand Canyon and other parks in the 

Colorado Plateau region by increasing the pollution of the air masses that typically bring 

clean air to the area. Increases in pollution are more noticeable when the air is initially 

clean. Small increments in pollution from the north would be more noticeable than the 

same increment from the southern California area. 

Back trajectory analyses are being conducted for other parks to identify likely locations of 

sulfate sources. These parks include Big Bend, Glacier, and Theodore Roosevelt National 

Parks. Results have shown the following: 

1. The primary source of high sulfate concentrations at Big Bend appears to be an 

urban and industrial region in north-central Mexico (Monterey) and the Gulf Coast 

of Texas, where there is extensive oil and gas production and refining. 

2. Areas identified as sources of high sulfate concentrations at Glacier are the Front 

Range of the Rocky Mountains in Canada, North Dakota, and the Pacific 

Northwest. 

2-25 
3. Areas identified as sources of high sulfate concentrations at Theodore Roosevelt 

are the Midwest, where there is extensive urban and industrial development and 

local areas near the park where there is oil and gas extraction. 

A state-of-the-art, long-range transport model has been developed and used by the 

National Park Service to estimate sulfur dioxide and sulfate concentrations within large 

regions of the eastern United States that include Shenandoah, Acadia, Great Smoky 

Mountains, and Mammoth Cave National Parks. To provide useful information for the 

Park Service, this model had to extend the cap-ability of available transport models to 

include tracking air pollution movement in complex terrain typical of areas where NPS 

units are located. 

The model was applied using data from selected time periods during the summer of 1978. 

Results have shown that a high percentage of the airborne sulfates at these four parks 

has resulted from emissions quite distant from the parks. Specific findings for each of the 

parks are as follows: 

1. Approximately three-fourths of the airborne sulfate concentration at Shenandoah 

is a result of source emissions located more than 100 kilometers from the park. 

2. Long-distance sources play a dominant role in the atmospheric sulfate and wet 

deposition at Acadia. In addition, the results suggest that the park appears 

particularly susceptible to the effects of long-distance transport during periods of 

persistent southwesterly flow when the Bermuda subtropical high-pressure system 

dominates the eastern United States. 

3. Approximately nine-tenths of the sulfate concentrations at Great Smoky 

Mountains is attributable to sources more than 250 kilometers from the park. 

4. At Mammoth Cave 40 to 60 percent of the sulfate concentrations are attributable 

to sources more than 150 kilometers from the park. 

These modeling analyses show that industrial areas in the Ohio River Valley and Midwest 

generally contribute substantially to high sulfate episodes in eastern park units. 

POINTS RAISED BY NPS VISIBILITY RESEARCH 

Research efforts to understand the effects of manmade pollution on visibility and to assist 

the National Park Service in visibility management decisions continue to raise concerns. 

This section provides a brief discussion of these concerns. 

Role of Organic Aerosols in Visibility Impairment 

NPS researchers have found evidence to suggest that organic aerosols, which are small 

airborne particles that undergo rapid change in the atmosphere, may 

2-26 


2-29 

be a more significant cause of visibility impairment than was previously believed. 

For example, when the known effects of different particles on visibility are used to predict 

the visual effects of a mixture of particulates measured at an NPS monitoring site, the 

predicted effect on visibility is less than what is actually measured. Even when the effects 

of water vapor, which also is not measured by a particulate sampler, are considered, it 

still appears as if there is something else that affects visibility. Organic aerosols may be 

contributing as much as 30 percent of all visibility impairment. In fact, results from a 

study at Grand Canyon suggest that 30 to 40 percent of visibility impairment may be due 

to organic aerosols which are more volatile than ammonium sulfates. Consequently, most 

of the particle monitors being used in NPS units have been upgraded so that a better 

estimate of these aerosol concentrations, including organic carbon, can be made. 

Appropriate Measurement of Visibility Conditions 

The selection of visibility monitoring instrumentation is made difficult by the lack of an 

officially accepted definition of visibility. However,, the following three distinct types of 

information are thought to be required in a visibility monitoring program: 

1. The characteristics of a scene viewed at a distance are monitored to document the 

scene-specific visibility. 

2. Optical properties of the atmosphere are monitored for a scene-independent 

measure of visibility. 

3. Aerosol characteristics are determined to associate atmospheric optical properties 

with the responsible pollutants. 

Monitoring techniques for each of these informational requirements were used before 

1986, but the recent deployment of upgraded particle monitors and transmissometers has 

improved visibility measurement methods substantially. 

Air Quality Simulation Models for Stagnation Conditions 

To better estimate the impact of air pollution on NPS resources, research includes the 

development and application of air quality simulation models. These models can be used 

to predict changes in air quality that might result from proposed changes in emissions. 

These are valuable tools for evaluating the possible effects of a proposed activity that 

would increase pollutant emissions in or near an NPS unit. Air quality simulation models 

need to be improved for application to stagnation conditions in complex terrain, which is 

typical of many parks. Stagnation conditions occur when there is little mixing in the 

atmosphere and pollutants are retained for several days in the lower layers of the air. This 

can result in a build up of pollutants and a layered haze when there are emissions in an 

area. Models that can be applied to these kinds of conditions will improve the ability of the 

Park Service to predict potential visibility effects and other air quality impacts of emissions 

from sources affecting park units. 

3.0 EFFECTS OF VISUAL AIR QUALITY ON VISITOR EXPERIENCE 

The Park Service is responsible for preserving and protecting the features and natural 

beauty of NPS units for the enjoyment of present and future generations. In meeting this 

responsibility, park managers not only need to understand how air pollution is affecting 

park resources, but also need to know how air pollution is perceived by visitors and 

whether it affects visitor enjoyment. This information can help the Park Service, other 

federal and state agencies, and industry make resource management and pollution 

control decisions that will minimize undesirable impacts on the visitor experience. 

The National Park Service is determining how visual air quality affects visitor perceptions 

and enjoyment because: 

1. Viewing natural scenery and vistas is a primary activity of most park visitors. 

2. Air pollution impairs views in almost all NPS units. 

3. Visibility was highlighted by Congress as an important air quality related value to 

be protected under the Clean Air Act, and specific scenic vistas are often cited as 

important in park enabling legislation. 

Most of the NPS research efforts concerning the effects of air pollution on visitor 

experience fall into one of two categories: (1) efforts to determine how the human observer 

perceives and judges visibility impairment, including what level is just perceptible; and (2) 

efforts to determine how perceived changes in visual air quality affect the visitor 

experience. Highlights of the findings of these two research categories are presented in 

Table 3-1. 

HUMAN PERCEPTION OF VISUAL AIR QUALITY 

In the first perception and judgment studies conducted by the National Park Service, 

subjects were asked to judge the visual air quality in several slides depicting vistas under 

different uniform haze conditions using a scale of 1 to 10, 1 being worst and 10 being 

best. Uniform haze is seen by a human observer as an overall reduction in air clarity. The 

1 to 10 judgment is called perceived visual air quality (PVAQ), and it reflects people's 

perceptions and judgments concerning the visual air quality depicted in the slide. 

Studying the differences among the slides and their average PVAQ has helped researchers 

determine what factors are most important to human observers in their judgments of 

visual air quality. 

These studies first addressed the question of whether individuals judged slides similarly 

to onsite views under the same air quality conditions. It was found that the PVAQ 

judgments are comparable, and the use of slides in studies concerning perceived visual 

air quality is valid and the findings are relevant to onsite viewing. 

3-1
Table 3-1. Highlights of NPS Visitor Experience Research 

HUMAN PERCEPTION OF VISUAL AIR QUALITY (CATEGORY 1) 

Study topic: Perceptions and Judgments of Visual Air Quality

Location and date: Canyonlands National Park (1979); Grand Canyon and Mesa 

Verde National Parks (1980) 

Important findings: 

• Where the existing air quality is relatively pristine, even small 

amounts of additional air pollution are noticeable and 

disturbing to the viewer. Where visibility is already diminished, 

it takes greater amounts of pollution before a change is either 

noticeable or objectionable. 

• Those scenic vistas that are colored and highly textured are 

perceptually sensitive to small changes in air pollution. 

Conversely, those vistas that lack color or textural detail show 

little sensitivity to small increases in atmospheric pollution. 

• Plumes with a center line contrast (the contrast between the 

center of the plume and the background) as low as .02 can be 

detected by about 75% of the observers. 

Study topic: Perceptions and Judgments of Plumes

Location and date: University of Arizona with photographs of Bryce Canyon National 

Park (1981) 

Important finding: 

• Plumes detract more from enjoyment of the view when they are 

dark rather than light in color and when they obscure some of 

the landscape features. 

IMPORTANCE OF VISUAL AIR QUALITY TO VISITOR EXPERIENCE (CATEGORY 2) 

Study topic: Importance of Park Features

Location and date: Grand Canyon and Mesa Verde National Parks (1983); Mount 

Rainier and Great Smoky Mountains National Parks (1984); 

Everglades National Park (1985) 

3-2
IMPORTANCE OF VISUAL AIR QUALITY TO VISITOR EXPERIENCE (continued) 

Important findings: • Visitors rank clean, clear air among the top 4 most important 

features of each park studied. 

• A group of features characterized by "naturalness" (meaning 

undisturbed by man) is the most important group of features at 

these parks. 

• The second most important group of features is associated with 

the underlying theme for which the park is famous. 

Study topic: Visibility and Visitor Enjoyment

Location and date: Grand Canyon and Mesa Verde National Parks (1983) 

Important findings: • Visitors' awareness of haze is closely correlated with standard 

visual range. 

• Impaired visibility detracts from visitors' enjoyment and 

satisfaction with their visit. 

Study topic: Willingness to Pay for Visual Air Quality

Location and date: Grand Canyon National Park (1980, 1983) and Mesa Verde 

National Park (1980) 

Important findings: • Visitors say they are willing to spend additional time traveling or 

pay additional entrance fees to obtain better visual air quality 

during their park visit. 

• Visitors appear to be more disturbed by deterioration in visibility 

when the air is relatively clean. 

Study topic: Willingness to Pay for Preservation of Visibility in Southwestern 

Parks

Location and date: Los Angeles, Denver, Chicago, and Albuquerque (1980) 

Important finding: • Households are willing to pay to preserve visual air quality at the 

Grand Canyon and other southwestern parks, whether or not 

they have visited or intend to visit the parks. This is called 

preservation value. 

3-3
3-4 

Another important finding is that the PVAQ judgments made by different people are 

reasonably consistent with each other, and do not appear to vary in any systematic way 

with the demographic characteristics of the individuals, such as age, sex, or education. 

This suggests that the average PVAQ judgment for a given slide can be interpreted as 

representative of the judgment of a typical viewer. 

The average PVAQ judgments for all the slides that showed various levels of uniform haze 

have been studied to determine their relationship to objective measures of visibility 

conditions, such as contrast, visual range, or light extinction. There appears to be a 

strong relationship between the PVAQ judgment and the contrast transmittance of the 

vista. Contrast transmittance is a measure of the ease with which the atmosphere 

transmits the image of the vista to the viewer. In cases when the foreground of the vistas 

is not affected, but the change in pollution affects the view of a dominant distant feature, 

then the change in the contrast of the dominant distant feature alone is adequate to 

explain the change in the PVAQ judgment. 

The analysis of the PVAQ judgments has revealed that increases in air pollution are more 

noticeable and objectionable to the human observer when the air is relatively clean. This 

is illustrated in Figure 3-1, which shows the relation-ship between the PVAQ judgment 

and ambient particulate levels. The curved line indicates that a one-unit increase in 

particulates will result in a much larger decrease in the PVAQ at the lower particulate 

levels than at the higher particulate levels. 

These studies were also able to test whether the perceived visual air quality is more 

sensitive to changes in air pollution at some vistas than at others. The results indicate 

that people find increases in air pollution more objectionable in vistas with features that 

are more highly colored and textured. 

NPS researchers have developed methods for determining when a layered haze or plume 

is just perceptible. A layered haze or plume results when pollutants are not uniformly 

mixed in the atmosphere making it possible to see the "edge" of the polluted air mass. 

Two plumes with center line contrast of -.11 and -.13 are shown in Figure 3-2 to 

illustrate what the contrast measures mean. Center line contrast is the contrast between 

the center of the plume and the background. It is negative if the plume is darker than 

the background and positive if it is lighter. 

Figure 3-3 shows the percentage of the observers who could detect a brown plume 

(caused by nitrogen dioxide) at various levels of the center line contrast of the plume. At a 

contrast of -.02 approximately 75 percent of the observers were able to detect the plume, 

and at -.04 nearly 100 percent were able to detect the plume. This study also found that 

viewers perceive a dark-colored plume to be more objectionable than a white plume. 

