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Memorandum 

To: Vicki Sandiford, Office of Air Quality Planning and Standards, 

U.S. Environmental Protection Agency

From: Leland Deck, Lauraine Chestnut, and Colleen Donovan, Stratus Consulting Inc. 

Date: 11/18/2008 

Subject: Summary of Urban Visibility Workshop 

On October 6 through 8, 2008, the U.S. Environmental Protection Agency’s (EPA’s) Office of 

Air Quality Planning and Standards (OAQPS) held an expert workshop on urban visibility 

preferences and valuation. The workshop was held in Lakewood, Colorado, at the offices of the 

Air Resources Division of the National Park Service (NPS). 

The purpose of the workshop was to identify and discuss methods and materials that could be 

used in “next step” projects to develop additional information about people’s preferences for 

reducing existing impairment of urban visibility, and about the value of improving urban 

visibility. The additional information obtained from such projects would be used to inform EPA 

considerations about the role of achieving acceptable levels of urban visibility in setting a 

secondary particulate matter (PM) National Ambient Air Quality Standard (NAAQS). Similar to 

the limited existing research on urban visibility preferences, the potential new projects would 

likely involve focus groups and survey methods to elicit information from individuals about their 

preferences and values. The workshop explored a set of eight specific issues (introduced in a 

white paper distributed prior to the workshop) about topics that could be considered in designing 

additional projects to better understand urban visibility preferences and valuation. The issue 

white paper is included as Appendix K. Prior to the workshop, the participants were also 

provided a background paper reviewing previous urban visibility valuation and preference 

studies (included as Appendix L). 

Prior to the workshop, OAQPS and Stratus Consulting identified a set of individuals with 

expertise in technical fields related to urban and rural visibility, preference elicitation, and 

valuing aesthetic environmental goods. The invited individuals came from a broad array of 

relevant technical and policy backgrounds, including visual air quality (VAQ) science, 

sociology, psychology, survey research methods, economics, and EPA’s process of setting 

NAAQS. The 23 people who attended the workshop (including one via teleconference line) came 

from EPA, the National Oceanic and Atmospheric Administration (NOAA), NPS, academia, 

regional and state air pollution planning agencies, and consulting firms. The list of attendees is 

included as Appendix A. 

The remainder of this memorandum summarizes the discussions in each of the workshop 

sessions on the eight issues introduced in the white paper. 
 

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Workshop Organization 

The workshop was organized into eight separate sessions, plus an initial session (moderated by 

Vicki Sandiford of OAQPS) and a summary session (moderated by Marc Pitchford of NOAA) at 

the end of the workshop. The agenda for the workshop is included as Appendix B. The initial 

session discussed the role of urban visibility in setting a secondary NAAQS for PM. The 

PowerPoint slides used in this presentation are included in Appendix C. 

The next eight sessions focused on each of the eight issues discussed in the white paper 

distributed prior to the workshop. A moderator led the discussion in each session. Some 

moderators used PowerPoint or Word to make a presentation as part of the session. These 

presentations are included as Appendices D through I. 

At the end of each session Marc Pitchford used a flipchart to identify the summary points of each 

session, with the aim of identifying any consensus items and any unresolved questions. Each 

session’s summary points are presented below in the section on each session. At the conclusion 

of the workshop, Marc moderated a final session that reviewed each of the key summary points 

from each previous session. 

Due to the integrated nature of the subject, the discussions in each session of the workshop were 

not necessarily confined strictly to the topic of the session. Instead of strictly following the 

chronological order of the discussions during the workshop, the remainder of this memorandum 

summarizing each session generally organizes all of the discussion pertaining to an issue under 

that issue’s section (regardless of when the discussion actually occurred). Because two pairs of 

the original eight issues were found to be closely integrated, this workshop summary combines 

the discussion of those pairs into a single review. The issues that are combined are regional 

differences and scene selection, and two topics focusing on economic valuation: joint goods and 

payment vehicles. 

Session on Framing the Questions about Preferences 

Leland Deck was the moderator of this session. His PowerPoint slides are included in 

Appendix D. The presentation reviewed the methods and findings of four previous preference 

studies (examining urban visibility in Denver; Phoenix; two locations near Vancouver, British 

Columbia; and Washington, DC), and introduced some of the challenges on how to present 

preference questions in a focus group or survey study. 

Discussion Topics 

One major topic of discussion in this session was the meaning of the terms “adverse” and 

“acceptable” when describing visibility conditions. Because of the importance of the 

interpretation of adverse and acceptable, the workshop discussion returned to this topic in many 
 

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of the later sessions. Because the Clean Air Act calls for secondary standards to protect the 

public welfare from any known or anticipated adverse effects, identifying “adverse” urban 

visibility conditions is likely to be a key element in assessments undertaken to inform the 

secondary NAAQS review process. The main goal of previous visibility preference studies, 

however, was identifying the visibility level felt to be “acceptable.” Each of the four previous 

preference studies asked people to evaluate a series of photographic depictions of VAQ and 

judge whether they were acceptable or unacceptable, for the purpose of identifying identify a 

threshold level of visibility impairment they consider unacceptable. The workshop participants 

felt it was critical that any future project on urban visibility preferences develop a clear 

understanding about how survey respondents are interpreting the term acceptable, and develop a 

successful approach to help the respondents reach a common understanding of how the term 

should be understood. 

The discussion pointed out that in the context of urban visibility, the term adverse does not refer 

to the minimal level of visibility impairment that people can notice, but rather a level of 

impairment people personally feel is “too much” in some fashion which begins to negatively 

affect a person’s enjoyment and sense of wellbeing. Alternative terms may more clearly 

communicate the concept instead of (or in complement to) the term adverse, such as acceptable 

or preferable. Several workshop participants suggested that the articulation of adverse, and the 

selection of words to communicate this idea, is a topic that should be explored in a preliminary 

focus group project. Open-ended discussions with participants would help determine the words 

that best describe this idea for the general public. Introductory material presented in any 

subsequent focus groups or surveys should use these words to explain the concept of adverse 

visibility impairment to respondents. 

A related topic of discussion was about how much, and what kind, of background and 

introductory material should be presented to focus group and survey respondents. One element of 

this discussion was about introducing survey respondents to the concept of the differences 

between natural visibility impairment (fog, rain, etc.) and pollution-related impairment, and the 

role of humidity. In the eastern United States, people may not be aware that much of visibility 

impairment is VAQ degradation related to pollution (perhaps thinking it is the result of humidity 

alone). The concern expressed was that if respondents believe the impairment is natural, this 

would influence how they answer questions about how they are affected by different levels of 

VAQ degradation. Workshop participants generally felt that people in the western United States 

are aware that pollution is involved with impairing visibility. 

Another topic discussed was whether introductory information presented to survey respondents 

should mention specific sources of pollution that may cause VAQ degradation. Some workshop 

participants felt very strongly that specific types of sources should not be mentioned when 

discussing visibility impairment. 
 

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The discussion identified that background information and “warm up” exercises in a survey 

where people get accustomed to reviewing and rating photographs can help educate people prior 

to asking the acceptability or adverse questions, and may provide a somewhat standardized 

framework of understanding among the participants. 

This session introduced the issue of separating out preferences for visibility from concern over 

health risks arising from observed pollution-related VAQ degradation. This topic arose in many 

of the subsequent sessions as well; it is a central issue confronting urban visibility preference and 

valuation assessments. The overall goal is to obtain information on the visibility component 

alone, separating visibility from preferences about the actual or perceived health risks of air 

pollutants. However, people are not accustomed to making this distinction; they generally form 

an overall impression about their preferences for improvements in VAQ. It can be very hard to 

get people to separate health from visibility. Even after asking people to make the separation, it 

is important to explore whether they have successfully done so. This is a critical issue because 

the primary NAAQS are set to protect health. A secondary NAAQS, which protects human 

welfare and wellbeing, is aimed at non-health issues. In the context of a secondary NAAQS, 

successfully making the distinction between health and visibility becomes very important and 

very challenging. 

Summary Consensus Points 

 We do not want to commingle natural and anthropogenic impairment to VAQ. 

Respondents need to be told they are viewing the anthropogenic effects. 

 We should not tell people about specific pollution sources that cause VAQ degradation, 

especially since it can be very location-specific. 

 Further study is needed to determine the best terms to use (e.g., acceptable vs. 

unacceptable; preferable vs. objectionable) to identify at what point noticeable 

impairment in VAQ is judged to be “adverse” by the respondent. 

 We need to provide a minimum amount of background information and context for 

people to be able to respond meaningfully to preference or valuation questions. 

 We need to understand people’s assumptions about the causes, remedies, and effects of 

VAQ degradation by exploring their understanding and assumptions in focus groups. 

This should be further explored in debriefing questions during the group interview stage 

to improve the understanding of respondent’s answers in a final survey. 

Session on Temporal Distribution of Visibility Conditions

Dan Ely was the moderator of this session. His PowerPoint slides are included in Appendix E. 
 

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Discussion Topics 

A basic policy relevant question is what are people’s preferences for changes in the distribution 

of visibility conditions, not just their preferences concerning visibility conditions on a single day. 

The first discussion topic was whether the annual distribution was the best temporal distribution 

to present and ask respondents about, or if seasonal or even monthly distributions would be 

required in some regions. It is likely that in some areas of the country people may be more 

concerned about visibility in certain months than in others, and that VAQ impairment may differ 

substantially by time of year as well. However, workshop participants noted that the concept of 

potentially setting a national visibility standard, and the desire to conduct consistent preference 

and valuation studies across the country, suggest that it will be difficult to use results from 

studies conducted with a location-specific, seasonal-based approach in some locations and an 

annual basis in others. 

Another topic discussed was whether 24-hour average VAQ was a desirable way to measure or 

describe relevant visibility impairment. During any given day people see a series of 

instantaneous visibility conditions, and visibility conditions can change rapidly. Some changes 

can occur minute-by-minute, with even a broader variation occurring across a day as both 

pollution levels and weather patterns change. The general workgroup consensus was that 

depicting visibility conditions averaged over a shorter timeframe, such as a four-hour, mid-day 

period, was preferable to using daylight or 24-hour averages. 

Weather-related visibility conditions also are a factor in presenting the distribution of visibility 

conditions. Workshop participants felt we need to be explicit in mentioning that natural weather 

conditions (such as rain, snow, and fog) impair visibility some of the time, but we are interested 

in their preferences for visibility conditions at the times when weather is not the main reason for 

impaired visibility. A study should present information describing the distribution of visibility 

conditions during periods not primarily affected by adverse weather. 

A fourth topic discussed in this session was how important it is to provide accurate information 

on existing (baseline) visibility conditions in the city being studied. One approach is to tell 

respondents how existing conditions relate to the photographs that are being presented, and ask 

questions directly about the acceptability of current conditions. An alternative approach is to 

present photographs spanning the full range of existing and potential conditions, but not directly 

inform the respondents about the current conditions (e.g., annual mean, 80th percentile day, or 

visibility conditions related to the level of the primary PM NAAQS). Opinions differed about 

which approach would be best in conducting a preference study (where some felt avoiding any 

reference to the existing conditions might be preferable), and which would be best in a valuation 

study (where a change from existing conditions plays a major role). 
 

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Summary Consensus Points 

 We should ask about the frequency of occurrence of impaired visibility to determine 

acceptability. 

 We should indicate clearly how many hours of the day are represented by the conditions 

we present. 

 We should not highlight seasonality issues, but concentrate on changes in the distribution 

of annual visibility conditions. 

 Only consider visibility impairment that occurs during daytime hours (e.g., do not include 

nighttime visibility). 

 We should tell people that visibility impairing weather conditions are excluded from the 

distributions we present, and that visibility conditions change throughout the day. 

 An open question was determining how important it is to tell respondents about the 

current visibility conditions and distributions. 

Sessions on Regional Differences in Visibility Preferences and Scene Selections 

Bruce Polkowsky was the moderator of the session on regional differences in preferences. His 

Word slides are included in Appendix F. Rich Damberg was the moderator of the session on 

scene selections; his PowerPoint slides are included in Appendix G. Mr. Damberg introduced his 

topic by showing a series of different urban scenes from around the country, ranging from iconic 

cityscape scenes to residential streets. Some photographs showed the impact of different 

visibility conditions on the scene, and others showed the differences in scenes and visibility 

issues in different regions of the country. He included the photographs used in the four 

preference studies. 

Discussion Topics 

One topic discussed was the importance of presenting photographs of scenes that are sensitive to 

visibility conditions. Long-sight distances, with both nearby and distant objects, can provide 

respondents information about the range of impacts of visibility impairment on different objects. 

Scenes without distant objects will make smaller differences in impairment levels difficult to see. 

In some cities long-sight distances may not be common. While in western cities mountains and 

other terrain features provide sight distances of perhaps hundreds of kilometers, flatter eastern 

and coastal cities often do not have such long-sight distance scenes (except perhaps from 

manmade objects such as tall buildings or observation towers). Clouds can provide targets with 

long-sight distances even in the East. People in the East may not be aware that cumulus clouds in 
 

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an otherwise clear sky are often present, and could be seen at a distance, if they were not 

obscured by impaired VAQ. Including clouds in photographs presented to respondents could 

help alleviate the restricted sight distance issues, although people may have to be informed that 

such clouds would be a much more frequent feature of a city scene if not for poor VAQ. The 

issue of whether to tell people “you could be seeing more than you are now” applies to all distant 

objects, not just clouds. Not introducing such additional information may bias valuation 

questions, but introducing such new information may change the context of the questions by 

altering the understanding of the status quo conditions. 

Workshop participants noted that people experience visibility where they live as a series of 

instantaneous visibility conditions involving a range of different scenes. They see some scenes 

on a nearly daily basis, others are seen perhaps once a week (e.g., different scenes on weekends), 

while others are actually seen occasionally during the year. Natural landmarks (e.g., mountains) 

and manmade features (e.g., prominent buildings or bridges) can make up a portion of the well 

recognized city scenes for a particular city, even if some residents do not see (or notice) that 

scene on a daily basis. More ordinary scenes, such as street and local park locations, make up 

more frequent opportunities for observing urban visibility conditions. There are wide ranges of 

patterns of which scenes different people living in a metropolitan area see during the course of a 

year. 

An important question discussed was whether it is necessary to present photographs of scenes 

from a respondent’s own metropolitan area. The general consensus of the workgroup was that a 

readily identified iconic scene from a respondent’s home city, such as a broad vista of a city with 

mountains in the background or a scene including a famous local manmade structure, would be 

immediately recognized. Using such iconic photographs from one city would not be acceptable 

in surveys conducted in another city. An early visibility valuation study used an easily identified 

skyline photograph from one city in surveys conducted in other cities, and was heavily criticized 

for it. The workgroup conclusion was that an immediately recognizable local broad vista or 

iconic photograph should only be used in focus groups or surveys conducted in that city. 

