Welfare Risk and Exposure Assessment 

for Ozone

First External Review Draft
DISCLAIMER

This preliminary draft document has been prepared by staff from the Ambient Standards Group, 

Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency. Any 

opinions, findings, conclusions, or recommendations are those of the authors and do not 

necessarily reflect the views of the EPA. This document is being circulated for informational 

purposes and to facilitate discussion with the Clean Air Scientific Advisory Committee 

(CASAC) on the overall structure, areas of focus, and level of detail to be included in an external 

review draft Policy Assessment, which EPA plans to release for CASAC review and public 

comment later this year. Questions related to this preliminary draft document should be 

addressed to Travis Smith, U.S. Environmental Protection Agency, Office of Air Quality

Planning and Standards, C539-07, Research Triangle Park, North Carolina 27711 (email: 

smith.jtravis@epa.gov). 
EPA 452/P-12-004

July 2012

Welfare Risk and Exposure Assessment for Ozone

First External Review Draft

U.S. Environmental Protection Agency

Office of Air and Radiation

Office of Air Quality Planning and Standards

Health and Environmental Impacts Division

Risk and Benefits Group 

Research Triangle Park, North Carolina 27711
This page left intentionally blank.
i

TABLE OF CONTENTS

Table of Contents....................................................................................................................................... i

List of Acronyms/Abbreviations............................................................................................................. iv

1 Introduction........................................................................................................................................ 1-1

1.1 History.................................................................................................................................... 1-3

1.2 Current Risk and Exposure Assessment: Goals and Planned Approach ............................... 1-6

1.3 Organization of Document..................................................................................................... 1-6

2 Conceptual Framework..................................................................................................................... 2-1

2.1 O3 Chemistry.......................................................................................................................... 2-2

2.2 Sources of O3 and O3 Precursors.............................................................................................. 2-4

2.3 Ecological Effects.................................................................................................................. 2-5

2.4 Ecosystem Services................................................................................................................ 2-8

2.5 Conclusions......................................................................................................................... 2-15

3 Scope.................................................................................................................................................... 3-1

3.1 Overview of Exposure and risk Assessment from Last Review............................................ 3-2

3.1.1 Exposure Characterization............................................................................................... 3-2

3.1.2 Assessment of Risks to Vegetation.................................................................................. 3-4

3.2 Overview of Current Assessment Plan .................................................................................. 3-6

3.2.1 Air Quality Considerations.............................................................................................. 3-8

3.2.2 National O3 Exposure Surface ......................................................................................... 3-8

3.3 Ecological Effects of Exposure............................................................................................ 3-10

3.3.1 National Scale Assessment ............................................................................................ 3-10

3.3.2 Case Study Areas........................................................................................................... 3-11

3.4 Ecosystem Services Evaluation ........................................................................................... 3-12

3.4.1 National Scale Assessment ............................................................................................ 3-13

3.4.2 Case Study Analysis ...................................................................................................... 3-14

3.5 Uncertainty and Variability.................................................................................................. 3-15

4 Air Quality Considerations............................................................................................................... 4-1

4.1 Introduction............................................................................................................................ 4-1

4.2 Overview of O3 Monitoring and Air Quality ......................................................................... 4-1
ii

4.3 Overview of Air Quality Inputs to Risk and Exposure Assessments .................................... 4-3

4.3.1 Recent Air Quality ........................................................................................................... 4-3

4.3.2 Air Quality After simulating “Just Meeting” Current O3 Standard ................................. 4-6

5 Ecological Effects............................................................................................................................... 5-1

5.1 Introduction............................................................................................................................ 5-1

5.2 Relative Biomass Loss........................................................................................................... 5-2

5.2.1 Species Level Analysis.................................................................................................... 5-5

5.2.2 Abundance Weighted Relative Biomass Loss............................................................... 5-14

5.2.3 Relative Biomass Loss in Federally Designated Areas ................................................. 5-21

5.2.4 National Park Case Study Areas.................................................................................... 5-29

5.3 Visible Foliar Injury............................................................................................................. 5-36

5.3.1 National-Scale Analysis of Foliar Injury ....................................................................... 5-37

5.3.2 Updated Assessment of Risk of Visible Foliar Injury in National Parks ...................... 5-38

5.3.3 National Park Case Study Areas.................................................................................... 5-46

5.4 Discussion............................................................................................................................ 5-47

6 Ozone Risk to Ecosystem Services.................................................................................................... 6-1

6.1 Introduction............................................................................................................................ 6-1

6.2 National Scale Ecosystem Serices Assessment ..................................................................... 6-1

6.2.1 Supporting Services......................................................................................................... 6-5

6.2.2 Regulating Services ......................................................................................................... 6-6

6.2.3 Provisioning Services..................................................................................................... 6-10

6.2.4 Cultural Services............................................................................................................ 6-18

6.3 Case Study Analysis .................................................................................................................. 6-27

6.3.1 Southeast Region – Great Smoky Mountains National Park......................................... 6-28

6.3.2 Intermountain Region – Rocky Mountain National Park .............................................. 6-33

6.3.3 Pacific West Region – Sequioa/Kings Canyon National Parks..................................... 6-36

6.3.4 Urban Case Study .......................................................................................................... 6-38

6.4 Discussion............................................................................................................................ 6-39

7 Synthesis.............................................................................................................................................. 7-1

7.1 Summary of Key Results of Biomass Loss Risk Assessment ............................................... 7-1

7.2 Summary of Key Results of Foliar Injury Risk Assessment ................................................. 7-2
iii

7.3 Summary of Key Results for Ecosystem Services Risk Assessment .................................... 7-3

7.4 Observations .......................................................................................................................... 7-5

8 References........................................................................................................................................... 8-1
July 2012 iv DRAFT - Do Not Quote or Cite

LIST OF ACRONYMS/ABBREVIATIONS

AGSIM Agriculture Simulation Model

AQCD Air Quality Criteria Document

AQS Air Quality System

CAA Clean Air Act

CAL FIRE California Department of Forestry and Fire Protection

CASAC Clean Air Science Advisory Committee

CASTNET Clean Air Status and Trends Network

CH4 methane

CMAQ Community Multi-scale Air Quality

CO2 carbon dioxide

C-R Concentration Response Function

CSTR continuous stirred tank reactors

EGU electric generating unit

EPA U.S. Environmental Protection Agency

ESRI Environmental Systems Research Institute, Inc.

FACA Federal Advisory Committee Act

FACE Free Air CO2 enrichment

FASOM Forest and Agricultural Sector Optimization Model

FASOMGHG Forest and Agriculture Sectors Optimization Model – Greenhouse 

Gas version

FHWAR Fishing, Hunting, and Wildlife-Associated Recreation

FIA U.S. Forest Service Forest Inventory and Analysis

GIS geographic information system

GSMNP Great Smoky Mountains National Park

HNO3 nitric acid

IPCC Intergovernmental Panel on Climate Change

IRP Integrated Review Plan

ISA Integrated Science Assessment

IV Importance Value
July 2012 v DRAFT - Do Not Quote or Cite

MATS Modeled Attainment Test Software

MEA Millennium Ecosystem Assessment

MT metric ton

NAAQS National Ambient Air Quality Standards

NCDC National Climatic Data Center

NCLAN National Crop Loss Assessment Network

NCore National Core 

NEI National Emissions Inventory

NHEERL-WED National Health and Environmental Effects Research Laboratory, 

Western Ecology Division

NO2 nitrite

NOAA National Oceanic and Atmospheric Administration

NOx nitrogen oxides

NPP net primary productivity

NPS National Park Service

NSRE National Survey on Recreation and the Environment

NTFP Non-timber forest products

O3 Ozone

OAQPS Office of Air Quality Planning and Standards

OH hydroxide

OIF Outdoor Industry Foundation

OTC open top chamber

PA Policy Assessment

ppm parts per million

RBL Relative Biomass Loss

REA Risk and Exposure Assessment

RMNP Rocky Mountain National Park

SAB Science Advisory Board

SKCNP Sequoia/Kings Canyon National Park

STE stratosphere-troposphere exchange

USDA U.S. Department of Agriculture
July 2012 vi DRAFT - Do Not Quote or Cite

USFS U.S. Forest Service

USGS U.S. Geological Survey

VNA Voronoi Neighbor Averaging

VOC volatile organic carbon

WTA willingness to accept

WTP willingness to pay
United States

Environmental Protection

Agency

Office of Air Quality Planning and Standards

Health and Environmental Impacts Division

Research Triangle Park, NC

Publication No. EPA-452/P-12-004

 July 2012
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1 1 INTRODUCTION

2 The U.S. Environmental Protection Agency (EPA) is presently conducting a review of 

3 the national ambient air quality standards (NAAQS) for ozone (O3) and related photochemical 

4 oxidants. An overview of the approach to reviewing the O3 NAAQS is presented in the 

5 Integrated Review Plan for the Ozone National Ambient Air Quality Standards (IRP, US EPA, 

6 2011a). The IRP discusses the schedule for the review; the approaches to be taken in developing 

7 key scientific, technical, and policy documents; and the key policy-relevant issues that will frame 

8 our consideration of whether the current NAAQS for O3 should be retained or revised. 

9 Sections 108 and 109 of the Clean Air Act (CAA) govern the establishment and periodic 

10 review of the NAAQS. These standards are established for pollutants that may reasonably be 

11 anticipated to endanger public health and welfare, and whose presence in the ambient air results 

12 from numerous or diverse mobile or stationary sources. The NAAQS are to be based on air 

13 quality criteria, which are to accurately reflect the latest scientific knowledge useful in indicating 

14 the kind and extent of identifiable effects on public health or welfare that may be expected from 

15 the presence of the pollutant in ambient air. The EPA Administrator is to promulgate and 

16 periodically review, at five-year intervals, “primary” (health-based) and “secondary” (welfare17 based) NAAQS for such pollutants. Based on periodic reviews of the air quality criteria and 

18 standards, the Administrator is to make revisions in the criteria and standards, and promulgate 

19 any new standards, as may be appropriate. The Act also requires that an independent scientific 

20 review committee advise the Administrator as part of this NAAQS review process, a function 

performed by the Clean Air Scientific Advisory Committee (CASAC).1

22 The current primary NAAQS for O3 is set at a level of 0.075 ppm, based on the annual 

23 fourth-highest daily maximum 8-hr average concentration, averaged over three years, and the 

24 secondary standard is identical to the primary standard (73 FR 16436). The EPA initiated the 

21

 1 The Clean Air Scientific Advisory Committee (CASAC) was established under section 109(d)(2) of the 

Clean Air Act (CAA) (42 U.S.C. 7409) as an independent scientific advisory committee. CASAC provides advice, 

information and recommendations on the scientific and technical aspects of air quality criteria and NAAQS under 

sections 108 and 109 of the CAA. The CASAC is a Federal advisory committee chartered under the Federal 

Advisory Committee Act (FACA). See 

http://yosemite.epa.gov/sab/sabpeople.nsf/WebCommitteesSubcommittees/CASAC%20Particulate%20Matter%20R

eview%20Panel for a list of the CASAC PM Panel members and current advisory activities. 
1-2

1 current review of the ozone NAAQS on September 29, 2008 with an announcement of the 

2 development of an ozone Integrated Science Assessment and a public workshop to discuss 

3 policy-relevant science to inform EPA’s integrated plan for the review of the ozone NAAQS (73 

4 FR 56581). The NAAQS review process includes four key phases: planning, science 

assessment, risk/exposure assessment, and policy assessment/rulemaking.2 5 A workshop was 

6 held on October 29-30, 2008 to discuss policy-relevant scientific and technical information to 

7 inform EPA’s planning for the ozone NAAQS review. Following the workshop, EPA developed 

8 a planning document, the Integrated Review Plan for the Ozone National Ambient Air Quality 

9 Standards (IRP; US EPA, 2011a), which outlined the key policy-relevant issues that frame this 

10 review, the process and schedule for the review, and descriptions of the purpose, contents, and 

approach for developing the other key documents for this review.3

19 The EPA’s Office of Air Quality Planning and Standards (OAQPS) has developed this 

20 quantitative welfare risk and exposure assessment (REA) describing the quantitative assessments 

21 of exposure to O3 and O3-related risks to public welfare to support the review of the secondary

22 O3 standards. This document is a concise presentation of the conceptual model, scope, methods, 

23 key results, observations, and related uncertainties associated with the quantitative analyses 

24 performed. The REA builds upon the welfare effects evidence presented and assessed in the 

25 ISA, as well as CASAC advice (Samet, 2011) and public comments on a scope and methods 

26 planning document for the REA (here after, “Scope and Methods Plan”, US EPA, 2011b). 