Plumes that obscure some of the features in the vista were also considered worse than 

plumes that were seen only against the sky. 

Additional work is being conducted to determine the amount of layered haze that is just 

perceptible to human observers and how the perceptibility of layered haze and plumes is 

affected by characteristics such as size, shape, and sharpness of the edge, and color of 

the polluted air mass. 



The first few NPS perception and judgment studies set the foundation for subsequent 

research on the effects of visual air quality on visitor experience. These studies suggested 

that visitors do have preferences concerning visibility conditions and that a variety of 

circumstances, such as vista content and initial air quality, influence changes in 

perceived visual air quality. The next question addressed was how perceived visual air 

quality affects the individual's visit to the park. 

IMPORTANCE OF VISUAL AIR QUALITY TO VISITOR EXPERIENCE 

One of the reasons people visit parks is to see and enjoy the scenery. Therefore, it is useful 

to consider visual air quality conditions from the point of view of the human observer. The 

National Park Service has conducted studies that examine the following: 

• The importance of clean air as a park feature. 

• Visitor awareness of visibility conditions. 

• The relationship between visibility conditions and satisfaction/ enjoyment of the 

park visit. 

• Willingness of the visitor to expend time and/or money to obtain improved 

visibility conditions. 

Findings obtained from these research efforts suggest that visitors are aware of visibility 

conditions and that clean, clear air is integral to the enjoyment of visiting the parks. The 

most important conclusions based on these findings to date are summarized. 

Finding: An Environment Undisturbed By Man, Including Clean, Clear Air. 

Is Very Important To Park Visitors 

In NPS studies during the summers of 1983, 1984, and 1985, visitors at Grand Canyon, 

Mesa Verde, Mount Rainier, Great Smoky Mountains, and Everglades National Parks were 

given a list of park features and asked how important each one was to their recreational 

experience. Some of the listed features were the same at all the parks and some were 

specific to each park. For example, "clean, clear air" and "interpretive signs" were listed for 

all the parks while "viewing canyon rims" was listed for Grand Canyon, "ruins on mesa 

tops" was listed for Mesa Verde, "alpine glaciers" was listed for Mount Rainier, "views of 

chimney tops" (natural landscape features in the area) was listed for Great Smoky 

Mountains, and "variety and presence of reptiles" was listed for Everglades. A total of 24 

features were included on the list for Grand Canyon and Mesa Verde, 23 at Great Smoky 

Mountains, 8 at Mount Rainier, and 31 at Everglades. 

At each of the five parks, "clean, clear air" was ranked among the top 4 features. For 

example, 82 percent of the 638 respondents at Grand Canyon rated "clean, clear air" as 

"very important" or "extremely important" to their recreational experience. Only 

"cleanliness of the park" and "deep gorges" were rated higher at Grand Canyon. Several of 

the scenery-related 

3-8 
features were also "very important" especially at Grand Canyon and Mount Rainier. 

Flora- and fauna-related features were "very important" at all five parks. 

Cluster analysis was used to determine if clusters, or groups of park features, could be 

identified based on visitors' responses. This analysis was performed not only to reduce 

the large number of variables involved, but also to determine which park features belong 

to certain "domains" of features in the visitors' minds. For example, it might be expected 

that features related to park management might cluster into one group, while features 

related to the park's natural resources would cluster into another group. Results showed 

five clusters of features at Grand Canyon and Mesa Verde, three at Mount Rainier, seven 

at Great Smoky Mountains, and nine at Everglades. 

The analysis yielded a number of interesting trends. First, a cluster of features was identified at all 

five parks that could be associated with the natural environment undisturbed by humans. This set of 

features is referred to as the naturalness cluster. "Clean, clear air" and "cleanliness of park" were in 

the naturalness cluster at every park. "Rivers and streams" and "clean, pure water in 

lakes" were in the naturalness cluster in the parks where these features were listed. 

Features related to vegetation and wildlife were also in the naturalness cluster at two of 

the five parks. 

Figure 3-4 shows the clusters of features and their relative importance at each park. The 

ratings are the averages of those given by all respondents. The most significant finding 

reflected in Figure 3-4 is that the naturalness cluster was rated the most important at 

each park. The cluster analysis suggests that the second most important set of features 

is associated with the underlying theme for which the park is famous. For example, while 

naturalness was the most important cluster of features at both Grand Canyon and Mesa 

Verde, a view-related cluster at Grand Canyon and an information-related cluster (which 

emphasized park history) at Mesa Verde ranked as the second most important cluster of 

features at those parks, respectively. At Ever-glades, fauna-related features were grouped 

into a separate cluster that was almost as important as the naturalness cluster. The 

viewing cluster, including views of distant horizons and sunrises/sunsets, was less 

important. 

It appears that people visit these parks first to experience a natural setting and second to 

enjoy specific unique features associated with various parks. The survey results show it 

is very important to visitors that parks be natural and free of pollution--undisturbed by 

man. These findings suggest that if these resources are allowed to deteriorate, visitor 

enjoyment of the parks would decline. 

Finding: Visitors Are Aware Of Visibility Conditions 

The visibility and visitor experience study conducted at Grand Canyon and Mesa Verde 

National Parks in 1983 found that visitors are able to perceive varying degrees of visibility 

impairment. Visitors interviewed as they left viewing points in the parks were asked if 

they had noticed haze and if so whether they thought it was slightly, moderately, very, or 

extremely hazy. Their responses were compared to standard visual range estimates based 

on teleradiometer readings taken three times daily. The comparison revealed that when 

standard 

3-9 

visual range was lower. visitors were more aware of haze and were more likely to say it 

was "very" to "extremely" hazy. 

The varying demographic backgrounds of those interviewed (size of home community. 

income. age, and sex) did not correlate with their perceptions of haze. Visibility at Grand 

Canyon is typically better than in many other places in the country, yet the survey 

results indicate that visitors are aware of visibility conditions and are able to detect the 

presence of haze. 

Finding: Visual Air Quality Influences Visitor Enjoyment And Satisfaction 

Results of the 1983 NPS visibility and visitor experience research at Grand Canyon and 

Mesa Verde National Parks show that those visitors who said they thought the view was 

"very" to "extremely" hazy also said they enjoyed the view less. enjoyed the park less, and 

were less satisfied with visibility conditions than those who said they were not aware of 

haze or were aware of only slight to moderate haze. This means that not only do most 

visitors notice haze, but when they consider the view to be relatively hazy it detracts from 

their enjoyment of the park. 

Visitors at Grand Canyon and Mesa Verde National Parks were asked to rate the 

importance of 33 recreational experiences at the park that they might find satisfying, 

such as learning about the park's history, knowing that the park resources and values 

are being protected, and doing something with one's family. Those experiences pertaining 

to the existence of the park, including the satisfaction of knowing that the park resources 

are being protected. were rated as the most important by visitors at both parks. When 

combined with the findings discussed earlier, these findings indicate that: 

• Visitors derive the most satisfaction from knowing that the park is there and that 

the park resources are being protected. 

• Visitors feel that the natural environment of the park (which includes clean, clear 

air) is the most important of all the park resources. 

Finding: Visual Air Quality Conditions Affect The Amount Of Time And Money 

Visitors Are Willing To Spend At NPS Units 

Three NPS studies have been conducted to evaluate whether visitors would be willing to 

spend more time traveling to vistas or pay higher entrance fees in order to obtain better 

visual air quality during their park visit. Those questioned generally responded that they 

would be willing to spend more time and money if visibility conditions were better and 

less if visibility conditions were worse. These results provide evidence that changes in 

visual air quality can be expected to affect visitors' enjoyment and satisfaction with park 

visits. 

These studies are based on the presumption that people will allocate the time and money 

available to them in such a way as to maximize their enjoyment. Therefore, a change in 

the amount of time or money they are willing to spend is a reflection of the change in 

enjoyment. 

3-11 
In the 1983 NPS study at Grand Canyon, 244 visitors were asked to rank possible 

alternative combinations of travel time to vistas and visibility conditions (illustrated with 

photographs). These rankings revealed that the average change in the amount of time the 

visitor was willing to spend traveling to a vista for every unit change in visibility (.01 km-1

extinction coefficient) was between 15 minutes and 4 hours. 

The differences in the amount of time visitors were willing to spend to obtain better 

visibility were related to the vista and the hypothesized initial visibility level. Vistas with 

more texture and color, dominant distant features, and better initial visibility levels were 

the most sensitive. For example. the average increase in the amount of time the visitors 

were willing to spend traveling to the San Francisco Peaks vista in exchange for a unit 

increase in visibility (.01 km-1 drop in extinction coefficient) was between 1.5 and 4 hours 

when the initial visual range was over 200 kilometers and was between 1 and 1.5 hours 

when the initial visual range was less than 200 kilometers. The average increase in travel 

time for the Desert View vista, where distant features are not dominant and the 

photographs were taken at a time of day when the vista was heavily shadowed and 

therefore showed little color or textural detail, was between 15 minutes and 1 hour. 

The findings of this study showing that visitors are more disturbed by deterioration in 

visibility when the air is relatively clean and when the vista is highly colored and textured 

are consistent with those of the human judgment studies discussed earlier in this 

chapter. This is also in agreement with the findings of the visitor experience studies 

which suggest that an environment undisturbed by man is one of the features most 

valued by visitors in a national park. The "willingness to pay" studies should not be 

interpreted as reflecting the total value of a visit to a park. Rather, willingness to pay for a 

change in visibility is one way to quantify the associated change in enjoyment, using 

dollars as an index of value. 

A 1980 NPS study at Grand Canyon and Mesa Verde National Parks examined the effect 

of visibility conditions on the amount visitors are willing to pay in park entrance fees. 

Average responses were about one dollar per visitor-party to have 160 kilometers visual 

range rather than 110 kilometers visual range, about two dollars to have 210 kilometers 

rather than 110 kilometers, and about three dollars to have 350 kilometers rather than 

110 Kilometers. Annual visitation at the Grand Canyon in 1980 was 2,305,000 people, 

with an average of about 3 people to each visitor-party. To prevent a visible plume over 

the Grand Canyon the average payment cited was about two dollars per visitor-party. 

Similar studies conducted by others outside the National Park Service have typically 

received comparable or higher willingness to pay responses. 

A study concerning willingness to pay for preservation of visibility at southwestern parks 

was funded by the U.S. Environmental Protection Agency and conducted in cooperation 

with the National Park Service in 1980. The focus of this study was the development of 

methods for quantifying preservation value, which is the value to the individual of 

knowing that the parks are being preserved whether or not the individual intends to use 

the park. It was found that users and nonusers throughout the country are willing to pay 

to preserve and protect visibility at Grand Canyon National Park and throughout the 

Southwest. The responses from those who did not plan to visit the area were 

3-12 
not significantly different from those who were planning to or had previously visited the 

area. 

The average household willingness to pay was about five dollars per month to prevent 

deterioration in visibility at Grand Canyon and an additional four dollars per month to 

prevent visibility deterioration throughout the remainder of the region. which includes 

several other NPS units. This suggests that preservation values for Grand Canyon may be 

considerably higher than for other 

parks. The finding that people who never intend to visit the parks are willing to pay to 

protect park resources supports the conclusion that simply knowing that the parks are 

there and being protected is important and valuable. 

POINTS RAISED BY NPS VISITOR EXPERIENCE RESEARCH 

The NPS visitor experience research has raised concerns on how best to protect and 

preserve NPS resources for the enjoyment of current and future visitors. This section 

summarizes two of these concerns. 

Developing Adverse Impact Determination Guidelines 

The National Park Service has defined several criteria for determining whether increases 

in air pollution will have an adverse effect on a park's air quality related values. (See 

Chapter 6 for more discussion of the adverse impact determination.) One of these criteria 

is whether the effects of the change in air quality impair the quality of the visitor 

experience. Visitor experience research findings have raised questions that could affect 

the interpretation of this criterion. For example. given the importance that visitors 

apparently place on the naturalness of the parks. what level of visibility impairment 

should be considered adverse? 

Determining Just Perceptible Changes in Visual Air Quality 

Progress has been made in determining when a plume will become just visible to the 

human observer. Work that has been done with plumes and layered hazes suggests that 

the size, shape, and color may be important factors influencing when the plume or 

layered haze will be just perceptible. but how these differences affect perceptions has not 

been quantified. Uniform haze raises a slightly different question in that the issue is 

usually not how much haze is just noticeable relative to a pristine atmosphere, but how 

much of a change is just noticeable when some haze already exists. Initial results suggest 

that the human observer finds the same increase in haze more undesirable in a clearer 

atmosphere than in a hazier atmosphere. Additional work is needed to quantify the 

minimum change in uniform haze that is just perceptible and to determine the factors 

that influence the perceptibility of changes in uniform haze. 

