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Out of Sight:The Science andEconomics ofVisibility Impairment
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Out of Sight:The Science and Economics of
Visibility Impairment
August 2000
Prepared for
Clean Air Task Force
Boston, MA
Project Manager:
Dr. L. Bruce Hill
Prepared by
Abt Associates Inc.
4800 Montgomery Lane
Bethesda, MD 20814-5341
www.abtassoc.com
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Abt Associates Environmental Research Area provides multi-disciplinary scientific research andenvironmental policy analysis to the EPA, the U.S. Agency for International Development, the Inter-American
Development Bank, the World Bank, and directly to foreign, state and local governments. Abt Associates has
extensive experience in estimating the potential public health improvements and economic costs and benefits
from improving ambient air quality. The Environmental Research Area conducted extensive health analysis
for the U.S. EPA in support of the 1997 revisions to both the ozone and the particulate matter National
Ambient Air Quality Standards. They also prepared the health and economic analyses for EPAs 1997 Report
to Congress The Benefits and Costs of the Clean Air Act: 1970 to 1990, and conducted similar policy, health
and economic analyses for EPA of regulations on the electric generating industry, automobile exhaust, and
potential policies for climate change mitigation strategies. Abt Associates Environmental Research Area
conducts public health analysis projects worldwide, including air pollution health assessment projects with the
environmental and health ministries in Argentina, Brazil, Canada, Chile, Korea, Russia, Thailand, the Ukraine
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Mr. Kenneth Davidson specializes in the analysis of air quality policy. He has a master's degree in resource
economics and policy from Duke University's Nicholas School of the Environment, and as a student workedwith the Innovative Strategies and Economics Group at the U.S. EPA's Office of Air Quality Planning and
Standards.
Dr. Leland Deck specializes in economic and risk analysis of environmental policies. His research projectsinclude estimating the risks and economic value of health and welfare benefits from reducing air pollution, the
costs of alternative pollution prevention technologies, and designing effective and enforceable economic
incentive programs as a part of an overall strategy for controlling pollution from stationary and mobile sources.
In addition to his own research projects, Dr. Deck manages Abt Associates Environmental Economics
Practice, and is a Vice President of Abt Associates.
Dr. Don McCubbin has eleven years of experience in the analysis of environmental issues, with a special
emphasis on the adverse effects of criteria air pollutants.
Dr. Ellen Post has fourteen years of experience in the scientific, economic, and policy analysis ofenvironmental issues, with particular emphasis on (1) criteria air pollution risk assessment and economic
benefit analysis, and (2) methods of assessing uncertainty surrounding individual estimates. She is one of the
primary analysts conducting a particulate matter air pollution risk assessment for EPAs Office of Air Quality
Planning and Standards, and has been a key economist in ongoing work analyzing the economic benefits
associated with risk reductions from a number of air quality regulations, including the implementation of
proposed particulate matter and ozone standards in the United States.
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Table of Contents
EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ES-1
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. VISIBILITY IMPAIRMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 Causes of Visibility Impairment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Observing and Measuring Visibility Impairment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 People Can Tell When Views Are Impaired . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 How Visibility Impairment is Measured . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3. TRENDS IN VISIBILITY IMPAIRMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1 Recent Visibility Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.1 Visibility at Parks Where the Vista Is Integral to the Experience . . . . . . . . . . . 14
3.1.2 Visibility at Smaller Parks and Wilderness Areas . . . . . . . . . . . . . . . . . . . . . . 22
3.1.3 Visibility in Urban Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4. LEGISLATIVE AND REGULATORY HISTORY OF VISIBILITY IMPAIRMENT . . . . . . . 26
5. ECONOMICS: VISIBILITY IMPAIRMENT AND PARK VISITATION . . . . . . . . . . . . . . . 31
5.1 An Undisturbed Environment, Including Clean, Clear Air and Good Visibility, is Very
Important to Park Visitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.2 Visitors are Willing to Alter Their Length of Stay Based on Visual Air Quality Conditions at
National Parks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.3 What is at Stake to the Economy if Visitation Rates Decline? . . . . . . . . . . . . . . . . . . . 34
5.4 Local Economic Benefits from Visibility Improvements . . . . . . . . . . . . . . . . . . . . . . . . 36
6. ECONOMICS: THE NON-MARKET VALUE OF VISIBILITY . . . . . . . . . . . . . . . . . . . . . . 416.1 The Economic Valuation of Visibility Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6.2 The Value of Visibility Improvements at National Parks: Evidence from Studies . . . . . 43
6.3 The Value of Visibility Improvements in Residential Areas: Evidence from Studies . . . 46
6.4 Applying the Information from Studies to Assess the Visibility Benefits of Reducing Air
Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7. POWER PLANT EMISSION REDUCTIONS AND ASSOCIATED VISIBILITY BENEFITS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
8. CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
9. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
APPENDIX A DETAILED TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
APPENDIX B METHOD TO ESTIMATE VISIBILITY BENEFITS . . . . . . . . . . . . . . . . . . . . . . . . B-1
B.1 Basic Utility Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
B.2 Measure of Visibility: Environmental Goods Versus Bads . . . . . . . . . . . . . . . . . . B-3
B.3 Estimating the Parameters for Visibility at Class I Areas: the (s and *s . . . . . . . . . . B-5B.3.1 Estimating Region-Specific Recreational Visibility Parameters for the Region
Covered in the Chestnut and Rowe Study (Regions 1, 2, and 3) . . . . . . . . . . B-8
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B.3.2 Inferring Region-Specific Recreational Visibility Parameters for Regions Not
Covered in the Chestnut and Rowe Study (Regions 4, 5, and 6) . . . . . . . . . . B-8
B.3.3 Estimating Park- and Wilderness Area-Specific Parameters . . . . . . . . . . . . . B-10
B.3.4 Derivation of Region-specific WTP for National Parks and Wilderness Areas
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-10
B.3.5 Derivation of park- and wilderness area-specific WTPs, given region-specific WTPs
for national parks and wilderness areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-11
B.3.6 Derivation of park- and wilderness area-specific parameters, given park- and
wilderness area-specific WTPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-12
B.4 Estimating the Parameter for Visibility in Residential Areas: 2 . . . . . . . . . . . . . . . . B-13
B.5 Putting it All Together: the Household Utility and WTP Functions . . . . . . . . . . . . . B-13
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List of Exhibits
Exhibit 1-1 Denver on a Clear Day and on a Hazy Day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Exhibit 2-1a Visible Plume from Local Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Exhibit 2-1b Layered Haze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Exhibit 2-1c Regional Haze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Exhibit 2-2 National Emissions of Nitrogen Oxides and Sulfur Dioxide by Source in 1998 . . . . . . . . . . . 4
Exhibit 2-3a Contribution to Visibility Impairment in the Eastern U.S. . . . . . . . . . . . . . . . . . . . . . . . . . 5
Exhibit 2-3b Contribution to Visibility Impairment in the Mid-West . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Exhibit 2-3c Contribution to Visibility Impairment in the West . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Exhibit 2-4 Scattering and Absorption of Image-Forming Light from the Observers Sight Path . . . . . . . 7
Exhibit 2-5 Aerosol Size and Light Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Exhibit 2-6 Types of Particulate Matter and Impact on Image-Forming Light . . . . . . . . . . . . . . . . . . . . 8
Exhibit 2-7 Relationship Between Perceived Visual Air Quality and the Amount of Particulate Matter in the
Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Exhibit 2-8 Inverse Relationship Between Visual Range and the Deciview Index . . . . . . . . . . . . . . . . . . 11
Exhibit 3-1 Airport Visual Data: Trend in 75th
Percentile Light Extinction Coefficient for July-September(measured in km-1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Exhibit 3-2 Visibility Trends at Acadia National Park, Maine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Exhibit 3-3 Visibility Trends at Grand Canyon National Park, Arizona . . . . . . . . . . . . . . . . . . . . . . . . 17
Exhibit 3-4 Visibility Trends at Great Smoky Mountains National Park, Tennessee . . . . . . . . . . . . . . . 18
Exhibit 3-5 Visibility Trends at Shenandoah National Park, Virginia . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Exhibit 3-6 Visibility Trends at Yosemite National Park, California . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Exhibit 3-7a Extreme Visibility Days at Acadia National Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Exhibit 3-7b Extreme Visibility Days at Grand Canyon National Park . . . . . . . . . . . . . . . . . . . . . . . . . 21