11 In June 2012, EPA 

12 completed the third draft of the ozone ISA, assessing the latest available policy-relevant 

13 scientific information to inform the review of the O3 standards. The Integrated Science 

14 Assessment for Ozone and Related Photochemical Oxidants - Third External Review Draft (ISA;

15 US EPA, 2012), includes an evaluation of the scientific evidence on the welfare effects of O3, 

16 including information on exposure, physiological mechanisms by which O3 might adversely 

17 impact vegetation, and an evaluation of the ecological evidence including information on 

18 reported concentration-response (C-R) relationships for O3-related changes in plant biomass.

 2 For more information on the NAAQS review process see http://www.epa.gov/ttn/naaqs/review.html. 3 On March 30, 2009, EPA held a public consultation with the CASAC Ozone Panel on the draft IRP. The 

final IRP took into consideration comments received from CASAC and the public on the draft plan as well as input 

from senior Agency managers.
1-3

1 Revisions to this draft RA will draw upon the final ISA and will reflect consideration of CASAC 

2 and public comments on this draft.

3 The ISA and REA will inform the policy assessment and rulemaking steps that will lead 

4 to final decisions on the primary O3 NAAQS, as described in the Integrated Review Plan for the 

5 Ozone National Ambient Air Quality Standards. The policy assessment will include staff 

6 analysis of the scientific basis for alternative policy options for consideration by senior EPA 

7 management prior to rulemaking. The PA integrates and interprets information from the ISA 

8 and the REA to frame policy options for consideration by the Administrator. The PA is intended 

9 to link the Agency’s scientific and technical assessments, presented in the ISA and REA, to 

10 judgments required of the Administrator in determining whether it is appropriate to retain or 

11 revise the current O3 standards. Development of the PA is also intended to facilitate elicitation 

12 of CASAC’s advice to the Agency and recommendations on any new standards or revisions to 

13 existing standards as may be appropriate, as provided for in the Clean Air Act (CAA). The first

14 draft PA is planned for release around the middle of August 2012 for review by the CASAC O3

15 Panel and the public concurrently with their review of this first draft REA September 11-13, 

16 2012. 

17 1.1 HISTORY

18 As part of the last O3 NAAQS review completed in 2008, EPA’s OAQPS conducted

19 quantitative risk and exposure assessments to estimate risks to human welfare based on 

20 ecological effects associated with exposure to ambient O3 (U.S. EPA 2007a, U.S. EPA 2007b). 

21 The assessment scope and methodology were developed with considerable input from CASAC 

22 and the public, with CASAC generally concluding that the exposure assessment reflected 

23 generally accepted modeling approaches, and that the risk assessments were well done, balanced 

24 and reasonably communicated (Henderson, 2006a). The final quantitative risk and exposure

25 assessments took into consideration CASAC advice (Henderson, 2006a; Henderson, 2006b) and 

26 public comments on two drafts of the risk and exposure assessments.

27 The assessments conducted as part of the last review focused on national-level O3-related 

28 impacts to sensitive vegetation and their associated ecosystems. The vegetation exposure 

29 assessment was performed using an interpolation approach that included information from 

30 ambient monitoring networks and results from air quality modeling. The vegetation risk 
1-4

1 assessment included both tree and crop analyses. The tree risk analysis included three distinct 

2 lines of evidence: (1) observations of visible foliar injury in the field linked to monitored O3 air 

3 quality for the years 2001 – 2004; (2) estimates of seedling growth loss under then current and 

4 alternative O3 exposure conditions; and (3) simulated mature tree growth reductions using the 

5 TREGRO model to simulate the effect of meeting alternative air quality standards on the 

6 predicted annual growth of mature trees from three different species. The crop risk analysis 

7 included estimates of crop yields under current and alternative O3 exposure conditions. The 

8 associated changes in economic value upon meeting the levels of various alternative standards 

9 were analyzed using an agricultural sector economic model. Key observations and insights from 

10 the ozone risk assessment, in addition to important caveats and limitations, were addressed in 

11 Section II.B of the Final Rule notice (73 FR 16440 to 16443, March 27, 2008). 

12 Prior to the issuance of a proposed rulemaking in the last review, CASAC presented 

13 recommendations to the Administrator supporting revisions of the O3 secondary standard. These 

14 recommendations cited the results of the quantitative risk assessment in recommending a range 

15 of ozone levels below the existing standard at the time (0.084 ppm) (Henderson, 2006a). In the 

16 2008 final rule, the EPA Administrator considered the results of the exposure and risk 

17 assessments and the potential magnitude of the risk to human welfare given recent air quality 

18 data and air quality simulated to meet the current standard and alternative standards. The EPA 

19 proposed to revise the level of the primary standard to a level within the range of 0.075 to 0.070 

20 ppm. Two options were proposed for the secondary standard: (1) replacing the current standard 

21 with a cumulative, seasonal standard, expressed as an index of the annual sum of weighted 

22 hourly concentrations cumulated over 12 daylight hours during the consecutive 3-month period 

23 within the O3 season with the maximum index value (W126), set at a level within the range of 7 

24 to 21 ppm-hrs, and (2) setting the secondary standard identical to the revised primary standard. 

25 The EPA completed the review with publication of a final decision on March 27, 2008 (73 FR 

26 16436), revising the level of the 8-hour primary O3 standard from 0.08 ppm to 0.075 ppm and 

27 revising the secondary standard to be identical to the revised primary standard.

28 In May 2008, state, public health, environmental, and industry petitioners filed suit 

29 against EPA regarding the 2008 final decision on the O3 NAAQS, and on December 23, 2008, 

30 the Court set a briefing schedule in the consolidated cases. On March 10, 2009, EPA requested 

31 that the Court vacate the briefing schedule and hold the consolidated cases in abeyance. This 
1-5

1 request for extension was made to allow time for appropriate EPA officials appointed by the new 

2 Administration to review the O3 NAAQS to determine whether the standards established in the 

3 March 2008 O3 NAAQS decision should be maintained, modified or otherwise reconsidered. In 

4 granting EPA’s request, the Court directed EPA to notify the Court by September 16, 2009 of the 

5 action it will be taking with respect to the 2008 O3 NAAQS rule and the Agency’s schedule for 

6 undertaking such action. The EPA notified the Court on September 16, 2009 of its decision to 

7 reconsider the primary and secondary O3 NAAQS set in March 2008 to ensure they are 

8 scientifically sound and protective of public health and the environment.

9 In 2010 the Administrator proposed to reconsider and revise parts of that 2008 final rule. 

10 Specifically, she proposed to revise the level of the primary standard to within the range of 0.060 

11 to 0.070 ppm and she proposed to revise the secondary standard by setting a new cumulative, 

12 seasonal standard in terms of the W126 metric, set within the range of 7-15 ppm-hours (FR 75 

13 2938). This proposal was based on the scientific and technical record from the 2008 rulemaking, 

14 including public comments and CASAC advice and recommendations. The information that was 

15 assessed during the 2008 rulemaking included information in the 2006 Criteria Document (EPA, 

16 2006a), the 2007 Policy Assessment of Scientific and Technical Information, referred to as the 

17 2007 Staff Paper (EPA, 2007a), and related technical support documents including the 2007 

REAs (U.S. EPA, 2007b; Abt Associates, 2007a,b).4

20 On September 2, 2011, the President requested that EPA withdraw the proposal to revisit 

21 and revise the 2008 Ozone National Ambient Air Quality Standards, noting that work was 

22 already underway on the next review (memo from President Obama, 

18 Scientific and technical information 

19 developed since the 2006 Criteria Document was not considered in the 2010 proposal. 

23 http://www.whitehouse.gov/the-press-office/2011/09/02/statement-president-ozone-nationalambient-air-quality-standards).5

 4

The EPA’s Office of Research and Development/National Center for Environmental Assessment 

(ORD/NCEA) also conducted a provisional assessment of pertinent studies investigating the health and ecological 

effects of O3 that were published after the cutoff for inclusion in the 2006 O3 Criteria Document. The provisional 

assessment was conducted for the purpose of determining if any recent studies would materially change the 

conclusions of the 2006 O3 Criteria Document. The provisional assessment concluded that, taken in context, results 

of more recent studies did not materially change any of the broad scientific conclusions regarding the health and 

ecological effects of O3 exposure made in the 2006 O3 Criteria Document. Thus, as stated above, the 2010 proposal 

was based solely on the record from the 2008 rulemaking and did not consider scientific and technical information 

developed since the 2006 Criteria Document. 

24 The proposed changes to the 2008 O3 NAAQS were not 

25 finalized. 

5

Also see letter from Cass Sunstein, Administrator of the Office of Information and Regulatory Affairs, to 

EPA Administrator Lisa Jackson 

(http://www.whitehouse.gov/sites/default/files/ozone_national_ambient_air_quality_standards_letter.pdf). 
1-6

1 1.2 CURRENT RISK ASSESSMENT: GOALS AND PLANNED APPROACH

2 The goals of the current quantitative welfare risk assessments are (1) to provide estimates 

3 of the ecological effects of O3 exposure across a range of environments; (2) to provide 

4 estimates of ecological effects within selected case study areas; (3) to provide estimates of the 

5 effects of O3 exposure on specific urban and non-urban ecosystem services based on the causal 

6 ecological effects; and (4) to develop a better understanding of the response of ecological 

7 systems and ecosystem services to changing levels of O3 exposure to inform the PA regarding

8 alternative standards that might be considered. This current quantitative risk and exposure

9 assessment builds on the approach used and lessons learned in the last O3 risk assessment and 

10 focuses on improving the characterization of the overall confidence in the risk estimates, 

11 including related uncertainties, by incorporating a number of enhancements, in terms of both the 

12 methods and data used in the analyses. This assessment considers a variety of welfare endpoints 

13 for which, in staff’s judgment, there is adequate information to develop quantitative risk 

14 estimates that can meaningfully inform the review of the secondary O3 NAAQS. 

15 This first draft REA provides an assessment of exposure and risk associated with recent 

16 ambient levels of ozone and ozone air quality simulated to just meet the current primary ozone 

17 standards. Subsequent drafts of the REA will evaluate potential alternative ozone standards 

18 based on recommendations provided in the first draft of the Policy Assessment. 