3-13

4.0 CRITERIA POLLUTANTS IN NPS UNITS 

Criteria air pollutants are those for which the U.S. Environmental Protection Agency has 

established National Ambient Air Quality Standards as directed by the Clean Air Act. 

These standards are established for those pollutants that are emitted in the greatest 

quantities throughout the country and are a danger to public health and welfare. Criteria 

air pollutants include ozone, carbon monoxide, nitrogen dioxide. sulfur dioxide. 

particulate matter, and lead. 

An extensive national network of monitoring for criteria pollutants is currently operated 

by state and local (city/county) air pollution control agencies. The focus of this 

monitoring network is urban areas and other areas where pollution levels are relatively 

high due to the impact of nearby emission sources such as coal-fired power plants, 

petrochemical plants, and pulp and paper mills. Little monitoring has been done in areas 

such as those in the National Park System that are thought to be relatively free of 

pollution. Research by the National Park Service and others, however, has found effects 

from some of these air pollutants on biological and visibility resources in some NPS areas. 

More information is needed on ambient pollution levels in the parks. 

The Park Service has responded by establishing a criteria pollutant monitoring program 

for the pollutants linked to effects on NPS resources. Results of this monitoring program 

indicate that elevated levels of some criteria pollutants occur in several NPS units. 

NPS CRITERIA POLLUTANT MONITORING PROGRAM 

The NPS criteria pollutant monitoring network has been designed to meet certain 

resource management objectives and to ensure collection of data needed for the Park 

Service to comply with regulatory requirements. One of the primary objectives is to 

establish baseline (or current) air quality conditions in NPS units so that trends can be 

analyzed and assessments made of whether an area is exceeding National Ambient Air 

Quality Standards or prevention of significant deterioration increments for clean air 

areas. A monitoring station may also be established if there is documented biological 

injury due to air pollution in the park unit. Information on ambient air pollution levels is 

an important supplement to research on effects of air pollutants on NPS resources and 

can help confirm suspected causes of observed effects. Information on air quality levels in 

NPS units is also used to evaluate the performance of atmospheric models. The models 

can help determine how pollutants are transported into an area and predict impacts of 

proposed new air pollution sources. 

Other monitoring objectives relate to collecting data needed to support the National Park Service's 

required involvement in the development of state air quality control plans and in the evaluation of 

permit applications for new or expanding air pollution sources wishing to locate near a class I area. 

The Clean Air Act gives federal land managers and superintendents an affirmative responsibility to 

protect air quality related values in class I areas and to assess whether new sources will have an 

adverse impact on park resources and values. Therefore, the presence or expectation of considerable 

permitting activity near an NPS unit makes it a good candidate for monitoring. 

4-1 
From 1981 through 1984 the NPS criteria air pollutant monitoring program was 

developed. As of the summer of 1985, one or more criteria pollutants were being 

monitored in 19 NPS units. The monitoring network has been extended to include more 

NPS units. During 1986 and 1987, at the request of Congress, criteria pollutant 

monitoring stations were established at 17 additional units including Arches, Badlands, 

Carlsbad Caverns, Haleakala, Hawaii Volcanoes. Isle Royale, Lassen Volcanic, Petrified 

Forest, Redwood, Virgin Islands, Voyageurs, and Yellowstone National Parks; Bandelier, 

Great Sand Dunes, and Pinnacles National Monuments; Denali National Park and 

Preserve; and Point Reyes National Seashore. 

Ozone, which is apparently responsible for widespread foliar injury and possible ecological 

effects in many NPS units, is measured at all monitoring sites. Sulfur dioxide is also 

monitored at most sites. Figure 4-1 shows the location of NPS ozone and sulfur dioxide 

monitoring sites. State or local agencies monitor nitrogen dioxide at Channel Islands 

National Park and Congaree Swamp National Monument. In addition, state agencies have 

established total suspended particulate matter monitoring stations (as distinguised from 

fine particle monitoring conducted by the NPS visibility program discussed in Chapter 2) 

at almost a dozen NPS units. 

Monitoring methods and quality assurance procedures used in the collection of criteria 

pollutant data for NPS units are those recommended by the U.S. Environmental 

Protection Agency and are consistent with applicable regulations (40 CFR Part 58). This 

allows for the direct comparison of NPS-collected data with that collected by state and 

local air pollution control agencies and by the U.S. Environmental Protection Agency, and 

acceptance of the data by state and EPA analysts. In addition, a computerized data base 

is being established that will allow for easy access and analysis of the data. 

CRITERIA AIR POLLUTANT LEVELS IN NPS UNITS 

There are two types of National Ambient Air Quality Standards--primary and secondary. 

The primary standards are set to protect human health. For some pollutants, public 

welfare might be endangered at pollution levels below those at which no human health 

effects are known to occur. For example, injury to plants and damage to materials may 

occur at ambient levels of sulfur dioxide that are not expected to have any effect on 

human health. In these cases, secondary standards are set to protect public welfare. The 

standards are also defined in terms of averaging times, such as annual or hourly, 

depending on the frequency and duration of exposure that is associated with health and 

welfare effects. For some pollutants, there are both short-term and long-term standards. 

The analysis of the monitoring data that are currently available shows that NPS units are 

not immune from elevated levels of ozone and sulfur dioxide and that elevated pollution 

levels are not limited to NPS units adjacent to large urban areas. Although levels of sulfur 

dioxide are well within the National Ambient Air Quality Standards, ozone levels have 

exceeded or have equaled the National Ambient Air Quality Standards at several NPS 

units. Data from the nitrogen dioxide and total suspended particulate matter monitoring 

at NPS units are not yet available. Similarly, data from monitoring sites established 

during 1986 and 1987 is still being validated and analyzed.

4-2 

The primary National Ambient Air Quality Standard for ozone is a 1-hour average of 120 

parts per billion (ppb) not to be exceeded more than once a year. The secondary standard 

is currently the same as the primary standard. Results of research by the Park Service 

and others, however, indicate that foliar injury to some native and cultivated plant 

species occurs at ozone concentrations as low as an 8-hour average of 60 ppb. The 

scientific basis for the current ozone standard is currently being reviewed by the U.S. 

Environmental Protection Agency, and possible changes are being considered. 

Table 4-1 shows the NPS units for which ozone data are available for 1982 through 1986. 

The maximum hourly average and the number of times the National Ambient Air Quality 

Standard was exceeded is listed for each year. The level of the National Ambient Air 

Quality Standard for ozone has been exceeded at three NPS units located near large 

urban areas: Channel Islands National Park, Indiana Dunes National Lakeshore, and 

Santa Monica Mountains National Recreation Area; and at three NPS units in more 

remote locations: Acadia National Park, Joshua Tree National Monument, and Sequoia 

National Park. Additionally, recorded ozone levels have equalled the level of the standard 

at Shenandoah National Park and Congaree Swamp National Monument, and have 

reached over 90 percent of the level of the standard at Great Smoky Mountains National 

Park and Saguaro National Monument. There are not sufficient data to show a significant 

trend over time, either increasing or decreasing, for any of these parks. 

The primary National Ambient Air Quality Standard for sulfur dioxide is set for two 

averaging times. The annual standard is 30 ppb, which is not to be exceeded, and the 24-

hour standard is 140 ppb, which is not to be exceeded more than once a year. There is 

also a separate secondary standard for a 3-hour averaging period of 500 ppb. This 

secondary standard takes into account evidence concerning foliar injury to sensitive tree 

species observed as a result of single exposures to sulfur dioxide concentrations of this 

level. There is also evidence that long-term exposures to sulfur dioxide below the primary 

annual standard result in the disappearance of sensitive lichen species. This is commonly 

observed at annual sulfur dioxide concentrations of about 15 ppb and has been observed 

at concentrations as low as 6 ppb. 

Table 4-2 shows available sulfur dioxide concentration data for NPS units for 1980 

through 1987. None of the National Ambient Air Quality Standards were exceeded at 

these parks during these years, but levels as high as 48 percent of the secondary 

standard have been recorded. The highest sulfur dioxide concentrations measured at the 

five parks in 1984 were at Olympic National Park. Sulfur dioxide concentrations 

measured at Indiana Dunes National Lakeshore have been about 20 to 40 percent of the 

standard each year. The monitoring results indicate a significant decrease in sulfur 

dioxide concentrations at Theodore Roosevelt National Park from 1982 to 1984. This 

reduction in observed levels is associated with control actions implemented by the North 

Dakota Department of Health in cooperation with the National Park Service. 

4-4 



5.0 AIR POLLUTION EFFECTS ON BIOLOGICAL RESOURCES 

Ozone affects biological resources in many NPS units. In a few areas, such as Sequoia 

and Acadia National Parks, the effects are dramatic. In many other areas more subtle 

effects have been found on vegetative types known to be sensitive to various air 

pollutants. For instance, at Indiana Dunes National Lakeshore there has been a large 

decrease in the kinds of lichens found there, with those known to be sensitive to sulfur 

dioxide now vanished or surviving only in greatly diminished numbers. 

The NPS air quality biological effects research program represents one of the most 

extensive efforts in the United States to study air pollution effects on native plant species. 

The program has focused on plants because they are usually more sensitive to air 

pollution than animals and show the first biologically detectable effects of air pollutants. 

The biological effects research program is designed to: 

1. Determine the sensitivity of native plants to different air pollutants. 

2. Identify air pollution impacts on sensitive plants. 

3. Establish baseline conditions of plants and monitor trends in NPS ecosystems. 

Information from this research program helps to identify current or potential problems 

that might be mitigated or eliminated through implementing alternative resource 

management strategies and cooperating with local authorities and industry. The 

information also helps in the review of permit applications and environmental impact 

assessments concerning proposed new sources of air pollution that might affect the 

biological resources of parks. 

This chapter describes the effects of air pollution on plants, explains the studies which 

have been conducted to determine the extent and severity of air pollution effects on NPS 

biological resources, and summarizes the findings of the NPS biological effects research 

program to date. 

EFFECTS OF AIR POLLUTION ON PLANTS 

The National Park Service is most interested in the effects of pollution on native. 

vegetation. Although extensive literature exists on the effects of air pollution on 

agricultural crops and commercial forests, this information is of limited use to the Park 

Service because most of it is not specifically applicable to native plant species. However, 

many of the research methods and general findings developed in previous applications 

can be applied to the study of native plants. For example, studies indicate that there is 

considerable injury to agricultural crops in the United States from ozone and sulfur 

dioxide, suggesting that these two pollutants may also be affecting native species in 

national parks. The Park Service is conducting studies and reviewing information that is 

available in the literature to determine possible effects of air pollution on natural 

vegetation. 

5-1 
The effects of an air pollutant on biological resources are influenced by various factors, 

including the following: 

• Toxicity of the pollutant. 

• Exposure of the organism to the pollutant. 

• Sensitivity of the organism, which varies with inherited factors, nutritional 

status, season, and age. 

• Potential for synergisms with other pollutants. 

Assessing the significance of air pollution injury requires knowing: 

• Affected organism's role in the ecosystem. 

• Persistence of the pollutants in the environment. 

• Potential reversibility of the effect on the organism and ecosystem. 

• Geographical scale of the injury. 

• Severity of the injury. 

Effects may be the result of acute or chronic exposures or both. The former are shortterm exposures to high pollution levels, whereas the latter are long-term exposures to 

lower pollution levels. 

Three categories of effects have been studied in the NPS biological effects research 

program: 

1. Foliar injury which may appear as spots on, or discoloration of, leaves. 

2. Ecological effects which include stunted growth, altered reproduction, and death 

of individual. plants or entire species. 

3. Elevated levels of potentially toxic trace elements, such as arsenic and lead, in 

plant tissue which have resulted from particulate deposition. These elevated levels 

may or may not be accompanied by detectable injury to the organism. 

Foliar Injury 

Leaves appear to be the most sensitive parts of plants to gaseous air pollutants. Visible 

foliar injury means that metabolic impairment and cell mortality have occurred and 

indicates there are probably additional effects occurring, e.g., effects on growth and 

reproduction. 