Exhibit 3-7c Extreme Visibility Days at Great Smoky Mountains National Park . . . . . . . . . . . . . . . . . 21
Exhibit 3-7d Extreme Visibility Days at Shenandoah National Park . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Exhibit 3-7e Extreme Visibility Days at Yosemite National Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Exhibit 3-8 Visibility Trends at San Gorgonio Wilderness Area, California . . . . . . . . . . . . . . . . . . . . . 23Exhibit 3-9 Visibility Trends at Chassahowitzka Wilderness Area, Florida . . . . . . . . . . . . . . . . . . . . . 23
Exhibit 3-10 Visibility Trends in Washington, D.C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Exhibit 4-1 Map of Mandatory Class I Areas with Visibility Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Exhibit 5-1 Visitor Rated Importance of Park Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Exhibit 5-2 Total Recreation Visits to U.S. National Parks, 1951-1998 . . . . . . . . . . . . . . . . . . . . . . . . 35
Exhibit 5-3 Sales Increase Near Park Due to an Increase in Park Visitation . . . . . . . . . . . . . . . . . . . . . 39
Exhibit 5-4 Tax Revenue Increase Near Park Due to an Increase in Park Visitation . . . . . . . . . . . . . . . 39
Exhibit 5-5 Local Job Increase Near Park Due to an Increase in Park Visitation . . . . . . . . . . . . . . . . . . 40
Exhibit 6-1 Economic Valuation Studies for Recreational and Residential Visibility . . . . . . . . . . . . . . . 44
Exhibit 6-2 Visibility Benefits from Different Policy Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Exhibit 7-1 Residential (Urban) Visibility Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Exhibit 7-2 Recreational Visibility Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Exhibit 7-3 State-Level Recreational Visibility Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Exhibit 7-4 WinHaze Split-Images at Great Smoky Mountains National Park for Status Quo, No-EGU, and
Partial-EGU Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Exhibit A-1 Percentage Contribution of Constituents to Visibility Impairment on Good, Mid-Range, and Poor
Visibility Days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
Exhibit A-2 Annual Slope Estimates with Probabilities for Rejection for the Average of the Worst, Median,
and Best Visibility Days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3
Exhibit A-3 Visibility Benefits from Different Policy Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4
Exhibit B-1 Available Information on WTP for Visibility Improvements in National Parks . . . . . . . . B-6
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Exhibit B-2 Summary of Region-Specific Recreational Visibility Parameters to be Estimated in Household
Utility Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7
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Exhibit 1-1 Denver on a Clear Day and on a Hazy Day
1. INTRODUCTION
Visibility impairment is a basic form of air pollution, one that people can see and recognize without
special instruments. It is also one of the scientifically best-understood air quality-related impacts of fossil fuel
combustion. Despite this common knowledge, the full costs of impaired visibility are not well understood by
policymakers and the public. Some people are not aware that visibility is impaired at all, incorrectly believing
that the milky-white haze that blankets parts of the country is somehow a natural phenomenon associated with
humidity, especially on hot summer days. In fact, visibility impairment is a major problem in the United States,
with both aesthetic and economic consequences.
A variety of sources contribute to the air pollutant
emissions that lead to visibility impairment, including power
plants, motor vehicles, wildfires and industrial processes like
smelting. The largest source in many areas is power plant
emissions. This report is meant to give the educated reader a
basic understanding of the nature and science of visibility
impairment and to provide an overview of the economic costsof visibility due to sources such as power plants. The report
is not, however, meant to go into great depth in every area,
although there is a large reference section that one can refer to
in order to get more detail on particular topic discussed here.
The report begins with a general overview of the basics behind the nature and science of visibility.
Included in this section is a discussion on what causes visibility impairment, how visibility is impaired, how
humans perceive visibility impairment, and how it is measured. The second section presents both historical
trends on national visibility and examples of visibility degradation at specific places. The legislative history
in specific regard to visibility regulation is then presented, along with a discussion on other air pollution
policies that have had an impact on visual air quality. The economics of visibility follows, and is presented
in two separate sections. The first discusses the economics of visibility in terms of its impact on the directconsumption of visibility as a resource, or, in other words, how visibility impacts visitation and tourism
behavior. The next section presents the economics of visibility in terms of non-direct consumption, or how
people value improvements in visibility in areas where they may or may not be experiencing it directly. Finally,
an applied example of the valuation of visibility improvements is provided, specifically calculating the visibility
benefits associated with reductions in power plant emissions.
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2. VISIBILITY IMPAIRMENT
Visibility impairment comes in a variety of forms: intrusive plumes from local smokestacks, a dirty
low-lying inversion layer, a milky or brown regional haze blanketing the view in all directions. Each of these
forms of visibility impairment is a function of the nature and source of emissions and the prevailing
meteorological conditions (Malm, 1999, p. 20). With stable atmospheric conditions and large, local emission
sources, plumes and layered hazes are likely to occur (Exhibits 2-1a and 2-1b). Regional haze occurs under
meteorological conditions favorable for regional transport (Exhibit 2-1c).
Plumes, layered haze, and regional haze differ from the clouds and fog that we might see on a rainy
day, and instead are manmade impediments to visibility that federal, state, and local governments are actively
trying to reduce. For regulatory purposes, the Environmental Protection Agency distinguishes between
visibility impairment that is caused by one or a small group of sources, such as a the plume from a smoke
stack, and visibility impairment that is caused by emissions over a wide geographic region. The distinction is
made because emissions over a wide region are more diffuse and less easy to attribute to specific sources and,
thus, more difficult to identify and control.
When the view is obscured by pollution, it especially affects peoples enjoyment and sense of
wilderness experience. Many visitors to our nations parks and wilderness areas are unable to see the
spectacular vistas they had expected, because a veil of white or brown haze hangs in the air blurring the view.
Because this reduction can significantly reduce peoples enjoyment of the views, and it may reduce the
likelihood that they come back to visit, this can have a significant local economic impact. As we discuss in
subsequent chapters, there is also evidence that people value visibility at parks even when they are at home,
whether they visited the area or not.
Exhibit 2-1a Visible Plume from Local StacksSource: Malm (1999, Figure 1-5) and NPS-CIRA (2000b).
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Exhibit 2-1b Layered HazeSource: Malm (1999, Figure 1-5) and NPS-CIRA (2000b).
Exhibit 2-1c Regional HazeSource: Malm (1999, Figure 1-5) and NPS-CIRA (2000b).
2.1 Causes of Visibility Impairment
Most visibility impairment is caused by human-induced particulate air pollution, the same pollutionlinked to premature death (Pope et al., 1995) and acid rain (NAPAP, 1990). Because of its very small particle
size, this pollution is often carried by the wind hundreds of miles from where it originated. The large coal-fired
electric utilities in the Ohio valley, some with stacks approaching 1000 feet tall, contribute the largest share
to visibility problems over a wide area of the Eastern and Midwestern U.S. Other contributors include motor
vehicles, industrial fuel burning, manufacturing operations, and natural sources such as windblown dust,
volatile organic compounds from plants, and soot from wildfires.
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0%
10%
20%
30%
40%
50%
60%
70%
Electric Utilities Industry Transport Other
Nitrogen Oxides Sulfur Dioxide
Exhibit 2-2 National Emissions of Nitrogen Oxides and Sulfur Dioxide by Source in 1998
These emission sources contribute primary particles, which are particulates emitted directly into the
air, and secondary particles, which form from gases often carried many miles from their source. Both
primary emissions and secondary formation of particles contribute to visibility impairment. Primary particles
come from a variety of sources including diesel and wood combustion, and dust from industrial activities and
natural sources. Secondary particles form in the atmosphere from gases emitted from power plants, cars, and
a number of other sources, and are the most important in forming haze. Sulfate is, in most areas, the most
important secondary particulate, and forms from sulfur dioxide and ammonia emissions. Other secondary
particulates include nitrates, forming from nitrogen oxide and ammonia emissions, and organic carbon particles
from condensed hydrocarbon emissions.