19 1.3 ORGANIZATION OF DOCUMENT 

20 The remainder of this document is organized as follows. Chapter 2 provides a conceptual 

21 framework for the risk and exposure assessment, including discussions of ozone chemistry, 

22 sources of ozone precursors, ecological exposure pathways and uptake into plants, ecological 

23 effects, and ecosystem services endpoints associated with ozone. This conceptual framework 

24 sets the stage for the scope of the risk and exposure assessments. Chapter 3 provides an 

25 overview of the scope of the quantitative risk and exposure assessments, including a summary of 

26 the previous risk and exposure assessments, and an overview of the current risk and exposure 

27 assessments. Chapter 4 discusses air quality considerations relevant to the exposure and risk 

28 assessments, including available ozone monitoring data, and important inputs to the risk and 

29 exposure assessments. Chapter 5 describes the ecological effects of O3 exposure and includes 

30 quantitative analyses of vegetation biomass loss and foliar injury. Chapter 6 describes the 
1-7

1 ecosystem services affected by the ecological effects analyzed in Chapter 5. Chapter 6 includes 

2 both quantitative assessments of the effects on ecosystem services as well as qualitative 

3 discussion of services for which effects are known to occur, but quantitative analyses were not 

4 possible. Chapter 7 provides an integrative discussion of the risk estimates generated in the 

5 analyses drawing on the results of the analyses based on quantitative analysis and incorporating 

6 considerations from the qualitative discussion of ecosystem services. 
2-1

1 2 CONCEPTUAL FRAMEWORK

2 In this chapter, we summarize the conceptual framework for assessing exposures of 

3 ecosystems to O3 and the associated risks to public welfare. This conceptual framework includes 

4 elements related to characterization of ambient O3 and its relation to ecosystem, exposures 

5 (Section 2.1), important sources of O3 precursors including oxides of nitrogen (NOx) and volatile 

6 organic compounds (VOC) (Section 2.2), ecological effects occurring in O3 sensitive ecosystems 

7 (Section 2.3), and ecosystem services that are likely to be negatively impacted by changes in 

8 ecological functions resulting from O3 exposures (Section 2.4). The chapter concludes with key 

9 observations relevant for developing the scope of the quantitative risk and exposure assessments.

10 In the previous review of the secondary standards, the focus of the ecological risk 

11 assessment was on estimation of changes in biomass loss and resulting impacts on forest and 

12 agricultural yields as well as qualitative consideration of effects on ecosystem services. In this 

13 review, EPA is expanding the analysis to consider the broader array of impacts on ecosystem 

14 services resulting from known effects of ozone on ecosystem functions. This is to address the 

15 objective of this risk assessment to quantify the risks not just to ecosystems but to the aspects of 

16 public welfare dependent on those ecosystems. EPA has begun using an ecosystem services 

17 framework to help inform determinations of the adversity to public welfare associated with 

18 changes in ecosystem functions (Rea et al, 2012). The Risk and Exposure Assessment 

19 conducted as part of the Review of the Secondary National Ambient Air Quality Standards for 

20 Oxides of Nitrogen and Oxides of Sulfur (U.S. EPA, 2009) presents detailed discussions of how 

21 ecosystem services and public welfare are related and how an ecosystem services framework 

22 may be employed to evaluate effects on welfare. In this risk assessment we will identify the 

23 ecosystem services associated with the ecological effects caused by O3 exposure for the national 

24 scale assessment and the more refined case study areas. These services may be characterized as: 

25 supporting services that are necessary for all other services (e.g., primary production); cultural 

26 services including existence and bequest values, aesthetic values, and recreation values, among 

27 others; provisioning services (e.g., food and timber); and regulating services such as climate 

28 regulation or hydrologic cycle (Millenium Ecosystem Assessment, 2005). Figure 2- 1 illustrates 

29 the relationships between the ecological effects of ozone and the anticipated ecosystem services 

30 impacts. Specific services to be evaluated are discussed in the following sections.
2-2

1

2

3 Figure 2- 1 Relationship Between Ecological Effects of Ozone Exposure and 

4 Ecosystem Services

5

6 2.1 O3 CHEMISTRY

7 O3 occurs naturally in the stratosphere where it provides protection against harmful solar 

8 ultraviolet radiation, and it is formed closer to the surface in the troposphere by both natural and 

9 anthropogenic sources. O3 is not emitted directly into the air, but is created when its two primary 

10 precursors, volatile organic compounds (VOC) and oxides of nitrogen (NOx), combine in the 

11 presence of sunlight. VOC and NOx are, for the most part, emitted directly into the atmosphere. 

12 Carbon monoxide (CO) and methane (CH4) are also important for O3 formation (US EPA, 2012, 

13 section 3.2.2).

14 Rather than varying directly with emissions of its precursors, O3 changes in a nonlinear 

15 fashion with the concentrations of its precursors. NOx emissions lead to both the formation and 

16 destruction of O3, depending on the local quantities of NOx, VOC, and radicals such as the 

17 hydroxyl (OH) and hydro-peroxy (HO2) radicals. In areas dominated by fresh emissions of NOx, 

Ambient 

Ozone 

Exposure

Ecological 

Effects

• Reduced 

productivity

• Foliar injury

• Stomatal 

functioning

Supporting Services

• Soil Formation

• Primary Productivity

• Community Structure

Provisioning Services

• Agricultural harvest

• Timber production

• Non-timber uses

Regulating Services

• Carbon Sequestration

• Nutrient Cycling

• Water Regulation

• Fire Ecology

• Pollination

Cultural Services

• Endangered Species

• Recreational Use

• Non-use Values
2-3

1 these radicals are removed via the production of nitric acid (HNO3), which lowers the O3

2 formation rate. In addition, the scavenging of O3 by reaction with NO is called “titration,” and is 

3 often found in downtown metropolitan areas, especially near busy streets and roads, and in 

4 power plant plumes. This titration results in local valleys in which ozone concentrations are low 

5 compared to surrounding areas. Titration is usually short-lived confined to areas close to strong 

6 NOx sources, and the NO2 formed this way leads to O3 formation later and further downwind. . 

7 Consequently, ozone response to reductions in NOx emissions is complex and may include ozone 

8 decreases at some times and locations and increases of ozone to fill in the local valleys of low 

9 ozone. In areas with low NOx concentrations, such as those found in remote continental areas to 

10 rural and suburban areas downwind of urban centers, the net production of O3 typically varies 

11 directly with NOx concentrations, and increases with increasing NOx emissions.

12 In general, the rate of O3 production is limited by either the concentration of VOCs or 

13 NOx, and O3 formation using these two precursors relies on the relative sources of OH and NOx. 

14 When OH radicals are abundant and are not depleted by reaction with NOx and/or other species,

15 O3 production is referred to as being “NOx-limited” (US EPA, 2012, section 3.2.4). In this 

16 situation, O3 concentrations are most effectively reduced by lowering NOx emissions, rather than 

17 lowering emissions of VOCs. When the abundance of OH and other radicals is limited either 

18 through low production or reactions with NOx and other species, O3 production is sometimes 

19 called “VOC-limited” or “radical limted” or “NOx-saturated” (Jaegle et al., 2001), and O3 is most 

20 effectively reduced by lowering VOCs. However, even in NOx-saturated conditions, very large 

21 decreases in NOx emissions can cause the ozone formation regime to become NOx limited. 

22 Consequently, reductions in NOx emissions (when large) can make further emissions reductions 

23 more effective at reducing ozone. Between the NOx-limited and NOx-saturated extremes there is 

24 a transitional region where O3 is relatively insensitive to marginal changes in both NOx and 

25 VOCs. 

26 In rural areas and downwind of urban areas, O3 production is generally NOx-limited. This 

27 is particularly true in rural areas such as national parks, national forests, and state parks where 

28 VOC emissions from vegetation are high and anthropogenic NOx emissions are relatively low.

29 Due to lower chemical scavenging in non-urban areas, O3 tends to persist longer in rural than in 

30 urban areas and tends to lead to higher cumulative exposures in rural areas than in urban areas. 

31 (US EPA, 2012a, Section 3.6.2.2).
2-4

1 2.2 SOURCES OF O3 AND O3 PRECURSORS 

2 O3 precursor emissions can be divided into anthropogenic and natural source categories, 

3 with natural sources further divided into biogenic emissions (from vegetation, microbes, and 

4 animals) and abiotic emissions (from biomass burning, lightning, and geogenic sources). The 

5 anthropogenic precursors of O3 originate from a wide variety of stationary and mobile sources. 

6 In urban areas, both biogenic and anthropogenic VOCs are important for O3 formation. 

7 Hundreds of VOCs are emitted by evaporation and combustion processes from a large number of 

8 anthropogenic sources. Based on the 2005 national emissions inventory (NEI), solvent use and 

9 highway vehicles are the two main sources of VOCs, with roughly equal contributions to total 

10 emissions (US EPA, 2012a, Figure 3-3). The emissions inventory categories of “miscellaneous” 

11 (which includes agriculture and forestry, wildfires, prescribed burns, and structural fires) and off12 highway mobile sources are the next two largest contributing emissions categories with a 

13 combined total of over 5.5 million metric tons a year (MT/year).

14 On the U.S. and global scales, emissions of VOCs from vegetation are much larger than

15 those from anthropogenic sources. Emissions of VOCs from anthropogenic sources in the 2005 

16 NEI were ~17 MT/year (wildfires constitute ~1/6 of that total), but were 29 MT/year from 

17 biogenic sources. Vegetation emits substantial quantities of VOCs, such as isoprene and other 

18 terpenoid and sesqui-terpenoid compounds. Most biogenic emissions occur during the summer 

19 because of their dependence on temperature and incident sunlight. Biogenic emissions are also 

20 higher in southern and eastern states than in northern and western states for these reasons and 

21 because of species variations.

22 Anthropogenic NOx emissions are associated with combustion processes. Based on the 

23 2005 NEI, the three largest sources of NOx are on-road and off-road mobile sources (e.g., 

24 construction and agricultural equipment) and electric power generation plants (EGUs) (US EPA, 

25 2012, Figure 3-3). Emissions of NOx therefore are highest in areas having a high density of 

26 power plants and in urban regions having high traffic density. However, it is not possible to 

27 make an overall statement about their relative impacts on O3 in all local areas because EGUs are 

28 sparser than mobile sources, particularly in the west and south and because of the nonlinear 

29 chemistry discussed in Section 2.1. 

30 Major natural sources of NOx in the U.S. include lightning, soils, and wildfires. Biogenic 

31 NOx emissions are generally highest during the summer and occur across the entire country,
2-5

1 including areas where anthropogenic emissions are low. It should be noted that uncertainties in 

2 estimating natural NOx emissions are much larger than for anthropogenic NOx emissions.

3 Ozone concentrations in a region are affected both by local formation and by transport 

4 from surrounding areas. Ozone transport occurs on many spatial scales including local transport 

5 between cities, regional transport over large regions of the U.S. and international/long-range 

6 transport. In addition, O3 is also transfered into the troposphere from the stratosphere, which is 

7 rich in O3, through stratosphere-troposphere exchange (STE). These inversions or “foldings” usually 

8 occur behind cold fronts, bringing stratospheric air with them (U.S. EPA, 2012, section 3.4.1.1). 

9 Contribution to O3 concentrations in an area from STE are defined as being part of background O3

10 (U.S. EPA, 2012, section 3.4).

11 Rural areas, such as national parks, national forests, and state parks, tend to be less 

12 directly affected by anthropogenic pollution sources than urban sites. However, they can be 

13 regularly affected by transport of O3 or O3 precursors from upwind urban areas. In addition,

14 biogenic VOC emissions tend to be higher in rural areas and major sources of O3 precursor 

15 emissions such as highways, power plants, biomass combustion, and oil and gas operations are 

16 commonly found in rural areas, adding to the O3 produced in these areas. Areas at higher 

17 elevations, such as many of the national parks in the western U.S., can also be affected more 

18 significantly by international transport of O3 or stratospheric intrusions that transport O3 into the 

19 area (US EPA, 2012a, section 3.7.3).