5-2 
Foliar injury from ozone is quite common in the eastern United States due to high 

sustained ambient ozone concentrations. Ozone injury appears as dark spots on the 

upper surfaces of leaves of deciduous species and as yellow mottling of the needles of 

evergreen species. Figures 5-1 and 5-2 show examples of ozone injury to evergreen and 

deciduous species. These types of ozone injury are frequently unique and can sometimes 

be identified in the field. Other air pollutants cause different types of foliar injury that are 

often more difficult to distinguish from the effects of natural causes. Some plant species 

are known to be sensitive to ozone levels slightly above natural background levels. 

Sulfur dioxide, fluorides, nitrogen dioxide, ethylene, chlorine, and ammonia can also 

cause foliar injury. 

Ecological Effects 

Exposures to air pollutants for long periods of time can cause effects on plant growth, 

reproduction, and mortality that can change the functioning and structure of the 

ecosystem.. However, ecological effects are more difficult, and take longer to identify than 

foliar injury. Ecological effects that have been observed within NPS areas are as follows: 

• Tree mortality. 

• Decreased Tree Growth 

• Premature leaf drop. 

• Reduced numbers of fruit and seed. 

• Smaller fruits and cones. 

• Impaired pollen germination. 

• Delayed bud break. 

• Decreased understory canopy coverage. 

• Lower shrub productivity. 

• Greater susceptibility to diseases and pests. 

• Altered plant competition. 

• Changes in species richness and diversity. 

• Lichen deserts (severe decreases in lichen diversity and abundance). 

The National Park Service is conducting studies to determine if air pollution may be the 

cause of these effects. 

Many of these observations of ecological effects have been made either on crop species in 

agricultural planting or in natural vegetation areas close to stationary pollution sources. 

In these situations, the ecological effects of air pollution are obvious due to strong spatial 

gradients in pollution levels near the source of pollution. Identifying such effects in 

remote natural areas, where the gradient in pollution concentrations over the area is not 

significant, is more difficult. 

Elevated Levels of Potentially Toxic Trace Elements 

Potentially toxic trace elements, primarily heavy metals, contained in particulate air 

pollutants are deposited on the surfaces of living organisms. These elements can in turn 

be metabolized by plants and consumed by animals. 

5-3 

Manmade pollutants that are most toxic to living organisms and can be trans-ported long 

distances to remote natural areas include lead, arsenic, mercury. cadmium, chromium. 

and beryllium. Elements such as iron, vanadium, and sulfur are less toxic but, because 

high concentrations are normally not found in natural systems, they can indicate the 

presence of manmade pollution. Elevated levels of trace elements can cause effects, such 

as foliar injury, stunted growth, or mortality of plants or animals, at various 

concentrations depending on the sensitivity of the exposed organism. Although direct 

effects are possible, effects due to cumulative exposure are of greater concern because 

trace elements once ingested are usually not excreted by the organism. Thus. even when 

elevated levels of these substances are not necessarily accompanied by detectable 

damage, continuing study is in order because of potential future effects. Continuing 

deposition of pollutants on plant leaf surfaces can lead to high ingested levels of trace 

elements by herbivores. Since these elements are typically not excreted, they accumulate 

and undergo "biomagnification," which is the accumulation and concentration of 

elements through the food chain. 

Lichens, mosses, orchids, and bromeliads are sensitive epiphytes used in NPS biological 

effects program studies. Epiphytes. which are sometimes called air plants, are plants 

growing on other plants and deriving no sustenance from the support, and obtaining their 

nutrients directly from the air. 

NPS BIOLOGICAL EFFECTS STUDIES 

Biological effects studies examine the effects of air pollution on a wide range of plant 

species in the parks. Figure 5-3 shows the NPS areas where biological effects studies 

have been or are being conducted. One or more types of effects studies, including 

biomonitoring studies, have been or are being conducted at a total of 65 parks. The 

emphasis has been on class I areas and areas where pollution effects are suspected due 

to proximity of air pollution sources, observed visible injury, or presence of known 

sensitive species. Table 5-1 summarizes the types of NPS biological effects studies. 

These studies involve taking samples of plant material for chemical analysis or surveying 

for foliar injury or ecological damage in one or more plots selected throughout a park. 

The National Park Service uses the biomonitoring studies to detect the first sign of air 

pollution effects on biological resources in an area. Biomonitoring studies typically use 

species that are native to the area and known to be sensitive to air pollution. 

Occasionally, a nonnative biomonitoring species will be used but conditions will be 

carefully controlled to ensure that the species (or genotype) is not introduced into the 

area. The sensitive species used in biomonitoring are called biomonitors or bioindicators. 

and include bioaccumulators. Lichens are an example of bioaccumulators that can be 

used to detect the presence of elevated levels of airborne elements because such 

substances tend to accumulate in their tissues. Lichens are also used as bioindicators of 

sulfur dioxide pollution because they are geographically widespread, and many species 

are very sensitive to sulfur dioxide and are 

5-5 


unable to survive when exposed to certain minimum levels. Milkweed is a bioindicator 

that has been widely used because of its sensitivity to ozone. 

The Park Service also conducts inventory and fumigation studies. These studies compile 

information on biological resources that may be sensitive to air pollutants to help 

determine whether increased air pollution emissions near an NPS area might endanger 

biological resources in the park. Inventory studies compile information about the presence 

and geographical extent of plant species in the parks and have focused on vascular plants 

and lichens. Fumigation studies involve exposing individual plants (field or laboratory) of 

a species to carefully controlled amounts of one or more air pollutants at varied 

frequencies of exposure. These studies help to determine the relationship between air 

pollution and effects. Species selected for fumigation include sensitive species, the most 

common species in NPS areas, dominant species, or rare and endangered species. 

FINDINGS OF NPS BIOLOGICAL EFFECTS RESEARCH PROGRAM 

Figure 5-4 shows the NPS areas where research results have demonstrated that biological 

resources have been affected by air pollutants. These findings-are the result of the studies 

shown in Figure 5-3. If effects are not shown in Figure 5-4 for parks where studies are 

shown in Figure 5-3. either no effects were found or the study is not yet complete. 

Some kind of effect of air pollution on biological resources has been found at 41 NPS 

areas to date. The most common effect is foliar injury due to ozone, which has been 

detected at many units in the eastern United States. Elevated levels of potentially toxic 

trace elements have been found at 9 NPS units. Ecological effects have also been found at 

9 NPS units; the Park Service is conducting studies to determine if air pollution is a 

cause. Of these 9 units, 3 (Cuyahoga Valley National Recreation Area. Indiana Dunes 

National Lakeshore, and Santa Monica Mountains National Recreation Area) are located 

near major urban areas. 

The remainder of this section discusses these findings. This research is ongoing with 

many studies either in progress or planned for the future. Results reported here indicate 

where biological effects of air pollution have been found as of the summer of 1985. 

Because it has not been possible to look for all categories of effects at every NPS unit, it is 

possible that injury may be occurring that has not yet been detected. 

Foliar Injury 

Table 5-2 shows those parks where foliar injury to common native vascular plants has 

been documented. Widespread or substantial foliar injury from ozone has been observed 

in all of these parks. Common trees sensitive to ozone include eastern white pine, tulip 

poplar, and ponderosa pine. 

In the East, foliar injury at Shenandoah National Park was documented on 90 percent of 

the plants of the most sensitive species (milkweed) and on about 8 percent of the plants of 

the least sensitive species (black locust) in 1982 and 1984 studies. Almost 70 percent of 

the eastern white pine trees observed at 

5-9 


Great Smoky Mountains National Park showed foliar injury, and more than half of the 

300 eastern white pine trees studied in 1984 a t Acadia National Park showed some 

foliar injury. In biomonitoring studies at Fredericksburg and Spotsylvania County 

Battlefields Memorial National Military Park, Gettysburg National Military Park, Hampton 

National Historic Site, and Petersburg National Battlefield, foliar injury due to ozone has 

been observed on many species of trees and shrubs. Injury to eastern white pine due to 

ozone has also been documented at Cape Cod National Seashore, Lyndon Baines Johnson 

Memorial Grove on the Potomac, and Saratoga National Historical Park. 

In the Midwest, foliar injury from ozone is common on white pine, jack pine, and other 

forest species at Indiana Dunes National Lakeshore. Foliar injury on eastern white pine 

has also been documented at Cuyahoga Valley National Recreation Area. 

In the West, many of the 225 ponderosa pine trees studied in 1984 at Saguaro National 

Monument showed foliar injury due to ozone. In Sequoia National Park, along the western 

border of the park adjacent to the polluted. San Joaquin Valley, 250 ponderosa and Jeffrey 

pine trees were evaluated for visible ozone injury. The injury increased from about 50 

percent of the trees in 1980-82 to more than 75 percent in 1984. Several species in the 

coastal sage community at Santa Monica Mountains National Recreation Area show 

extensive foliar injury due to ozone. Injury to ponderosa and Jeffrey pines due to ozone 

has also been documented at Yosemite National Park. 

Little or no foliar injury due to ozone has been detected by surveys of trees and shrubs in 

the following 9 NPS units: Big Bend, Canyonlands, Mesa Verde, Rocky Mountain, 

Theodore Roosevelt, and Voyageurs National Parks; Big Thicket National Preserve; 

Colorado National Monument; and Glen Canyon National Recreation Area. Foliar effects 

studies are in progress at 15 areas: Acadia, Biscayne, Everglades, Great Smoky 

Mountains, Mammoth Cave, Petrified Forest, Sequoia, and Yosemite National Parks; 

Bandelier, Joshua Tree, and Saguaro National Monuments; Big Cypress National 

Preserve; Chaco Culture National Historical Park; Cuyahoga Valley National Recreation 

Area; and Indiana Dunes National Lakeshore. 

In the late 1960s, the Park Service found foliar injury at Glacier National Park due to 

elevated hydrogen fluoride levels. Some injury to herbivores in the park was also 

observed. The source of the hydrogen fluoride was a nearby aluminum smelter. Controls 

to reduce emissions were subsequently added to the smelter, and hydrogen fluoride levels 

have now dropped to natural background levels in vegetation in the park. 

A summer of 1984 survey of 25 eastern parks showed widespread foliar injury to 

milkweed, confirming that ozone is a regional problem. Ozone levels are typically highest 

during the summer so this is the time when the most injury would be expected. Extensive 

injury was found at Catoctin Mountain Park, Cuyahoga National Recreation Area, and 

Shenandoah National Park, with between 67 and 100 percent of the milkweed plants 

surveyed showing injury on more than 14 percent of the leaf area. Injury on 67 to 100 

percent of the milkweed plants surveyed was also found at 8 other parks, although the 

percentage of leaf area injured was somewhat less. The findings of the milkweed study are 

summarized in Table 5-3. 

5-13 
Table 5-3. NPS 1984 Milkweed Study Findings 

 Percentage of Plants with Injury

0-33% 34-66% 67-100% 

 Percentage of Leaf Area Injur

0-7% 8-14% 

Antietam Fort Necessity Cumberland Gap Natchez Trace Saratoga Petersburg Rock Creek Gettysburg Homestead Chesapeake & Friendship Hill Ohio Canal Delaware Water Gap Fredericksburg & Spotsylvania Pipestone Manassas Morristown Mammoth Cave Valley Forge 

 Indiana Dunes 

 Appomattox Court 

 House  Saint Gaudens  New River Gorge 

Rock Creek Natchez Trace Homestead Saratoga Delaware Water Gettysburg  Gap Pipestone Manassas Mammoth Cave Valley Forge Appomattox Court 

House 

Chesapeake &  Ohio Canal New River 

Gorge 

Saint Gaudens 

Fort Necessity Shenandoah Cuyahoga Valley Antietam Cumberland Gap Friendship Hill Fredericksburg & 

Spotsylvania 

Morristown Indiana Dunes Catoctin Petersburg 
Ecological Effects 

An ecological effect is defined as the alteration of the normal growth, reproduction, or 

survivorship at the individual, population, or community level. Ecological effects are 

more complex to identify than foliar injury, since they may result after long exposures to 

low levels of pollution, and the causal agents may no longer be identifiable. Nevertheless, 

ecological effects 

have been observed in several NPS areas across the country. As previously noted, lichens 

are particularly susceptible to sulfur dioxide. Disappearance or decreases of any lichen 

species constitute an ecological effect and indicate a potential for ecological effects on 

vascular plants. Lichens are a primitive type of plant composed' of an alga and fungus 

living cooperatively. 

Lichen deserts commonly occur in most urban areas as a result of air pollution. Some 

species of lichens may die in areas with average annual concentrations of sulfur dioxide 

as low as 6 ppb (15 micrograms per cubic meter). (See Chapter 4 for a discussion of 

sulfur dioxide levels at NPS areas.) Because different lichen species have different 

sensitivities to sulfur dioxide, an inventory study of lichen species in NPS areas can 

provide an indication of air quality for the area. If many or all of the sensitive species are 

absent from an area where they would be expected, a high probability exists that air 

quality is degraded. 