Some particles, like sulfates and nitrates become more effective during humid conditions as they absorb
atmospheric moisture and grow (Day et al., 2000, p. 716; Sisler, 1996, p. 4-7; U.S. EPA, 1996, p. 8-44).
Sulfates and nitrates can more than triple in size as relative humidity increases, thus making visibility worse
during periods of high humidity, such as the humid summer months in the East (National Research Council,
1993, p. 103). However, humidity alone does not cause visibility impairment.
The impact of particles can be measured many miles away. California and Mexico both make
substantial contributions to sulfate particles in the Grand Canyon (Eatough et al., 2000, Figure 9; Malm, 1999,p. 51). The U.S., east of the Mississippi, and Canada are both affected by emissions from power plants.
Electric utilities are perhaps the single largest contributor to poor visibility. Nationwide in 1998, electric
utilities contributed 67 percent of sulfur dioxide emissions and 25 percent of nitrogen oxide emissions (Exhibit
2-2 based on U.S. EPA, 2000, Tables A-2 and A-4). Coal-powered electric utilities dominate these emissions,
contributing 94 percent of sulfur dioxide and 88 percent of nitrogen oxide emissions from electric utilities.
Sulfur dioxide gas is especially important because it contributes to the formation of sulfates, which
often dominate other causes of visibility impairment, particularly in the Eastern U.S. Exhibits 2-3a, 2-3b, and
2-3c present the average contribution to visibility impairment of different particulate matter constituents at a
variety of mainly rural monitoring sites through out the U.S., and Exhibit A-1 presents the park-level data
underlying these regional averages. The exhibits present the contribution on a good, medium and bad visibility
days. The sites presented in the exhibits are typically located in national parks, with the exception of
Washington D.C.
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0%
10%
20%
30%
40%
50%
60%
70%
80%
ContributiontoVisib
ilit
Impairment(%)
Good Day Median Day Poor Day
Eastern U.S.
Sulfate
Nitrate
Organic Carbon
Light Absorbing
Carbon
Coarse Matter and
Fine Soil
0%
10%
20%
30%
40%
50%
60%
70%
80%
ContributiontoVisibility
Im
pairment(%)
Good Day Median Day Poor Day
Mid-Western U.S.
Sulfate
Nitrate
Organic Carbon
Light Absorbing
Carbon
Coarse Matter and
Fine Soil
In the eastern and mid-western U.S., sulfates account for the majority of visibility impairment. In the
West, sulfates and organic carbon play about equal roles. Throughout the U.S., nitrates typically account for
less than 10 percent of visibility impairment in most locations, with a notable exception of San Gorgonio,
located in southern California, where nitrates can contribute over 30 percent of visibility impairment (Exhibit
A-1). Perhaps most significantly, in almost all locations, sulfates are responsible for a greater percentage of
visibility impairment on bad visibility days than on good visibility days. In Great Smoky Mountains National
Park, sulfates account for 46 percent of impairment on a good day, 63 percent on a median day, and 76 percent
on a bad visibility day. In Acadia, sulfates account for 37 percent, 48 percent, and 69 percent, respectively
(Exhibit A-1). In most of the East, sulfur dioxide emissions, largely from electric utilities, account for two
thirds to three quarters of the visibility impairment on haziest days.
Exhibit 2-3a Contribution to Visibility Impairment in the Eastern U.S.Source: NPS-CIRA (2000a).
Exhibit 2-3b Contribution to Visibility Impairment in the Mid-WestSource: NPS-CIRA (2000a).
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0%
10%
20%
30%
40%
50%
60%
70%
80%
ContributiontoVisibility
Impairment
(%)
Good Day Median Day Poor Day
Western U.S.
Sulfate
Nitrate
Organic Carbon
Light Absorbing
Carbon
Coarse Matter and
Fine Soil
Exhibit 2-3c Contribution to Visibility Impairment in the WestSource: NPS-CIRA (2000a).
2.2 Observing and Measuring Visibility Impairment
To better understand visibility impairment it is useful to consider the nature of light and how the human
eye functions. The human eye recognizes a spectrum of colors from blues with a wavelength of about 0.4
microns to reds with a wavelength of 0.7 microns (Malm, 1999, p. 3). We perceive a rose to be red because
it absorbs all of the wavelengths in the visible spectrum except for those around 0.7 microns, and we perceive
a blue butterfly because it absorbs most of the visible spectrum except for those wavelengths around 0.4
microns. The range of color we see are simply light with different wavelengths reflected back to us and
captured by our eyes. The same process of differential absorption and reflection of light occurs with visibility
impairment.
When we observe a low-lying brownish layered haze caused by nitrogen dioxide emissions, it appears
brown because nitrogen-dioxide absorbs blue light and reflects back to us the remainder of the spectrum
(Malm, 1999, p.4). When we see a dark plume coming from a smokestack, it appears black because the carbon
soot and other emissions absorb all of the visible spectrum. Conversely, a white plume of water vapor coming
from a power plants cooling tower appears white because it absorbs none of the incoming light and simply
scatters and reflects back the full spectrum to the eye.
When we are on a mountain top enjoying a view of the landscape or just walking down the street and
looking at a distant object, a number of processes interfere with the light that is reflected from objects that we
are trying to see (Exhibit 2-4). Our ability to see a distant mountain depends on transmission radiance and
air light (U.S. EPA, 1996, p. 8-23). Transmission radiance refers to the light reflected from the mountainand the subsequent interaction of this light in the atmosphere. As this light is absorbed and scattered by gases
and particles in the atmosphere, our ability to see the mountain is reduced. Scattering by particles is usually
the most important source of interference. Another source is air light, which has a variety of effects and refers
to the light from sources other than the object of interest that are scattered towards us and affect what we are
trying to see. Air light scattered from behind the mountain provides backlighting and makes the mountain
standout, while air light scattered from particles and gases between the mountain and our eye obscures our
vision (National Research Council, 1993, p. 82).
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Exhibit 2-4 Scattering and Absorption of Image-Forming Light from the Observers Sight PathSource: Malm (1999, Figure 1-5) and NPS-CIRA (2000b).
Transmission radiance usually dominates visibility impairment, and the scattering of photons is the
most important process in transmission radiance. Although gaseous pollutants, such as nitrogen dioxide,
contribute to visibility impairment, they usually play a small role, and instead scattering due to particulates
dominate the visibility impairment. However, not all particles are equally important in scattering light (Exhibit
2-5). Particles about the same size as the visible spectrum are the most efficient at scattering light (Malm,
1999, p.8).
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Exhibit 2-5 Aerosol Size and Light ScatteringSource: Malm (1999, Figure 1-5) and NPS-CIRA (2000b).
These fine particles, ultra-efficient at scattering light, include: sulfates, nitrates, organics, and soil
(Malm, 1999, p. 26). Elemental carbon is another fine particle that contributes to visibility impairment by
efficiently absorbing light because of its black color (Exhibit 2-6). In contrast to white sulfur, which absorbs
little light and instead scatters it effectively, elemental carbon absorbs light, much like a blacktop absorbs heat
on a hot summer day. However, the contribution of absorption by elemental carbon is generally less than 10
percent of the loss in transmission radiance. Sulfates often dominate, particularly in the East, and can
contribute 80 percent or more of the loss in transmission radiance (Exhibit 2-3a).
Exhibit 2-6 Types of Particulate Matter and Impact on Image-Forming LightSource: Malm (1999, Figure 1-5) and NPS-CIRA (2000b).
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1
2
3
4
5
6
7
8
9
1 2 3 4 5 6 7 8 9 10
Particulate Concentration (ug/m3)
Poor
-------------------------------------------------
Good
Per
ceivedVisualAirQuality(PVAQ)
Exhibit 2-7 Relationship Between Perceived Visual Air Qualityand the Amount of Particulate Matter in the Air
2.2.1 People Can Tell When Views Are Impaired
It is well known how visibility is impaired by air pollution, and how the human eye perceives these
changes. However, do humans regard visibility impairment in a consistent and equal fashion? That is, when
visibility is impaired, do humans perceive that visibility has changed equally? This is an important question
to answer because, if impaired visibility is not perceived equally between people from region to region, it would
be nearly impossible to measure and regulate.