20 2.3 ECOLOGICAL EFFECTS

21 Recent studies reviewed in the ISA support and strengthen the findings reported in the 

22 2006 O3 AQCD (U.S. EPA, 2006a). The most significant new body of evidence since the 2006 

23 O3 AQCD comes from research on molecular mechanisms of the biochemical and physiological 

24 changes observed in many plant species in response to O3 exposure. These newer molecular 

25 studies not only provide very important information regarding the many mechanisms of plant 

26 responses to O3, they also allow for the analysis of interactions between various biochemical 

27 pathways which are induced in response to O3. However, many of these studies have been 

28 conducted in artificial conditions with model plants, which are typically exposed to very high, 

29 short doses of O3 and are not quantifiable as part of this risk assessment, which is focused on 

30 ambient conditions.
2-6

1 Chapter 9 of the O3 ISA (U.S. EPA, 2012a) provides a detailed review of the effects of 

2 O3 on vegetation including the major pathways of exposure and known ecological and ecosystem 

3 effects. Figure 9-1 of the ISA is reproduced below (Figure 2- 2) as a summary of exposure and 

4 effects. In general, O3 is taken up through the stomata into the leaves. Once inside the leaves, O3

5 affects a number of biological and physiological processes, including photosynthesis. This leads, 

6 in some cases, to visible foliar injury as well as reduced plant growth, which are the main 

7 ecological effects assessed in this review. Visible foliar injury and reduced growth can lead to a 

8 reduction in ecosystem services, including crop and timber yield loss, decreased C sequestration, 

9 alteration in community composition and loss of recreational or cultural value.

10

11 Figure 2- 2 Conceptual diagram of the major pathway through which O3 enters 

12 plants and the major endpoints that O3 may affect in plants and 

13 ecosystems. Figure numbers in this figure refer to Chapter 9 of the 

14 ISA.

15 Overall causal determinations are made based on the full range of evidence including 

16 controlled exposure studies and ecological studies. Figure 2- 3 shows the O3 welfare effects 

O3 exposure

O3 uptake & physiology (Fig 9-2) •Antioxidant metabolism up-regulated

•Decreased photosynthesis

•Decreased stomatal conductance 

or sluggish stomatal response

Effects on leaves

•Visible leaf injury

•Altered leaf production 

•Altered leaf chemical composition

Plant growth (Fig 9.8) •Decreased biomass accumulation

•Altered reproduction

•Altered carbon allocation

•Altered crop quality

Belowground processes (Fig 9.8) •Altered litter production and decomposition

•Altered soil carbon and nutrient cycling

•Altered soil fauna and microbial communities

Differential O3 sensitivity

Affected ecosystem services

•Decreased productivity 

•Decreased C sequestration

•Altered water cycling (Fig 9-7)

•Altered community composition 

(i.e., plant, insect & microbe)
2-7

1 which have been categorized by strength of evidence for causality in the O3 ISA (US EPA, 

2 2012a, chapter 2). These determinations support causal or likely causal relationships between 

3 exposure to O3 and ecological and ecosystem level effects. 

4

5

6 Figure 2- 3 Causal Determinations for O3 Welfare Effects

7

8 The adequate characterization of the effects of O3 on plants for the purpose of setting air 

9 quality standards is contingent not only on the choice of the index used (i.e. W126) to summarize 

10 O3 concentrations (Section 9.5), but also on quantifying the response of the plant variables of 

11 interest at specific values of the selected index. The factors that determine the response of plants 

12 to O3 exposure include species, genotype and other genetic characteristics, biochemical and 

13 physiological status, previous and current exposure to other stressors, and characteristics of the 

14 exposure itself. Establishing a secondary air quality standard requires the capability to generalize 

15 those observations, in order to obtain predictions that are reliable enough under a broad variety 

16 of conditions, taking into account these factors. 

17 Quantitative characterization of exposure-response in the 2006 O3 AQCD was based on 

18 experimental data generated for that purpose by the National Crop Loss Assessment Network 

Not likely Inadequate 

to infer Suggestive Likely Causal

Alteration of 

terrestrial ecosystem 

water cycling

Reduced carbon 

sequestration in 

terrestrial ecosystems

Visible foliar injury 

effects

Reduced vegetation growth

Reduced productivity in 

terrestrial ecosystems

Reduced yield and 

quality of agricultural 

crops

Alteration of below 

ground biogeochemical 

cycles

Alteration of 

terrestrial community 

composition
2-8

1 (NCLAN) and EPA National Health and Environmental Effects Research Laboratory, Western 

2 Ecology Division (NHEERL-WED) projects, using OTCs to expose crops and trees seedling to 

3 O3. In recent years, yield and growth results for two of the species that had provided extensive 

4 exposure-response information in those projects have become available from studies that used 

5 FACE technology, which is intended to provide conditions much closer to natural environments 

6 (Pregitzer et al., 2008; Morgan et al., 2006; Morgan et al., 2004; Dickson et al., 2000). 

7 The quantitative exposure-response relationships described in the 2006 O3 AQCD have 

8 not changed in the current draft ISA, with the exception of the addition of one new species. e

9 assessment of quantitative exposure-response relationships that was presented in that document. 

10 The exposure-response models are summarized in the 3rd draft ISA summarizes computed using 

11 the W126 metric, cumulated over 90 days. These response functions provide an adequate basis 

12 for quantifying biomass loss damages. 

13 Visible foliar injury resulting from exposure to O3 has also been well characterized and 

14 documented over several decades of research on many tree, shrub, herbaceous, and crop species 

15 (U.S. EPA, 2006, 1996a, 1984, 1978). Ozone-induced visible foliar injury symptoms on certain 

16 bioindicator plant species are considered diagnostic as they have been verified experimentally in 

17 exposure-response studies, using exposure methodologies such as continuous stirred tank 

18 reactors (CSTRs), OTCs, and free-air fumigation. Experimental evidence has clearly established 

19 a consistent association of visible injury with O3 exposure, with greater exposure often resulting 

20 in greater and more prevalent injury. This general relationship provides an adequate basis for 

21 qualitative assessment of the risk of visible foliar injury, but a detailed quantitative assessment is 

22 not possible because there are no concentration-response functions for foliar injury that can be 

23 applied across a range of ecosystems.

24 2.4 ECOSYSTEM SERVICES

25 The Risk and Exposure Assessment evaluates the benefits received from the resources and 

26 processes that are supplied by ecosystems. Collectively, these benefits are known as ecosystem 

27 services and include products or provisions, such as food and fiber; processes that regulate 

28 ecosystems, such as carbon sequestration; cultural enrichment; and supportive processes for 

29 services, such as nutrient cycling. Ecosystem services are distinct from other ecosystem products 
2-9

1 and functions because there is human demand for these services. In the Millennium Ecosystem

2 Assessment (MEA), ecosystem services are classified into four main categories:

3 • Provisioning. Includes products obtained from ecosystems, such as the production of

4 food and water.

5 • Regulating. Includes benefits obtained from the regulation of ecosystem processes, such

6 as the control of climate and disease.

7 • Cultural. Includes the nonmaterial benefits that people obtain from ecosystems through 

8 spiritual enrichment, cognitive development, reflection, recreation, and aesthetic 

9 experiences.

10 • Supporting. Includes those services necessary for the production of all other ecosystem

11 services, such as nutrient cycles and crop pollination (MEA, 2005).

12 The concept of ecosystem services can be used to help define adverse effects as they pertain 

13 to NAAQS reviews. The most recent secondary NAAQS reviews have characterized known or 

14 anticipated adverse effects to public welfare by assessing changes in ecosystem structure or 

15 processes using a weight-of-evidence approach that uses both quantitative and qualitative data. 

16 For example, the previous ozone review evaluated changes in foliar injury, growth loss, and 

17 biomass reduction on trees beyond the seedling stage using the TREGRO model. The presence 

18 or absence of foliar damage in counties meeting the current standard has been used as a way to 

19 evaluate the adequacy of the secondary NAAQS. Characterizing a known or anticipated adverse 

20 effect to public welfare is an important component of developing any secondary NAAQS. 

21 According to the Clean Air Act (CAA), welfare effects include the following:

22

23 “Effects on soils, water, crops, vegetation, manmade materials,

24 animals, wildlife, weather, visibility, and climate, damage to and

25 deterioration of property, and hazards to transportation, as well as

26 effect on economic values and on personal comfort and well-being,

27 whether caused by transformation, conversion, or combination

28 with other air pollutants.” (Section 302(h))

29
2-10

1 In other words, welfare effects are those effects that are important to individuals and/or

2 society in general. Ecosystem services can be generally defined as the benefits that individuals

3 and organizations obtain from ecosystems. EPA has defined ecological goods and services as the

4 “outputs of ecological functions or processes that directly or indirectly contribute to social

5 welfare or have the potential to do so in the future. Some outputs may be bought and sold, but

6 most are not marketed” (U.S. EPA, 2006). Conceptually, changes in ecosystem services may be

7 used to aid in characterizing a known or anticipated adverse effect to public welfare. In the 

8 context of this review, ecosystem services may also aid in assessing the magnitude and

9 significance of a resource and in assessing how O3 concentrations may impact that resource.

10 Figure 2- 4 provides the World Resources Institute’s schematic demonstrating the

11 connections between the categories of ecosystem services and human well-being. The

12 interrelatedness of these categories means that any one ecosystem may provide multiple services.

13 Changes in these services can impact human well-being by affecting security, health, social

14 relationships, and access to basic material goods (MEA, 2005).

15

16

17 Figure 2- 4 Linkages between categories of ecosystem services and components of 

18 human well-being that are commonly indications of the extent to 

19 which it is possible for socioeconomic factors to mediate the linkage. 

20 The strength of the linkages, as indicated by arrow width, and the 
2-11

1 potential for mediation, as indicated by arrow color, differ in different 

2 ecosystems and regions (MEA, 2005).

3

4 Historically, ecosystem services have been undervalued and overlooked; however, more 

5 recently, the degradation and destruction of ecosystems has piqued interest in assessing the value 

6 of these services. In addition, valuation may be an important step from a policy perspective 

7 because it can be used to compare the costs and benefits of altering versus maintaining an 

8 ecosystem (i.e., it may be easier to protect than repair ecosystem effects). In this Risk and 

9 Exposure Assessment, valuation is used, where possible, based on available data in the national 

10 scale analyses and case study areas.

11 The economic approach to the valuation of ecosystem services is laid out as follows in

12 EPA’s Ecological Benefits Assessment Strategic Plan: “Economists generally attempt to estimate 

13 the value of ecological goods and services based on what people are willing to pay (WTP) to 

14 increase ecological services or by what people are willing to accept (WTA) in compensation for 

15 reductions in them” (U.S. EPA, 2006). There are three primary approaches for estimating the 

16 value of ecosystem services: market-based approaches, revealed preference methods, and stated 

17 preference methods (U.S. EPA, 2006). Because economic valuation of ecosystem services can be 

18 difficult, nonmonetary valuation using biophysical measurements and concepts also can be used.

19 Examples of nonmonetary valuation methods include the use of relative-value indicators (e.g., a

20 flow chart indicating uses of a waterbody, such as boatable, fishable, swimmable); another 

21 assigns values to ecosystem goods and services through the use of the common currency of 

22 energy. Energetic valuation attempts to assess ecosystem contributions to the economy by using 

23 one kind of energy (e.g., solar energy) to express the value of that type of energy required to 

24 produce designated services (Odum, 1996). This energy value is then converted to monetary 

25 units. This method of valuation, however, does not account for the premise that values arise from 

26 individual or societal preferences.

27 Valuing ecological benefits, or the contributions to social welfare derived from 

28 ecosystems, can be challenging, as noted in EPA’s Ecological Benefits Assessment Strategic

29 Plan (U.S. EPA, 2006). It is necessary to recognize that in the analysis of the environmental 

30 responses associated with any particular policy or environmental management action, some of 

31 the ecosystem services likely to be affected are readily identified, whereas others will remain 
2-12

1 unidentified. Of those ecosystem services that are identified, some changes can be quantified, 

2 whereas others cannot. Within those services whose changes can be quantified, only a few will 

3 likely be monetized, and many will remain unmonetized. Similar to health effects, only a portion 

4 of the ecosystem services affected by a policy can be monetized. The stepwise concept leading 

5 up to the valuation of ecosystems services is graphically depicted in Figure 2- 5.