Scenes such as photographs of local parks, however, were felt to be much more generic than 

iconic photos. The participants discussed that residents of one city are not likely to notice that a 

local park scene photograph was actually taken in another city. If successful, this would not 

compromise the believability of the study materials. This could offer appreciable cost-savings in 

a project by avoiding the need to prepare local park photographs in each city included in a study, 

and would have the additional advantage of eliminating possible variations in preference 

responses associated with having different base photographs for each of the urban areas. 

An important topic discussed in this session was how many scenes need to be used in a study to 

show the impact of different visibility conditions across a range of scenes. Using more scenes 

can help respondents better understand that visibility does not impact all scenes equally, and 
 

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demonstrate that many common scenes are less sensitive to visibility than less frequently 

observed scenes including longer sight distances. Presenting multiple scenes, however, creates 

logistical difficulties, and can lead to information overload. 

The general consensus of the group was that while more scenes were desirable, practical 

presentation logistics limit the number of scenes to two. In a print setting (hard copy 

photographs), three scenes could potentially be used but the size of the photographs must 

become smaller to avoid unwieldy photograph presentations. 

Summary Consensus Points 

 As long as we have objects that disappear or become less distinct under poor VAQ 

conditions, people will be able to express preferences for different VAQ levels. All 

images must have some sensitivity to changes in VAQ (e.g., range of sight distances) to 

be useful for eliciting preferences. 

 Two scenes, an iconic or broad vista of a city and a generic local park scene, may be 

sufficient. 

 May be able to use the same generic local park scene in all studies, regardless of region. 

 Focus groups and survey need to allow respondents the option of saying they do not care 

about visibility impairment separate from health concerns. 

 Group interviews during the survey development process should include a debriefing 

session in order to better understand sources of preference differences (e.g., what people 

are thinking, what assumptions they were making when answering questions). 

 Need to test some of these questions or assumptions in a focus group setting. 

 Scene selection: Can a single generic local park scene be used in multiple cities? 

Is an iconic scene from each surveyed city also necessary? 

 To what degree does context of the questions affect the stated preferences? 

— Does information/knowledge regarding the sources of pollution affect 

local VAQ affect preferences? 

— Does information or knowledge regarding the costs of controls of sources 

affect preferences? 

— Does information, knowledge, or assumptions about associations between 

VAQ and human health effects affect preferences? 
 

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 Regional differences: Are there regional differences in preferences? 

— Does preference for blue sky/cloud conditions vary between the East and 

West)? 

— Do people notice or react to different components of visibility impairment 

(e.g., loss of scenic detail and color or changes in sky color) differently by 

region? 

Session on Number and Composition of Focus Group and Survey Respondents 

Robert Mitchell was the moderator of this session. 

Discussion Topics 

The discussion began by clarifying terminology used to differentiate different components of a 

study, and the following distinctions were offered. 

Focus groups (referred to as investigative focus groups in the issue paper) are used to initially 

develop a survey design, and find out what people are thinking and understanding about the 

topics they are being asked about. Different focus groups are needed to explore separate 

questions in the survey design. These are very interactive sessions, with a greater focus on 

understanding what people are thinking than on the answers they provide. Focus groups can use 

participants from either convenience groups (e.g., students, civic clubs, church groups) or 

individuals selected from the general population (known as a random recruitment process). In a 

random recruitment process, the developers of the focus group identify a profile of the 

mandatory attributes of individuals they wish to have participate (e.g., have lived in the 

metropolitan area for at least 5 years, have adequate vision, and understand English), as well as a 

profile of the distribution of the mix of individuals they wish to have participate (e.g., a 

minimum of 40% male, and 20% with less than a college education). 

Group interviews are used to test a survey instrument, and can serve as a pilot study for a full 

field survey. Background material may be shown to the group without a group discussion. 

Individual responses to survey questions are then collected with relatively little feedback or 

discussion. The moderator may answer questions to clarify what is meant by a question, or the 

directions on how to complete the survey. After the survey instrument questions are answered, an 

interactive session can be held to help improve the survey instrument. 

Individual interviews are the final survey component to determine respondents’ preferences and 

valuation responses. Individual interviews can be held in group sessions for efficiency (such as 

to show slides to a large group of people simultaneously), but the responses are collected from 

each individual. In person interviews, or surveys completed at home, can also be used as an 

individual interview. 
 

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A survey project must be designed to be able to consider both the reliability and validity of the 

responses. Reliability has to do with understanding the consistency of people’s responses. This 

includes examining both the consistency for an individual’s responses (e.g., do they give the 

same VAQ rating to the same photograph?) and within groups. As opinions and preferences vary 

by individuals, do different groups of individuals and different methods of asking the questions 

result in reasonably consistent results? Validity deals with the issue of whether we are measuring 

the correct concept we are interested in. In some contexts it may be easier to design a survey that 

measures a related concept, but not the one we are most interested in. An example in urban 

visibility is it could be easier to design a study to examine preferences for reducing VAQ 

impairment that combine health and visibility effects in a single concept. This would not be a 

valid survey of preferences for the visibility component alone. 

The discussion concluded that we would likely need focus groups in two to four locations, 

selected to provide considerable regional variability. Perhaps four sessions (two sessions on two 

days) would be appropriate in each location to cover the range of topics raised in the workshop 

as needing investigation in the process of developing a survey instrument. The actual content of 

each focus group would evolve as results from earlier focus groups help refine the content of 

subsequent groups. 

Participants noted that the Office of Management and Budget (OMB) review under the 

Paperwork Reduction Act will be a necessary component of any substantive project. An 

Information Collection Request (ICR) is required for any focus group project with more than 

nine total participants. Asking different questions in different focus group sessions does not 

avoid the ICR requirements. We would need to go through this process separately for focus 

groups and for the final survey. The ICR approval process works best if EPA staff have early and 

continual communication with OMB through the EPA OMB liaison. Using ICR application 

materials developed for the ongoing NPS study of visibility in National Parks and Class I areas 

may speed the ICR approval process. The NPS study has received approval for the focus group 

phase; approval for the survey phase is still under review. We need to make a schedule to see if 

conducting focus groups and/or the main survey is feasible given EPA’s timeline. 

Summary Consensus Points 

 Focus groups may use either convenience groups or random recruitment. 

 Random recruitment is needed for group interview and survey phases. 

 Screen participants for adequate vision, including adequate color vision. 

 Early involvement with OMB can greatly increase the speed of the ICR approval process. 
 

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Session on Presenting Visibility Conditions 

John Molenar was the moderator of this session; his PowerPoint presentation slides are included 

in Appendix H. 

Discussion Topics 

The range of presentation options includes new generation digital image projectors, high 

dynamic range (HDR) monitors, light emitting diode (LED) monitors, and reflection prints (hard 

copy photographs). Emerging technologies (such as HDR) are very expensive, and perhaps not 

practical for field studies at this time. High-quality digital image projection is a substantially 

better technology than reflection prints for accurately reproducing visibility conditions. Home 

computer monitors are too variable for use in accurately presenting visibility conditions. 

The use of projection equipment requires respondents (in focus groups or surveys) to be in a 

suitable room; reflection prints create the possibility of mailing materials to respondents in a 

survey phase of the project. Completing the survey in a respondent’s home using reflection prints 

creates unknown viewing conditions. Using projection equipment can allow better control of 

these variables. The lighting conditions used in viewing printed photographs can have a very 

substantial impact on what people are able to see in a photograph, and how they respond to the 

images they do see. 

The size of the image presented is important to accurately represent the real world situation. 

When held at a normal viewing distance, an 8” by 10” hard copy photograph taken with a nontelephoto lens is a reasonably accurate depiction of a normal, real world viewing situation. A 

projection setting, with proper arrangement of seating distance to the screen, allows a more 

accurate depiction of the real world (e.g., onsite field of view, or FOV). It is difficult to maintain 

these accurate rendition conditions in a large group (e.g., 50 persons) viewing situation because 

of how the effective image size changes with the distance between each observer and the 

projection screen. 

One issue that participants felt has been underemphasized in previous urban visibility studies is 

transparency, which refers to how well an object can be seen through a three-dimensional haze. 

Most studies have found that people focus on whether they can see a distant object at all, but 

react differently when they become aware that they are viewing an object through a tangible haze 

and pay less attention to how well objects appear when there is some haze between the observer 

and the object. It is difficult to present transparency accurately in a two-dimensional format 

(such as a slide projection or a printed photograph); however, realistic three-dimensional 

presentation may not be possible in an urban visibility study. 
 

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Differing visibility conditions can be presented using images prepared using WinHaze, a 

computer software application developed for the NPS by Air Resource Specialists. Starting with 

a suitable base photograph taken when atmospheric loadings (and hence visibility impairment) is 

as low as typically occurs in a year, the WinHaze program can simulate visibility conditions 

under alternative loadings of different chemical aerosols. This technology allows the creation of 

images of a constant scene showing the full range of relevant VAQ levels. WinHaze images have 

been used in previous preference and valuation studies. Air Resource Specialists have a large 

collection of photographs suitable for the original “pristine” air quality conditions needed in 

WinHaze, including some urban visibility scenes, and have conducted the extensive analysis on 

them that is necessary to prepare images accurately depicting alternative visibility levels. 

Preparing a WinHaze rendition of a new scene requires both an original base photograph taken 

when visibility conditions are excellent, as well as information about the sight distance between 

the camera and each point in the picture. WinHaze can prepare both digital images for projection 

as well as images for making hard copy reflection prints. 

There was consensus among the workshop participants that projecting WinHaze generated slides 

in a controlled situation was preferable to using a printed presentation. There are, however, 

considerable cost differences and survey recruitment issues. This is not as relevant in focus 

group projects (e.g., where respondents would be coming to a single location anyway), but could 

be a major concern in a full survey implementation. Recruiting a representative sample, with an 

adequate response rate, of any population to come to a location to participate in a survey using 

slides will be far more difficult than getting a representative sample using an in-home survey 

method and mailing hard copy images to the respondents. 

John Molenar presented a pair of slides (Appendix H) in this session showing the dramatic 

difference that composition of the aerosol makes in visibility conditions. At the same level of PM 

concentrations and extinction level for the same scene, the color differences between visibility 

conditions with aerosols dominated by local urban anthropogenic sources and the conditions 

when the aerosol was dominated by rural (primarily natural) sources were dramatic. Tom Moore 

also provided two photographs from Phoenix showing visibility when PM2.5 concentrations were 

75 μg/m3

 and 93 μg/m3 (the NAAQS is 35 μg/m3); these slides are included in Appendix J. 

One innovative idea that was discussed was using high-quality, calibrated computer monitors in 

a controlled setting (i.e., not on home computers). A set of six or eight computers and monitors 

could allow a large number of survey participants to participate in a 15-minute survey collection. 

Perhaps this could occur after introducing each group to the subject via projected slides 

(e.g., running groups of people through a two-step process in rapid sequence). The workgroup 

discussed adapting the WinHaze software to allow the participants to use a mouse or keyboard 

with a slider to rapidly identify the level of visibility they find adverse (rather than viewing 

multiple pictures and rating each one individually). 
 

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One idea mentioned was using a personal slide viewer to present the visibility conditions in an 

at-home survey. 

Summary Consensus Points 

 Projection slides are preferred, but require that participants come to a location. 

 Print images may be mailed for in-home surveys, but are not as good as projected images. 

 There is no simple relationship between PM loadings and visibility conditions, but 

holding scene content and other variables constant, there is a relationship between 

judgments of VAQ and light extinction due to pollutants. 

 Use of in-home computers would create substantially varying viewing conditions and 

inconsistent responses. 

 Investigate idea of allowing respondents to “dial in” a level to quickly find an acceptable 

level. 

Sessions on Economic Valuation: Joint Benefits and Payment Vehicle 

Laurie Chestnut was the moderator for the session on joint benefits (also known as mental 

accounts), and Robert Mitchell was the moderator for the session on payment vehicle (asking the 

valuation question). Because both of these topics deal with eliciting economic valuation 

(willingness to pay, or WTP) information and the discussions intertwined the two subjects, the 

summary of both sessions are presented together. Laurie Chestnut’s PowerPoint slides are 

included in Appendix I. 

Discussion Topics 

Throughout the workshop, the issue of clearly defining the good in question (i.e., acceptable 

visibility conditions) came up. Separating health from visibility was extensively discussed and 

needs further consideration. One suggestion was that a way to clearly state the essential 

preference question is “At what level is enjoyment of daily activities reduced?” 

A question discussed is how to measure strength of preferences, rather than looking for a single 

“bright line” between acceptable and unacceptable conditions. A WTP approach lends itself to 

exploring the strength of preferences in a straightforward manner, but it may be possible to 

design good strength of preference questions that use metrics other than dollars to investigate this 

as well. 
 

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One of the initial questions was whether to include WTP questions as part of a study also 

investigating preferences and adverse levels, or is it necessary (or desirable) to conduct separate 

studies? WTP responses can help analysts understand the strength of preferences, furthering 

understanding about what level is adverse. WTP estimates would also be very helpful to OAQPS 

staff who prepare the risk and benefits assessments for the secondary standards, because the 

visibility improvements (benefits) could also then be presented in economic terms. Including 

WTP questions will likely require some additional focus group effort to develop a good WTP 

framework, but will probably not add much to the length or complexity of an eventual survey 

instrument. 

It is important to use a plausible scenario to ask valuation questions in a realistic and 

understandable context in which visibility improvements will occur. Reflecting the earlier 

conversations about avoiding mentioning specific sources of visibility impairment (e.g., power 

plants, transportation), the context must strike a balance between being overly general and too 

specific. The context has to be clear enough to be understood and accepted by the participants in 

order to standardize people’s assumptions about the situation. 

The specific context of the WTP questions will be paying something for going from condition A 

to condition B, or to prevent going from condition A to B. The form of payment must be 

plausible and understandable. Possible examples include taxes, special fees, increases in general 

prices or in prices of specific items, etc. The payment vehicle should be logically tied to 

improving visibility, and be collectable from everyone. A complication to selecting a specific 

context for payment is the possibility of “scenario rejection” where a respondent’s strong 

preexisting opinions about a particular issue mentioned in framing the questions (such as an 

increase in residential electricity prices) could lead to the individual inaccurately stating they 

have no interest in improving visibility. 

Workshop participants noted there is a difference between asking respondents to select a single 

level of VAQ impairment they consider unacceptable and asking them about their WTP for a 

specific change from one VAQ condition to another. It is difficult to ask WTP questions about a 

series of gradual changes in VAQ; it is easier to ask about a more abrupt change. The study 

design team must select the before and after VAQ levels about which to ask the WTP questions. 

Showing multiple VAQ levels simultaneously (on the projection screen or on printed paper) will 

help people focus on the different choice levels rather than using their memory about the changes 

in VAQ from previous photographs. Focus group results can be useful for selecting the change in 

VAQ levels to be investigated, and the range of relevant policy choices can also factor into the 

decision. 