In the first perception and judgement studies, conducted by the NPS (NPS, 1988), people were asked
to judge the visual air quality in several slides depicting vistas under different visibility conditions using a scale
of one to ten, one being worst and ten being best. The one to ten judgement is called perceived visual air
quality (PVAQ), and it reflects peoples perceptions and judgements 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 judgements of visual air quality.
These studies first addressed the question of whether individuals judged poor visibility in the slides
similarly to actual views under the same air quality conditions. It was found that the PVAQ judgements were
comparable and that the use of slides in studies concerning perceived visual air quality was a valid method forcomparing perceptions of visual air quality. They also found that, regardless of the demographic
characteristics of the individual (age, sex, education), PVAQ judgements made by different people were
consistent with each other. This suggested that for a given slide, people generally judged air quality in a similar
fashion.
The analysis of the PVAQ
judgments revealed that increases in
air pollution are more noticeable and
objectionable to the human observer
when the air is relatively clean.
Exhibit 2-7, based on NPS (1988,
Figure 3-1), demonstrates therelationship between the PVAQ
judgement and ambient particulate
levels. The curved line indicates that
a one-unit increase in particulates will
result in a much larger decrease in an
individuals PVAQ at the lower
particulate levels than at the higher
particulate levels.
These studies were also able
to test whether the visual air qualityperceived by individuals 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.
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1 The Federal Register (July 1, 1999, vol. 64, no. 126, p. 35,725) discusses the choice of the deciview index for EPA'sregional haze program.
Abt Associates Inc. August 200010
These first few perception and judgement studies set the foundation for subsequent research on the
effects of visual air quality on the visitor experience. These studies suggested that visitors do have preferences
concerning visibility conditions and that a variety of circumstances, such as what is actually being viewed and
how good the air quality was prior to the pollution, influence changes in perceived visual air quality.
2.2.2 How Visibility Impairment is Measured
It is important to determine that people can actually perceive changes in visibility condition, which is
why the perceived visual air quality (PVAQ) index was developed. However, this index is not an actual
measure of visibility conditions as they exist from place to place. To conduct meaningful analyses of how
visibility changes due to the presence of pollution in the atmosphere, there must be some standardized approach
to measuring visual air quality. Visibility conditions are, therefore, commonly expressed in terms of three
mathematically related metrics: standard visual range (SVR), light extinction (ext), and deciviews (dv).
Standard visual range is the metric best known by the general public. It is the maximum distance at which one
can identify a black object against the horizon, and is typically described in kilometers (or miles). Higher visual
range estimates mean better visibility. While the theoretical maximum is 391 kilometers on a perfectly clear
day, this is never achieved due to the natural scattering of light by gases in the atmosphere, so-called Rayleighscattering (U.S. EPA, 1996, p. 8-12). While standard visual range is a simple measure that can be easily used
to characterize visual conditions, it is somewhat imprecise and cannot be used to effectively determine the
relative importance of the contributors to reduced visibility. It is also useless in cloudy conditions near
monitors.
Light extinction is a somewhat better alternative than visual range because it allows one to express
more objectively the relative contribution of a PM constituent to overall visibility impairment. Light extinction
is the sum of the light scattering and light absorption by particles and gases in the atmosphere, and is measured
in inverse megameters (Mm-1), relating how much light is extinguished per megameter. Higher extinction
values mean worse visibility. This is the inverse of visual range, where higher visual range estimates suggest
better visibility (U.S. EPA, 1996, p. 8-56). For example, in the Great Smoky Mountains, a relatively clear day
has an extinction of 47 Mm-1 and a visual range of 82 kilometers, and a hazy day has an extinction of about211 Mm-1 and a visual range of 19 kilometers. Both extinction and visual range are similar in that they are not
proportional to human perception (Malm, 1999, p. 35). In other words, a one unit change in either light
extinction or visual range is perceived differently, depending on the starting point. For example, a five mile
change in visual range can be either very apparent or not perceptible, depending on whether the starting point
is a clear day or a hazy one.
A third measure of visibility is the deciview index, which EPA selected as the standard metric for
tracking progress in EPA's regional haze program, largely because it provides a linear scale for perceived visual
changes over a wide range of conditions.1 On a particle-free, pristine day, the deciview index has a value of
zero (SVR=391 km). On a relatively clear day in the Great Smoky Mountains the deciview index might be
about 16 (SVR=79 km) and on a relatively hazy day the deciview index might be about 31 (SVR=201 km).For each 10 percent increase in light-extinction, the deciview index goes up by one. So, higher deciview values
mean worse visibility (Exhibit 2-8). This logarithmic scaling is analogous to the decibel scale used for the
perception of sound (U.S. EPA, 1996, p. 8-57). Under many scenic conditions, a change of one deciview is
considered to be just perceptible by the average person. However, it is important to understand that the same
amount of pollution can have dramatically different effects on visibility depending on existing conditions. Most
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0
50
100
150
200
250
300
350
400
0 5 10 15 20 25 30 35 40 45
Deciview Index
VisualRange(km)
Grand Canyon Good Day
Shenandoah Bad Da
Shenandoah Good Day
Shenandoah Median Day
importantly, visibility in cleaner environments is more sensitive to increases in particle concentrations than
visibility in more polluted areas.
Exhibit 2-8 Inverse Relationship Between Visual Range and the Deciview IndexSource: NPS-CIRA (2000a).
Visibility impairment is roughly proportional to the product of ambient particle levels and viewing
distance (National Research Council, 1993, Figure 4-3). As particle levels increase, we must move closer to
an object to see it as well as before. This phenomenon is particularly a problem in pristine areas, where long-
range transport of pollution may increase naturally low particulate levels and significantly reduce viewing
distance. For example, in pristine areas of the Southwest, where visibility is exceptionally good, small
increases in sulfate concentrations can lead to readily apparent reductions in visibility (National Research
Council, 1993, p. 106).
This principle is illustrated in Exhibits 2-9, which characterize a range of visibility conditions at
Shenandoah National Park. Generated by the WinHaze computer program (Air Resource Specialists Inc.,
1998), the two top scenes in Exhibit 2-9 are of a clear day at Shenandoah in 1998 with a visual range of 94
miles, and a day slightly worse than the median, with a visual range of 40 miles. The two bottom scenes areof relatively hazy days with a visual range of 13 and 11 miles. In both the top and bottom sequences, the
difference in visual range is the result of an additional five g/m 3of sulfates in the atmosphere. This illustrates
that the perceived change in visibility due to an additional five g/m 3 of sulfates to an already degraded
atmosphere is less noticeable than adding it to a pristine atmosphere. Thus, to achieve a given level of
perceived visibility improvement, a larger reduction in fine particle concentrations is needed in more polluted
areas. Conversely, a small amount of pollution in a clean area can dramatically decrease visibility.
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(a) Clear Day visual range 94 kilometers
0
20
40
60
80
100
13 18 23 28 33 38 43Deciview Index
VisualRange(km)
Clear Day
Clear Day + 5 ug/m3
sulfate
Haz Day
Hazy Day + 5 ug/m3
sulfate
(b) Clear Day + 5 g/m3 sulfate visual range 40 kilometers
(c) Hazy Day visual range 18 kilometers (d) Hazy Day + 5 g/m3
sulfate visual range 14 kilometers
Exhibit 2-9 Shenandoah National Park: WinHaze Photos Showing Effect of a Five g/m3 Incrementof Sulfate on a Clear Day and a Hazy Day
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Exhibit 3-1 Airport Visual Data: Trend in 75th
Percentile Light Extinction Coefficient for July-
September (measured in km-1)
3. TRENDS IN VISIBILITY IMPAIRMENT
Historical airport visibility data shows that visibility declined significantly in the 1940s up through the
1960s in the Western U.S. In the East, this decline continued up until about 1980. Based on EPA (1998,
Figure 6-4), Exhibit 3-1 depicts 75 th percentile light extinction at airports across the U.S. from 1970 to 1990.
Since then, while there have been some areas of improvement, significant problems remain.
A variety of ways to record atmospheric
visibility have been used to provide an idea of
how visibility impairment has changed over time.