6

7

8 Figure 2- 5 Representation of the benefits assessment process indicating where

9 some ecological benefits may remain unrecognized, unquantified, or 

10 unmonetized. (Modified based on the Ecological Benefits Assessment 

11 Strategic Plan report [U.S. EPA, 2006]).

12
2-13

1 Under Section 108 of the CAA, the secondary standard is to specify an acceptable level 

2 of the criteria pollutant(s) in the ambient air that is protective of public welfare. For this review, 

3 the relevant air quality indicator is interpreted as ambient O3 concentrations that can be linked to 

4 adverse ecological effects. The air quality analyses described in Chapter 4 explore the sources 

5 and emissions, and their current contributions to ambient conditions. The national scale and case 

6 study analyses (described in Chapters 5 and 6) link O3 effects in sensitive ecosystems (e.g., the 

7 exposure pathway) to changes in a given ecological indicator (e.g., biomass loss to changes in 

8 ecosystems and the services they provide (e.g., commercial timber production). To the extent 

9 possible for effect, ambient concentrations of O3 (i.e., ambient air quality indicators) were linked 

10 to effects in sensitive ecosystems (i.e., exposure pathways), and then O3 concentrations were 

11 linked to system response as measured by a given ecological indicator (e.g., biomass loss). The 

12 ecological effect (e.g., changes in tree growth) was then, where possible, associated with changes 

13 in ecosystem services and their ecological benefits or welfare effects (e.g., timber production).

14 Knowledge about the relationships linking ambient concentrations and ecosystem 

15 services can be used to inform a policy judgment on a known or anticipated adverse public 

16 welfare effect. For example, changes in biodiversity would be classified as an ecological effect, 

17 and the associated changes in ecosystem services—productivity, recreational viewing, and 

18 aesthetics—would be classified as ecological benefits/welfare effects. This information can then 

19 be used to characterize known or anticipated adverse effects to public welfare and inform a 

20 policy based on welfare effects.

21 The ecosystems of interest in this Risk and Exposure Assessment are impacted by the 

22 effects of anthropogenic air pollution, which may alter the services provided by the ecosystems 

23 in question. For example, changes in forest health as a result of O3 exposure may affect 

24 supporting services such as net primary productivity; provisioning services such as timber 

25 production; and regulating services such as climate regulation. In addition, such changes may

26 provide provisioning services such as food; and cultural services such as recreation and 

27 ecotourism.

28 Where possible, linkages to ecosystem services from indicators of each effect identified 

29 in the ISA (U.S. EPA, 2012a) were developed. These linkages were based on existing literature 

30 and models, focus on the services identified in the peer-reviewed literature, and are essential to 

31 any attempt to evaluate air pollution-induced changes in the quantity and/or quality of ecosystem 
2-14

1 services provided. According to EPA’s Science Advisory Board Committee on Valuing the 

2 Protection of Ecological Systems and Services, these linkages are critical elements for 

3 determining the valuation of benefits of EPA-regulated air pollutants (SAB CVPESS, 2009). 

4 We have identified the primary ecosystem service(s) potentially impacted by O3 for

5 major ecosystem types and components (i.e., terrestrial ecosystems, productivity) under 

6 consideration in this risk and exposure assessment. The impacts associated with various 

7 ecosystem services for each targeted effect are assessed in Chapter 6 at a national scale and in 

8 case studies. 

9

10 2.5 CONCLUSIONS

11 The conceptual basis for estimating exposures to O3 and resulting welfare effects is strong. The 

12 ISA provides clear scientific evidence linking ambient concentrations of O3 to a number of 

13 ecological effects, and science-based air quality models along with O3 monitoring data, show 

14 that important ecosystems throughout the U.S. are exposed to O3 concentrations that may result 

15 in adverse ecological impacts. There are field and laboratory studies that provide adequate 

16 information to construct concentration-response functions that can be used to estimate risk given 

17 estimates of tree or ecosystem level O3 exposure.

18

19 Presented below are key observations for this conceptual overview of the assessment of ambient 

20 O3 exposure and welfare risk.

21

22 • O3 in ambient air is formed primarily by emissions of NOx and VOC and 

23 photochemical reactions in the atmosphere. Both natural and anthropogenic sources 

24 contribute to O3 formation. Solvents, on-road and off-road mobile sources and electric 

25 power generation plants represent significant anthropogenic sources of precursors to O3

26 in ambient air. Vegetation, lightning, soils, and wildfires are significant natural sources 

27 of O3 precursor emissions.

28 • The ISA has determined that the evidence supports a causal relationship between 

29 exposure to O3 and visible foliar injury, reduced vegetation growth, reduced agricultural 

30 yield, and alteration of below ground biogeochemical cycles, and a likely causal 
2-15

1 relationship exposure to O3 and reduced carbon sequestration, alteration of terrestrial 

2 water cycling, and alteration of terrestrial community composition. 

3 • The causal and likely causal ecological effects identified in the ISA have an effect 

4 on regulating, supporting, cultural and provisioning ecosystem services. 

5

6
3-1

1 3 SCOPE

2 This chapter provides an overview of the scope and key design elements of this 

3 quantitative exposure and welfare risk assessment. The design of this assessment began with a 

4 review of the exposure and risk assessments completed during the last O3 NAAQS review (US 

5 EPA, 2007a,b), with an emphasis on considering key limitations and sources of uncertainty 

6 recognized in that analysis.

7 As an initial step in the current O3 NAAQS review, in October 2009, EPA invited outside 

8 experts, representing a broad range of expertise to participate in a workshop with EPA staff to 

9 help inform EPA’s plan for the review. The participants discussed key policy-relevant issues 

10 that would frame the review and the most relevant new science that would be available to inform 

11 our understanding of these issues. One workshop session focused on planning for quantitative 

12 risk and exposure assessments, taking into consideration what new research and/or improved 

13 methodologies would be available to inform the design of quantitative exposure and welfare risk 

14 assessment. Based in part on the workshop discussions, EPA developed a draft IRP (US EPA, 

15 2009) outlining the schedule, process, and key policy-relevant questions that would frame this 

16 review. On November 13, 2009, EPA held a consultation with CASAC on the draft IRP (74 FR 

17 54562, October 22, 2009), which included opportunity for public comment. The final IRP 

18 incorporated comments from CASAC (Samet, 2009) and the public on the draft plan as well as 

19 input from senior Agency managers. The final IRP included initial plans for the quantitative risk 

20 and exposure assessments for both human health and welfare (US EPA, 2011a, chapters 5 and 6).

21 As a next step in the design of these quantitative assessments, OAQPS staff developed 

22 more detailed planning documents, O3 National Ambient Air Quality Standards: Scope and 

23 Methods Plan for Health Risk and Exposure Assessment (Health Scope and Methods Plan; US 

24 EPA, 2011b) and O3 National Ambient Air Quality Standards: Scope and Methods Plan for 

25 Welfare Risk and Exposure Assessment (Welfare Scope and Methods Plan, US EPA, 2011c). 

26 These Scope and Methods Plans were the subject of a consultation with CASAC on May 19-20, 

27 2011 (76 FR 23809, April 28, 2011). Based on consideration of CASAC (Samet, 2011) and 

28 public comments on the Scope and Methods Plan and information in the second draft ISA, we 

29 modified the scope and design of the quantitative risk assessment and provided a memo with 

30 updates to information presented in the Scope and Methods Plans (Wegman, 2012). The Scope 
3-2

1 and Methods Plans together with the update memo provide the basis for the discussion of the 

2 scope of this exposure and risk assessment provided in this chapter. 

3 In presenting the scope and key design elements of the current risk assessment, this chapter first 

4 provides a brief overview of the quantitative exposure and risk assessment completed for the 

5 previous O3 NAAQS review in section 3.1, including key limitations and uncertainties associated 

6 with that analysis. Section 3.2 provides a summary of the design of the exposure assessment. 

7 Section 3.3 provides a summary of the design of the risk assessment based on application of 

8 results of human clinical studies. Section 3.4 provides a summary of the design of the risk 

9 assessment based on application of results of epidemiology studies. 

10 3.1 OVERVIEW OF EXPOSURE AND RISK ASSESSMENTS FROM LAST REVIEW

11 The assessments conducted as part of the last review focused on national-level O3-related 

12 impacts to sensitive vegetation and their associated ecosystems. The vegetation exposure 

13 assessment was performed using an interpolation approach that included information from 

14 ambient monitoring networks and results from air quality modeling. The vegetation risk 

15 assessment included both tree and crop analyses. The tree risk analysis included three distinct 

16 lines of evidence: (1) observations of visible foliar injury in the field linked to monitored O3 air 

17 quality for the years 2001 – 2004; (2) estimates of seedling growth loss under then current and 

18 alternative O3 exposure conditions; and (3) simulated mature tree growth reductions using the 

19 TREGRO model to simulate the effect of meeting alternative air quality standards on the 

20 predicted annual growth of mature trees from three different species. The crop risk analysis 

21 included estimates of crop yields under current and alternative O3 exposure conditions. The 

22 associated changes in economic value upon meeting the levels of various alternative standards 

23 were analyzed using an agricultural sector economic model. Key elements and observations 

24 from these exposure and risk assessments are outlined in the following sections.

25 3.1.1 Exposure Characterization

26 In many rural and remote areas where sensitive species of vegetation can occur, 

27 monitoring coverage remained limited. Thus, the 2007 Staff Paper concluded that it was 

28 necessary to use an interpolation method in order to better characterize O3 air quality over broad 

29 geographic areas and at the national scale. Based on the significant difference in monitor 
3-3

1 network density between the eastern and western U.S., the Staff Paper further concluded that it 

2 was appropriate to use separate interpolation techniques in these two regions: The Air Quality 

3 System (AQS; http://www.epa.gov/ttn/airs/airsaqs) and Clean Air Status and Trends Network 

4 (CASTNET; http://www.epa.gov/castnet/) monitoring data were solely used for the eastern 

5 interpolation, and in the western U.S., where rural monitoring is more sparse, O3 outputs from 

6 the EPA/NOAA Community Multi-scale Air Quality (CMAQ) model system 

7 (http://www.epa.gov/asmdnerl/CMAQ, Byun and Ching, 1999; Byun and Schere, 2006) were 

8 used to develop scaling factors to augment the monitor interpolation. In order to characterize 

9 uncertainty associated with the exposure estimates generated using the interpolation method, 

10 monitored O3 concentrations were systematically compared to interpolated O3 concentrations in 

11 areas where monitors were located. In general, the interpolation method performed well in many 

12 areas in the U.S. This approach was used to develop a national vegetation O3 exposure surface. 

13 To evaluate changing vegetation exposures under selected air quality scenarios, a number 

14 of analyses were conducted. One analysis adjusted 2001 base year O3 air quality distributions 

15 using a rollback method (Rizzo, 2005, 2006) to reflect meeting the current and alternative 

16 secondary standard options. For “just meet” and alternative 8-hr average standard scenarios, the 

17 associated maps of estimated 12-hr, W126 exposures were generated. Based on these 

18 comparisons, the following observations were drawn: (1) current O3 air quality levels could 

19 result in significant cumulative, seasonal O3 exposures to vegetation in some areas; (2) overall 3-

20 month 12-hr W126 O3 levels were somewhat but not substantially improved under the “just 

21 meet” current (0.08 ppm) scenario; (3) exposures generated for just meeting a 0.070 ppm, 4th22 highest maximum 8-hr average alternative standard (the lower end of the then proposed range for 

23 the primary O3 standard) showed substantially improved 3-month cumulative, seasonal O3 air 

24 quality when compared to just meeting the current 0.08 ppm, 8-hr average standard. 