A conjoint analysis approach can be used for either preference or valuation questions. Conjoint 

analysis does not directly ask a WTP question, but instead forces respondents to make a choice 

between two or more bundles of different conditions. A conjoint approach may be useful in 
 

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forcing respondents to separate the health effects from visibility effects, for example, by offering 

choices between bundles of conditions that differ in visibility conditions, health risks, and overall 

price levels. The ongoing NPS study of National Park visibility is using a conjoint analysis form 

of question. 

Summary Consensus Points 

 Presenting a plausible scenario of both VAQ improvements and payment methods is 

critical, but scenario rejection needs to be evaluated in any final instrument. 

 Valuation questions are a low-cost add-on to preference studies. 

 WTP studies can help capture strength of preferences, not just a yes/no level of 

preference. 

 WTP studies need to define a set of specific VAQ changes to estimate values. 

Compilation of Recommended Topics for Investigating in Focus Groups 

In the closing session of the workshop, the workgroup participants expressed a general consensus 

that a high-quality survey project on a complex topic such as preferences and the valuation of 

urban visibility will need to be developed by initially conducting a series of focus groups to gain 

insight into a set of issues and questions. The following list of ideas for investigating in focus 

groups is not intended to be a list of mandatory topics that must be explored or an exhaustive list 

of important topics to explore in a focus group setting. 

 Investigate alternative wording to present the concept of selection of words to 

communicate the concept of adverse or unacceptable. 

 Explore the type, depth, and wording of introductory materials presented to explain 

visibility and VAQ impairment to the participants. 

 Investigate whether respondents are aware of the role of pollution in VAQ impairment, 

especially to learn whether people living in the eastern United States know pollution is 

involved. 

 Explore people’s assumptions about the causes, remedies, and effects of VAQ 

degradation by exploring their understanding and assumptions in focus group debriefs. 

 Investigate alternative ways of getting respondents to separate their preferences for 

avoiding health risks arising from noticing VAQ conditions from their preferences for 

visibility conditions alone. 
 

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 Explore the impact of telling respondents how existing conditions relate to the 

photographs that are being presented, or to present photographs spanning the full range of 

existing and potential possible conditions but not directly inform the respondents about 

the current conditions. 

 Investigate whether including cumulus clouds in a blue sky will provide a useful longsight distance to observe the effects of increasing VAQ impairment, especially in the 

eastern United States. 

 Investigate whether a single set of photographs of a generic park scene could be 

acceptable for use in surveys in cities throughout the United States. 

 Conduct initial focus groups in cities in different regions of the country to gain an 

understanding about whether visibility preferences substantially differ across the country. 

 Investigate whether people are able to use a high-quality computer monitor equipped with 

“dial in” visibility impairment software to identify their acceptable level of visibility. 

 Investigate alternative wording of WTP questions, including variations in both context 

and payment vehicle (including whether to specifically mention costs of control). 

 Investigate the level of change in VAQ best suited to asking WTP questions. 

 Explore what combinations of alternative bundles of conditions are best suited for use in 

a conjoint analysis approach to valuation. 
 

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A. Participants List, EPA Workshop on Urban Visibility Preference and Valuation 

Name Affiliation E-mail 

Paul Bell Colorado State University, Department of 

Psychology 

Paul.Bell@colostate.edu 

Laurie Chestnut Stratus Consulting lchestnut@stratusconsulting.com 

Rich Damberg EPA/OAQPS Damberg.Rich@epamail.epa.gov 

Leland Deck Stratus Consulting ldeck@stratusconsulting.com 

Colleen Donovan Stratus Consulting cdonovan@stratusconsulting.com 

Dan Ely Colorado Department of Public Health and 

Environment (Air Pollution Control Division) 

dan.ely@state.co.us 

Bryan Hubbell EPA/OAQPS (via telephone) Hubbell.Bryan@epa.gov 

Doug Jeavons BBC Research and Consulting, Inc. djeavons@bbcresearch.com 

Susan Johnson NPS Susan_Johnson@nps.gov 

Amy Lamson EPA/OAQPS Lamson.Amy@epa.gov 

Bill Malm NPS and Cooperative Institute for Research in the 

Atmosphere/Colorado State University 

malm@cira.colostate.edu 

Robert Mitchell Clark University, Department of Geography rmitchell@clarku.edu 

John Molenar Air Resources Specialists jmolenar@air-resource.com 

Tom Moore Western Regional Air Partnership and Western 

Governors Association 

MooreT@cira.colostate.edu 

Kris Novak EPA/National Center for Environmental Assessment novak.kris@epa.gov 

Chip Patterson Industrial Economics Inc. rwp@indecon.com 

Marc Pitchford NOAA Marc.Pitchford@noaa.gov 

Richard Poirot Vermont Air Pollution Control Division rich.poirot@state.vt.us 

Bruce Polkowsky NPS bruce_polkowsky@nps.gov 

Bob Rowe Stratus Consulting browe@stratusconsulting.com 

Steve Sakiyama British Columbia Ministry of Environment Steve.Sakiyama@gov.bc.ca 

Vicki Sandiford EPA/OAQPS Sandiford.vicki@epa.gov 
 

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B. Agenda, EPA Workshop on Urban Visibility Preferences and Valuation, 

October 6-8, 2008 

Monday, October 6 Discussion leader 

 1:00 PM Welcome and introduction Marc Pitchford 

 1:45 PM Role of urban visibility in secondary PM NAAQS Vicki Sandiford 

 2:30 PM Break 

 2:45 PM Framing the questions about preferences (#3 in Issue Paper) Leland Deck 

 4:00 PM Session wrap-up, summary 

 4:15 PM Temporal distribution of urban visibility conditions (#2 in Issue Paper) Dan Ely 

 5:15 PM Session wrap-up, summary 

 5:30 PM END OF DAY 

Tuesday, October 7 

 8:00 AM Review of yesterday, finish #2 if necessary 

 8:15 AM Differences in regional preferences (#5 in Issue Paper) Bruce Polkowsky 

 9:30 AM Session wrap-up, summary 

 9:45 AM Break 

 10:00 AM Scene selection (#1 in Issue Paper) Rich Damberg 

 11:45 AM Session wrap-up, summary 

 12:00 PM Lunch – bring in 

 1:00 PM Number and composition of focus group and survey respondents 

(#7 in Issue Paper) 

Robert Mitchell 

 2:30 PM Session wrap-up, summary 

 2:45 PM Break 

 3:00 PM Method of presenting visibility conditions (#4 in Issue Paper) John Molenar 

 5:15 PM Session wrap-up, summary 

 5:30 PM END 

 7:00 PM Informal dinner (TBA) 

Wednesday, October 8 

 8:00 AM Review of yesterday, finish #4 if necessary 

 8:15 AM Joint Benefit or “Mental Accounts” (#6 in Issue Paper) Laurie Chestnut 

 9:30 AM Session wrap-up, summary 

 9:45 AM Break 

 10:00 AM Payment vehicle (#8 in Issue Paper) Robert Mitchell 

 11:45 AM Session wrap-up, summary 

 12:00 PM Workshop review and summary; next steps Marc Pitchford 

 1:30 PM END OF WORKSHOP 
 

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C. Vicki Sandiford PowerPoint Slides on Role of Visibility in Secondary NAAQS 
Role of Urban Visibility in Particulate 

Matter National Ambient Air Quality 

Standards (PM NAAQS) Reviews

Vicki Sandiford

Ambient Standards Group

Health and Environmental Impacts Division

Office of Air Quality Planning and Standards

U.S. EPA, RTP, NC

October 6, 2008

2

Overview

Clean Air Act (CAA): NAAQS program

Current NAAQS review process 

Current PM NAAQS review schedule

1997 & 2006 PM NAAQS reviews

Genesis of 2008 PM Visibility Workshop

Ongoing Litigation
3

Clean Air Act NAAQS Program

Sections 108/109 direct the Administrator to:

 Publish and if necessary revise a list of ambient air pollutants that 

threaten public health or welfare

 Issue air quality “criteria” for each pollutant reflecting latest science 

useful in indicating kind and extent of health/welfare effects

 Periodically review science/standards (5 year intervals) and, if

appropriate, revise primary (health) and secondary (welfare) standards 

 Establish independent scientific review committee (Clean Air Scientific 

Advisory Committee - CASAC) to:

– Review air quality criteria 

– Recommend to the Administrator any new standards and revision 

of existing criteria and standards as may be appropriate 

4

Clean Air Act NAAQS Program: Clean Air Act NAAQS Program:

Section 302 (h) public welfare definition: Section 302 (h) public welfare definition:

All language referring to effects on welfare All language referring to effects on welfare 

includes, but is not limited to, effects on includes, but is not limited to, effects on 

soils,...weather, weather, visibility, and climate, , and climate, 

...hazards to transportation hazards to transportation, as well as effects , as well as effects 

on economic values economic values and on personal comfort and on 

and well-being, whether caused by , whether caused by 

transformation, conversion, or combination transformation, conversion, or combination 

with other air pollutants. with other air pollutants.”
5

*Current NAAQS Review Process

Integrated Review 

Plan

timeline and key 

policy-relevant 

scientific questions

Integrated Science Assessment: 

concise evaluation and synthesis of most 

policy-relevant studies

Risk/Exposure Assessment:

concise, quantitative assessment 

focused on key results, observations 

and uncertainties

Workshop on 

science-policy 

issues

Public hearings/ 

comment period

Final 

Rule

Interagency 

review

Interagency 

review

Agency decision 

making and 

draft proposal 

notice

Agency decision 

making and draft 

final notice

Review by CASAC

and the public

CASAC review and public comment Draft Policy 

Assessment/ANPR

Interagency 

review

Public comment period 

and CASAC review

Proposed 

Rule

Policy 

Assessment/

ANPR

Peer-reviewed 

scientific studies

6

Current PM NAAQS Review Schedule Current PM NAAQS Review Schedule

(Some dates subject to change) (Some dates subject to change)

 PM Secondary Kickoff Workshop PM Secondary Kickoff Workshop – Jul ’07

 Final Integrated Review Plan Final Integrated Review Plan – Mar ’08

 PM Visibility Workshop PM Visibility Workshop – Oct. ‘08

 1st Draft Integrated Sc Draft Integrated Science Assessment ience Assessment – Dec ’08

 Draft Scope and Methods Plan Draft Scope and Methods Plan – Feb ’09

 1st Draft REA Draft REA – Aug ‘09

 Final ISA Final ISA – December December ‘09

 Final REA Final REA – July ’10

 ANPR – August ‘10

 Proposed Rule Proposed Rule – January January ‘11

 Final Rule Final Rule – October October ‘11
7

Planning (OAQPS and NCEA)

Joint sponsorship of “kickoff” workshops

– Receive early input from experts, including CASAC members

– Broadly discuss and identify key policy-relevant issues 

around which we would structure the review and the most 

meaningful new science available to inform those issues

 Preparation of one integrated review plan (IRP) to guide 

the entire review 

– Specifies schedule, process, and key policy-relevant science 

issues defining this review

– Includes very general outline of planned assessments

 CASAC consultation/public review of draft IRP

8

Integrated Science Assessment (ISA)

(NCEA)

ISA Document provides:

 a concise and peer-reviewed (CASAC/public) evaluation 

and synthesis of the most policy-relevant science

 a clear characterization of the strengths and uncertainties 

of the available scientific evidence

additional supporting scientific evidence in accompanying 

detailed “annexes”

the scientific foundation that informs the design and 

development of the Risk/Exposure Assessment (REA) and 

the Policy Assessment/ANPR
9

Risk/Exposure Assessment (REA) 

(OAQPS)

 REA initiated through preparation of Draft Scope and Methods 

Planning document

 Draft Scope and Methods Document: 

 considers need for risk and/or an exposure assessment

 if needed, considers what scope and methods/approaches would 

provide information most useful for decision-makers 

 developed in parallel with preparation of second draft ISA

 CASAC consultation/public review of draft Scope and Methods 

Plan

 CASAC/public review of 1st/2nd Draft REAs

 Final REA and ISA inform Policy Assessment

10

Policy Assessment (PA)

(Agency)

 Policy assessment initiated by preparation of draft Advance 

Notice of Proposed Rulemaking (ANPR) 

 Draft ANPR:

– Presents wide range of policy options being considered by 

the Agency for standard setting

– Discusses the underlying interpretation of the scientific 

evidence and risk/exposure information drawn from the 

ISA and REA that might support each option

 Inter-Agency review of draft ANPR

 Publish final ANPR

 *CASAC and public review of ANPR
11

Proposed and Final Rules

 Notice of Proposed Rulemaking (NPR) 

– Published in Federal Register Notice (FR)

– Public comment period, including public hearings, following 

publication of NPR

 Final Rulemaking Notice (FRN) in FR

 Response-to-Comments document (RTC) 

 prepared/finalized in parallel with FRN

 NAAQS rulemaking may be accompanied by or 

combined with rulemaking changes to monitoring and/or 

implementation regulations

12

Recent History of NAAQS Visibility Recent History of NAAQS Visibility 

Protection Protection

 1997 PM NAAQS Review: 1997 PM NAAQS Review:

 Most data available in non-urban, rural or Class I areas

 Regional differences in relationship between PM fine and rural Regional differences in relationship between PM fine and rural visibility visibility impairment limited consideration impairment limited consideration of separate secondary NAAQS of separate secondary NAAQS 

 Focus on protection of rural visibility impairment led to secondary 

standard set in context of upcoming Regional Haze Rule

 Final decision Final decision – make secondary equal to primary

 Post 1997 Developments

 Increase in urban PM2.5 data availability

 Increase in number of State and Increase in number of State and local standards and programs to local standards and programs to protect VAQ beyond the degree protect VAQ beyond the degree provided by current NAAQS

 Availability of simulated images and actual photographs to help Availability of simulated images and actual photographs to help inform 

judgments about the acceptability of judgments about the acceptability of varying levels of VAQ in ur varying levels of VAQ in urban 

areas across U.S. areas across U.S. 
13

Recent History of NAAQS Visibility Recent History of NAAQS Visibility 

Protection (cont.) Protection (cont.)

 Staff Paper (2005) assessments included: Staff Paper (2005) assessments included:

– air quality analyses for air quality analyses for both urban and rural areas both urban and rural areas

– evaluation of standards and programs developed in evaluation of standards and programs developed in 

some areas to address urban visibility some areas to address urban visibility

– evaluation of photographic evidenc evaluation of photographic evidence

–Pilot Study Pilot Study- Results of small study conducted by EPA Results of small study conducted by EPA in Washington, D.C. consistent with earlier perception in Washington, D.C. consistent with earlier perception studies studies

 Staff Paper recommendation: Staff Paper recommendation:

 A PM2.5 secondary standard with an averaging time A PM2.5 secondary standard with an averaging time 

from 4 -8 hrs. daylight set within the range of 20-30 

mg/m3 should be considered

Recent History of NAAQS Visibility Recent History of NAAQS Visibility 

Protection (cont.) Protection (cont.)