Human eye observations of visual range have
been recorded at airport weather stations for most
of the 20th century and have only recently been
phased out in favor of more quantitative
measures. One of the best sources of recent data
is the Interagency Monitoring of Protected Visual
Environments (IMPROVE) program, which wasestablished in 1987 to provide a variety of
visibility measurements including detailed
measurements of particulate constituents (U.S.
EPA, 1996, Table 8-3).
The airport data are the most extensive,
as they cover hundreds of stations across the
United States, and go back to the early 1900s.
While these data are somewhat limited because of
variations in observers and inconsistent reporting
procedures, they are nevertheless useful in
developing historical trends. After analyzingthese data, Malm (1999, pp. 39-41) reported that
in the East visibility has generally worsened
between the late 1940s and early 1980s, especially
during the summer in the Southeast. This decline
in visibility is closely matched with an increase in
sulfur emissions (Malm, 1999, Figure 6.16b). In
the Rocky Mountains southwest, the trends are
mixed from 1948-1976. While in California
visibility declined from the late 1940s to 1966,
and has since generally improved. However,
Malm noted that while the overall average isimproving in California, the number of very good
or superior visibility days at a couple of pristine
monitoring sites has gradually declined.
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2 Air Resources Specialists, Inc. (2000c) did not report the deciview levels for the pictures of Half Dome, Yosemite. Using
a guide of roughly 4 deciviews for a good day and 16 deciviews for a poor day, we chose Half Dome pictures that comparedreasonably well with WinHaze photos of comparable deciview levels.
Abt Associates Inc. August 200014
3.1 Recent Visibility Trends
In this section, we consider more closely how visibility has changed in specific areas throughout the
country; in areas where the vista is an integral characteristic of the place itself, at smaller parks and wilderness
areas, and in urban settings with scenic, postcard skylines. We have comprehensive visibility data since
1987, when the IMPROVE network of monitors was established at national parks throughout the nation.
3.1.1 Visibility at Parks Where the Vista Is Integral to the Experience
Pristine national parks and wilderness areas are clearly some of the areas where visibility is extremely
important. To provide a sample of visibility at national parks where the vista is integral to the experience, we
chose five well-known parks from throughout the country. They are Acadia National Park in Maine, Grand
Canyon National Park in Arizona, Great Smoky Mountain National Park in Tennessee and North Carolina,
Shenandoah National Park in Virginia, and Yosemite National Park in California.
The National Park Service (NPS-CIRA, 2000a) sorted each park's daily visibility measurements from
low to high for each year, and placed them into three groups for analysis: good visibility days are the lowest20 percent of daily measurements, mid-range days are the middle 40-60 percent, and poor visibility days are
those days above the 80th percentile of the ordered data. We then plotted the annual average visibility
measurement for each of these categories. To put the visibility category ranges observed at each park into
perspective, we present actual photographs that represent the deciview levels for each national park for the
good and poor visibility categories.2 Exhibits 3-2 through 3-6 present the trends graph and companion photos
for each park. These trends were also examined by Sisler and Malm (2000), who conducted a statistical
analysis of the slopes of the park-specific visibility trend lines. Exhibit A-2 contains the slope of the visibility
trend line for each park, and many additional parks, over the last decade and identifies whether or not the trend
identified by the slope is statistically significant.
The good, midrange, and poor categories that we considered represent averages for the visibility
levels within each group, and do not capture the full range of visibility levels at these parks. In Exhibit 3-7 wepresent photographs to capture the range of conditions for each park, from pristine to extremely poor visibility
days.
Over the last decade there were no major changes to visibility levels at the parks examined in this
analysis. Both improvements and declines in visibility were generally very slight between 1988 and 1998,
though there was a significant amount of variation in visibility in the range of years. The points plotted on the
graphs do not lead to smooth trend lines in one direction or another for any of the parks. It appears that some
of the air quality controls already in effect may be preventing significant additional deterioration to visibility
at these national parks.
At Acadia National Park, visibility improved slightly from 1988 to 1998 in each of the three visibilitycategories, however, only the visibility trends in the good visibility and median visibility categories were
statistically significant (Exhibit A-2). Like Acadia, visibility improved slightly at Grand Canyon National Park
in each of the three categories over the last decade. However, only the trend over good days was even
marginally significant. Between 1988 and 1998, visibility at Great Smoky Mountains National Park worsened
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on the poorest days, and improved slightly on mid-range days and good days. None of the trends, though, were
statistically significant. Shenandoah National Park experienced declines in visual air quality on the poorest
visibility days and improvements in visibility on the mid-range and good days. Only improvements on the mid-
range days were found to be marginally significant. Finally, at Yosemite National Park, visibility improved
on the good and mid-range days, and worsened on the poor visibility days. None of the Yosemite trends,
however, were found to be significant.
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Acadia National ParkMeasurements of haze (in deciviews) and its effect on visibility
9
11
13
15
17
19
21
23
25
27
88 89 90 91 92 93 94 95 96 97 98
Year
Deciviews
Good Visibi lity Days Mid-Range Poor Visibili ty Days
Good Visibility Day (10 deciviews) Poor Visibility Day (23 deciviews)
Exhibit 3-2 Visibility Trends at Acadia National Park, Maine( Photos: Air Resource Specialists Inc., 2000a, Img0004.pcd and Img0009.pcd; IMPROVE data: NPS-CIRA, 2000a)
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17Abt Associates Inc. August 2000
Grand Canyon National ParkMeasurements of haze (in deciviews) and its effect on visibility
4
6
8
10
12
14
89 90 91 92 93 94 95 96 97 98
Year
Deciviews
Good Visibility Days Mid-Range Poor Visibil ity Days
Good Visibility Day (5 deciviews) Poor Visibility Day (13 deciviews)
Exhibit 3-3 Visibility Trends at Grand Canyon National Park, Arizona( Photos: Air Resource Specialists Inc., 1997, Img0015.pcd and Img0023.pcd; IMPROVE data: NPS-CIRA, 2000a)
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Great Smoky Mountains National ParkMeasurements of haze (in deciviews) and its effect on visibility
13
15
17
19
21
23
25
27
29
31
88 89 90 91 92 93 94 95 96 97 98
Year
Deciviews
Good Visibility Days Mid-Range Poor Visibil ity Days
Good Visibility Day (15 deciviews) Poor Visibility Day (28 deciviews)
Exhibit 3-4 Visibility Trends at Great Smoky Mountains National Park, Tennessee( Photos: Air Resource Specialists Inc., 2000b, Img0008.pcd and Img0013.pcd; IMPROVE data: NPS-CIRA, 2000a)
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Shenandoah National ParkMeasurements of haze (in deciviews) and its effect on visibility
14
16
18
20
22
24
26
28
30
32
88 89 90 91 92 93 94 95 96 97 98
Year
Deciviews
Good Visibility Days Mid-Range Poor Visibility Days
Good Visibility Day (16 deciviews) Poor Visibility Day (33 deciviews)
Exhibit 3-5 Visibility Trends at Shenandoah National Park, Virginia( Photos: Air Resource Specialists Inc., 1999, Img0082.pcd and Img0085.pcd; IMPROVE data: NPS-CIRA, 2000a)
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20Abt Associates Inc. August 2000
Yosemite National ParkMeasurements of haze (in deciviews) and its effect on visibility
3
5
7
9
11
13
15
17
19
21
88 89 90 91 92 93 94 95 96 97 98
Year
Deciviews
Good Visibili ty Days Mid-Range Poor Visibi lity Days
Poor Visibility DayGood Visibility Day
Exhibit 3-6 Visibility Trends at Yosemite National Park, California( Photos: Air Resource Specialists Inc., 2000c, Img0002.pcd and Img0004.pcd; IMPROVE data: NPS-CIRA, 2000a)
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Excellent Visibility Day (3 deciviews) Bad Visibility Day (33 deciviews)
Excellent Visibility Day (0 deciviews) Bad Visibility Day (22 deciviews)
Excellent Visibility Day (4 deciviews) Bad Visibility Day (37 deciviews)
Exhibit 3-7a Extreme Visibility Days at Acadia National Park(Air Resource Specialists Inc., 2000a, Img0001.pcd and Img0012.pcd)
Exhibit 3-7b Extreme Visibility Days at Grand Canyon National Park(Air Resource Specialists Inc., 1997, Img0010.pcd and Img0024.pcd)
Exhibit 3-7c Extreme Visibility Days at Great Smoky Mountains National Park(Air Resource Specialists Inc., 2000b, Img0016.pcd and Img0026.pcd)
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Excellent Visibility Day (4 deciviews) Bad Visibility Day (44 deciviews)
Excellent Visibility Day Bad Visibility Day
Exhibit 3-7d Extreme Visibility Days at Shenandoah National Park(Air Resource Specialists Inc., 1999, Img0001.pcd and Img0011.pcd)
Exhibit 3-7e Extreme Visibility Days at Yosemite National Park(Air Resource Specialists Inc., 2000c, Img0001.pcd and Img0005.pcd)
3.1.2 Visibility at Smaller Parks and Wilderness Areas
We may only think of major national parks when we think of the impacts of visibility impairment, but
poor visual air quality impacts smaller parks and wilderness areas, as well. Though the data may be sparse
for these parks, more data are added annually as the IMPROVE system includes new areas into the monitoring
system (NPS-CIRA, 2000a). We considered visibility trends at two lesser known areas, San Gorgonio
Wilderness Area in California and Chassahowitzka in Florida to demonstrate that visibility trends observed
at larger, well known parks can also be observed at smaller parks and wilderness areas.