25 A second analysis described in the Staff Paper was performed to evaluate the extent to 

26 which county-level O3 air quality measured in terms of various levels of the current 8-hr average 

27 form overlapped with that measured in terms of various levels of the 12-hr W126 cumulative, 

28 seasonal form. While these results also suggested that meeting a proposed 0.070 ppm, 8-hr 

29 secondary standard would provide substantially improved vegetation protection in some areas, 

30 the Staff Paper recognized that this analysis had several important limitations. In particular, the 

31 lack of monitoring in rural areas where sensitive vegetation and ecosystems are located, 
3-4

1 especially at higher elevation sites, could have resulted in an inaccurate characterization of the 

2 degree of potential overlap at sites that have air quality patterns that can result in relatively low 

3 8-hr averages while still experiencing relatively high cumulative exposures (72 FR 37892). 

4 Thus, the Staff Paper concluded that it is reasonable to anticipate that additional unmonitored 

5 rural high elevation areas with sensitive vegetation may not be adequately protected even with a 

6 lower level of the 8-hr form. The Staff Paper further indicated that it remained uncertain as to 

7 the extent to which air quality improvements designed to reduce 8-hr O3 average concentrations 

8 would reduce O3 exposures measured by a seasonal, cumulative W126 index. The Staff Paper 

9 indicated this to be an important consideration because: (1) the biological database stresses the 

10 importance of cumulative, seasonal exposures in determining plant response; (2) plants have not 

11 been specifically tested for the importance of daily maximum 8-hr O3 concentrations in relation 

12 to plant response; and (3) the effects of attainment of a 8-hr standard in upwind urban areas on 

13 rural air quality distributions cannot be characterized with confidence due to the lack of 

14 monitoring data in rural and remote areas.

15 The Staff Paper also presented estimates of economic valuation for crops associated with 

16 the then current and alternative standards. The Agriculture Simulation Model (AGSIM) (Taylor, 

17 1994; Taylor, 1993) was used to calculate annual average changes in total undiscounted 

18 economic surplus for commodity crops and fruits and vegetables when then current and 

19 alternative standard levels were met. Meeting the various alternative standards did show some 

20 significant benefits beyond the 0.08 ppm, 8-hr standard. However, the Staff Paper recognized 

21 that the modeled economic impacts from AGSIM had many associated uncertainties, which 

22 limited the usefulness of these estimates.

23 3.1.2 Assessment of Risks to Vegetation

24 The risk assessments in the last review reflected the availability of several additional 

25 lines of evidence that provided a basis for a more complete and coherent picture of the scope of 

26 O3-related vegetation risks, especially those faced by seedling, sapling and mature tree species 

27 growing in field settings, and indirectly, forested ecosystems. Specifically, new research 

28 available at the time reflected an increased emphasis on field-based exposure methods (e.g., free 

29 air exposure and ambient gradient), improved field survey biomonitoring techniques, and 
3-5

1 mechanistic tree process models. Highlights from the analyses that addressed visible foliar 

2 injury, seedling and mature tree biomass loss, and effects on crops are summarized below.

3 With regard to visible foliar injury, the Staff Paper presented an assessment that 

4 combined recent U.S. Forest Service Forest Inventory and Analysis (FIA) biomonitoring site 

5 data with the county level air quality data for those counties containing the FIA biomonitoring 

6 sites. This assessment showed that incidence of visible foliar injury ranged from 21 to 39 

7 percent of the counties during the four-year period (2001-2004) across all counties with air 

8 quality levels at or below that of the then current 0.08 ppm 8-hr average standard. Of the 

9 counties that met an 8-hr average level of 0.07 ppm in those years, 11 to 30 percent of the 

10 counties still had incidence of visible foliar injury. 

11 With respect to tree seedling biomass loss, concentration-response (C-R) functions 

12 developed from Open Top Chamber (OTC) studies for biomass loss for available seedling tree 

13 species and information on tree growing regions derived from the U.S. Department of 

14 Agriculture's Atlas of United States Trees were combined with projections of air quality based 

15 on 2001 interpolated exposures, to produce estimated biomass loss for each individual seedling 

16 tree species. These analyses predicted that biomass loss could still occur in many tree species 

17 when O3 air quality was adjusted to meet the then current 8-hr average standard. Though this 

18 type of analysis was not new to this review, the context for understanding these results had 

19 changed due to recent field work at the AspenFACE site in Wisconsin on quaking aspen 

20 (Karnosky et al., 2005) and a gradient study performed in the New York City area (Gregg et al., 

21 2003), which confirmed the detrimental effects of O3 exposure on tree growth in field studies 

22 without chambers and beyond the seedling stage (King et al., 2005). 

23 With respect to risk of mature tree growth reductions, a tree growth model (TREGRO) 

24 was used to evaluate the effect of changing O3 air quality scenarios from just meeting alternative 

O3 standards on the growth of mature trees.1

 1 TREGRO is a process-based, individual tree growth simulation model (Weinstein et al, 1991) that is linked with 

concurrent climate data to account for O3 and climate/meteorology interactions on tree growth. TREGRO has been 

used to evaluate the effects of a variety of O3 scenarios on several species of trees in different regions of the U.S. 

(Tingey et al., 2001; Weinstein et al., 1991; Retzlaff et al., 2000; Laurence et al., 1993; Laurence et al., 2001; 

Weinstein et al., 2005).

25 The model was run for a single western species 

26 (ponderosa pine) and two eastern species (red maple and tulip poplar). Staff Paper analyses 

27 found that just meeting the then current standard would likely continue to allow O3-related 
3-6

1 reductions in annual net biomass gain in these species. Though there was uncertainty associated 

2 with the above analyses, it was important to note that recent evidence from experimental studies 

3 that go beyond the seedling growth stage continued to show decreased growth under elevated O3

4 (King et al., 2005); some mature trees such as red oak have shown an even greater sensitivity of 

5 photosynthesis to O3 than seedlings of the same species (Hanson et al., 1994); and the potential 

6 for cumulative “carry over” effects as well as compounding should be considered (Andersen, et 

7 al, 1997). 

8 With respect to risks of yield loss in agricultural crops and fruit and vegetable species, 

9 little new information was available beyond that of the previous review. However, limited 

10 information from a free air field based soybean study (SoyFACE) and information on then 

11 current cultivar sensitivities led to the conclusion that C-R functions developed in OTCs under 

12 the National Crop Loss Assessment Network (NCLAN) program could still be usefully applied. 

13 The crop risk assessment, like the tree seedling assessment, combined NCLAN C-R information 

14 on commodity crops, fruits and vegetables, crop growing regions, and interpolated exposures 

15 during each crop growing season. The risk assessment estimated that just meeting the 0.08 ppm, 

16 8-hr standard would still allow O3–related yield loss to occur in some sensitive commodity crops 

17 and fruit and vegetable species growing at that time in the U.S.

18 3.2 OVERVIEW OF CURRENT ASSESSMENT PLAN 

19 Since the 2008 review, new scientific information on the direct and indirect effects of O3

20 on vegetation and ecosystems, respectively, has become available. With respect to mature trees 

21 and forests, the information regarding O3 impacts to forest ecosystems has continued to expand, 

22 including limited new evidence that implicates O3 as an indirect contributor to decreases in 

23 stream flow through direct impacts on whole tree level water use. Newly published results from 

24 the Long-term FACE (Free Air CO2 enrichment) studies provide additional evidence regarding 

25 chronic O3 exposures in closed forest canopy scenarios including interspecies interactions such 

26 as decreased growth of branches and root mass in sensitive species. Also, lichen and moss 

27 communities on trees monitored in FACE sites have been shown to undergo species shifts when 

28 exposed to O3. In addition, recent available data from annual field surveys conducted by the 

29 USFS to assess foliar damage to selected tree species is available. In light of this new scientific 

30 information, we are including additional analyses, such as combining the USFS data with recent 
3-7

1 air quality data to determine the incidence of visible O3 damage occurring across the U.S. at air 

2 quality levels that meet or are below the current standard. Some of these analyses are not 

3 included in this first draft REA, but will be included in the second draft REA. To the extent 

4 warranted, based on new information regarding O3 effects on forest trees, both qualitative and 

5 quantitative assessments are included in an effort to place both the estimates of risk from more 

6 recent long-term studies and historic shorter-term studies in the context of ecosystem services. 

7 Additional information relevant to vegetation risk assessments available includes that 

8 regarding the interactions between elevated O3 and CO2 with respect to plant growth and how 

9 these interactions might be expected to be modified under different climatic conditions, and 

10 potential reactions of O3 with chemicals released by plants to attract pollinators that could 

11 decrease the distance the floral “scent trail” travels and potentially change the distance 

12 pollinators have to travel to find flowers. The REA also provides an assessment of impacts 

13 occurring in designated habitat for threatened or endangered species.

14 To the extent warranted, qualitative and/or quantitative assessments of ecosystem 

15 services impacted by O3 are considered to inform the current review. For example, the 

16 ecosystem services evaluation in this review includes tree biomass and crop analyses, and where

17 possible includes impacts on ecosystem services such as impacts on biodiversity, biological 

18 community composition, health of forest ecosystems, aesthetic values of trees and plants and the 

19 nutritive quality of forage crops. Carbon sequestration is another important ecosystem service 

20 (regulating) that may be affected by O3 damage to vegetation. New preliminary evidence of O3

21 effects on the ability of pollinators to find their target is also of special interest with respect to the 

22 possible implication for ecosystem services. Impairment of the ability of pollinators to locate 

23 flowers could have broad implications for agriculture, horticulture and forestry. 

24 We are using the Forest and Agricultural Sector Optimization Model Greenhouse Gas 

25 version (FASOM) to assess the economic impacts of O3 damage to forests, taking into account 

26 the tradeoffs between land use for forestry and agricultural. FASOM is a dynamic, non-linear 

27 programming model designed for use by the EPA to evaluate welfare benefits and market effects 

28 of carbon sequestration in trees, understory, forest floor, wood products and landfills that would 

29 occur under different agricultural and forestry scenarios. We use FASOM to model damage by 

30 O3 to the agriculture and forestry sectors and quantify how O3-exposed vegetation affects the 

31 ecosystem service of carbon sequestration. See Appendix X for details of the model and
3-8

1 methodology. [An appendix covering details of the model and methodology will be provided in 

2 supplemental materials.]

3 3.2.1 Air Quality Considerations 

4 Air quality analyses are necessary to inform and support welfare-related assessments. The 

5 air quality analyses for this review build upon those of the ISA and include consideration of: (1) 

6 summaries of recent ambient air quality data, (2) estimation approaches to extrapolate air quality 

7 values for rural areas without monitors as well as federally designated Class I natural areas 

8 important to welfare effects assessment, (3) air quality simulation procedures that modify recent 

9 air quality data to reflect changes in the distribution of air quality estimated to occur after just 

10 meeting current or alternative O3 standards. . In addition to updating air quality summaries 

11 since the last review, these air quality analyses include summaries of the most currently available 

12 ambient measurements for the current and potential alternate secondary standard forms, and 

13 comparisons among them . These air quality analyses use monitor data from the AQS database 

14 (which includes National Park Service monitors) and the CASTNET network. In the last review, 

15 the vegetation exposure analysis used a spatial interpolation technique to create an interpolated 

16 air quality surface to fill in the gaps in ambient monitoring data, especially those left by a sparse 

17 rural monitoring network in the western United States. In this review, additional approaches that 

18 potentially could be used to fill in the gaps in the rural monitoring network, as well as 

19 opportunities for enhancing the fusion of monitoring and modeled O3 data, are explored. 

20 As part of the air quality analyses supporting the assessments, it is necessary to adjust recent 

21 O3 air quality data to simulate just meeting the current standard and any alternative O3 standards. 

22 In this first draft REA, consistent with the previous review, we are using a quadratic air quality 

23 rollback approach (U.S. EPA, 2007b), but we are evaluating alternative air quality simulation 

24 procedures for use in simulating just meeting the current and alternative standards for the second 

25 draft REA.