CASAC Comments and Contributions: CASAC Comments and Contributions: 

Poirot comments key to EPA moving forward with Poirot comments key to EPA moving forward with 

urban risk assessment in 2006 review

Clear support for sub-daily standard daily standard 

Continued comment and Continued comment and feedback throughout feedback throughout 

review

14
15

Recent History of NAAQS Visibility Recent History of NAAQS Visibility 

Protection (cont.) Protection (cont.)

 2006 Proposal: 2006 Proposal:

 Appropriate to revise 24-hr. PM2.5 standard to provide standard to provide protection from visibility protection from visibility impairment principally in impairment principally in urban areas urban areas 

 Indicator Indicator – PM2.5

 Averaging times Averaging times – retain 24 hr. Took comment on a retain 24 hr. Took comment on a 

range of averaging times from 4 to 8 daylight hours. 4 to 8 daylight hours. 

 Level – Equal to revised primar Equal to revised primary (35 mg/m3). Took y (35 mg/m3). Took 

comment on 20-30 mg/m3 of PM2.5 corresponding to 30 mg/m3 of PM2.5 corresponding to 

a range of median visual ranges between 25-35 km 

 Form –A concentration-based percentile form based percentile form consistent with the pr consistent with the primary of the 92 to 98th

percentile, representative of the mean of the of the mean of the 

distribution of the 20 per distribution of the 20 percent most impaired days cent most impaired days

16

Recent History of NAAQS Visibility Recent History of NAAQS Visibility 

Protection (cont.) Protection (cont.)

 2006 Final Rule: 2006 Final Rule:

 Need to revise existing secondary to provide secondary to provide 

additional protection for additional protection for urban visibility impairment urban visibility impairment

 Public perception and attitude surveys provided ttitude surveys provided 

useful but quite limited information on the range of formation on the range of 

levels appropriate for a levels appropriate for a national standard, given the national standard, given the 

subjective nature of subjective nature of the welfare effect the welfare effect

 Percent of areas covered Percent of areas covered by primary similar to by primary similar to 

secondary secondary

 Set secondary equal to revised primary Set secondary equal to revised primary
17

Genesis of Oct. PM Visibility Workshop Genesis of Oct. PM Visibility Workshop

CASAC advice (June 6, 2005 letter) CASAC advice (June 6, 2005 letter)

– “...developing a more specific (and more protective) developing a more specific (and more protective) 

level in future standards would require updated and level in future standards would require updated and 

refined public visibility val refined public visibility valuation studies. Agency staff uation studies. Agency staff 

are strongly encouraged to s are strongly encouraged to support such studies prior upport such studies prior 

to the next round of NAAQS review....”

18

NAAQS TTN Webpage Set-Up  Contact: Name, email address, and phone number 

(HEID Overall Coordinator)

 Documents from Current Review

– Planning Documents

– Integrated Science Assessments

– Risk and Exposure Assessments

– Policy Assessments

– Other Technical Documents

– CASAC Documents

– Federal Register Notices

– Response to Comments Document

– Regulatory Impact Analysis

– Litigation

 Documents from Review Completed in xxxx

 Air Quality Index

 Plain Language Information About Pollutant

 Summary of Current NAAQS Table
 

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D. Leland Deck PowerPoint Slides on Framing the Question 
1

STRATUS CONSULTING

What Are The Questions ?

Key questions we want to explore in a project on preferences 

for urban visibility

Leland Deck

October 6, 2008

# 2 STRATUS CONSULTING

What did Phoenix study ask ?

 Report form (not journal article) provides detailed 

script of material presented to participants

 Warm up ranking questions

– Familiarize participants with photo, observing 

differences in VAQ

 Ranking (0-7) of VAQ

– 25 slides (5 repeats), random order 

 Reviewed slides again, rated “acceptable or not”
2

# 3 STRATUS CONSULTING

Details of how questions are phrased 

matter

 “seeking public input in acceptable visibility quality”

 Base your answers on 3 factors

– For city area, not a pristine area

– Unacceptable means unreasonable or 

objectionable, not merely some haze detected

– Base answers only on visibility

• Do not consider health

• Do not consider cost

# 4 STRATUS CONSULTING

More on acceptability questions

 Answer what is acceptable to you

 Time dimension

– Right now

– Not if lasting several hours or all day
3

# 5 STRATUS CONSULTING

Third exercise: # of days acceptable

 Used 7 slides (not all 25)

 Asked how many days would this visibility be 

acceptable

– Range of answers 0 to 365 days

# 6 STRATUS CONSULTING

Denver variations

 Asked everything in context of a visibility 

STANDARD

– E.g., ‘would this be an acceptable standard’

 Defined acceptable for a standard

– VAQ is unreasonable, objectionable and 

unacceptable

 Cost never mentioned, ignore health was
4

# 7 STRATUS CONSULTING

Washington variations 

 Background provided

– VAQ is caused by pollution from various 

sources, near and distant

 Walk through initial slides

– Notice colors shift, crispness, distant objects

 “visibility only”, but health or cost NOT mentioned 

in script 

 Acceptable is personal, varies; no definition given

# 8 STRATUS CONSULTING

Washington and time

 Provided background on time

– Sometimes this condition lasts for a few hours

– Sometimes lasts for a number of days

 For small set of slides (5)

– Consider this is worst in day

– How long would this be unacceptable

• Hours or days are possible responses

 Valuation question implied asking about annual 

mean
5

# 9 STRATUS CONSULTING

Questions for discussion

 What context to mention?

– Standard setting or “just your opinion”?

 Ask Yes/No Acceptable question, or 3 way

– Acceptable

– Unacceptable

– Objectionable

 Is numerical ranking exercise useful, done right?

 Something Else? Not yet mentioned ???

# 10 STRATUS CONSULTING

Questions for discussion

 Provide background on visibility science, photos?

 How important is issue of “visibility only” ?

– Health and costs?

 What aspects of temporality do we care about ?
 

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E. Dan Ely PowerPoint Slides on Temporal Distribution 
1

Issue 2

Temporal Distribution of 

Visibility Conditions

Dan Ely

Colorado Dept of Public Health & Environment

Air Pollution Control Division

10/6/08

The Temporal Realms of Concern

1. Annual Distribution

– Assume there is an annual distribution of 

visibility conditions in an urban area that 

can be described/presented

• What are people’s preferences concerning 

changes in different parts of the distribution?

– More interested in changes in the worse days?

– More interested in increasing the number of good 

days?

– Thru what mechanism do we determine 

what is the policy relevant shift?
2

0

25

50

75

100

125

150

175

200

225

250

275

300

19901991199219931994199519961997199819992000200120022003

Year

Extinction in Inverse Megameters

The standard level is represented by the dark blue line.

Trend in Daily Max Extinction - Denver

Temporal Realms of Concern

2. Seasonal-ish Distributions

– Some potential control strategies combined 

with natural met conditions will likely 

influence some seasons more than others

• This will vary by location in the country

– Do people have a preference?

• Seasonal? Winter/Summer? Other periods?
3

Temporal Realms of Concern

3. Natural Visibility Impairment

– Any presentation of a distribution of visibility 

conditions must deal with natural impairment (?)

• e.g., % of time fog, rain, snow, volcanic ash, wildfire 

smoke, fallout from meteor strike, etc.

– How convey natural viz information?

• e.g., include RH% on each slide

• People are often confused by the natural impairment 

issue

– “How much of what I’m seeing is natural? Should I 

consider it somehow? Discount it? Why don’t I skip this 

slide...”

– Exclude any slide with obvious snow storm, rain 

etc and/or above X% RH?

Temporal Issues

4. Partial day visibility impairment

• Anthropogenic visibility impairment varies 

throughout daylight hours

– Are some times more important than others?

– Do people’s preferences differ for early morning, 

mid-afternoon, late-in-the-day visibility?

• How treat/address heterogeneous visibility 

conditions in calculating/presenting visibility 

conditions?

• How many hours of “unacceptable” visibility 

does it take to count as an exceedance?
4

Temporal Issues

5. Nighttime visibility

– Impairment of surface features at night is 

potentially of interest

– Do people consider nighttime visibility in 

their preferences of overall urban 

visibility?

– Should nighttime viz be excluded from this 

round of focus group projects?
 

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F. Bruce Polkowsky Presentation on Regional Distribution 
Do people’s preferences for urban visibility vary substantially in different regions of the 

country? 

Sight Path 

Personal Experiences within the urban area (daily, weekly, seasonally) 

 Landmarks (natural, man made) 

Pollution impacts (episodic, frequent, magnitude) 

Education about what is lost 

 Eastern pollution levels 

 Attributes of a “clear sky” (clouds, blue color) 

 Summer Humidity exacerbates but does not cause visibility 

Impact on Survey Instrument: 

 What is the “appropriate” level of education on current visibility conditions? 

 Is it beneficial to have the survey indicate “best science” on natural visibility 

 
 

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G. Rich Damberg Presentation on Scene Selection 
1

PM NAAQS Review

Urban Visibility Workshop

Scene Selection Issues

Rich Damberg

EPA Office of Air Quality Planning and Standards

October 7, 2008

Scene Selection Issues

• What type of scene should be used in a focus group or 

survey study?

– Scenes specific to each urban area (e.g. St. Louis Arch), or 

generic urban area scenes?

– The iconic postcard scene or skyline scene? 

– Scenes that are less dramatic but experienced more frequently 

(e.g. on ride to work; or walking / driving around town)?

– Scenes that are associated with positive outdoor experiences 

(e.g. urban park)?

– Use multiple scenes per urban area, or a single scene?

– Should people or cars be present in the scene?

• Select scenes where change in haze appearance is 

sensitive to PM changes

– Traditionally, scenes with distant features have been used in 

western studies. 

– However, this is more challenging for Eastern urban areas, 

where expansive vistas are not as common. In some cases, sky 

color and/or cloud appearance may be the most sensitive scenic 

elements.
2
3
4

5 ug/m3
5

35 ug/m3

Burlington, Vermont
6
7
8
9

Brookfield, WI
10
11
12
13

Cranbrook, British Columbia

Commercial strip
14
15
 

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H. John Molenar Presentation on Presenting Visibility Conditions 
1

Use of Visuals in

Visibility Surveys

(and some other comments)

John V. Molenar

Air Resource Specialists, Inc. 

Ft. Collins, Co.

jmolenar@air-resource.com

10/07/2008

Onsite Observations

• Would mimic the actual visual air quality 

experience.

However:

• Uncontrollable visual air quality and/or 

scenic beauty levels.

• Unless observers are brought to location, 

limited to respondents who are onsite.
2

Possibilities Instead of Onsite 

Observations

• Projected 35 mm Slide

• Digital Image Projector

• Computer Monitor

• Reflection Print

• Virtual Reality

Seeing is a psychophysical

phenomenon not easily modeled or 

reproduced by any process that is 

strictly physical in origin.
3

Requirements For Match

• Spectral Sensitivities

• Color Gamuts

• Dynamic Range
4

Color Reproduction

Spectral: Equality of spectral reflectances or 

spectral power distributions.

Colorimetric: Equality of chromaticities and 

relative luminances.

Exact: Equality of chromaticities and 

relative and absolute luminances.
5

Color Reproduction

Equivalent: Chromaticities and relative 

luminances are set such as to ensure equality 

of appearance.

Corresponding: Chromaticities and relative 

luminances are set such as to ensure equality 

of appearance when the the original and 

reproduction luminances are the same.

Dynamic Range

• Human visual system: 100,000 : 1

• HDR Monitor 50,000 : 1

• LED or Plasma Monitor: 3000 : 1

• Projected slides: 500 : 1

• CRT Monitor: 200 : 1

• Reflection Prints: 

Highest Quality 50 : 1

Newspaper 15 : 1
6

Transparency Effects

A subjective phenomenon when the 

observer has the impression that he is 

looking at a scenic feature through a 

distinct semi-transparent surface.

Advantages of Projected 35 mm Slides or 

High Quality Digital Projector

• Best Color Saturation and dynamic range

• Proven (35mm slides) to be valid 

representations of actual scenes for judgments 

of perceived scenic beauty, landscape 

preferences and visual air quality

• Can easily design survey to include preview 

images, control scenes and multiple visual air 

quality scenarios
7

500 5 41.2 55.0 68.7 82.5 96.2 109.9

300 8 25.7 34.3 42.9 51.5 60.1 68.6

135 18 11.4 15.2 18.9 22.7 26.5 30.3

105 23 8.8 11.8 14.7 17.7 20.6 23.6

70 34 5.9 7.9 9.8 11.8 13.7 15.7

50 47 4.1 5.5 6.9 8.3 9.7 11.0

28 75 2.3 3.1 3.9 4.7 5.5 6.3

36” 48” 60” 72” 84” 96”

Camera Lens (mm) degrees

Focal Length of Field of View

Viewer distance from screen in feet for

Width of Projected Image in Inches

Slide Viewing Distance To Match Onsite 

Field of View (FOV)

Lengths Photographic Companies 

Have Gone To !!!

• “The experiment was conducted in a dark 

environment. The monitor was put on a desk 

resulting in eye-level viewing for the subjects. 

The viewing distance was maintained at about 

16 inches by fixing the position of the subject’s 

chair ... (no head-bar was used) ...”

“Comparison of Color Difference Perception on Soft-Display Versus Hardcopy”, 

King F. Choi, Eastman Kodak Company, Rochester, New York
8

Slides vs. Onsite Judgments

Slide Perceived Visual Air Quality

1 2 3 4 5 6 7 8 9 10

Onsite Perceived Visual Air Quality

1

2

3

4

5

6

7

8

9

10
9

Projected 35 mm Slides

Disadvantages

• Must be viewed in darkened room

• Respondents must be brought to central 

facility

• Slides degrade rapidly with projection time

Degradation of 35 mm slides

0

0.5

1

1.5

2

2.5

3

3.5

4 8 16 32

Cumulative Projection Time (mins)

deltaE From Unprojected Slide
10

Reflection Prints: Advantages

• Easily transportable so can be brought to 

respondents

• Do not degrade as fast as 35 mm slides

• Have been used in most previous CV 

studies of visibility benefits

Reflection Prints: Disadvantages

• Limited dynamic range means small changes 

in visual air quality cannot be presented

• Must use small focal length lens and large 

print size to mimic onsite field of view

• Difficult to efficiently present multiple visual 

air quality levels with prints
11

Reflection Prints: Sizing

The visual angle subtended by objects on a print is 

determined by the focal length of the lens and the 

dimensions of the image plane of the camera system used 

to take the image; that is if the print is created without 

additional sizing and cropping. 