Table 5-4 lists the NPS units where ecological effects are being investigated and the type 

of effects being studied. All of these parks also exhibit foliar injury to vascular plants, 

except Big Thicket National Preserve where Spanish moss is the affected plant. 

Table 5-4. Ecological Effects Being Investigated at NPS Units 

Geographical 

Region Park Effect Being Investigated 

East 

South 

Midwest 

West

Shenandoah 

Big Thicket 

Great Smoky 

Mountains 

Indiana Dunes 

Cuyahoga 

Valley 

Sequoia/Kings 

Canyon

Decreased growth of eastern white pine 

Decline of red spruce and other species 

Decreased abundance of Spanish moss 

Decreased growth of eastern white pine 

Decline of red spruce 

Decreased growth of eastern white pine, 

jack pine, and other species 

Loss of lichen diversity and abundance 

Decreased growth of eastern white pine 

and other species 

Loss of lichen diversity and abundance 

Decreased growth of Jeffrey pine

5-15 
In the East, studies are ongoing at Acadia National Park to relate eastern white pine foliar 

injury to decreased wood production. Some of the ecological effects here may be due to 

ozone, although acid deposition may also affect this park. Increased red spruce mortality 

has been observed in Shenandoah National Park, but the cause of the decline is not clear 

because both ozone and acid deposition are, present. Only one locality in Shenandoah 

shows significant effects on red spruce. 

In the South, elevated metal levels in Spanish moss are one possible cause of the 

decreased abundance of the species throughout Big Thicket National Preserve. In Great 

Smoky Mountains National Park, preliminary evidence indicates a narrower distribution 

of genotypes than expected. Although large numbers of trees show foliar injury due to 

ozone, the severity of the injury is generally low. Local and regional sources of ozone, 

heavy metals, and acid rain may be the causes of the ecological effects at this park. 

Increased red spruce mortality has been observed in Great Smoky Mountains. The effects 

on red spruce appear to be extensive and are receiving detailed study. 

In the Midwest, at Indiana Dunes National Lakeshore, patterns of injury and growth changes in 

several species have been documented. For example, growth of jack pine juveniles and white pine 

adults has been reduced due to ozone in certain areas of the park. Also, a decrease in lichen diversity 

has been documented. Local and regional sources of ozone, sulfur dioxide, and heavy 

metals are possible causes of these effects. In Cuyahoga Valley National 

Recreation Area, decreases in eastern white pine growth and severe decreases in lichen 

diversity and abundance are being documented throughout the unit. Possible causes of 

these effects are ozone, sulfur dioxide, and heavy metals from regional and local sources. 

In the West, at Sequoia/Kings Canyon National Parks, studies are currently underway to 

determine the relationship between foliar ozone injury and ponderosa pine growth, 

particularly near the western border of the park where foliar injury is substantial. Studies 

are also being done at these parks to determine the role of ozone in sequoia seedling 

establishment. At Santa Monica Mountains National Recreation Area reduced growth has 

been related to the substantial foliar injury on several species in the coastal sage 

community. These biological effects could lead to soil destabilization and increased fuel for 

wildfires. Preliminary surveys indicate that lichen diversity and abundance is generally 

low. Injury is due to ozone and sulfur dioxide pollution and increases from west to east, as 

do the pollutant levels. 

Biomonitoring plots at Big Bend, Zion, Theodore Roosevelt, and Redwood National Parks have so far 

shown no ecological effects on lichens due to air pollution. Biomonitoring plots at Colorado National 

Monument have shown no ecological effects on lichens or vascular plants. The following 15 parks 

are being investigated for possible ecological effects, but results are not yet available: Acadia, 

Biscayne, Canyonlands, Everglades, Great Smoky Mountains, Isle Royale, Mammoth Cave, Mount 

Rainier, Olympic, Petrified Forest, Sequoia/Kings Canyon, and Shenandoah National Parks; 

Bandelier National Monument; Big Cypress National Preserve; and Chaco Culture National 

Historical Park, 

5-16 
Elevated Levels of Potentially Toxic Trace Elements 

Table 5-5 lists the NPS units where elevated levels of potentially toxic trace elements have 

been documented, and identifies the elements and organisms in which trace elements 

have been found. 

Table 5-5. NPS Areas Where Elevated Levels of Toxic Trace Elements Have Been 

Documented 

Geographical 

Region 

Park Findings 

East Shenandoah Sulfur and lead in lichens 

Everglades Sulfur in epiphytes and bromeliads 

Arsenic and mercury in wildlife 

Great Smoky 

Mountains 

Sulfur in lichens 

Lead in leaf litter 

Heavy metals in trees rings 

South 

Big Thicket Sulfur and heavy metals in Spanish 

mosses 

Midwest Isle Royale Sulfur and heavy metals in mosses 

and lichens 

Theodore 

Roosevelt 

Zinc in lichens 

Mount Rainier Arsenic and heavy metals in 

subalpine fir and lichens 

North Cascades Arsenic in goat hair 

Olympic Lead and copper in lichens and 

mosses 

West 

Grant-Kohrs Ranch Copper, arsenic, and cadmium in 

red top grass 

In the East, abnormally high concentrations of lead and sulfur have been found in 

lichens in parts of Shenandoah National Park near urban areas and along roads. 

In the South, much evidence for elevated levels of sulfur, lead, and other trace elements 

has been found in Great Smoky Mountains National Park. Elevated sulfur levels have 

been measured in epiphytes at several sites near the eastern edge of Everglades National 

Park. NPS research done at Everglades in 1974 found elevated levels of arsenic and 

mercury in wildlife. Elevated sulfur and 

5-17 
heavy metals concentrations have been found in Spanish moss at Big Thicket National 

Preserve. 

In the Midwest, elevated levels of sulfur and heavy metals were measured in streams at 

the north end of Isle Royale National Park in recent NPS research. Elevated 

concentrations of several heavy metals were also found in mosses and lichens. 

In the West, elevated levels of arsenic, lead, cadmium, copper, and zinc were found in 

subalpine fir foliage and lichens at Mount Rainier National Park. Arsenic levels in fir 

needles at high elevations were found to be twice what they were at low elevations in the 

park. A project is underway to determine whether wildlife is being affected by elevated 

trace elements at Mount Rainier. At Olympic National Park, elevated levels of lead and 

copper in lichens and mosses have been found, although the levels are lower than at 

Mount Rainier. At Theodore Roosevelt National Park, some elevated levels of zinc have 

been documented in lichens. 

Ecological effects that may be related to trace elements have also been found in Big 

Thicket National Preserve and Great Smoky Mountains and Shenandoah National Parks. 

(These findings were discussed in the previous section on ecological effects.) Studies of 

the possible ecological effects of elevated trace elements are just beginning at Everglades, 

Isle Royale, Mount Rainier, and Olympic National Parks. In Theodore Roosevelt, studies 

have found no current ecological effects from trace elements. 

Studies at Big Bend and Redwood National Parks found no elevated levels of heavy metal 

concentrations. Studies concerning trace elements are currently in progress at Bandelier 

National Monument; Big Cypress National Preserve; Chaco Culture National Historical 

Park; and Biscayne, Canyonlands, Everglades, and Petrified Forest National Parks. 

Inventory and Fumigation Studies 

The National Park Service is developing a computerized inventory of vascular plants 

throughout the National Park System called NPFLORA. The computerized data base has 

information on 108 units and data on about 64,000 occurrences of some 14,000 plant 

species. This data base continues to be expanded. 

An inventory' of all known lichens, an important bioindicator, in 44 NPS class I areas in the 

conterminous United States has been compiled. Lichen species lists and known sulfur 

dioxide sensitivities for each park have been assembled. 

Fumigations are being carried out at four federal government and university laboratories 

and two national parks (Sequoia/Kings Canyon and Great Smoky Mountains) to 

determine the air pollution sensitivities of selected plant species. Plants being studied 

include namesake species--those for which parks are named--and species that are 

widespread throughout the National Park System and suspected of being relatively 

sensitive. Giant sequoia are an example of namesake species being examined, while 

chokecherry and aspen are examples of common species under study. 

5-18
In fumigation studies of six deciduous tree species in the East, individual trees of the 

same species collected in different parks have been grown together in a common garden 

and exposed to controlled amounts of ozone. Data from these studies indicate that 

quaking aspen from Isle Royale and Voyageurs National Parks are more sensitive to injury 

from ozone than those from Acadia National Park, Cuyahoga Valley National Recreation 

Area, and Saratoga National Historical Park. Ozone levels are higher at Acadia, Cuyahoga 

Valley, and Saratoga than at Isle Royale and Voyageurs. Therefore, one hypothesis is that 

adaptation to elevated ozone levels may have occurred in the more polluted parks. The 

Park Service is testing this hypothesis. If sensitive genotypes are being eliminated from 

more polluted NPS units, the species may become more vulnerable to other stresses due to 

decreased fitness. 

POINTS RAISED BY NPS BIOLOGICAL EFFECTS RESEARCH PROGRAM 

There are many unanswered questions concerning biological impacts of air pollution in 

NPS units. Two important questions discussed in this section are currently being studied 

through the NPS biological effects research program. 

1. What Is the Relationship Between Foliar Injury and Ecological Effects? 

In several parks where foliar injury is widespread or substantial, data on plant 

growth or productivity are being collected in order to quantify the relationship 

between this effect and ecological damage. At Acadia 

National Park, eastern white pine is the species of interest. At 

Sequoia National Park, ponderosa pine is being studied. Coastal sage species have 

been studied at Santa Monica Mountains National Recreation Area. 

The relationship between foliar injury and plant growth would be expected to differ 

between species and to vary with factors, including inherited characteristics, 

season, altitude, soils, geographical location, and nutritional status and age of 

plant parts. The relationship of foliar injury to ecological effects is a complex one 

and NPS work can only be 

expected to elucidate some aspects of it. The analogous questions concerning the 

relationship of elevated levels of potentially toxic trace elements to ecological effects 

has similar or greater complexities and uncertainties. 

2. What Are the Ecological Implications of Adaptation to Air Pollution? 

In order to survive any environmental stress or change, organisms must adapt; 

that is, through time, less fit individuals are selected against by environmental 

stress. The degree to which this is occurring in response to air pollution is 

unknown and difficult to determine, but some NPS research findings suggest that 

adaptation may be occurring in 

some parks. It is also not clear how adaptation of some organisms may affect the 

structure and function of a park's ecosystem. The adaptation mechanism needs to 

be understood in order for the National Park Service to judge whether such 

adaption is a problem from the point of view of the NPS mandate to preserve and 

protect park resources. 

5-19 
In Great Smoky Mountains National Park, a genetic study has shown that genetic 

diversity In white pine is less than the overall level of diversity throughout the rest 

of the natural range of white pine. Air pollution may be playing a role in this 

reduction of genetic diversity by eliminating sensitive genotypes. In Great Smoky 

Mountains, preliminary evidence indicates that sensitive strains of eastern white 

pine may be disappearing. Data from fumigation studies have shown that the 

ozone sensitivity of quaking aspen in Acadia National Park, Cuyahoga Valley 

National Recreation Area, and Saratoga National Historical Park (parks with high 

ozone levels) is lower than the sensitivity in Isle Royale and Voyageurs National 

Parks (parks with relatively clean air). These data suggest the possibility that 

adaptation to air pollution may have occurred and that genetic diversity may have 

been affected. These changes may leave the species more vulnerable to other 

stresses by reducing the diversity within the species. 

5-20 
6.0 NPS PARTICIPATION IN PROTECTION OF AIR QUALITY RESOURCES 

Information from the air quality research program is used to support NPS participation in 

decisions for protecting and managing air resources. In most cases, the air pollution 

affecting park resources and values comes from outside the parks. NPS concerns and 

recommendations regarding proposed or existing air pollution sources are directed to the 

governmental agency that has permitting or regulatory authority. Cooperation is also 

elicited from industry to ensure protection of NPS resources. The Clean Air Act requires 

that the National Park Service be involved in reviewing state implementation plans 

designed to prevent significant deterioration of air quality and to protect visibility. The 

Park Service is also required to evaluate the effects that a new air pollution source might 

have on nearby park resources. The NPS Air Quality Division has servicewide 

responsibility for ensuring compliance with Clean Air Act requirements, in coordination 

with NPS regional offices and park units. 

This chapter discusses this process and presents some case studies showing how 

research findings have been used to protect NPS air resources. 