26 3.2.2 National O3 Exposure Surface

27 Since the last review, little has changed in terms of the extent of monitoring coverage in 

28 non-urban areas. We consider both past and alternative approaches for generating estimates of 

29 national O3 exposures in an effort to continue enhancing our ability to characterize exposures in 
3-9

1 these non-monitored areas. The vegetation exposure assessments conducted include assessments 

2 of recent air quality, air quality associated with just meeting the current standard and, for the 

3 second draft REA, any alternative standards that might be considered.

4 In addition, given the importance of providing protection for sensitive vegetation in areas 

5 afforded special protections, such as in federally designated Class I natural areas, we may also 

6 consider alternative sources of O3 exposure information for those types of sites. For example, 

7 portable O3 monitors are being deployed in some national parks and a current exploratory study 

is underway to measure O3 concentration variations with gradients in elevation.2

12 To generate a national O3 exposure surface, staff is considering several interpolation 

13 methods. We have used a previously modeled O3 surface generated by the CMAQ model based 

14 on 2005 emissions at a 12 km grid resolution in conjunction with monitor data (2004-2006) to 

create a fused surface with the Modeled Attainment Test Software (MATS).

8 Information 

9 from these monitors could potentially inform our understanding of uncertainties associated with 

10 assessing O3 distribution patterns in complex terrain and high elevations. New exposure data 

11 that would inform this assessment will be considered where appropriate.

3 15 We have also used

16 the Voronoi Neighbor Averaging (VNA) interpolation method in the BenMAP model (Abt 

17 Associates, Inc., 2010) to create a national O3 surface from more recent monitor data (e.g., 2008-

2010).4

21 In order to generate the national O3 surface in terms of a particular index, the monitored 

22 data and CMAQ model outputs that form the basis for the interpolation need to be characterized 

23 in terms of that index. At a minimum, staff plans to generate the national surface in terms of the 

24 current secondary standard. Staff recognizes that additional indices may be selected for further 

25 evaluation upon review of the information contained in the ISA and may perform additional air 

26 quality analyses based on those indices. Any expanded evaluation of additional indices would be 

27 contained and discussed in the Policy Assessment. 

18 Staff will also evaluate alternate interpolation methods and sources of air quality data to 

19 assess which option is most appropriate given the analysis requirements, desire for consistency 

20 with the health risk assessment, and available resources. 

 2 For more information on portable ozone monitors in National Parks, please see 

http://www.nature.nps.gov/air/studies/portO3.cfm 3 More information on CMAQ is available at http://www.epa.gov/amad/CMAQ/index.html. More information on 

MATS is available at http://www.epa.gov/scram001/modelingapps_mats.htm.

4 More information on the VNA method in BenMAP is available at 

http://www.epa.gov/air/benmap/models/BenMAPManualAugust2010.pdf
3-10

1 In conjunction with the health risk assessors, staff is currently considering various 

2 approaches to simulate just meeting the current and alternative standards, including the quadratic 

3 air quality “rollback” adjustment that was used in the last review (Johnson, 1997) and variations 

4 of the proportional adjustment method. However for this first draft we have used the eVNA 

5 approach for the rollback adjustment. In addition, we are currently investigating methods for 

6 generating adjusted air quality in non-monitored areas. 

7 The national O3 surface, depicted as a GIS layer, provides the exposures needed as input to 

8 the crop and tree seedling risk and ecosystem service assessments described in subsequent 

9 sections.

10 3.3 ECOLOGICAL EFFECTS OF EXPOSURE

11 3.3.1 National Scale Assessment

12 3.3.1.1 Tree Seedling Concentration-Response Functions

13 We are analyzing the 11 OTC tree seedling C-R functions identified and assessed in the 

14 2007 O3 Staff Paper in terms of the current exposure metrics. This analysis enabled direct 

15 evaluation of estimated seedling biomass loss values expected to occur under air quality 

16 exposure scenarios expressed in terms of recent air quality and after simulation of just meeting 

17 current the standard. 

18 3.3.1.2 Estimation of Biomass Loss for Tree Seedlings 

19 In the 2007 O3 Staff Paper, information on tree species growing regions was derived from 

20 the USDA Atlas of United States Trees (Little, 1971). We are using more recent information 

21 from the USDA Forest Service FIA database in order to update growing ranges for the 11 tree 

22 species studied by NHEERL-WED. The national O3 surface is combined with the C-R function 

23 for each of the tree seedling species and information on each tree species growing region to 

24 produce estimates of biomass loss for each of the 11 tree seedling species. We are also including 

25 an additional analysis incorporating the Importance Values derived using FIA data. From this 

26 information, GIS maps are generated depicting biomass loss for each species for each air quality 

27 scenario.
3-11

1 3.3.2 Case Study Areas

2 In order to assess the ecological effects of O3 staff will analyze ecosystem level effects in 

3 several case study areas. These areas have been selected to allow a more refined assessment of 

4 the extent of foliar injury, biomass loss and welfare related services. Criteria that were used to 

5 select case study areas include:

6 • Occur in areas expected to have elevated levels of O3 where ecological effects might be 

7 expected to occur.

8 • Availability of vegetation mapping including estimates of species cover. 

9 • Geographic coverage representing a cross section of the nation, including urban and 

10 natural settings.

11 • Occurrence of O3 sensitive species and/or species for which O3 concentration-response 

12 curves have been generated.

13 3.3.2.1 Estimation of Vegetation Effects in National Parks

14 The National Parks provide several potential case study areas. The United States 

15 Geological Survey (USGS) in conjunction with the National Park Service (NPS) is actively 

16 creating maps of the vegetation communities within the National Parks 

17 (http://biology.usgs.gov/npsveg/index.html). This provides a consistent vegetation map to 

18 compare across park units, which includes species coverage data. The NPS has also generated a 

19 comprehensive list of plant species that are known to exhibit foliar injury at ambient O3 levels 

20 (Porter, 2003). 

21 We have selected Great Smoky Mountains National Park, Rocky Mountain National 

22 Park, and Sequoia/Kings National Park. All three of these park units occur in areas with elevated 

23 ambient O3 levels, have vegetation maps, and have species that are considered O3 sensitive. We 

24 considered including Acadia National Park however it was determined not to fit our selection 

25 criteria for O3 exposure.

26 The NPS vegetation maps are compared, using GIS, to the national O3 surface to provide 

27 an overall estimate of foliar damage and total biomass loss. Potential ecological metrics that are 

28 being calculated include:

29 • Percent of vegetation cover affected by foliar injury.
3-12

1 • Percent of trails affected by foliar injury.

2 • Estimate of species specific biomass loss within the case study area.

3 3.3.2.2 Estimation of Effects in Urban Areas

4 Several urban areas nationally have extensive habitat management plans that include 

5 resource and vegetation mapping. These data are not as consistent or as readily available as the 

6 NPS units but in some cases can provide adequate vegetation maps in regions where O3 sensitive 

7 species occur. We are using the iTree model developed by the U.S. Forest Service to estimate 

8 impacts on vegetation in Atlanta, Baltimore, Syracuse, the Chicago region, and the urban areas 

9 of Tennessee. We are presenting preliminary results for model runs representing current ambient 

10 conditions and runs simulating just meeting the current standard in this draft of the REA. Model 

11 runs simulating any alternative standards that may be considered will be presented in the second 

12 draft REA. [The first draft results and an appendix with details regarding the model and 

13 methodology will be included in supplemental materials.] 

14 3.4 ECOSYSTEM SERVICES EVALUATION

15 One of the objectives of the risk assessment for a secondary NAAQS is to quantify the 

16 risks to public welfare. The Risk and Exposure Assessment for Review of the Secondary 

17 National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur (U.S. EPA, 

18 2009) has detailed discussions of how ecosystem services and public welfare are related and how 

19 a services framework may be employed to evaluate effects on welfare. We have identified the 

20 ecosystem services associated with the ecological effects described in Chapter 5 of this 

21 document for the national scale assessment and the more refined case study areas. These 

22 services may be characterized as: supporting services that are necessary for all other services 

23 (e.g., primary production); cultural services including existence and bequest values, aesthetic 

24 values, and recreation values, among others; provisioning services (e.g., food and timber); and 

25 regulating services such as climate regulation or flood control. Specific services to be evaluated 

26 are discussed in the following sections. 
3-13

1 3.4.1 National Scale Assessment

2 Depending on data and resource availability, we are attempting to develop an estimate of 

3 ecosystem service impacts broadly across the United States for selected cultural, regulating, and 

4 provisioning services.

5 3.4.1.1 Cultural Services

6 We are using GIS mapping developed for the ecological effects analysis to illustrate 

7 where effects may be occurring and relate those areas to national scale statistics for recreational 

8 use available through the National Survey of Fishing, Hunting, and Wildlife-Associated 

9 Recreation (U.S. DOI, 2007) and the National Survey on Recreation and the Environment 

10 (USDA,2012) . The resulting estimates of service provision are then scaled to the current 

11 population and values assigned using existing meta-data on willingness to pay from the 

12 Recreation Values Database available at: http://recvaluation.forestry.oregonstate.edu/

13 We are aware that these estimates are limited to current levels of service provision and 

14 provide a snapshot of the overall magnitude of services potentially affected by O3 exposure. At 

15 this time estimates of service loss due to O3 exposure is beyond the available data and resources; 

16 however, estimates of the current level of services would have embedded within them the current 

17 losses in service due to O3O3 exposure. 

18 3.4.1.2 Regulating Services

19 The regulating services associated with O3 exposure include fire regimes and fire 

20 recovery due to O3 effects on community composition and diversity, and fuel loading due to 

21 early senescence and insect attack. There is data available through the CAL-FIRE on fire 

22 incidence, risk, and expenditures related to fires in California.

23 We are considering using the PnET model to estimate impacts on the hydrologic cycle for 

24 the second draft of this document. We considered the DLEM model however the resources 

25 required proved prohibitive.

26 3.4.1.3 Provisioning Services

27 Below we outline potential methods for assessing the provisioning services associated with 

28 crop yield loss and tree biomass loss, which are consistent with the methods from the previous 

29 review.

30 Estimation of Yield Loss and Economic Valuation for Timber and Crops - The FASOM model 

31 has been utilized recently in many evaluations of effects on the timber and agriculture market 
3-14

1 sectors. We are using FASOM to assess the economic impacts of O3 damage to forests and 

2 agricultural crops jointly. FASOM is a dynamic, non-linear programming model designed for 

3 use by the EPA to evaluate welfare benefits and market effects of O3 induced biomass loss in 

4 trees that would occur under different agricultural and forestry scenarios. It is possible to use 

5 FASOM to model damage by O3 to the agriculture and forestry sectors and quantify how O3-

6 exposed vegetation affects the provision of timber and crops. [An appendix with details of the 

7 model and methodology will be provided in supplemental materials.]

8 FASOM has been used to calculate the economic impacts of yield changes between the

9 current ambient conditions and simulated ‘just meet’ scenarios for a base year. This approach 

10 will also be used to calculate the economic valuation of any alternative standards under 

11 consideration in the second draft. 

12 3.4.1.4 Supporting Services

13 The supporting services associated with the vegetation effects of O3 exposure include 

14 potential impacts on net primary productivity, and community composition. We considered 

15 using the DLEM model to estimate impacts on net primary productivity however this proved 

16 prohibitive in terms of resource availability. For the second draft we are exploring the possibility 

17 of using the PnET model to estimate these service impacts. 