For 35mm slides taken in the IMPROVE monitoring 

program the image plane is 24 x 36 mm. Two lenses were 

typically used, a 135mm or a 50mm focal length lens. The 

horizontal field of view (FOV) in degrees is approximately 

40O for the 50mm lens and 15O for 135mm lens. Objects 

imaged onto the focal plane by the 135mm lens will be 

approximately 2.7 times larger than when imaged by the 

50mm lens. 

Reflection Prints: Sizing

Thus, if prints are viewed at the same distance, those made 

from images taken with a 50mm lens will have to be 2.7 

times larger than the prints from the 135mm image for 

objects to have the same visual dimensions.

If the prints are the same size, the print from a 135mm lens 

will have to be 2.7 times farther away as the print from a 

50mm lens for objects to be the same size.

If one views prints at a distance such that the FOV of the 

print as viewed by the eye matches the FOV of onsite 

image as captured by the lens onto the image plane, 

objects will subtend the same visual angle (appear to be 

the same size on the print as in the actual scene). 
12

Reflection Prints: Sizing

The basic equation to calculate this distance is

Distance = [Width / 2] / TAN(FOV/2)

Where:

Distance = distance from eye that print must be held 

Width = horizontal dimension of print 

(in same units as distance)

FOV = Horizontal FOV of camera in degrees

TAN = tangent of angle

Reflection Prints: Sizing

13.3 20.0 91.3 33.0

10.7 16.0 73.0 26.4

8.0 12.0 54.8 19.8

6.7 10.0 45.6 16.5

5.3 8.0 36.5 13.2

4.0 6.0 27.4 9.9

Height Width 135mm lens 50 mm lens

Distance in inches from eye of 

print to match FOV of 35 mm 

slide taken with lens

Print Dimensions

(inches)
13
14
15
16

Describing Visual Air Quality Is A

Complex Issue Depending On:

• characteristics of observer

• optical characteristics of target

• illumination of scene

• optical characteristics of 

atmosphere
17
18
19

Urban Images
20
21
22
23
24
25
26
27
28

Regional Haze Rule metric is based on a 

geographically non-uniform weighted 

partially speciated PM10

   

  

  

 

 

 

 

  ppb)(NO0.33

Rayleigh Specific)iteS(Scattering

6.0

SaltSeaRH)(f1.7

1

10

Small2.8 Organic OrganicargeL6.1Mass Mass

RH)(f2.4 SmallNitrate NitrateargeLRH)(f5.1

RH)(f2.2 SmallSulfate SulfateargeLRH)(f4.8

2

SS

S L

S L













 

 

   

Coarse Mass

SoilFine

Elemental Carbon

bext

So what happens when 

the metric is collapsed to 

a single measurement of 

Fine Mass ???
29

Effects of Various Aerosol Types

73.5 Mm-1 45.0 Mm-1 142.0 Mm-1 95% rh

61.2 Mm-1 33.6 Mm-1 87.5 Mm-1 80% rh

56.5 Mm-1 27.5 Mm-1 65.0 Mm-1 50% rh

Coarse Mass 3.75 3.75 3.75

Fine Mass 12.5 12.5 12.5

Soil 0.60 10.0 1.0

LAC 1.25 0.0 2.0

Organic 3.15 0.5 8.0

Nitrate 1.25 0.5 0.5

Sulfate 6.25 1.0 1.0

Sulfate Aerosol Soil Aerosol Organic Aerosol

Soil Aerosol at 50% rh: bext = 27.5 Mm-1 dv = 10 
30

Soil Aerosol at 95% rh: bext = 45.0 Mm-1 dv = 15

Sulfate Aerosol at 50% rh: bext = 65.0 Mm-1 dv = 19
31

Organic Aerosol at 95% rh: bext = 73.5 Mm-1 dv = 20

Sulfate Aerosol at 95% rh: bext = 142.0 Mm-1 dv = 27
32
 

Stratus Consulting Memorandum (11/18/2008) 

Page 25 

SC11568

I. Laurie Chestnut Presentation on the Joint Benefits 
1

STRATUS CONSULTING

Joint Benefits / Mental Accounts

 Defining the good: what you are trying to measure?

 What level of visibility impairment begins to cause 

an adverse welfare effect? At what level is 

enjoyment of daily activities reduced? 

 Basic issue: Are people considering more than you 

want them to when answering the preference 

questions? Are answers biased?

 Focus groups to figure out what words/context are 

best to describe measure for general public?

STRATUS CONSULTING

STRATUS CONSULTING

Strength of preference measure

 Binary: zero/one Is this good or bad?

 Scale: 3 to 7 levels How good or bad?

 Willingness to pay: tradeoffs between personal 

cost and air quality improvement

– requires a specified “mechanism” by which 

change is implemented

 Need to allow people to say they are not affected 

by visibility conditions
2

STRATUS CONSULTING

Examples of associations people may 

make that can bias preference responses

 That haze is natural humidity, therefore it is 

acceptable because it is natural.

 That smog must be bad to breathe, so it is 

unacceptable.

 If something is unacceptable, then something 

should be done to change it and that will cost 

money, so I’ll say some level of pollution is 

acceptable.

 The oil companies make so much money, I 

shouldn’t have to pay for cleaner fuel. 

STRATUS CONSULTING

Results from previous urban visibility 

valuation studies 

 Need a payment mechanism--adds complications 

 Telling people to think only about visibility was not 

sufficient to eliminate health concern bias.

 Approaches to disentangle

– varying combinations of visibility and health risk 

(conjoint)

– ask total value with follow-up to partition 

 Visibility about 20-40% of total value for air 

pollution change
3

STRATUS CONSULTING

Questions to assess/explore nondollar 

preference measurement

 Open-ended questions about how it affects you when 

seeing different visual air quality in day-to-day activities. 

 Reactions to different preference wording: acceptable, 

bothersome, enjoyable.

 Can I convince you to focus on only visibility?

 How much do you need to know about natural variations 

versus anthropogenic pollution?

 How much are they thinking about policy or control 

measures when giving preferences?

 Frequency versus level—need to ask these jointly?

STRATUS CONSULTING

Debrief questions for consistency/validity 

evaluation

 Repeat some images to check consistency of 

ratings.

 Multiple choice of what influenced responses

 Agreement/disagreement with various statements

 Would you change your answer if....?
4

STRATUS CONSULTING

Feasibility of adding economic valuation

 Low marginal cost for additional useful information

 Several bits of information needed to set the dollar 

valuation context:

– Payment mechanism

– Alternative reduction levels

 Probably have to look at total value of change in 

air quality to disentangle health concerns

 Need to be careful about fatigue factor of 

lengthening questionnaire, but can explore in 

focus groups
 

Stratus Consulting Memorandum (11/18/2008) 

Page 26 

SC11568

J. Tom Moore PowerPoint Slides on Phoenix Visibility Conditions 
1

North Mountain Camera

December 25, 2006 10:00am

PM2.5 at W. Phoenix 75 μg/m3 (the standard is 35 μg/m3)

North Mountain Camera

January 1, 2007 10:00am

PM2.5 at W. Phoenix 93 μg/m3 (the standard is 35 μg/m3)
 

Stratus Consulting Memorandum (11/18/2008) 

Page 27 

SC11568

K. Urban Visibility Issues 
Background Issues Relevant to Investigating Urban Visibility Preference 

and Valuation 

EPA wishes to develop additional information that could be used to inform a decision as to 

whether a secondary standard for PM might be justified based on achieving an acceptable level 

of visibility in urban areas. There is some information from a few existing focus group and 

survey studies on urban visibility (Denver and Phoenix) that found encouragingly similar levels 

of acceptable visibility impairment. An additional smaller EPA focus group project provided 

information about urban visibility preferences in Washington, DC. Critical questions remain 

whether these findings are robust, and whether these initial findings are valid in all regions of the 

country. 

Additional data collection and investigations concerning what individuals find to be acceptable 

urban visibility levels in other regions of the country will help to better understand individuals’ 

preferences about urban visibility. Measuring preferences for urban visibility in terms of 

economic value is also an important component in understanding visibility preferences and 

supporting EPA programs affecting visibility. Thus, EPA is sponsoring an expert workshop 

designed to explore or evaluate potential focus groups and survey projects that could produce 

useful information for consideration in the review of an appropriate secondary PM standard (e.g., 

information to support consideration of a secondary standard indicator, averaging time, level and 

form). The potential projects could lead to a better characterization of the economic value of 

public welfare visibility benefits across a range of alternative secondary PM standard options 

that potentially achieve acceptable urban visibility. 

Potential urban visibility projects could involve multiple project elements, which could have 

different objectives and use different methods. There are at least three different types of project 

components that could be a part of the overall project, and other substantially different types of 

project elements could also be important components of the project. While different terminology 

is sometimes used to describe each type of components, in this paper the terms used for the three 

identified types of potential components are: 

• Investigative focus groups, which are used to explore questions such as the issues 

discussed later in this paper. Alternative materials depicting urban visibility, and 

alternative approaches to eliciting individuals preferences and valuations are used in 

different focus groups to gain an understanding of the effective structure, format and 

content for conducting a focus group on urban visibility. 

• Applied focus groups, which use one established set of materials and questions in each 

of a series of focus groups. These focus groups would not only allow for larger numbers 

of participants to be involved, but could also be conducted in different locations to 

investigate differences between responses of people who live in different areas. The 

Denver and Phoenix urban visibility studies conducted applied focus groups, conducting 

17 and 27 focus group sessions, respectively. 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 2 

• Survey Methods, which strive to reach a statistically representative sample of the 

population. This can include a nationwide survey (infeasible for a focus group 

approach), or a significantly larger number of participants within a single metropolitan 

area than is possible using focus groups. Valuation research projects have tended to use 

survey methods (although there are alternatives recently developed). An ongoing 

National Park Service study of visibility valuation in National Parks (as well as previous 

studies of National Park visibility), and EPA’s 1990 and 1991 studies of urban visibility 

valuation in Denver, Atlanta and Chicago, used survey methods. 

The specific goals of EPA’s upcoming urban visibility expert workshop are: 

• Reach consensus (if possible) on what are the key questions for a set of “next step” urban 

visibility projects to expand the current state of knowledge about urban visibility. Identify 

any of the key methods questions which cannot be adequately resolved a priori and 

incorporated into an applied focus group project, but which will require investigation as 

an integral part of investigative focus group activities. 

• Design a project (or a sequential set of projects) using investigative and/or applied focus 

groups that will expand the existing knowledge base about individuals preferences for 

urban visibility, with particular emphasis on what level of urban visibility impairment is 

considered “acceptable”. 

• Develop a portion of the investigative and applied focus group activities that can best 

support development of a follow-on survey project focusing on valuation (willingness to 

pay) for improving urban visibility. 

This issues paper introduces eight key issues that are relevant for further investigations in urban 

visibility preferences and valuation. The identified issues can be used to help organize the topics 

that will be discussed in the urban visibility workshop. While all of these issues are relevant for 

designing and conducting a full scale urban visibility project including a survey-based 

component, each issue identified here would not necessarily become an explicit topic of 

discussion during the workshop. There are likely to be additional issues raised by the workshop 

participants that will need to be considered in developing a focus group or survey project. 

The issues included here are directly relevant for projects investigating urban visibility 

preferences, as well as those additional issues relevant for valuation purposes. Though the issues 

relevant for a preference-related investigation are also directly relevant (and in fact required) for 

any valuation project, the opposite is not necessarily the case; some of the valuation-related 

issues are not relevant or essential for a study limited to preferences. 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 3 

This document briefly describes each of the eight key issues, and in a few cases introduces 

associated contextual issues that may be relevant. It is not intended as an extended discussion of 

any one issue. 

In this background paper the term “urban visibility” refers to visibility conditions across an entire 

metropolitan area. This includes downtowns, central city residential areas, suburban areas, local 

parks and recreational areas, etc. The primary distinction is that “urban visibility” is not meant to 

include; 

• visibility in Class I areas (including both “destination” iconic National Parks and 

Wilderness Areas as well as Class I areas and similar locations likely to be of interest 

primarily to regional residents), 

• visibility in such land uses as agriculture and forests, small towns, remote lakes and 

rivers, beaches, etc., or 

• night sky visibility (i.e., viewing of stars, planets, and similar features). It is an open 

question whether viewing of ground level features at night, such as observing the 

expanse of a city at night from popular elevated locations, seeing “the city lights” such 

as in Los Vegas and on Broadway, nighttime sporting events, etc. should be included as 

part of the description of urban visibility 

Issue # 1: Scene Selection 

Key Question: What urban scenes, and how many scenes, should be used in a focus group 

or survey study? 

Background Discussion: 

There are a wide variety of settings (or scenes) where a person may observe 

visibility in an urban area. One specific question is in what type of urban scenes 

are visibility conditions important to people? A practical related question for 

designing a project is what scenes, and how many scenes, are needed to give the 

participants an adequate understanding of visibility conditions in their 

metropolitan area. 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 4 

There is a very broad range of possible scenes in a metropolitan area where 

visibility may be important. The range of scenes may include: 

• Iconic “picture postcard” scenes of a famous city scene that includes a long sight 

distance, such as a photo including downtown Manhattan, the Seattle Space 

Needle with Mt. Rainier in the background, or the St. Louis Arch with the 

Mississippi River. Virtually every city will have some scene that local residents 

describe as a classic place to “enjoy the view” of the city. 

• Highway photos, such as from an interstate-type expressway through the heart of 

a city. These scenes, while not necessarily beautiful settings in and of themselves, 

may make up a substantial portion of a routine “viewing opportunity” of urban 

visibility conditions for many people on a daily basis. Highway settings provide 

some of the longest sight distances within an urban setting that people routinely 

experience. 

• Downtown city streets; the “urban canyons” type of photo with long sight 

distances (down the middle of the street), short sight distances of nearby 

buildings, and with increasing amounts of sky appearing in the middle and far 

distances. These are a very urbanized setting, including city street traffic, 

pedestrians, commercial buildings, etc. 

• Urban park scenes; the green grass, big trees, open areas with sport fields is an 

iconic American scene which connotes outdoor recreation and leisure to many. 

Unlike some of the other urban scenes, parks have a familiar look to them 

throughout the country. Also when people are in parks they have an opportunity 

to spend more time viewing the sky, clouds and other available long-distant views 

than possible in most other urban scenes. 

• Suburban major commercial streets, while similar to downtown “urban canyons” 

with traffic and commercial activity, typically have with lower buildings and 

often much wider streets and more open sky. Like the major highway scene, this 

type of scene can make up an important portion of daily “viewing opportunities” 

for local residents. 

• Residential streets, which may have rather limited sight distances. In the eastern 

portion of the country where deciduous trees line residential streets there may be 

relatively little sky exposure due to the tree canopy and limited sight distances. 