At the San Gorgonio Wilderness Area, visibility on poor days improved between 1988 and 1998
(Exhibit 3-8), due primarily to a reduction in ambient ammonium nitrate (NPS-CIRA, 2000a). This trend was
found to be statistically significant (Exhibit A-2). Mid-range days and good days also experienced
improvements in visibility, though they were slight and not statistically significant. At the Chassahowitzka
wilderness area, where visibility data has only been collected since 1993, we again see the visibility day
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San Gorgonio Wilderness AreaMeasurements of haze (in deciviews) and its effect on visibility
468
101214
161820222426
88 89 90 91 92 93 94 95 96 97 98
Year
Deciviews
Good Visibility Days Mid-Range Poor Visibility Days
Chassahowitzka Wilderness AreaMeasurements of haze (in deciviews) and its effect on visibility
17
1921
23
25
27
29
93 94 95 96 97 98
Year
Deciviews
Good Visibility Days Mid-Range Poor Visibility Days
categories remained relatively constant over the six year time period (Exhibit 3-9). The significance of the
trends for each of the visibility day categories, however, were not calculated, so no inference on the statistical
significance of the trends can be made. There appears, however, to be a slight increase in 1998 deciview levels
compared to those in 1993. The absence of large swings in visual air quality echo the trends seen at the larger
parks that visibility has not changed dramatically over the last decade and that improvements can still be
made.
Exhibit 3-8 Visibility Trends at San Gorgonio Wilderness Area, California(IMPROVE data: NPS-CIRA, 2000a)
Exhibit 3-9 Visibility Trends at Chassahowitzka Wilderness Area, Florida(IMPROVE data: NPS-CIRA, 2000a)
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3 Savig (2000) did not report the deciview levels for a series of five pictures of Washington, D.C., ranging from excellent to
very poor visibility. To estimate good and poor visibility levels, we present the second and fourth pictures of the series.
Abt Associates Inc. August 200024
3.1.3 Visibility in Urban Settings
Urban settings are also impacted by trends in visibility. The IMPROVE network has acknowledged
this fact by placing a monitor in Washington, D.C., a tourist destination where the vistas of the historical sights
and monuments play an integral role to the attraction of the city. Though data and photos are only examined
here for Washington, D.C., the importance of visibility in other urban areas with a postcard skyline, like New
York City, San Francisco, or Boston, should not be overlooked. Exhibit 3-10 shows that visibility levels for
all visibility day categories have improved slightly between 1988 and 1998, though the trends were not found
to be significant (NPS-CIRA, 2000a).3
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Washington, DCMeasurements of haze (in deciviews) and its effect on visibility
17
19
21
23
25
2729
31
33
89 90 91 92 93 94 95 96 97 98
Year
Deciviews
Good Visibi lity Days Mid-Range Poor Visibility Days
Good Visibility Day Poor Visibility Day
Exhibit 3-10 Visibility Trends in Washington, D.C.( IMPROVE data: NPS-CIRA, 2000a; Savig, 2000, naca_2.jpg and naca_4.jpg)
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Abt Associates Inc. August 200026
4. LEGISLATIVE AND REGULATORY HISTORY OF VISIBILITY IMPAIRMENT
Over the past 25 years there have been a number of legislative and regulatory initiatives designed to
improve visibility, such as the Clean Air Act Amendments of 1977 and the 1999 Regional Haze Rule. In
addition, there are a number of other legislative and regulatory initiatives that should reduce visibility
impairment in addition to the primary goal of reducing ambient pollutant levels. For example, the Title IV acid
rain provision of the Clean Air Act is reducing SO2 emissions, which will reduce the visibility impairment
related to sulfate aerosols. Similarly, tighter tailpipe emission standards for gasoline and diesel-powered
vehicles, along with programs for cleaner-burning fuels, will further reduce visibility impairment in some areas.
The Clean Air Act Amendments of 1977 included the first significant federal legislation that
specifically addresses visibility impairment. The 1977 Amendments established a national goal of prevention
of any future, and the remedying of any existing, impairment of visibility in Class I Areas which impairment
comes from manmade pollution. It included two programs aimed at visibility impairment in Class I Areas
(pristine wilderness locations of great scenic importance). The first is the prevention of significant
deterioration (PSD) program outlined in Sections 160-169, which is aimed at reducing ambient levels of criteria
pollutants. The PSD program requires that new or modified major emitting facilities must not adversely affectnearby Class I Areas. The second is the Section 169 regional haze program, where Congress set a national
goal of preventing and remedying visibility impairment in pristine areas of the U.S.
The pristine areas identified in the legislation come from a group of so-called mandatory Class I
Areas, which are selected national monuments, wilderness, wildlife refuge and memorial areas and parks
larger than 5,000 acres, national parks over 6,000 acres, and all international parks in existence on the day
President Carter signed the 1977 Amendments into law. The legislation required EPA to identify from the 158
mandatory Class I Areas those in which visibility is an important value. In November 1979, EPA complied
and identified 156 areas including one international park in the Virgin Islands (Scott and Stonefield, 1990,
Table 1). Three federal agencies have primary responsibility for most of these areas: Forest Service (98
wilderness areas), National Park Service (36 national), and Fish & Wildlife Service (21 wilderness areas).
Exhibit 4-1 maps the 156 parks and wilderness areas chosen by EPA. Adding new Class I Areas would requirean Act of Congress.
In addition to identifying areas where visibility is an important value, the 1977 Amendments require
EPA to promulgate regulations to assure reasonable progress in meeting the goal of preventing and remedying
visibility impairment. Impairment causes were categorized as either reasonably attributable to an individual
source or small group of sources, or as regional haze, which emanate(s) from a variety of ...regionally
distributed sources. As a first major step in 1980, EPA established regulations to address visibility
impairment in Class I Areas that could be reasonably attributed to major stationary air pollution sources (U.S.
EPA, 1996, p. 8-2). At that time, EPA deferred regulatory action on regional haze until they had better
scientific tools, and instead focused on more local problems.
Responsibility for identifying and regulating specific sources that impair visibility involves three
different parties: the federal agency managing a Class I Area , the state where the source is located, and the
EPA. If a Federal Land Manager establishes that visibility at the Class I Area is impaired, the EPA must make
a reasonably attributable decision linking the impairment with a specific source. The State then conducts
a case-by-case review to determine what is the best available retrofit technology (BART) to control the sources
emissions. The BART determination for a specific source depends on a number of factors, including the
control technologies that are available, the cost installing and operating the available technologies, all
environmental impacts of compliance, pollution control equipment already existing at the source, the remaining
useful life of the source, and the degree of improvement in visibility that may result from the use of BART.