REVIEW OF PERMIT APPLICATIONS AND ENVIRONMENTAL ASSESSMENTS 

If potential or existing air quality effects on NPS resources occur, and an industrial or 

energy resource developer wishes to construct a new air pollution source near an NPS unit, 

the environmental assessment or permit application prepared by the applicant is 

reviewed. Comments are provided to the governmental agency with the authority to issue 

air quality permits, which is usually the state in which the proposed project would be 

located. 

More than 250 permit applications were reviewed between 1979 and 1987. Figure 6-1 

shows the locations of those proposed projects. The Air Quality Division has had 

questions or comments on about half of the permits reviewed. Often these comments 

involve requests for more complete air quality modeling and analysis in order to better 

substantiate the case made by the applicant that no adverse effects on NPS resources 

would occur. In some cases, modifications in the proposed emission control technology 

have been requested to further reduce potential impacts on NPS resources and values. 

States and applicants often, but not always, comply with the NPS requests. 

The state makes the final decision on the approval or denial of the permit application. The 

permit. will be denied if the applicant cannot demonstrate compliance with the applicable 

air quality standards (increments). If the Park Service certifies that no adverse impact on 

park resources would occur at the predicted level of emissions, the permit may be 

approved. However, if the Park Service demonstrates to the satisfaction of the state that 

an adverse impact would occur even though the standards are expected to be met, the 

state may then deny the permit. The Clean Air Act requires the federal land manager to 

make judgments, in some situations, about whether or not a change in air quality will 

result in an adverse effect on park resources. 

When determining whether the changes caused by air pollutants constitute an adverse impact on air 

quality related values, the Park Service primarily looks at whether the national significance of the 

area would be diminished, whether the structure and functioning of ecosystems would be impaired, 

or whether the

6-1 

quality of the visitor experience would be impaired. The frequency, magnitude, 

duration, location, and reversibility of the potential impact are also taken into account 

by answering the following questions: 

1. Will the effects last long enough and/or occur frequently enough to impair the 

structure and functioning of ecosystems in the park, impair visitor experience, 

or diminish the national significance of the area? 

2. Will the effects occur on a scale large enough to impair the structure and 

functioning of the ecosystems in the park, impair the visitor experience, or 

diminish the national significance of the area? 

3. Are the effects reversible if the stress causing them is removed from the area? 

Although the National Park Service carefully evaluates information submitted by 

permit applicants, and often performs an independent analysis of potential effects on 

air quality related values, no formal adverse impact determinations have been made 

that would have prevented the approval of any of the permits issued to date. 

The following sections give some examples of the NPS involvement in the review 

process. 

Permit Reviews at Theodore Roosevelt National Park 

Between 1977 and 1979, s i x permit applications were submitted to the state of 

North Dakota for proposed fac ilities--three gas-processing plants, one synthetic 

fuels plant, and two power plants--near Theodore Roosevelt National Park and 

Lostwood National Wildlife Refuge. Air quality models predicted that the prevention of 

significant deterioration class I air quality increments for sulfur dioxide would be 

exceeded by the emissions from five of these sources, and the applicants requested a 

certification of no adverse impact from the NPS. Responding to these requests required 

using data available from the visibility monitoring network and the biological effects 

research program; new analyses were also conducted to determine the potential effects 

of estimated emissions of fine particulates and sulfur dioxide from the facilities. 

In order to assess what effects the facilities might have on visibility at the park, 

the Air Quality Division, in cooperation with the North Dakota Department of Health, 

estimated the total amount of fine particulates expected to be added to the air as a 

result of emissions from the proposed fac ilities, including the formation of sulfates 

as a result of sulfur dioxide emissions. Photographs of poor and good v i s i b i l i t y 

conditions at the park were selected from the inventory compiled by the monitoring 

efforts at the park; two more photographs were then selected to illustrate the change in 

visibility that would occur as a result of the new emissions. It was then possible to 

judge the visual effects of the increase in fine particulates when background conditions 

were poor or good. The National Park Service found the differences between the latter 

two photographs and the original two were virtually imperceptible, and therefore 

judged that no adverse effect on visibility would occur. 

6-4 
To assess the potential effects on biological resources, data from the biological effects 

research program were used and two additional field studies were conducted. Previous 

research by the Park Service and others indicated that no injury to the plant species 

present in the park had ever been observed at pollution concentrations predicted to occur 

as a result of the facilities. 

The only potential effects predicted were an increase in sulfur content in lichens and a 

possible decline in abundance of a few of the most sensitive lichen species. The potential 

decline was not expected to be of sufficient magnitude to diminish the role of lichens in the 

park ecosystems. Therefore, the National Park Service concluded that no adverse impact 

was likely to occur. However, continued study and monitoring of biological resources in the 

park was recommended to ensure that existing and potential future development in the 

area would not threaten park ecosystems. As was noted in Chapter 4, monitoring at 

Theodore Roosevelt National Park indicates that ambient sulfur dioxide levels have fallen 

from 1982 to 1984. This is associated with efforts by the State, in cooperation with 

National Park Service, to reduce emissions from all oil and gas production activities in the 

area. 

The NPS decision regarding these permit applications was summarized in the Federal 

Register, September 20, 1982 (47 FR 41480). 

Permit Reviews at Shenandoah National Park 

Industrial development near Shenandoah National Park has presented some special 

problems. Foliar injury due to ozone has been documented on several plant species in 

Shenandoah, and ambient levels of ozone measured in the park are close to, but not 

violating, the National Ambient Air Quality Standards. The reason for this high ozone 

concentration is particularly difficult to deter-mine, because ozone is not directly emitted, 

but is formed in the atmosphere as the result of the interaction of several different pollutants. 

Ozone can also be transported long distances. 

A number of permit applications have been reviewed' for small industrial facilities near 

Shenandoah which were expected to emit hydrocarbons (key precursors in ozone 

formation). These sources may, in aggregate, contribute to the formation of ozone in the 

area, but due to the complexities in the formation of ozone in the atmosphere, it is 

difficult to determine how much each additional new source might contribute. There are 

no prevention of significant deterioration increments for ozone; the state is allowed to issue 

a permit to a new source unless the Park Service can convince the state that an 

adverse impact on NPS resources would occur. With foliar injury already documented in 

the park, the Park Service is concerned that adverse impacts may be occurring due to 

combined emissions from local and distant sources. Recommendations for additional 

emission controls or emission offsets (requiring a reduction in emissions in one place 

before allowing increases in another) have been made in several instances in order to 

minimize the increase in ambient ozone levels. 

The Air Quality Division is currently conducting research to identify whether air quality 

models can be used to determine the sources of ozone pollution at Shenandoah. 

Preliminary results indicate that as much as 50 percent of the ozone in the Shenandoah 

area may be the result of emissions in other states. 

6-5 
The National Park Service, the Virginia State Air Pollution Control Board, and the U.S. 

Environmental Protection Agency are currently working together in formulating possible 

alternative approaches for addressing the ozone problem at Shenandoah. 

Proposed High-Level Nuclear Waste Repository Near Canyonlands National Park 

Davis and Lavender Canyons near Canyonlands National Park were being considered by 

the U.S. Department of Energy, along with several other locations in the United States, 

for a high-level nuclear waste repository. The Park Service reviewed the environmental 

assessment prepared by the U.S. Department of Energy and was concerned about the 

possible impact on park resources and visitors' experiences at Canyonlands if the site 

were selected. 

The Air Quality Division provided technical assistance to the park in analyzing potential 

impacts on air quality related values. One aspect of the proposed repository of particular 

concern was that it would be brightly lit for security reasons. This concern prompted an 

analysis of how the light might affect the view of the night sky from within the park. A 

model was developed to predict the intensity of the glow and how much of the night sky 

would be obscured by the glow under different air quality conditions. The results 

indicated that the light would be noticeable from within the park whether the air were 

"clean" or "dirty" and the glow would be bright enough to obscure some stars and the 

Milky Way in some portion of the sky. As would be expected, the night glow was predicted 

to be greatest at the viewing sites in the park closest to the proposed repository site, but 

some glow was predicted to be visible from as far away as Grand View Point, about 15 

miles from the proposed repository site. 

NPS comments on the environmental assessment expressed concern that night lighting at 

the nuclear repository would detract from visitor enjoyment of the park. Because of this 

and other potential impacts on park resources and values, the National Park Service 

asked the U.S. Department of Energy to disqualify the proposed site near Canyonlands. 

The U.S. Department of Energy subsequently decided not to recommend the Davis or 

Lavender Canyon sites for more detailed site characterization studies. 

DEVELOPMENT OF PROCEDURES FOR PROTECTION OF NPS RESOURCES 

While the Park Service has responsibilities for protecting the air resources of the National 

Park System, other federal or state agencies are charged with developing air quality 

control plans. Consequently, the Park Service is an active participant in the regulatory 

development process and works cooperatively with other agencies to promote NPS 

resource protection objectives. 

6-6 
Incorporation of Park Air Resource Protection Goals in State Implementation Plans 

States are required to develop implementation plans detailing how they plan to protect air 

quality. These plans must include strategies needed to attain National Ambient Air 

Quality Standards, to prevent significant deterioration of air quality in clean air areas, 

and to make reasonable progress toward the 

national visibility goal. Using information and analytical tools developed through the NPS 

air quality research and monitoring program, the Air Quality Division works with the 

states to develop their plans to help ensure consistency with federal requirements and 

park protection goals. For example, states are encouraged to incorporate measures into 

their plans that provide the National Park Service with sufficient opportunities to be 

involved in the formal review process for pollution sources that might have an effect on 

NPS resources. In response to NPS suggestions, some states have established 

requirements for permit applicants to conduct preconstruction monitoring of air quality 

related values in affected NPS units. 

States are also required to consult with the Park Service before developing visibility 

protection plans for class I areas. Information from the NPS visibility monitoring network 

has been used to document existing visibility impairment at all monitored parks. If the 

Park Service certifies that existing impairment exists in a park area, then a regulatory 

requirement is triggered. In this case, the states must determine whether the impairment 

is reasonably attributable to a specific source or small group of sources. The Air Quality 

Division has developed analytical tools that can be used to identify the major source 

areas contributing to visibility impairment in a park unit. Information generated through 

application of these techniques is shared with the states for their consideration in 

developing visibility protection strategies. 

Cooperative Studies 

In addition to the required regulatory programs that states must administer, some states 

have been voluntarily working together to analyze and develop regional approaches to 

pollution control. The National Park Service participated in a cooperative multi-state 

(Colorado, Wyoming, Montana, Utah, Idaho, and New Mexico) effort, in conjunction with 

the U.S. Forest Service and Bureau of Land Management, to evaluate options for the 

ultimate development of state visibility standards. This two-year study, called the Rocky 

Mountain Visibility Project, was completed in early 1985. A document was prepared that 

describes the parameters that could be used to define a visibility standard and discusses 

the technical and policy issues related to such a standard. 

These same states plus six additional western states (Arizona, Washington, Oregon, 

California, North Dakota, and Nevada) conducted a two-year acid deposition study that 

began in September 1985 called State Acid Rain Project (STAR). As part of this study, 

emissions inventories for acid deposition and visibility-reducing precursor pollutants were 

compiled and refined, atmospheric aerosols were characterized, existing and potential 

options for regional cooperation were analyzed, and model permitting procedures to 

address acid deposition effects of new air pollution sources on air quality-related values 

are being developed. The Air Quality Division has provided technical assistance to STAR 

participants to ensure that NPS concerns are addressed. 

6-7 
Interagency Visibility Task Force 

The Park Service has participated in interagency task forces convened by the U.S. 

Environmental Protection Agency to help develop federal regulations to protect visibility. 

The National Park Service had a major role in establishing a visibility impact analysis 

requirement for all new sources that might affect visibility in a class I area. In addition 

the Park Service successfully encouraged the U.S. Environmental Protection Agency to 

establish a national visibility monitoring network, using state-of-the-art equipment to 

document existing conditions and assess long-term trends. Air Quality Division staff 

have also been involved in an interagency study of long-term strategies for controlling 

regional haze. The report issued by this task force examined regulatory and research 

issues related to developing haze control approaches and included findings and 

recommendations. 

EFFECTS ON AIR QUALITY FROM ACTIVITIES WITHIN NPS UNITS 

When the sources of air pollutants are within the parks themselves, the Park Service 

must make resource management decisions balancing the need for the activities emitting 

pollutants and the need to protect park resources from the pollutants. In any event, all 

air pollution sources within parks, including prescribed fires, must comply with all 

federal, state, and local laws and regulations. 