Many western residential streets have very different attributes, with longer vistas 

and more sky exposure. Apartments and similar high density housing are 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 5 

residential settings that can be substantially different than detached, single family 

housing, creating a different type of visibility situations. 

In selecting among scene types, it is important to make sure at least some scenes 

include elements that are sensitive to changes in visibility impairment. 

Traditionally that included distant terrain features. Large man-made structures 

such as city skylines and bridges viewed from a distance are also sensitive to air 

quality changes. For scenes that don’t include such distant visible features (i.e., 

they either don’t exist or are blocked by mid-ground features), sky color and the 

clarity of viewing clouds may well be the most sensitive scenic element to 

perceptible changes in visibility impairment. Specific questions include; 

• How much of a role do specific details within a scene play in presenting the 

visibility conditions? For example, when asking questions about their visibility 

preferences, do the responses differ if the park scene is deserted, shows children 

playing, or includes a homeless man on the park bench? 

• What role do preferences for a clear blue sky have in overall urban visibility 

preferences? An unresolved issue is whether preferences for visibility quality 

differ between days with clear skies (with or without isolated clouds) and overcast 

days with the identical surface level visibility degradation conditions. In general, 

the question is how much is the preference for good visibility tied to the 

preference for blue sky conditions, compared with the ability to see surface level 

features clearly? A related question is what role nighttime visibility impairment of 

surface level features (i.e., haze degrading views of the skyline and other urban 

scenes at night) has in urban visibility preferences. 

• Another group of scene selection topics pertain to how site specific the presented 

photographs need to be. For example, while it is likely a “picture postcard” scene 

would be immediately recognizable to most people (whether it is from their city 

or not); other potential scenes may not vary so much between cities. For example, 

a residential street scene photograph from the Midwest may not be recognized as 

from another location and may be satisfactory for use in many Eastern cities, but 

that Midwestern residential photograph may not be appropriate for use in 

Southwestern cities which have very different styles of architecture and 

vegetation. In contrast, the appearance of urban park scenes, with grass, trees and 

sport fields may be more universal across various regions. Thus, the questions that 

must be addressed with respect to implementing an urban visibility study include: 

Must a unique set of photos be developed for each location in which a study is 

conducted or could at least some common urban scene photographs (e.g., parks) 

be successfully used in multiple locations? Would using non-local photographs 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 6 

influence a respondent’s answers in a meaningful way? If a respondent is able to 

understand that a set photograph is meant to represent conditions in their city, 

does it matter that some or all the photographs actually are from another city? 

• In addition to these basic questions about scene selection, other fundamental 

visibility attributes which are important underlie some of the scene selection 

questions. For example, do preferences concerning brown colored visibility 

impairment differ from white visibility impairment (haze viewed toward the sun 

tends to be white, while the same haze viewed away from the sun tends to be 

darker)? Are preferences for urban layered or bounded haze (such as the Denver 

and Phoenix brown clouds) different than preferences for more regionally 

homogeneous impairment? Are preferences affected by how well you can see at 

short distances (e.g., under one mile), or is it only longer sight distances that 

matter? 

Issue # 2: Temporal distribution of urban visibility conditions 

Key Question: What information about the seasonal or daily distribution of visibility 

conditions should be used in a focus group or survey study? 

Background Discussion: 

There are a number of different topics associated with temporal (time related) 

distribution. These topics deal jointly with “what do people care about” and also 

“what would a study have to present.” Potential time periods of concern are: 

• Annual distribution: Any realistic policy influencing urban visibility will shift the 

entire annual distribution, with the largest changes most likely near the upper end 

of the distribution that describes the worse days. Further investigation is needed 

about what people’s preferences are concerning changes in different portions of 

the overall annual temporal visibility distribution. Are people most interested in 

the improvements on bad days? Increases in the number of good days? A design 

question is what mechanisms can be used, either in a focus group or a survey 

instrument, to convey what a policy-relevant shift in annual distribution will be. 

While presenting multiple scenes with multiple visibility conditions is feasible 

(with hard copy photos at least), a remaining question is how many different 

combinations of scenes and photographs can a viewer understand and interpret 

simultaneously (e.g., 5 scenes and 5 photographs).
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 7 

• Seasonal distribution: In Class I visibility research there is concern that the high 

visitation, summer season may be more important (i.e., people may have stronger 

preferences for good visibility) than the rest of the year. Certain policies, 

combined with natural meteorological conditions, will likely influence some 

seasons more than others. This will vary by location in the country. What are 

people’s preferences for the seasonal distributional change in visibility? Are the 

preferences equal for all seasons or months, or are certain intra-annual periods 

more important? 

• Natural visibility impairment: A project design question is should any 

presentation of a visibility distribution include information about naturally 

occurring reduced visibility days due to rain, natural fog, night time, etc. The 

amount of time that there is naturally occurring reduced visibility changes 

throughout the year and varies in different locations. A specific question involves 

how information about natural visibility obstruction should be conveyed. For 

example, would a spoken or written description be enough, or do distribution 

diagrams or photos need to include this information? 

• Partial day visibility impairment: A given level of anthropogenic visibility 

impairment may occur during a portion of the daylight hours, but a very different 

impairment occurs at other times (due to storms, weather patterns changing, 

changing light angles, etc.). Are some times of the day more important to people 

than other times? Do people’s preferences differ for early morning visibility, midafternoon visibility, or later in the day visibility? How do you treat heterogeneous 

visibility conditions (in both the day and night) in calculating and presenting the 

annual or seasonal visibility conditions? 

• Nighttime visibility: Visibility impairment of surface features at night is 

potentially also of interest. Like daytime visibility, particulate matter pollution at 

night impairs people’s ability to see roads, buildings, illuminated areas, city 

skylines and “city lights”, etc. Manmade illumination plays an important role in 

nighttime visibility impairment, as particles both deflect light (softening the light 

into a halo like event) and decrease the amount of light transmitted from the 

source to a scene. Nighttime visibility conditions are frequently different from 

daytime conditions, due to decreased temperatures, higher relative humidity, 

changing wind patterns, etc. Do people consider nighttime visibility important in 

their preferences of overall urban visibility? Should nighttime visibility be 

excluded from this round of focus group projects (and postponed for future 

projects)? How do a heterogeneous day in calculating and presenting annual or 

seasonal visibility conditions? 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 8 

Issue # 3: Framing the questions about preferences 

Key Question: Is the key preference question to find more information about some version 

of the question “At what level of visibility impairment does it become unacceptable to 

you?” 

Background Discussion: 

In the previous three focus group studies, a key question on preferences came down to 

asking what level of visibility impairment do you find unacceptable. For example, the 

Phoenix study used the following language; 

In this exercise we are seeking public input on acceptable visibility levels for the greater 

Phoenix area. Part II involves looking at the slides again and deciding whether a particular 

view has an acceptable level of visibility for an urban area. 

Please base your decision on the following: 

 Consider that this is a view in a city. In other words, please take into account that you are 

judging the visibility in an urban area, and not a pristine desert area, where standards might 

be stricter. 

 Consider “unacceptable” as visual air quality that is unreasonable or objectionable visibility. 

Please do not mark a slide “unacceptable” just because you can see some haze, unless you 

believe that any amount of haze is more than you would tolerate. 

 The acceptable visibility levels should be based solely on visibility. Do not try to guess what 

might be the health effects of haze or how much it might cost to have better visibility. Your 

decision should be based on how the air looks—this is about visibility only. 

Please indicate in the spaces provided whether the visibility in a given slide is acceptable to 

you.

The Washington and Denver focus group studies used variations on the same 

questions. Is the question of unacceptable the most important concept in 

preferences to expand our knowledge of urban visibility for use in setting a 

secondary NAAQS? Is there alternative language, or entirely different concept 

about preferences, that would also be important to investigate? 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 9 

Issue # 4: Method of presenting visibility conditions 

Key Question: How can photographs showing different visibility conditions be presented in 

a focus group or in survey? 

Background Discussion: 

The use of photographs is essential in virtually any study about perception and 

preferences for visibility. Photographs are especially critical for investigating how 

much visibility impairment is unacceptable, or for presenting relatively subtle 

visibility changes such as from a policy-relevant emission control plan. All 

photographs, no matter how presented, are representations of real world 

conditions, and do not completely accurately convey all aspects of visibility 

conditions. Different methods vary in the accuracy of the overall depiction of 

visibility conditions, and also impact the sheer logistics of presenting multiple 

scenes and visibility conditions. There are three primary alternatives: projection 

screens, printed photographs, and images viewed on a computer monitor. 

• Projection Screen. Perhaps the highest quality way to present photos of visibility 

conditions is using photographic slide transparencies, projected onto a large, high 

quality reflective projection screen. The amount of light from the projected scene 

that is received by the eye, and the relatively wide portion of an individual’s field 

of vision, provides a very high quality viewing situation. A large sized slide 

projection approach, however, creates practical obstacles for any visibility study. 

The size alone makes it difficult to show multiple photos simultaneously. You can 

use a screen very effectively to present a split shot image, with one visibility 

condition on one side and of the picture, and another condition on the other side 

(Winhaze, a computer-imaging software program that simulates visual air quality 

differences of various scenes developed by Air Resource Specialists, Inc., can 

prepare such images). However it is difficult to use a projection screen to 

simultaneously show a distribution of visibility conditions (for example using 5 

photos to present the quintiles of the distribution) without loosing some of the 

inherent advantages of using a screen in the first place (large size). Another 

consideration with this approach is that high quality photographic slides should be 

used to enable the viewer to perceive small changes in visibility. Slides of this 

type degrade rapidly, however, so multiple copies are needed in administering 

focus group sessions. 

A projection screen can be used in a focus group, such as was used in the 2000 

focus group project for OAQPS about urban visibility perception and preferences. 

A large, high quality projection screen, with participants seated 8 to 15 feet away, 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 10 

provides optimal viewing conditions, and can be used in focus group settings. 

However, a projection screen would be a serious obstacle for use in a full field 

survey. It is challenging enough in any survey to get an adequate response rate 

and demographic/economic sample of the target population. However, requiring 

appropriate survey respondents to come to a specific location to complete the 

survey in a preference or valuation study create enormous participation and 

response rate difficulties, even with participation incentives. 

• High quality prints on photograph quality paper are the other main option. One 

key question is how large any photographs need to be. Larger size prints do 

present a better overall depiction of the visibility conditions throughout the scene. 

Larger sizes are more expensive, of course, and are more cumbersome to present 

multiple photos simultaneously. Conversely smaller print sizes are less expensive 

and easier to manipulate. Smaller photos may enable simultaneously showing 

more scenes and various visibility conditions. Identifying a minimal acceptable 

print size to adequately convey the visibility situation is an important goal in 

initial design of an urban visibility project. 

• Presenting visibility via a computer monitor is a potential third option, but there 

are significant drawbacks. Using individual home computers in a survey is 

impractical, because the size, quality and color of the image as presented will vary 

for every user. Using a computer monitor in a focus group setting may be 

possible, but may still have presentation quality concerns. 

Issue # 5: Differences in regional preferences for urban visibility 

Key Question: Do people’s preferences for urban visibility vary substantially in different 

regions of the country? 

Background Discussion: 

An important question is whether preferences for urban visibility differ in various 

regions of the country, or even in individual cities within a region. In part due to 

limited research on urban visibility preferences, this has been often raised as a 

concern. Without using the same protocol in multiple cities, it is very difficult to 

know whether this issue is a significant factor. 

The leading hypothesis as to why there may be regional differences in visibility 

preferences is the “good” in question may be fundamentally different in different 

locations. For example, urban visibility in cities such as Seattle and Denver 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 11 

includes majestic snow-capped mountains as part of the “urban visibility 

landscape” of the city. Visibility impairment in those cities includes the potential 

for a degraded quality of the visibility of the iconic symbols of these cities; the 

high altitude backdrop visible anywhere in the city on a clear day. Layered haze, 

such as the Denver and Phoenix “brown clouds,” become an important aspect of 

such visibility degradation, creating different visibility impairment for seeing the 

lower parts of the mountains than for the mountain tops and more distant peaks. 

Even while both have mountains within view of the city, residents in Denver and 

Seattle may well have different preferences for urban visibility. For example, the 

significant differences in weather between those two cities might make 

summertime visibility very important in Seattle, but wintertime visibility not as 

important. Denver, with clear weather on many days throughout the year, may 

have a very different set of preferences for both winter and annual visibility. 

All cities have their own unique special visibility circumstances. Whether because 

of a well known urban skyline (e.g., Chicago), a famous bridge (e.g., San 

Francisco) or tall structures (e.g., the St. Louis Arch or Seattle Space Needle), 

their own unique surrounding terrain or ocean (e.g., the Los Angeles basin 

mountains and ocean), or many other possibilities, it is possible that location 

really does matter, and preferences do differ in important ways in different cities 

or regions. 

The practical project design question is how can we determine if visibility 

preferences do differ by location. A number of specific implications arise from 

this topic. How many cities are needed as sites for focus group or survey projects 

in order to provide sufficient data to expand our knowledge in a meaningful way? 

What methods can be used to investigate this issue? What is the scope, funding 

and timeframe needed to conduct such investigations? 

An alternative approach is whether there are attributes that can be used to group 

cities in such a way that all cities within a group can be treated as having 

sufficiently similar preferences. While identifying such groupings (by region or 

using some other method) would not avoid all uncertainty about precise benefits 

estimation, it would go a long way to relieving the need to conduct a project in 

each city. While it may be possible to conduct a high quality investigation in 5 or 

10 cities if necessary, it is impractical to conduct detailed projects in 100 or more 

cities. 

A related question is how many focus groups, and how many participants at each, 

need to be help in any city to obtain sufficient information to meaningfully 

compare the results from multiple cities. 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 12 

A significant challenge (and opportunity) is to design project in such as way as to 

investigate this issue, help reach a conclusion about whether a national approach 

will be sufficient, and (if necessary) determining what city-specific attributes 

could be used for eventual groupings. 

Issue # 6: Joint Benefit or “Mental Accounts” 

Key Question: Can people separate visibility from other air quality related issues, 

especially health concerns? 

Background Discussion: 

When looking at an obscured visibility scene, either in a photograph or viewing it 

live, a viewer receives information about the overall air quality. This information 

can be used as they consider their preferences for visibility per se, but their 

preferences for visibility will also be influenced by their concerns about risks to 

human health. Concerns for other air quality welfare and ecological concerns may 

play a role as well. To the extent individuals consider air quality or visibility at 

all, the typical individual has not separated his/her preferences into separate 

components (or “mental accounts”) for individual benefit categories. 

Understanding the mental accounts of observed air quality and visibility, and 

disentangling the intertwined preferences, can be a substantial challenge for both 

visibility preference and valuation analysis. 