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Aside from the possibility that large point sources chose not to locate near Class I Areas, the 1980
regulations developed by EPA had limited impact on existing point sources. Identifying specific sources that
impair visibility has proven to be difficult, in large part because visibility is a regional problem with
contributions from many sources over a wide area (Latimer, 1990, p. 51). EPA has initiated separate studies
of the Navajo Generating Station (NGS) and the Mojave Power project. To date only the NGS, a large power
plant in Page, Arizona, has added BART to its facility. Extensive atmospheric studies demonstrated that the
NGS, located on the Colorado River at the north-eastern edge of the Grand Canyon National Park, was a major
cause of haze within the Canyon during certain wintertime conditions. At other times of the year the NGS is
only one of many sources that contribute to the major haze problem within the Canyon. In 1991 the NGS
BART review resulted in a negotiated settlement to reduce sulfur emissions from NGS by 90 percent, with
additional reductions in NOx fine particle emissions. Those emissions controls are now operating at the NGS,
helping to improve visibility not only at the Grand Canyon but throughout the golden circle of National Parks
and Monuments on the Colorado Plateau
Negotiated agreements to improve Class I visibility have also been reached involving two other major
western power plants: the Mojave and Centralia Power Plants. A 1996 negotiated settlement avoided a formal
and potentially lengthy BART proceeding, while successfully leading to a reduction in emission producing haze
at Mt. Rainier National Park in the State of Washington. The Centralia Power Plant is located 50 milessouthwest of Mt. Rainier, and is the largest remaining point source of sulfur emissions in the western United
States. Emitting over 69,000 tons of sulfur annually, Centralia is estimated to cause a third of the visibility-
impairing sulfur concentrations at Mr. Rainier NP, and a quarter of the haze-induced bad visibility days. The
agreement reached by the State of Washington, local regulatory agencies, the National Park Service, the EPA,
and PacifiCorp (one of the plants owners) will reduce sulfur emissions by 90 percent by 2002 (National Park
Service, 1997).
Another negotiated agreement reached in 1999 involves the Mojave Power Plant, located 75 miles west
of the Grand Canyon in Laughlin, Nevada. Like NGS, Mojave has also been linked to haze in the Grand
Canyon. The settlement will reduce Mojaves sulfur emissions by over 85 percent. Construction planning is
beginning, and Mojave will meet the new emission limits by the end of 2005.
Progress on controlling regional haze began with the 1990 Clean Air Act Amendments, which added
Section 169B authorizing EPA to conduct research on regional haze (National Research Council, 1993, p. 61).
The research involves an expansion of visibility-related monitoring, assessment of sources of visibility-
impairing pollution, adaption of air quality models to measure visibility, studies on the chemistry and physics
of visibility, and an assessment of visibility levels in Class I Areas every five years. The 1990 Amendments
also allowed EPA to establish visibility transport regions for any Class I Area whose visibility is impaired
by the interstate transport of air pollution, and required establishing a transport region for the Grand Canyon
National Park. EPA later expanded this to include 15 other Class I parks and wilderness areas on the Colorado
Plateau (U.S. EPA, 1996, p. 8-2). The Grand Canyon Transport Commission must assess current and
projected emission sources and suggest corrective action, and in turn EPA must develop regulations that result
in reasonable progress toward reducing visibility impairment. The regulations to protect the Colorado Plateaumust also be coordinated with other federal regional haze and PM programs.
In response to the problem of regional haze, the National Academy of Science established a committee
to address regional haze in national parks and wilderness areas. The committee considered the state of
knowledge on a variety of issues including determining individual source contributions to visibility impairment,
factors that affect haze, improvements in air quality models, and emission controls. In 1993, the committee
published an influential report of their findings (National Research Council, 1993). The report stated that the
current state of science is adequate and control technologies are available to improve and protect visibility.
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However, a regional approach is necessary to control visibility impairment, and an approach that focuses on
individual emission sources is doomed to failure (p. 7).
In part propelled by this report, on July 31, 1997, EPA published proposed amendments to its 1980
regulations that would require control of regional haze. TheRegional Haze Rule calls for state and federal
agencies to work together to improve visibility, and establishes goals for each Class I Area that are designed
to improve visibility on the worst days and prevent degradation of visibility on the best days. Each state must
address its contribution to visibility problems in national parks and wilderness areas both within and outside
its borders, and to develop long-term strategies aimed at returning visibility to natural conditions. The first
State plans for regional haze are due by 2008.
The Grand Canyon Visibility Transport Commission (GCVTC) is the only visibility transport
commission established to date. The GCVTC consists of the governors of eight western states, leaders of five
Native American Tribes, and five federal agencies. They conducted an extensive scientific and policy analysis
project designed to identify an effective combination of policy recommendations to protect and improve
visibility at 16 National Parks and Wilderness Areas that make up the Golden Circle of parks on the
Colorado Plateau. The GCVTC emphasized the importance of active participation by a broad range of stake
holders, and participants ranged from individual firms to environmental organizations. In 1996 the GCVTCcompleted their recommendations, designed to improve visibility on the Colorado Plateau by limiting emissions,
protecting clean air corridors, increasing the monitoring, and integrating visibility considerations into forest
fire management policies.
Although the GCVTC is the only visibility transport commission, other multi-state organizations are
involved with regional visibility as part of integrated regional air quality planning activities covering all
portions of the continental United States. These organizations are sponsoring a wide range of activities to
understand the unique causes, effects, and policy alternatives for improving all aspects of air pollution
including visibility within their region. Currently, regional organizations include:
! The Western Region Air Partnership, or WRAP [http://www.wrapair.org] is a successor
organization to the GCVTC, with a goal of implementing the GCVTC recommendations. Itincludes 12 states: Arizona, California, Colorado, Idaho, Montana, New Mexico, North
Dakota, Oregon, South Dakota, Utah, Washington and Wyoming.
! The Western States Air Resources Council, WESTAR [http://www.westar.org] is an
organization of air agencies from 15 western states: Alaska, Arizona California, Colorado,
Hawaii, Idaho, Montana, Nevada, New Mexico, North Dakota, Oregon, South Dakota, Utah,
Washington, Wyoming.
! The Central States Air Resource Agencies, CesSARA [http://www.censara.org] includes air
agencies from nine states: Nebraska, Kansas, Oklahoma, Texas, Minnesota, Iowa, Missouri,
Arkansas and Louisiana.
! The Lake Michigan Air Directors Consortium, LADCO [http://www.ladco.org] includes the
four states: Illinois, Indiana, Michigan, and Wisconsin.
! The Mid-Atlantic Regional Air Management Association, MARAMA
[http://www.marama.org] includes nine states: Delaware, the District of Columbia, Maryland,
New Jersey, North Carolina, Pennsylvania, Virginia, West Virginia and the District of
Columbia.
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! The Northeast States for Coordinated Air Use Management, NESCAUM
[http://www.nescaum.org] includes eight states: Maine, New Hampshire, Vermont,
Massachusetts, Connecticut, Rhode Island, New York and New Jersey.
! The Southeastern States Air Resources Managers, SESARM [http://www.metro4.org]
includes 8 states: Florida, Georgia, Alabama, Mississippi, Tennessee, Kentucky, North
Carolina and South Carolina..
! The Ozone Transport Commission, OTC [http://www.sso.org/otc] includes 14 states:
Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New
Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Virginia .
! The Southern Appalachian Mountains Initiative, SAMI [http://www.saminet.org] focuses on
the mountainous regions of 8 states: Alabama, Georgia, Kentucky, North Carolina, South
Carolina, Tennessee, Virginia, and West Virginia
The EPA maintains a website [http://www.epa.gov/oar/vis/] with links to each of the regional visibility
planning organizations, as well as other federal agencies and programs involved with regional visibility issues.
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Exhibit 4-1 Map of Mandatory Class I Areas with Visibility Value(Source: http://www.epa.gov/oar/vis/)
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5. ECONOMICS: VISIBILITY IMPAIRMENT AND PARK VISITATION
Most people would probably say they want good visibility both in the communities where they live,
and in the national parks and scenic areas they visit for relaxation and recreation and the evidence suggests
that it is not just talk. It is one thing to say you want something; it is another to actually be willing to pay for
it. In fact, that is how economists measure the economic value of something by how much people are willing
to pay for it. If it is a good that can be bought in a store, the market price reflects its value. Visibility,
however, is a commodity that can not be bought or sold; in economic terms, visibility is considered a non-
market good. This makes it difficult to measure what it is worth to people.