Smoke Management Plan for Grand Canyon National Park 

The Park Service uses controlled burning to manage the forests in NPS areas and to thin 

forest stands and reduce the risk of wildfires. Burning, however, produces smoke that can 

affect visibility and visitor enjoyment in the parks. An incident in September 1980 served 

to increase public awareness of this problem when smoke from a burn on the North Rim 

of the Grand Canyon was transported into the canyon. The smoke significantly reduced 

visibility, impairing the visitors' view of the canyon. The Air Quality Division is conducting 

a smoke management research program in an attempt to develop a procedure to be used 

by park personnel to help select optimal times for conducting burns in order to minimize 

undesirable effects on visibility. 

This research includes developing the capability of forecasting weather conditions in order 

to begin burns when optimal conditions are expected for adequate smoke dispersal. An 

objective forecasting technique is being developed that will be used by park personnel to 

predict the likelihood of optimal conditions over a 24- or 48-hour period. If this program is 

successful at Grand Canyon, it may be possible to apply the same approach at several 

other parks with similar problems. 

Yellowstone Boilers 

The boilers used by the concessionaires at Yellowstone National Park to produce heat for 

the lodging facilities were old and emitting enough sulfur dioxide to cause noticeable 

problems in the park. In addition to concerns about potential effects on park resources 

and visitors, there were suspicions that the 

6-8 
pollution was actually damaging the paint on employees' cars. Everyone agreed that the 

situation should be corrected and the NPS Denver Service Center was retained to design 

new boilers for the park. Through the use of air quality models, the Air Quality Division 

helped develop a design and select a fuel that would minimize future pollution emissions. 

INCORPORATION OF AIR QUALITY CONCERNS INTO PLANNING AND INTERPRETIVE 

ACTIVITIES 

Air pollution has been recognized as one of the most serious threats to the resources and 

values of the National Park System. Since the Park Service holds these resources in trust 

for present and future generations, it is important for the public to understand how air 

pollution affects park resources. Interpretive activities and park management plans 

provide excellent vehicles for conveying and documenting air quality concerns. 

Encouragement of Public Awareness of Air Quality 

Air quality information is disseminated to NPS units for use in interpretive activities and 

exhibits. Visibility and biological effects data obtained through the NPS air quality 

research program have been summarized in slide presentations, pamphlets. reports, 

posters, and wayside exhibits. In 1983, only a half dozen parks were using air quality 

information in interpretive activities. By 1987, over 70 park units had received a set of 

slides compiled by the Air Quality Division, depicting air pollution sources and effects on 

park resources; also, 20 parks had developed air quality exhibits. The information is used 

by park personnel to promote public awareness of the air resource in the parks. Air 

quality interpretive activities have also informed park visitors about the air-resource 

issues facing the National Park Service. 

Participation in Resource Management Planning 

The Air Quality Division works with individual parks, regional offices, and the Denver 

Service Center to ensure that air quality is adequately addressed in NPS planning 

documents, such as the statements for management, resource management plans, 

general management plans, and specific project plans. One of the goals is to encourage 

the treatment of air quality as a resource that should be protected and managed. Park 

plans provide good vehicles for documenting current air quality conditions and any air 

quality monitoring or research being done in the park. The Air Quality Division provides 

technical information for use in planning documents and reviews project statements to 

ensure that their goals are consistent with the needs that have been identified by research 

that has been conducted to date. 

6-9

7.0 SELECTED REFERENCES 

VISIBILITY 

Background Literature on Visibility Measures and Research 

Bhardwaja, Prem S., ed. 1987. Visibility Protection: Research and Policy

Aspects. Transactions of Air Pollution Control Association Specialty 

Conference, Grand Teton National Park, Wyoming, September 1986. 

Malm, W.C. 1983. Introduction to Visibility. National Park Service, Air and Water 

Division, Air Research Branch. Fort Collins, Colorado. 

Malm. W.C. 1979. "Considerations in the Measurement of Visibility." Journal

of Air Pollution Control Association 29(10). 

Summaries of Visibility Conditions, in NPS Units and Throughout the United States 

Air Resource Specialists, Inc. 1986. Final Report, National Park Service

Visibility Monitoring and Data Analysis Project, Winter 1983 - Winter 1985.

Volume I and II Technical Report. NPS Contract No. CX-0001-3-0057. Air 

Resource Specialists, Inc. Ft. Collins, Colorado. 

Cahill, T.A., R.A. Eldred, and P.J. Feeney. 1986. Particulate Monitoring and Data Analysis

for the National Park Service 1982 - 1985. NPS Contract Number USDICX-0001-3-

0056. Air Quality Group, University of California. Davis, California. 

Husar, R.B., J.M. Holloway, and D.E. Patterson. 1981. "Spatial and Temporal 

Pattern of Eastern U.S. Haziness: A Summary." Atmospheric Environment

15(10/11): 1919-1928. 

Malm, W.C. and J.V. Molenar. 1984. " V i s i b i l i t y Measurements in National Parks in 

the Western United States." Journal of the Air Pollution Control Association 34(9): 899-

904. 

Malm, W.C. and E.G. Walther. 1979. “The Excellent but Deteriorating Air Quality in the 

Lake Powell Region." Journal of the Air Pollution Control Association 29(4). 

R.W. Beck and Associates. 1984. Washington State Regional Haze/Visibility Report. For 

 the State of Washington, Department of Ecology. Olympia, Washington. 

U.S. Environmental Protection Agency. 1979. Protecting Visibility: An EPA

Report to Congress. Office of Air Quality Planning and Standards. 

Research Triangle Park, North Carolina. 

U.S. Environmental Protection Agency. 1985. Developing Long-Term Strategies for

Regional Haze: Findings and Recommendation of the Visibility Task

Force. Research Triangle Park, North Carolina. 

7-1. 
Yarborough, K.A., W.C. Maim, and J. Moyers. 1985. "Visibility in Southwest National Park 

Service Areas." The Southwestern, Review of Management and Economics 4(1). 

Papers and Reports Based on NPS Visibility Research 

Cahill, T.A., R.A. Eldred, P.J. Feeney, and L.L. Ashbaugh. 1985. 1983-1984

Annual Report to the National Park Service for Particulate Monitoring and

Data Analysis. NPS Contract No. USDICX-0001-3-0056. Crocker Nuclear 

Laboratory, University of California. Davis, California. 

Johnson, C.E. and W.C. Maim. 1984. "Optical Characteristics of Fine and Coarse 

Particulates in Four National Park Service Sites." Proceedings of Air Pollution Effects 

on Parks and Wilderness Areas Conference, Mesa Verde National Park. May 20-23. 

1984. 

Malm, W.C., R.A. Eldred, T. Cahill, and J.V. Molenar. 1985. "Visibility and Particulate 

Measurements in the Western United States." Proceedings of the 78th Annual Meeting 

of the Air Pollution Control Association, Detroit, June 1985. 

Malm, W.C. and C.E. Johnson. 1984. "Optical Characteristics of Fine and Coarse 

Particulates at Grand Canyon, Arizona." Atmospheric Environment 18(6): 1231-1237. 

Pitchford. A., M. Pitchford, W.C. Malin, R. Flocchini, T. Cahill, and E.G. Walther. 1981. 

"Regional Analysis of Factors Affecting Visual Air Quality." Atmospheric Environment

15(10). 

SOURCES AND TRANSPORT OF AIR POLLUTANTS 

Ashbaugh, L.L. 1984. "An Investigation of High Sulfate Episodes in the Northern Great 

Plains." In Proceedings of the Fourth Joint Conference on Application of Air Pollution 

Meteorology, October 16-19, 1984, Portland, Oregon. 

Ashbaugh, L.L., W.C. Malm, and W.Z. Sadeh. 1986. "A Residence Time Probability 

Analysis of Sulfur Concentrations at Grand Canyon National Park." Atmospheric 

Environment.

Ashbaugh, L.L., L.O. Myrup, and R.G. Flocchini. 1984. "A Principle Component Analysis of 

Sulfur Concentrations in the Western United States." Atmospheric Environment 18: 

783-791. 

Eldred, R.A., T.A. Cahill, L.L. Ashbaugh, and J.S. Nasstrom. 1984. "Long 

Range Transport and Transformation of Anthropogenic Pollutants Observed in a 

PIXE Based Monitoring Network." Nuclear Instruments and Methods B3: 

479-482. 

Henderson, D., M.K. Liu. and D.A. Stewart. 1984. "Long-Distant Transport of Man-Made 

Air Pollution." Park Science 5: 6. 

7-2 
Liu. M.K., R.E. Morris, and J.P. Killus. 1984. "Development of a Regional Oxidant Model 

and Applications to the Northeastern United States." Atmospheric Environment 18: 

1145-1161. 

Malm, W.C. 1987. "Atmospheric Haze: Its Sources and Effects on Visibility In Rural Areas 

of the Continental United States." Paper presented at 4th World Wilderness Congress, 

Symposium on Acid Rain Impacts on Wilderness, Parks, and Nature Reserves, Estes 

Park, Colorado, September 14-17, 1987. 

Malm, W.C. 1984. "Origins of Atmospheric Sulfur at Chaco Culture National 

Historic Park." In Proceedings of Air Pollution Effects on Parks and 

Wilderness Areas, Mesa Verde National Park, May 20-23, 1984. 

Stewart, D.A.. R.E. Morris, A.B. Hubischewskj, M.K. Liu, and D. Henderson. 

1983a. Evaluation of Episodic Regional Transport Models of Interest to 

the National Park Service. Systems Applications, Inc., San Rafael, California (SYSAPP83/020). 

Stewart, D.A.. R.E. Morris, and M.K. Liu. 1983b. Evaluation of Long-Term

Regional Transport Models of Interest to the National Park Service. Systems 

Applications, Inc., San Rafael, California (SYSAPP-83/215). 

Stewart, D.A., R.E. Morris, and M.K. Liu. 1984. Application of Regional Air

Quality Modeling to National Parks. Part I: Final Report. Systems 

Applications, Inc., San Rafael. California (SYSAPP-84/139). 

Stewart, D.A., R.E. Morris, and M.L. Liu. 1984. Application of Regional Air

Quality Modeling to National Parks. Part II: Simulations of Air Quality And Sulfur

Deposition at Shenandoah, Great Smoky Mountains, and Acadia National Parks. 

Systems Applications. Inc., San Rafael, California. 

VISITOR EXPERIENCE 

Human Perceptions of Visibility Conditions 

Bell, P.A., R.J. Loomis, and W.C. Malm. 1984. "Rationale and Method for Studying the 

Impact of Impaired Visibility on National Parks." Rocky Mountain Psychological 

Association Annual Convention, Las Vegas, Nevada, April 25-28, 1984. 

Kiphart, R.J. Loomis, H.A. Cross, W.C. Malm, and J. Molenar. 1984. "Laboratory 

Assessment of Visual Sensitivity to Layered Haze Formation." Rocky Mountain 

Psychological Association Annual Convention, Las Vegas, Nevada, April 25-28, 1984. 

Loomis, R.J. and W.C. Malm. "Human Perceptions of Visual Air Quality." In Proceedings

of Air Pollution Effects on Parks and Wilderness Areas Conference, Mesa Verde 

National Park, May 20-23. 1984. 

Loomis, R.J., W.C. Maim, and J. Molenar. 1984. "Psychological Assessment of Layered 

Haze." 77th Annual Meeting and Exhibition of the Air Pollution Control Association, 

San Francisco, June 1984. 

7-3 
Malm, W.C. 1985. "An Examination of the Ability of Various Physical Indicators to 

Predict Judgment of Visual Air Quality." In Proceedings of the 78th Annual Meeting 

of the Air Pollution Control Association, Detroit, Michigan, June 16-21, 1985. 

Malm, W.C., K. Kelley, and J.V. Molenar. 1981. "Human Perception of Visual Air 

Quality (Regional Haze)." Atmospheric Environment 15(10). 

Malm, W.C., K.K. MacFarland, J.V. Molenar, and T. Daniel. 1983. "Human Perception of 

Visual Air Quality (Layered Haze)." In Managing Air Quality and Scenic Resources at 

National Parks and Wilderness Areas. R.D. Rowe and LG. Chestnut, eds. Boulder, 

Colorado: Westview Press. 

Effects of Visual Air Quality on Visitor Experience 

Bell, P.A., D.B. Garnand, G.E. Haas, M.J. Kiphart, R.J. Loomis, W.C. Maim, G.E. 

McGlothin, J.V. Molenar, D.M. Ross, and S. Solmonson. 1985. Assessment of 

Visibility Impairment on Visitor Enjoyment and Utilization of Park Resources. Report 

by Cooperative Institute for Research in the Atmosphere, Colorado State University. 