Many research projects investigating preferences air quality use an overall metric 

such as Visual Air Quality (VAQ). For the purposes of some VAQ research, it is 

not necessary to separate the components of the joint benefits (e.g., health and 

welfare as well as visibility will be improved simultaneously with improving air 

quality).1

 In these studies, the goal is to understand preferences for overall air 

quality, without regard for identifying the role of health and visibility 

individually. 

However, for certain of EPA’s purposes, isolating the preferences for visibility 

from preferences for other air quality-related benefit categories may be essential. 

 

1

 The benefit improvements are not necessarily proportional however. For example, the mix of chemical 

species involved in an improvement of 1 μg/m3 of PM2.5 concentration is not known be important in 

estimating health risks. The mix does make a difference in visibility, however, because the same mass of 

sulfate particles scatter light (i.e., degrade visibility) much more than road dust particles. 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 13 

Failing to adequately identify separable preferences can lead to double counting 

in an economics benefits analysis, which would diminish its usefulness in the 

context of estimating the economic benefits or value of improved urban visibility. 

Economic benefits are relevant both in EPA’s policy analysis associated with 

setting alternative primary and secondary National Ambient Air Quality 

Standards. The project would also support the subsequent regulatory impact 

assessment conducted by EPA on other proposed and final rules, including 

implementation-related rules. An important question for the workshop is whether 

carefully dealing with intertwined mental accounts is also critical component of 

conducting a useful preference-oriented project. 

While joint benefits are a major challenge in visibility investigations, there are 

applied approaches that can be used to help address the multiple attribute issue. 

These methods are referred to as conjoint, or multi-attribute, analytical 

approaches. This issue may become one of the dominating design considerations 

for any urban visibility project, particularly a project including visibility 

valuation. A specific question is which of the available multi-attribute available 

research methods (especially survey instrument design and question formulation) 

would be most appropriate for separating the multiple attributes associated with 

urban visibility and air quality improvements? 

Issue # 7: Number and composition of survey respondents

Key Question: How many, and what type, of people would we need to conduct a useful 

survey project? 

Background Discussion: 

A number of additional questions about the number of survey respondents, and 

areas of the country to include in a survey arise when considering the possible 

next steps beyond an initial focus group approach. Considering these issues may 

become a factor in developing the initial phase of an investigation, including 

developing the objectives of a focus group project and selecting locations for 

focus group. 

One fundamental question is how many survey respondents are needed in a full 

field survey. The potential for heterogeneous preferences between cities was 

discussed in Issue # 4, but preferences will also differ between people living in 

the same city. The more people’s preferences vary, the larger the number of 

survey respondents needed to produce a satisfactory estimate of central preference 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 14 

tendencies, or to identify whether substantially different preferences exist among 

different portions of the population. Without having some information (or 

estimates) about how widely individual preferences differ, it is impossible to 

mathematically estimate an appropriate target for the number of completed survey 

responses. 

The sampling strategy, for both a focus group phase and a survey phase project, is 

another basic design question. The central questions are what is the demographic 

profile of the desired audience, and how will recruitment (for either phase) be 

conducted? For example, whether to include non-English speakers in the urban 

visibility project, and at what stage (focus group or survey), has important 

ramifications as to how a project could be conducted. Targeting recruitment to 

include any narrow population group (such as highly educated, low income, racial 

minorities) has implications for the strategies for selecting focus group locations, 

recruitment methods, etc. Another question is whether to do new, population-wide 

recruitment for the survey, and if so what population lists to use (such as phone 

book, voter or automobile registrations, home ownership, or random digit 

dialing). Alternatively, some survey-based valuation research uses already 

established representative groups of consumers (such as provided by Knowledge 

Networks, Inc. and other vendors), which can offer significant cost and timing 

advantages. 

Specific detailed questions that would have to be addressed in designing a survey 

include: Do we want both local residents and tourists/visitors? Those who moved 

to location recently as adults, or only those who were born there? Do preferences 

differ for people who choose to work the night shift versus day? Indoor workers 

or outdoor workers? Such survey design questions could be explored in the focus 

group phase if sufficient variation in participant characteristics were achieved. 
Stratus Consulting Urban Visibility Background Paper, 8/7/08 

Page 15 

Issue # 8: Payment vehicle 

Key Question: What type of valuation question can be used for urban visibility? 

Background Discussion: 

While the inherent joint benefit problem will likely lead to using a conjoint (also 

known as an attribute-based) approach in investigating valuation, that does not 

solve the issue of the form the valuation questions will take. Visibility, along with 

many other environmental effects, is not naturally bought or sold in a 

marketplace, and people are not accustomed to thinking about values for 

nonmarket environmental goods. There are many possibilities that have been 

developed in valuation survey work of environmental topics (as well as other 

settings involving preferences for complex tradeoffs) to help people to think 

clearly about monetary tradeoffs. 

The context of the survey questions is important, and survey methods work best 

when there is an understandable connection between the environmental good in 

question and how the costs of control would be paid. Fitting the question context 

to the situation is an important aspect of designing a successful survey instrument. 

There are a wide range of possibilities about how to present the visibility 

valuation questions, such as in the context of electricity price increases, or in 

likely voting on a ballot referendum initiative, or acceptability of a transportationrelated emission reduction program, or property tax increases, etc. 

While more specific questions about exact survey instrument design may be 

appropriately left for later detailed project development, the type of diverse 

experts expected to be involved with the expert workshop (including visibility, 

emissions, air control policy, and stated preference experts) will provide an 

excellent opportunity to consider the most appropriate context for an urban 

visibility valuation project. 
 

Stratus Consulting Memorandum (11/18/2008) 

Page 28 

SC11568

L. Valuation and Preference Literature 
September 30, 2008 Stratus Consulting Inc. p. 1 

Urban Visibility Valuation and Preference 

The Clean Air Act ∫302(h) defines public welfare to include the effects of air pollution on 

“...visibility, ... and personal comfort and wellbeing.“ Though good visibility conditions in Class I 

(e.g. National Parks) and wilderness areas have long been recognized as important to the public 

welfare (see discussions in EPA (2004 and 2005) and Chestnut and Dennis (1997)), visibility 

conditions in urban areas also contribute to the public welfare. Visibility impairment may be caused 

by either natural or manmade conditions (or both), but it is only impairment that occurs as a result 

of air pollution (either alone or in combination with water vapor or other atmospheric conditions) 

that can be mitigated by regulations such as the Regional Haze Rule (40 CFR 51.300 through 309) 

or the Secondary National Ambient Air Quality Standards (NAAQS). Visibility impairment 

resulting from air pollution is referred to as visual air quality (VAQ). 

Visibly poor air quality causes people to be concerned about substantive health risks, but degraded 

VAQ adversely affects people in additional ways. These include the aesthetic benefits of better 

visibility, improved road and air safety, and enhanced recreation in activities like hiking and 

bicycling. Because the human health impacts of air pollution are regulated under the Primary 

NAAQS, it is necessary to separate out the aesthetic and wellbeing components associated with the 

visibility condition produced by a given level of air pollution when assessing the need for additional 

regulation to protect the public welfare effect of visibility under the Secondary NAAQS. The degree 

to which previous human preference and valuation studies for VAQ have adequately made this 

distinction and separation is an important issue in applying results from available studies in a 

Secondary NAAQS (or benefits estimation for any policy effecting VAQ) context. The remainder 

of this discussion is focused on the aesthetic and wellbeing qualities associated with a given VAQ 

in urban areas. 

The term “urban visibility“ is used to refer to VAQ throughout a city or metropolitan area. Urban 

visibility includes the VAQ conditions in all locations that people experience in their daily lives, 

including scenes such as residential streets and neighborhood parks, commercial and industrial 

areas, highway and commuting corridors, central downtown areas, and views from elevated 
September 30, 2008 Stratus Consulting Inc. p. 2 

locations providing a broad overlook of the metropolitan area. Thus urban visibility, which is 

sometimes referred to as ‘residential visibility’, encompasses more than the visibility conditions 

only at an individual’s specific place of residence, but all the VAQ they see on a regular basis. 

Urban visibility includes not only major cities, but VAQ conditions in smaller towns and cities. The 

key distinction is between visibility conditions in urban and suburban locations and visibility in 

rural or wilderness settings such as the Class 1 areas defined by the Clean Air Act, which include 

National Parks and similar natural settings. 

Visibility has direct significance to people’s enjoyment of daily activities and their overall 

wellbeing. Visibility conditions can be described both as an aesthetic quality as well as a 

scientifically measurable set of atmospheric conditions. Due to the subjective nature of aesthetics, 

people’s preferences with respect to visibility are difficult to express or quantify, but people have 

expressed in many different ways that they enjoy and value a clear view. A number of social 

science disciplines have undertaken to link perceived urban visibility to an array of effects 

reflecting the overall desire for good VAQ, and the benefits of improving currently degraded VAQ. 

This wide range of diverse studies have identified types of benefits of good VAQ in addition to 

those directly connected with air-pollution related health effects such as respiratory diseases and 

premature mortality. 

For example, psychological research has demonstrated that people are emotionally affected by VAQ 

such that their overall sense of wellbeing is diminished (e.g., Bickerstaff and Walker, 2001). 

Researchers have also shown that perception of pollution is correlated with stress, annoyance, and 

symptoms of depression (Mace et al., 2004; Evans and Jacobs, 1982, Jacobs et al., 1984). 

Sociological research has demonstrated that VAQ is deeply intertwined with a “sense of place,“ 

effecting people’s sense of the desirability of a neighborhood quite apart from the actual physical 

conditions of the area (e.g., Elliot et al, 1999, Howel et al, 2002, Day, 2007, SAMI, 2002). Public 

policy research finds that people think it is important to protect visibility, and accept the concept of 

setting standards to protect visibility (e.g., Ely et al., 1991, Pryor, 1996, Abt Associates, 2001, BBC 

Research and Consulting, 2003). Finally, economic valuation research has measured the amount of 

money that people are willing to pay to protect or improve both urban visibility (e.g., summary 
September 30, 2008 Stratus Consulting Inc. p. 3 

review in Chestnut and Dennis, 1997, and Beron et al., 2001) and natural locations such as National 

Parks and other locations defined by the Clean Air Act as Class I visibility areas (e.g., summary 

review in Chestnut and Dennis, 1997). 

The purpose of the remainder of this paper is to review four urban preference studies, as well as one 

new urban visibility valuation study not previously discussed in an EPA Criteria Document or 

OAQPS Staff Paper. This literature is relevant to the review of a Secondary NAAQS standard 

concerning VAQ, as well as a review of potentially including urban visibility valuation in a damage 

function approach (separately estimating individual effect categories) an economic benefit analysis. 

Urban visibility has been examined in two types of studies directly relevant to the NAAQS process: 

urban visibility preference studies and urban visibility valuation studies. Both types of studies are 

designed to evaluate individuals’ desire (or demand) for good VAQ where they live, using different 

metrics to evaluate demand. Urban visibility preference studies examine individuals’ demand by 

investigating the basic question “what level of visibility degradation is unacceptable,” while 

economic studies examine demand by investigating “how much would you be willing to pay to 

improve visibility.“ 

Urban Visibility Preference Studies 

One group of urban visibility research projects focused on identifying preferences for urban VAQ 

without necessarily estimating the economic value of improving visibility. This group of preference 

studies used a common focus group method to estimate the level of visibility impairment that 

respondents described as “acceptable.“ The specific definition of acceptable was largely left to each 

individual respondent, allowing each to identify their own preferences. 

There are three completed studies that used this method, and one additional pilot study (designed as 

a survey instrument development project) that provides additional information. The completed 

studies were conducted in Denver, Colorado (Ely et al., 1991), two cities in British Columbia, 

Canada (Pryor, 1996), and Phoenix, Arizona (BBC, 2003). The pilot study was conducted in 

Washington, DC (Abt Associates, 2001). 
September 30, 2008 Stratus Consulting Inc. p. 4 

Each study collected information in a focus group setting, presenting slides depicting various 

visibility conditions. All four studies used photographs of a single scene from the study’s city; each 

photo included images of the broad downtown area and spreading out to the hills or mountains 

composing the scene’s backdrop. The maximum sight distance under good conditions varied by 

city, ranging from 8 kilometers in Washington, DC to mountains hundreds of kilometers away in 

Denver. Multiple photos of the same scene were used to present approximately 20 different levels 

of visibility impairment. The Denver and British Columbia studies used actual photographs taken in 

the same location to depict various visibility conditions. The Phoenix and Washington, DC pilot 

study used photographs prepared using the WinHaze software from Air Resource Specialists (ARS). 

WinHaze is a computer-imaging software program that simulates visual air quality differences of 

various scenes, allowing the user to “degrade“ an original near-pristine visibility condition 

photograph to create a photograph of each desired VAQ level. 

One notable finding of the three visibility preference studies and the one pilot study is the general 

degree of consistency in the median preferences for an acceptable level of visibility degradation. 

The range of median acceptable preference level from the four studies is 19 to 25 deciviews (dv), 

the preferred measure1

 of visibility impairment. Measured in terms of visual range (VR), the median 

acceptable levels in the four studies are between 30 and 55 km. 

Table 1 summarizes the primary design and summary results of the four studies. A brief description 

of each study follows.

 

1

There are 3 common visibility metrics. Extinction, measured in inverse Megameters (Mm-1), is proportional to the 

amount of light lost as it travels over 1 million meters (1000 km). Deciview (dv) is a unitless metric defined in 

terms of extinction, but scaled in such a way as to be perceptually correct. A 1 dv change on a day with 20 dv 

conditions will be perceived as the same change on a day with excellent visibility (5 dv). Visual range, measured 

in km or miles, is inversely related to extinction and measures how far away a large black object against the 

horizon sky. The colors and fine detail of many objects will be lost at distance than the visual range. The 

following diagram (from Malm, 1999) shows the relationship between deciview, extinction and visual range. 
September 30, 2008 Stratus Consulting Inc. 