Another fundamental challenge to valuing visibility is that a change in visibility must be perceptible
to people if they are going to place some value on that change. However, it is not so obvious how small
changes in visibility conditions should be treated when trying to gauge how people feel about visibility
impairment. Some changes, especially when measured in seasonal or annual averages, may not exceed
perception thresholds. For instance, a change in visibility may be less than one deciview, though one deciview
is approximately described as a just noticeable difference in visual air quality. When visibility changes are this
low, it is often suggested that they have no value. This conclusion, however, is wrong for two reasons. First,whether or not a change is interpreted as perceptible may depend on the averaging time used to measure the
change. Visibility changes may be largest during certain times of the year on certain days. When these changes
are averaged over a season or the entire year, however, the overall change may appear to be quite small and
incorrectly treated as having no value. Second, while a single change may not be perceptible, the cumulative
effect of all visibility changes over an extended time period may be perceptible. Yet, specific policy decisions
that affect visibility are most always evaluated individually and incrementally. A policy scenario may only
create a small, perhaps even imperceptible, change in visibility. The change should still be valued, however,
because this change contributes to overall visibility improvements and may make a very large difference over
time.
Despite these obstacles that visibility is a non-market good and visibility often changes in increments
the public may or may not notice economists are devising ways of measuring the value of changes invisibility. One approach that has been used by economists measures what improved visibility is worth to
people based upon what they say their willingness to pay for better visibility is, both at home and in natural
settings. This approach does not depend on a persons actual behavior, but on what they say their behavior
would be with better visibility. Chapter 6 discusses this approach in detail.
Another approach is to measure the economic impacts of peoples behavior based upon improvements
or declines in a particular resource. There are a number of behavioral changes people may make when
confronted with poor visual air quality. For instance, people may base their decision to purchase a house, at
least in part, on the quality of the surrounding views and visibility, which can impact the housing market. If
the decision to relocate to an entirely new area is also influenced by visual air quality, the economic impacts
could reach beyond just the housing market and impact the entire local economy. These types of economicimpacts have the potential to be quite substantial if visibility is extremely poor. However, to isolate that
portion of the impact due to poor visibility from all of the additional factors that go into purchasing a house
or relocating to another area is extremely difficult to do.
Another type of behavioral change that is much easier to measure, and easier to attribute to visibility,
is the affect poor air quality has on a persons decision to recreate. If, because of poor visibility, a person
decides to shorten their visit to a particular park, or go to another recreation site altogether, the economic
impacts will be felt in the way of lost revenue at the recreation site (park fees, lodging, concessions) and lost
revenue in the communities close to the site (gas, food, lodging, concessions, additional tourist attractions).
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While visibility degradation is likely to affect most types of outdoor recreation to one degree or another, the
impacts of impaired visibility are perhaps most pronounced at national parks.
5.1 An Undisturbed Environment, Including Clean, Clear Air and Good Visibility, is VeryImportant to Park Visitors
It has consistently been shown that American vacationers believe that one of the leading attributes of
a desirable travel destination is beautiful scenery and clean, clear air. In fact, the National Park Service (NPS)
has conducted a number of studies that have examined the importance of clean air as a park feature. The
results of these studies were summarized by the NPS (1988).
A 1983 NPS study confirmed that visitors are able to perceive different degrees of visibility
impairment. Visitors were asked if they had noticed haze at the parks, and if so, whether they thought it was
slightly, moderately, very, or extremely hazy. After comparing their responses to actual visibility measures
taken on the same day, they found that when the range of view was lower, visitors were more aware of haze
and were more likely to say it was very to extremely hazy. This same study also found that visitors to the
Grand Canyon and Mesa Verde National Parks who said the view was hazy enjoyed the park less than thosevisitors who said they were not aware of haze or were aware of only slight to moderate haze. This meant that
not only did park visitors notice haze, but when they considered the view to be relatively hazy, it detracted from
their enjoyment of the park.
Another series of NPS studies conducted during the summers of 1983, 1984, and 1985, found that
people visit parks first to experience a natural setting and second to enjoy specific unique features associated
with various parks. Surveys were given to visitors at Grand Canyon, Mesa Verde, Mount Rainier, Great
Smoky Mountains, and Everglades National Parks. The surveys listed a number of park features and asked
visitors 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/information were listed for all the parks while viewing canyon rims was listed for the Grand Canyon,
ruins on mesa tops was listed for Mesa Verde, and views of chimney tops (natural landscape features inthe area) was listed for Great Smoky Mountains.
The survey results revealed that it is very important to visitors that parks be natural and free of
pollution; in other words, as undisturbed by humans as possible. In fact, the survey consistently showed the
importance of clean air to the recreational experience, with clean, clear air one of the top four features at
every park. At the Grand Canyon, over 80 percent of the respondents rated clean, clear air as very important
or extremely important to their recreational experience.
Additional analysis of these surveys was conducted to determine if, when asked what the most
important features were at these parks, visitors identified features that belonged to a common recreational
theme. For example, features such as clean, clear air and park cleanliness were grouped into anaturalness category. Based on work by the National Park Service (1988), Exhibit 5-1 shows the groups
of park features and their relative importance at three sample parks: Grand Canyon, Mesa Verde, and Great
Smoky Mountain. The most significant finding was that the group of naturalness features (which included
clean, clear air) was rated the most important at each park. The second most important set of park features
was associated with each parks unique qualities. For example, while naturalness was the most important
group of features at both Grand Canyon and Mesa Verde, viewing scenic vistas at Grand Canyon and
information/park history at Mesa Verde ranked as the second most important group of features at those
parks, respectively.
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Viewing
Information
Naturalness
Activity Related
Visual Obscurement
Not at AllImportant
SlightlyImportant
ModeratelyImportant
VeryImportant
ExtremelyImportant
Grand
Canyon
Naturalness
Viewing
Information
Activity Related
Visual Obscurement
Mesa
Verde
Naturalness
Backcountry
Information
Flora-Fauna
Viewing
Management
Backcountry Reservations
Great Smoky
Mountains
Exhibit 5-1 Visitor Rated Importance of Park Features
5.2 Visitors are Willing to Alter Their Length of Stay Based on Visual Air Quality Conditions atNational Parks
The above findings suggest that if visibility as a park resource was allowed to deteriorate, visitor
enjoyment of the parks would decline. But how would a change in visual air quality affect visitation patterns?
When confronted with poor visibility at their destination, it is likely that travelers will do one of two things:
shorten their stay at a national park or go elsewhere. In either case, we assume that people will allocate the
time available to them in such a way as to maximize their enjoyment. There have been a number of studies
conducted to evaluate whether visitors would be willing to spend more time traveling to alternative viewing sites
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in order to obtain better visual air quality during their park visit. Results from these studies provide evidence
that changes in visual air quality affects visitor use patterns.
Summarized in NPS (1988), a 1983 NPS study conducted at Grand Canyon National Park asked
visitors to rank possible alternative combinations of travel time to vistas and visibility conditions through the
use of photographs. These rankings revealed that the average change in the amount of time a visitor was
willing to spend traveling to a vista for a 10 Mm-1 change in visibility was between 15 minutes and 4 hours.
Studies conducted outside the scope of the NPS also support the finding that as perceived visual air
quality gets worse, visitation patterns to national parks is altered. One study found that if visibility at a vista
in either the Grand Canyon or Mesa Verde national parks changed from average to poor, 61 percent of
the survey participants said they would spend less time at the vista, while 80 percent said they would spend less
time total at the park (MacFarland et al., 1983). The average stated reduction in park visitation was about 13
hours, which is quite significant when compared to the average park visit of 14 hours.
In a 1985 study conducted at Grand Canyon National Park (Bell et al., 1985), visitors were asked to
participate in a simulation where they could choose between four hypothetical activities: viewing three vista
points (depicted on photographs) and touring an archaeological site. The driving time, scenic beauty, andvisibility