Fort Collins, Colorado. 

MacFarland, K.K., W.C. Malm, and J.V. Molenar. 1983. "An Examination of 

Methodologies for Assessing the Value of Visibility." In Managing Air Quality and 

Scenic Resources at National Parks and Wilderness Areas. R.D. Rowe and, L.G. 

Chestnut, eds. Boulder, Colorado: Westview Press. 

Malm, W.C., P. Bell, and G.E. McGlothin. 1984. “Field Testing a Methodology for 

Assessing the Importance of Good Visual Air Quality.” In Proceedings 77th Annual 

Meeting of the Air Pollution Control Association, San Francisco, California. June 24-

29, 1984. 

Ross, D.M., G.E. Haas, R.J. Loomis, and W.C. Malm. 1984. "Visibility Impairment and 

 Visitor Enjoyment." In: Proceedings of the 77th Annual Meeting of the Air Pollution 

 Control Association. San Francisco, California, June 24-29, 1984. 

Ross. D.M. and W.C. Malm. 1985. "Visual Air Quality and the National Park Visitor." 

Park Science (Fall). 

Ross, D.M.. W.C. Malm, and R.J. Loomis. 1985. . " The Psychological Valuation of Good 

Visual Air Quality by National Park Visitors." In Proceedings of the 78th Annual 

Meeting of the Air Pollution Control Association, Detroit, Michigan, June 16-21, 

1985. 

Schulze, W.D., D.S. Brookshire, E.G. Walther, K.K. MacFarland, M.A.Thayer, R.L. 

Witworth, R. Pozand, S. Ben-David, W.C. Malm, and J.V. Molenar. 1983. "The 

Economic Benefits of Preserving Visibility in the National Parklands of the 

Southwest." Natural Resources Journal.

7-4
BIOLOGICAL EFFECTS 

Background Literature on Air Pollution Effects on Vegetation 

Ferry, B.W., M.S. Baddeley, and D.L. Hawksworth (eds.). 1973. Air Pollution and Lichens.

London: Athlone Press. 

Heck, W.W., S.V. Krupa, and S.N. Linzon (eds.). 1979. Methodology for the Assessment 

of Air Pollution Effects on Vegetation. Minneapolis, Minnesota: Air Pollution Control 

Association. 

Jacobson, J.S. and A.C. Hill (eds.). 1970.Recognition of Air Pollution Injury to Vegetation:

A Pictorial Atlas. Pittsburgh, Pennsylvania: Air Pollution Control Association. 

Lepp, N.W. (ed.). 1981. Effect of Heavy Metal Pollution on Plants. Vols. 1 and 2. London: 

Applied Science Publishers. 

 

Manning, W.J. and W.A. Feder. 1980. Biomonitoring Air Pollutants with Plants. 

 London: Applied Science Publishers. 

Mudd, J.B. and T.T. Kozlowski (eds.). 1975. Responses of Plants to Air Pollution. New 

York: Academic Press. 

Smith, W.H. 1981. Air Pollution and Forests. New York: Springer-Verlag. 

Steubing, L. and H.J. Jager (eds.). 1982. Monitoring of Air Pollutants by Plants, 

Methods and Problems. The Hague: W. Junk Publishers. 

Summaries of NPS Biological Effects Reports and Selected General NPS Reports 

Armentano, T.V. and E.S. Menges. 1984. Research Plan: Analysis of Air Pollution 

 Sensitive Vegetation in Indiana Dunes National Lakeshore. NPS Contract CX-0001- 

 1-0112/PX-0001-3-0787. 

Bennett, J.P. 1982. "Biological Effects of Air Pollution: A Nationwide Perspective." Park 

Science 2: 10. 

Bennett, J.P. 1982. "A Computerized Flora of the National Parks." George Wright Soc. 

Forum 2: 14-16. 

Bennett. J.P. 1984. "Air Pollution Effects on Vegetation: Monitoring and Research." 

Presented at NPS Conference on Air Pollution Effects on Parks and Wilderness Areas, 

Mesa Verde National Park, May 20-23, 1984. 

Bennett. J.P. 1985, "Known Air Pollution Effects on Vegetation in National Parks." 

Testimony presented to the House Subcommittee on National Parks and Recreation. 

Committee on Interior and Insular Affairs, U.S. Congress, may 1985. 

Bennett, J.P., M.K. Esserlieu, and R.J. Olson. 1986. "Ranking Wilderness Areas for 

Sensitivities and Risks to Air Pollution." U.S. Forest Service.

7-5 
Wetmore, C.M. 1983.Lichens of the Air Quality Class I National Parks. NPS Contract CX- 

 0001-2-0034. 

Westman, W.E. 1984. A Preliminary Survey of VegetationInjury From Air Pollution in the 

 Santa Monica Mountains National Recreation Area. NPS Contract CX-0001-1- 

 0112/PX-0001-3-0745. 

Biological Effects Program Reports 

Armentano, T.V., E.S. Menges. and J. Molofsky. 1984. Analysis of Air Pollution Sensitive 

Vegetation at Indiana Dunes National Lakeshore. NPS Contract CX-0001-1-0112/PX0001-3-0787. 

Bledsoe, C.S., R.J. Zasoski, and J.K. Agee. 1985. Sulfur Concentrations in Native

Vegetation of Western Washington in Relation to Distance From Point Source 

Pollution. NPS Contract CX-9000-3-E004. 

Davis, D.D. 1984. Evaluation of Air Pollution Injury to Vegetation in a

Historic Site and Three National Parks. Draft Final Report. NPS Contract 

CX-0001-1-0112/PX-0001-4-0982. 

Davis, D.D. and J.P. Bennett. 1985. Evaluation of Air Pollution Injury to Vegetation in 

 Four Mid-Atlantic National Park Service Areas. NPS Contract CX-0001-1-0112/PX- 

 0001-4-0982. 

Dawson, J.L. 1984. Research Plan: Effects of Chronic Air Pollution on Forests of 

Shenandoah National Park and Mammoth Cave National Park. NPS Contract CX0001-1-0112/PX-0001-4-0924. 

Dawson, J.L. and J.P. Bennett. 1983. Effects of Chronic Air Pollution on Forests of 

Shenandoah National Park: Research Plan. NPS ContractCX-0001-1-0112/PX-0001-3-

0696. 

Del Moral, R., D.M. Wood. S. VanHook, and C.A. Clampitt. 1984. Bole Lichens in

Redwood National Park: A Baseline Study. NPS Contract CX 8480-4-0007. 

Drake. R.L. and L. Matamala. 1985. Zonal Air Pollution System Data Analysis and

Modeling. Vols. I & II. NPS Contract CX-0001-1-0113/PX-0001-4-1114. 

Esserlieu, M.K. and R.J. Olson. 1985. Biological Sensitivity of National Park Service 

Class I Areas to Atmospheric Pollutants. NPS Interagency Agreement IA-0492-82-02 

(Final Report). 

Hogsett, W.E., M. Plocher, V. Wildman, D.T. Tingey, and J.P. Bennett. 1984. Growth 

Response of Two Varieties of Slash Pine Seedlings to Chronic Ozone Exposures.

(Accepted for publication in Canadian J. of Botany) NPS Interagency Agreement No. 

0492-82-05. 

Glime. J.M., J.E. Longwith. and C. Meston. 1983. Baseline Bryological Survey to Assess

PotentialEcological Effects of Atmospheric Deposition in Isle Royale National Park.

NPS Contract CX-0001-1-0112/PX-0001-2-0704. 

7-6 
Glime, J.M. 'and G. Raeymaekers. 1984. The Effect of Wet and Dry Fallout and the

Assessment of Criteria to Use Bryophytes as Monitors of Acid Rain on Isle Royale

National Park. NPS Cooperative Agreement CA 6000-3-0000. 

Karnosky, D.F., P. Berrang, and R. Mickler. 1984. A Genecological Evaluation of Air

Pollution Tolerances in Hardwood Trees in Eastern Forest Parks. First Year Annual 

Report. NPS Contract CX-0001-1-0112/PX-0001-3-0744. 

Lang, D.S. 1983. Establishment of a Biological Air Quality Monitoring Site in Voyageurs

National Park. NPS Contract PX-2000-2-0785. 

Lawrey, J.D. 1985. Lichens as Lead and Sulfur Monitors in Shenandoah National Park,

Virginia. NPS Contract CX-0001-1-0114/PX-0001-4-1128. 

McClenahen, J.R.. and N.H. McCarthy. 1983. Forest Responses to Anthropogenic Stress

in the Cuyahoga Valley National Recreation Area. NPS Contract PX-2000-2-0874. 

McClenahen, J.R. and N.H. McCarthy. 1984. Report on Tree-Ring Responses to Site. Climate, and

Air Pollutants in the Cuyahoga Valley National Recreation Area. NPS Contract PX-2000-3-

9760. 

McLaughlin, S.B., T.J. Blasing, D.N. Duvick, T.N. Doyle, and L.K. Mann. (No date, received in

1984) Forest: Summary of a Two Year Study of Forest Responses to Anthropogenic Stress. 

Draft Final Report. NPS Interagency Agreement No. 0492-82-02.

Miller, P. R. and K.W., Stolte. 1983. Effects of Ozone and Sulfur Dioxide on Giant Sequoia 

Seedlings. From Sequoia and Kings Canyon National Parks. NPS Interagency 

Agreement IA-0492-82-04. 

Miller, P.R., K.W. Stolte, T.L. Franklin, A.P. Gomez, and C.A. Kazimer. 1984. Ozone

Effects on Important Tree Species of the Sequoia-Kings Canyon National Parks. NPS 

Interagency Agreement No. 0492-82-04. 

Minnesota Environmental Quality Board. 1984. Maintenance of a Biological Air Quality Monitoring

Site iln Voyageurs National Park. NPS Contract PX-2000-3-1253. 

Peard, J.L., B.F. Arbogast, S.W. Snow, and E.E. Engleman. 1984. The Element Contents of

Parmelia Sulcatta and P. Chlorochroa in Theodore Roosevelt National Park, North Dakota. 

(Abstract) NPS IAA with U.S.G.S., Denver, Colorado.

Rydout. G.B., A. Matthias, J. Bowers, and C.F. Hutchinson. 1983. A_ Preliminary

Analysis of the Effect of Air Pollutants on Vegetation in the Rincon Mountains District

of the Saguaro National Monument, Arizona. NPS Cooperative Agreement CA-8000-1-

0002. 

Sanchini, P.J., J.H. Bock, and S. Stein. 1.983a. An Air Quality Monitoring 

 System for Colorado National Monument Using Plants as Indicators: 1982

 Survey Results. NPS Contract PX-0001-2-0324

7-7 
Sanchini, P.J., J.M. Bock, and S. Stein. 1983b. How to Assess the Effects of Air

Pollution on Native Plant Populations at Colorado National Monument: A_ 

Manual for Park Management. NPS Contract PX-0001-2-0324. 

Taylor, F.G. and P.D. Parr. 1983. Fluoride Survey in the Great Smoky

Mountains National Park Vegetation and Soils. NPS Interagency 

AgreementIA-0492-82-02. 

Treshow, M. 1985. Establishment of White Pine Biomonitoring Plots in Acadia

National Park. NPS Contract CX-0001-1-0112/PX-0001-4-0922. 

Turner, R.R., M.A. Bogle, and C.F. Baes.. No Date. Survey of Lead in Vegetation.

Litter and Soils of the Great Smoky Mountains National Park. NPS 

Interagency Agreement IA-0492-82-02. Final Report received 6/84. 

Waggoner, G.S. and N.K. Thorwardson. 1982, 1983. . & 1984. NPFLORA: A

Computerized Vascular Flora of the National Parks, Annual Status Reports.

NPS transfer of funds to the Science Section, Denver Service Center. 

Wetmore, C.M. 1.983a. Lichens and Air Quality in Voyageurs National Park. NPS 

Contract CX-0001-2-0034. 

Wetmore. C.M. 1983b. Lichens and Air Quality in Theodore Roosevelt National

Park. NPS Contract CX-0001-2-0034. 

Wetmore, C.M. 1984. Lichens and Air Quality in Acadia National Park. NPS 

Contract CX-0001-2-0034. 

Wetmore, C. M. 1985a. Lichens and Air Quality in Isle Royale National Park. NPS

Contract CX-0001-2-0034. 

Wetmore, C.M. 1985b. Lichens and Air Quality in Sequoia National Park. NPS 

Contract CX-0001-2-0034. 

7-8