Table 1 Summary of Urban Visibility Preference Studies 

Denver, CO Phoenix, AZ 2 British Columbia cities Wa

Report Date 1991 2003 1996 Duration of session 45 min 50 minutes Compensation None (civic groups) $50 

None (class room 

exercise) 

# focus group sessions 17 

27 total at 6 locations, 

Including 3 in Spanish 4 

# participants 214 385 180 Age range adults 18-65+ University students Annual or seasonal Wintertime Annual Summertime # total scenes presented 

Single scene of downtown with mountains in background 

Single scene of downtown and mountains, 42 km maximum distance 

Single scene from each city 

Singand max

# of total visibility conditions presented 20 levels (+ 5 duplicates) 21 levels (+ 4 duplicates) 

20 levels (10 each from each city) 20 l

Source of slides 

Actual photos taken between 9am and 3pm WinHaze 

Actual photos taken at 1pm or 4pm Win

Medium of presentation Slide projection Slide projection Slide projection SlidRanking scale used 7 point scale 7 point scale 7 point scale 7 poVisibility range presented 11 to 40 dv 15 to 35 dv 

13 to 25 dv (Chilliwack) 13.5 to 31.5 dv (Abbotsford) 9 to 

Health issue directions 

Ignore potential health impacts; visibility only 

Judge solely on visibility, do not consider health 

Judge solely on visibility, do not consider health 

Hea“Foc

Key Questions asked a) Rank VAQ (1-7 scale) a) Rank VAQ (1-7 scale) a) Rank VAQ (1-7 scale) a) R

b) Is each slide “acceptable“ 

b) Is each slide “acceptable“ 

b) Is each slide “acceptable“ 

b) Is “acc

c) “How much haze is too much?“ 

c) How many days a year would this picture be “acceptable“ 

c) if houacce

d) v

Mean dv found “acceptable“ 20.3 dv 23 to 25 dv 

~23 dv(Chilliwack), 

~19 dv(Abbotsford) ~
September 30, 2008 Stratus Consulting Inc. p. 6 

Denver, Colorado Urban Visibility Preference Study 

The Denver urban visibility preference study (Ely et al., 1991) was conducted on behalf of the 

Colorado Department of Public Health and Environment (CDPHE). The study conducted a series 

of focus group sessions with 17 civic and community groups in which a total of 214 individuals 

were asked to rate slides. The slides depicted varying levels of VAQ for a well-known Denver 

vista, including a broad view of downtown Denver with the mountains to the west composing the 

scene’s background. The participants were instructed to base their judgments on three factors: 

1) the standard was for an urban area, not a pristine national park area where the standards 

might be more strict; 

2) the level of an urban visibility standard violation should be set at a VAQ level considered 

to be unreasonable, objectionable, and unacceptable visually; and 

3) judgments of standards violations should be based on visibility only, not on health 

effects. 

Participants were shown 25 randomly ordered slides of actual photographs. The visibility 

conditions presented in the slides ranged from 11 to 40 dv, approximating the 10th to 90th

percentile of wintertime visibility conditions in Denver. The participants rated the 25 slides 

based on a scale of 1 (poor) to 7 (excellent), with 5 duplicates included. They were then asked to 

judge whether the slide would violate what they would consider to be an appropriate urban 

visibility standard (i.e., whether the level of impairment was “acceptable“ or “unacceptable“). 

The individual’s judgment of a slide’s VAQ and whether the slide violated a visibility standard 

were highly correlated (Pearson correlation coefficient greater than 80%), as were the VAQ 

ratings and the yes/no “acceptable“ response. The participant’s median response was that a 

visibility level of 20.3 dv (extinction coefficient bext = 76Mm-1, or VR ~ 51 km) was judged as 

“acceptable.“ The CDPHE subsequently established a Denver visibility standard at this level 

(defined as bext = 76Mm-1), based on the median 50% acceptability findings from the study. 
September 30, 2008 Stratus Consulting Inc. p. 7 

Phoenix, Arizona Urban Visibility Preference Study 

The Phoenix urban visibility preference study (BBC Consulting, 2002) was conducted on behalf 

of the Arizona Department of Environmental Quality. The Phoenix study patterned its focus 

group survey process after the Denver study. The study included 385 participants in 27 separate 

focus group sessions. Participants were recruited using random digit dialing to obtain a sample 

group designed to be demographically representative of the larger Phoenix population. Focus 

group sessions were held at six neighborhood locations throughout the metropolitan area to 

improve the participation rate. Three sessions were held in Spanish in one region of the city with 

a large Hispanic population (25%), although the final overall participation of native Spanish 

speakers (18%) in the study was modestly below the targeted level. Participants received $50 as 

an inducement to participate. 

Participants were shown a series of 25 images of the same vista of downtown Phoenix, 

with South Mountain in the background at a distance of about 40 km. Photographic slides of the 

images were developed using WinHaze. The visibility impairment levels ranged from 15 to 35 

dv (the extinction coefficient, bext , range was approximately 45Mm-1 to 330Mm-1, or a visual 

range of 87 to 12 km). Participants first individually rated the randomly shown slides on a VAQ 

scale of 1 (unacceptable) to 7 (excellent). Participants were instructed to rate the photographs 

solely on visibility, and to not base their decisions on either health concerns or what it would cost 

to have better visibility. Next, the participants individually rated the randomly ordered slides as 

“acceptable“ or “unacceptable,” defined as whether the visibility in the slide is unreasonable or 

objectionable. Better visibility conditions (15 dv and 20 dv) were judged “acceptable“ by 90 

percent of all participants. At 24 dv nearly half of all participants thought the VAQ was 

“unacceptable,“ with almost three-quarters judging 26 dv as unacceptable. 

The Phoenix urban visibility study formed the basis of the decision of the Phoenix Visibility 

Index Oversight Committee for a visibility index for the Phoenix Metropolitan Area (Arizona 

Department of Environmental Quality, 2003). The Phoenix Visibility Index establishes an 

indexed system with 5 categories of visibility conditions, ranging from “Excellent“ (14 dv or 
September 30, 2008 Stratus Consulting Inc. p. 8 

less) to “Very Poor“ (29 dv or greater). The “Good“ range is 15 to 20 dv. The environmental 

goal of the Phoenix urban visibility program is to achieve continued progress through 2018 by 

moving the number of days in lower quality categories into better quality categories. 

British Columbia, Canada Urban Visibility Preference Study 

The British Columbia (BC) urban visibility preference study (Pryor, 1996) was conducted on 

behalf of the BC Ministry of Environment. The BC study conducted focus group sessions that 

were also developed following the methods used in the Denver study. Participants were students 

at the University of British Columbia , who participated in one of four focus group sessions with 

between 7 and 95 participants. A total of 180 respondents completed surveys (29 did not 

complete the survey). 

Participants in the study were shown slides of two suburban locations in British Columbia: 

Chilliwack and Abbotsford. Using the same general protocol as the Denver study, Pryor found 

that responses from this study found the acceptable level of visibility was 23 dv in Chilliwack 

and 19 dv in Abbotsford. Pryor (1996) discusses some possible reasons for the variation in 

standard visibility judgments between the two locations. Factors discussed include the relative 

complexity of the scenes, potential bias of the sample population (only University students 

participated), and the different levels of development at each location. Abbotsford (population 

130,000) is an ethnically diverse suburb adjacent to the Vancouver Metro area, while Chilliwack 

(population 70,000) is an agricultural community 100 km east Vancouver in the Frazier Valley. 

The British Columbia urban visibility preference study is being considered by the B.C. Ministry 

of the Environment as a part of establishing urban and wilderness visibility goals in British 

Columbia. 

Washington, DC Urban Visibility Pilot Preference Study 

The Washington, DC urban visibility pilot study (Abt Associates 2001) was conducted on behalf 

of the EPA, and was designed to be a pilot focus group study, an initial developmental trial run 

of a larger study. The intent of the pilot study was to study both focus group method design and 
September 30, 2008 Stratus Consulting Inc. p. 9 

potential survey questions. Due to funding limitations, only a single focus group session was 

held, consisting of one extended session with 9 participants. No further urban visibility focus 

group sessions were held in Washington, DC. 

Due to the small number of participants, it is not possible to make statistical inferences about the 

opinions of the general population. The study does, however, provide additional useful 

information about urban visibility studies, potentially helping to both better understand previous 

studies as well as design future studies. 

The study also adopted the general Denver study method, modifying it as appropriate to be 

applicable in an eastern urban setting which has substantially different visibility conditions than 

any of the three western locations of the other preference studies. Washington’s (and the entire 

East) visibility is typically substantially worse than western cities, and has different 

characteristics. Washington’s visibility impairment is primarily a uniform whitish haze 

dominated by sulfates, relative humidity levels are higher, the low lying terrain provides 

substantially shorter maximum sight distances, and many residents are not well informed that 

anthropogenic emissions impairs visibility on hazy days. 

The Washington focus group session included questions on valuation, as well as on preferences. 

The focus group was asked to state their preferences measured in an increase in the general cost 

of living for certain levels of improvement in visibility on a typical summer day. A general cost 

of living approach is one payment vehicle approach that can be used in willingness to pay 

studies, especially for environmental issues arising from multiple diverse emission sources (e.g., 

transportation, electricity generation, industry, etc.) making a specific price increase potentially 

misleading. 

The first part of the focus group session was designed to be an hour long, and was comparable to 

the focus group sessions in the Denver and Phoenix studies. A single scene was used; a 

panoramic shot of the Potomac River, Washington mall and downtown Washington, DC. In the 

first part of the session people were asked to rate the VAQ of 25 photographs (prepared using 
September 30, 2008 Stratus Consulting Inc. p. 10 

WinHaze, and projected on a large screen), judge the acceptability of visibility level in each 

slide, and answer the valuation questions. The second half of the session, however, was a 

moderated discussion session about the format and content of the first phase of the session. In 

this moderated discussion, participants were asked about their understanding of each questions 

asked in the first half of the session. Particular issues in designing a focus group session were 

also explored. Important participant comments included: 

1) Participants had been asked how they reacted to the initial direction to base their answers 

only on visibility, but health was never explicitly mentioned by the focus group 

moderator. Participants strongly agreed with the decision to not mention that health 

effects are associated with visibility impairment. They understood the directions as 

meaning they should ignore health issues, and said their answers would have been 

different if they included health as well as visibility in their judgments. 

2) Differentiating between haze and weather conditions was difficult. Weather was not 

discussed in the focus group session, and the photographs were WinHaze altered photos 

with identical weather conditions. Participants mentioned they were still confused about 

the role of weather and humidity in the different visibility conditions presented in the 

photos. 

3) Questions about how many hours an impairment level would be acceptable were 

confusing. Most participants were normally indoors during most of the day, so questions 

about duration of outdoor conditions were difficult to answer. 

4) Participants strongly agreed that not mentioning the purpose of the study, or the sponsor, 

until the very end (after all the questions were answered) was viewed as very important. 

Most felt this information would have influenced their answers. 

Urban Visibility Valuation Studies 

The economic importance of urban visibility has been examined by a number of studies designed 

to quantify the benefits (or willingness to pay) associated with potential improvements in urban 

visibility. Urban visibility valuation research prior to 1997 was summarized in Chestnut and 

Dennis (1997), and were also described in the 2004 Air Quality for Particulate Matter (p. 4-186 

to 4-190, EPA, 2004) and the 2005 OAQPS PM NAAQS Staff Paper (EPA, 2005). These 
September 30, 2008 Stratus Consulting Inc. p. 11 

reviews summarize 34 estimates (based on different cities or model specifications) from six 

different studies. Since the mid 1990s, however, only one new valuation study of urban visibility 

has been published. 

One urban visibility benefit assessment not included in those reviews is “The Benefits of 

Visibility Improvement: New Evidence from the Los Angeles Metropolitan Area“ (Beron et al., 

2001). Rather than a contingent valuation method (CVM) technique used in the majority of other 

urban visibility valuation studies, Beron et al. used a housing market hedonic technique. The 

housing hedonic methods were used in previous urban visibility studies by Murdoch and Thayer, 

1988, and Trijonis et al., 1985. A housing market hedonic study views a housing unit as 

composed of a bundle of attributes, and uses housing sale price data from a large number of units 

in a metropolitan area to estimate the value of each component. Hedonic pricing has been used to 

estimate economic values for environmental effects that have a direct effect on housing market 

values. It relies on the measurement of differentials in property values under various 

environmental quality conditions including air pollution, visibility and other environmental 

amenities such as access to nearby beaches and parks, as well as by physical attributes of the 

house and attributes of the neighborhood. 

 

Beron et al. obtained data on approximately 840,000 owner-occupied, single family housing 

sales between 1980 and 1995 from the California South Coast Air Basin (composed of Los 

Angeles and Orange Counties, and the portions of Riverside and San Bernardino Counties in the 

greater metropolitan area). The real estate data included information on the sale price of the 

house, 13 housing attributes (square footage, number of bathrooms, etc.), 9 neighborhood 

attributes (percent poverty, school quality, FBI crime index, etc.), and three air pollution 

variables: ozone, particulates (measured by total suspended particulates, or TSP), and visibility. 

Visibility was measured as the annual average of visual range, measured in miles, and was 

obtained from seven airports within the study region. The visibility range was from 12.4 miles 

(Los Angeles International Airport, 1991) to 31.9 miles (Palm Springs Airport, 1995). Ozone 

data (39 monitors) and TSP data (40 monitors) were obtained from the South Coast Air Quality 

Management District. Annual mean values for each year were calculated for ozone and TSP. 
September 30, 2008 Stratus Consulting Inc. p. 12 

Beron et al. presented results for a hypothetical basin-wide 20% visibility improvement, or an 

increase from 15.3 to 18.4 miles, which is equivalent to approximately 27.6 dv to 25.8 dv. The 

initial results reflect the change in the purchase price of a house associated with this difference in 

VAQ, which can be interpreted as a present value of a stream of annual values over the lifetime 

of the house. The authors therefore selected a time horizon (30 years) and an interest rate (8%) to 

calculate an annual per household benefit per dv ranging from $484 to $1,756. The Beron results 

are higher than the CVM-based values summarized in Chestnut and Dennis (1997), which ranged 

from $12 to $132 per dv. It should be noted that the $132 CVM values cited by Chestnut and 

Dennis is from a study in the Los Angeles area (Brookshire et al., 1979). The Beron et al. results 

are also higher than the Trijonis et al. hedonic study in the Los Angeles area, which had a range 

of $134 to $360 per dv. All values reported here are in terms of 1994 prices. 

A critical question for all urban visibility valuation studies is the extent to which the estimated 

values strictly reflect preferences for visibility, and do not include a component of preferences 

for reducing health risk from air pollution. The ability to isolate the value of visibility from 

within the collection of intertwined benefits from visual air quality, which is inherently multiattributed, is a challenge for all visibility valuation studies. Each study attempts to isolate 

visibility from other effect categories, but different studies take different approaches. 

Beron et al. include two measures of air pollution directly related to health effects in their 

housing market hedonic study, ozone and particulates (using TSP as the metric for particulates), 

as well as visibility. They argue that the presence of the two health-related pollution levels 

results in a estimated hedonic demand function for visibility that successfully separates the 

health component of demand for overall air quality from the visibility component. An alternative 

interpretation is that the estimated visibility function still includes a component of health risk 

because the housing market data does not support completely isolating the demand for visibility 

(due to correlated variables, omitted variables, measurement error, model specification error, 

etc.) from demand for health risk reductions measured by the two health related air quality 

metrics. 
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A key issue in interpreting the Beron et al. results is whether the objective measures of air quality 

characteristics (e.g., visibility, particulate matter concentrations, etc.) capture people’s 

perceptions of the different aspects of air quality in a given location. To the extent the people 

simultaneously use what they see regarding VAQ as an indicator of the overall air quality 

including potential health risks, then including all the measures in the equation is not necessarily 

sufficient to isolate one effect from the other. 

References 

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