18 3.4.2 Case Study Analysis

19 3.4.2.1 National Park Areas

20 We are using GIS mapping produced for the ecological effects analysis to illustrate where 

21 effects may be occurring as a starting point to illustrate and, if possible, quantify the ecosystem 

22 services at potential risk. These are primarily, in national parks, cultural values that include 

23 existence, bequest and recreational values. We also overlay the ecological effects maps with data 

24 on where hiking trails, campgrounds, or other park amenities are found to intersect potentially 

25 affected areas. We then relate those areas to case study specific statistics for recreational use 

26 available through the National Park Service. In addition, we have described the other nonuse 

27 values associated with national parks including existence and bequest values. For the resulting 

28 estimates of service provision values are then assigned using existing meta-data on willingness to 

29 pay from Kaval and Loomis (2003). We are aware that these estimates will be limited to current 
3-15

1 levels of service provision. At this time estimates of service loss due to O3 exposure may be 

2 beyond the available data and/or resources for many if not all ecosystem services listed above.

3 3.4.2.2 Urban Areas

4 We are using the i-Tree model to assess effects on ecosystem services provided by urban 

5 forests, pollution removal, and carbon storage and sequestration. The i-TREE model is a publicly 

6 available peer-reviewed software suite developed by the U.S. Forest Service and its partners to 

7 assess the ecosystem service impacts of urban forestry (available here: 

8 http://www.itreetools.org/). We are collaborating with the U.S. Forest Service to vary the tree 

9 growth metric in the model, which allows us to assess the effects of O3 exposure on the ability of 

10 the forests in the selected case study area to provide the services enumerated by the model. See 

11 Appendix 6A for a description of the model and methodology. [Preliminary results will be 

12 provided in supplemental materials.]

13 3.5 UNCERTAINTY AND VARIABILITY

14 An important issue associated with any ecological risk assessment is the characterization 

15 of uncertainty and variability. Variability refers to the heterogeneity in a variable of interest that 

16 is inherent and cannot be reduced through further research. For example, there may be 

17 variability among C-R functions describing the relation between O3 and vegetation injury across 

18 selected study areas. This variability may be due to differences in ecosystems (e.g., diversity, 

19 habitat heterogeneity, and rainfall), levels and distributions of O3 and/or co-pollutants, and/or 

20 other factors that vary either within or across ecosystems. 

21 Uncertainty refers to the lack of knowledge regarding both the actual values of model input 

22 variables (parameter uncertainty) and the physical systems or relationships (model uncertainty –

23 e.g., the shapes of concentration-response functions). In any risk assessment, uncertainty is, 

24 ideally, reduced to the maximum extent possible, through improved measurement of key 

25 parameters and ongoing model refinement. However, significant uncertainty often remains and 

26 emphasis is then placed on characterizing the nature of that uncertainty and its impact on risk 

27 estimates. The characterization of uncertainty can include both qualitative and quantitative 

28 analyses, the latter requiring more detailed information and often, the application of sophisticated 

29 analytical techniques.
3-16

1 While the goal in designing a quantitative risk assessment is to reduce uncertainty to the 

2 extent possible, with variability the goal is to incorporate the sources of variability into the 

3 analysis approach to insure that the risk estimates are representative of the actual response of an 

4 ecosystem (including the distribution of that adverse response across the ecosystem). An 

5 additional aspect of variability that is pertinent to this risk assessment is the degree to which the 

6 set of selected case study areas provide coverage for the range of O3-related ecological risk 

7 across the U.S.

8 For this first draft we have not included detailed analyses of uncertainty or variability. For 

9 the second draft of this document we plan to more fully differentiate variability and uncertainty 

10 in the design of the risk assessment to more clearly address (a) the extent to which the risk 

11 estimates represent the distribution of ecological impacts across ecosystems, including impacts 

12 on more sensitive species, and (b) the extent to which risk estimates are impacted by key sources 

13 of uncertainty which could prevent a clear differentiation between regulatory alternatives based 

14 on risk estimates. 
4-1

1 4 AIR QUALITY CONSIDERATIONS

2 4.1 INTRODUCTION

3 Air quality information is used in the welfare risk and exposure analyses, described in 

4 Chapters 5 and 6, to assess risk and exposure resulting from recent O3 concentrations, as well as 

5 to estimate the relative change in risk and exposure resulting from adjusted O3 concentrations

6 after simulating just meeting the current O3 standard of 0.075 ppm. To complete these analyses, 

7 ambient monitoring data is provided for all AQS monitors in the U.S. for several relevant metrics

8 for 2006-2010. In addition, a national-scale spatial surface is generated that estimates W126 

9 concentrations throughout the U.S. for 2006-2008 and for simulating just meeting the current O3

10 standard of 0.075 ppm. This chapter describes the air quality information used in these analyses, 

11 providing an overview of monitoring data and air quality (section 4.2) as well as an overview of 

12 air quality inputs to the welfare risk and exposure assessments (section 4.3).

13 4.2 OVERVIEW OF O3 MONITORING AND AIR QUALITY

14 To monitor compliance with the NAAQS, state and local monitoring agencies operate O3

15 monitoring sites at various locations, depending on the size of the area and typical peak O3

16 concentrations (US EPA, 2012, sections 3.5.6.1, 3.7.4). In 2010, there were 1,250 State and 

17 Local O3 monitors reporting concentrations to EPA (US EPA, 2012, Figures 3-21 and 3-22). 

18 The minimum number of O3 monitors required in a Metropolitan Statistical Area (MSA) ranges 

19 from zero, for areas with a population under 350,000 and with no recent history of an O3 design 

20 value greater than 85% of the NAAQS, to four, for areas with a population greater than 10 

million and an O3 design value greater than 85% of the NAAQS.1 21 For areas with required O3

22 monitors, at least one site must be designed to record the maximum concentration for that 

23 particular metropolitan area. Since O3 concentrations decrease significantly in the colder parts of 

24 the year in many areas, O3 is required to be monitored only during the “O3 season,” which varies 

by state (US EPA, 2012, section 3.5.6 and Figure 3-20).2

28 

25 Figure 4-1 shows the location and 8-h 

O3 design values (4th 26 highest 8-h daily max O3 concentration occurring within a three-year 

27 period) for all available monitors in the US for the 2008-2010 period.

29

30

 1

The current monitor and probe siting requirements have an urban focus and do not address siting in non-urban, rural 

areas. States may operate O3 monitors in non-urban or rural areas to meet other objectives (e.g., support for research 

studies of atmospheric chemistry or ecosystem impacts). 

2

Some States and Territories operate O3 monitors year-round, including Arizona, California, Hawaii, Louisiana, 

Nevada, New Mexico, Puerto Rico, Texas, American Samoa, Guam and the Virgin Islands.
4-2

1

2 Figure 4- 1 Individual monitor 8-h daily max O3 design values displayed for the 2008-

3 2010 period (U.S. EPA, 2012, Figure 3-52A)

4

5 In 2010, there were approximately 112 monitoring sites being operated in rural areas. 

6 These sites included 15 National Core (NCore) monitors, 80 Clean Air Status and Trends 

7 Network (CASTNET) monitors, and 17 Portable O3 Monitoring Systems (POMS) network

8 monitors operated by the National Park Service (NPS). The location of these monitors is shown 

9 in Figure 4-2.

10
4-3

1

2 Figure 4- 2 U.S. Rural NCore, CASTNET and NPS POMS O3 sites in 2010 (U.S. EPA, 

3 2012, Figure 3-22)

4

5 4.3 OVERVIEW OF AIR QUALITY INPUTS TO RISK AND EXPOSURE 

6 ASSESSMENTS

7 The air quality information input into the welfare risk and exposure assessments includes 

8 recent air quality measurement data from the years 2006-2010, as well as a national-scale 

9 “fused” spatial surface of air quality data for recent air quality, 2006-2008, and adjusted to 

10 reflect just meeting the current O3 standard of 0.075 ppm. In this section, we summarize these air 

11 quality inputs and discuss the methodology used to simulate air quality to meet the current 

12 standard. More details on these data and methodologies can be found in Wells et al. (2012).

13

14 4.3.1 Recent Air Quality

15 The air quality monitoring data used to inform the first draft O3 Risk and Exposure 

16 Assessments were hourly O3 concentrations collected between 1/1/2006 and 12/31/2010 from all 

17 US monitors meeting EPA’s siting, method, and quality assurance criteria in 40 CFR Part 58. 
4-4

These data were extracted from EPA’s Air Quality System (AQS) database3

8 4.3.1.1 Ambient Measurements and Air Quality Metrics

1 on June 27, 2011. 

2 Regionally concurred exceptional event data (i.e. data certified by the monitoring agency to have 

3 been affected by natural phenomena such as wildfires or stratospheric intrusions, and concurred 

4 upon by the EPA regional office) were not included in the assessments. However, concurred 

5 exception events were rare, accounting for less than 0.01% of the total observations. All 

6 concurred exceptional events in 2006-2010 were related to wildfires in California in 2008. There 

7 were no concurrences of exceptional event data for stratospheric intrusions in 2006-2010.

9 EPA focused the analysis in the welfare exposure and risk assessment on the W126 O3

10 exposure metric. The W126 metric is a seasonal aggregate of hourly O3 concentrations, designed 

11 to measure the cumulative effects of O3 exposure on vulnerable plant and tree species. The 

12 metric uses a logistic weighting function to place less emphasis on exposure to low 

13 concentrations and more emphasis on exposure to high concentrations (Lefohn et al, 1988). 

14 The first step in calculating W126 values was to sum the hourly O3 concentrations within 

15 each month, resulting in monthly index values. Since most plant and tree species are not 

16 photochemically active during nighttime hours, only O3 concentrations observed during daytime 

17 hours (defined as 8:00 AM to 8:00 PM local time) were included in the summations. The 

18 monthly W126 index values were calculated as follows:

∑∑= = + − =

N

d h dh

dh

C

C Monthly W

1

19

8 1 4403*exp( 126* )

19 126

20 where N is the number of days in the month,

21 d is the day of the month (d = 1, 2, ..., N),

22 h is the hour of the day (h = 0, 1, ..., 23),

23 Cdh is the O3 concentration observed on day d, hour h, in parts per million.

24 Next, the monthly W126 index values were adjusted for missing data. If Nm is defined as 

25 the number of daytime O3 concentrations observed during month m (i.e. the number of terms in 

26 the monthly index summation), then the monthly data completeness rate is Vm = Nm / 12 * N. 

27 The monthly index values were adjusted by dividing them by their respective Vm. Monthly index 

28 values were not computed if the monthly data completeness rate was less than 75% (Vm < 0.75). 

 3 EPA’s Air Quality System (AQS) database is a state-of-the-art repository for many types of air quality and related 

monitoring data. AQS contains monitoring data for the six criteria pollutants dating back to the 1970’s, as well as more recent 

additions such as air toxics, meteorology, and quality assurance data. At present, AQS receives O3 monitoring data collected 

hourly from over 1,300 monitors, and quality assured by one of over 100 state, local, or tribal air quality monitoring agencies.
4-5

1 Finally, annual W126 index values were computed as the maximum sum of their 

2 respective adjusted monthly index values occurring in three consecutive months (January –

3 March, February – April, etc.). Three-month periods spanning two years (November – January, 

4 December – February) were not considered because the seasonal nature of O3 dictates that it is 

5 very unlikely for the maximum values to occur at that time of year. The W126 metric was 

6 analyzed for each individual year of 2006 to 2008 and for the three year period of 2006-2008.

7 For the specific application of the Kohut analysis, N100 and SUM06 metric were also 

8 computed. The procedures used to calculate N100 and SUM06 values are similar to the 

9 calculation of the W126 metric that is described above. Hourly O3 concentrations are summed 

10 within each month, resulting in monthly index values, and only O3 concentrations observed 

11 during daytime hours (defined as 8:00 AM to 8:00 PM local time) were included in the 

12 summations. The monthly N100 and SUM06 values were calculated as follows:

∑∑= = 











>

≤ =

N

d h dh

dh

if C ppm

if C ppm Monthly N

1

19

8 1, 0.100

0, 0.100

13 100

∑∑= =

= −

N

d h

Monthly SUM Cdh

1

19

8

14 06 max(0, ( 0.060))

15 The monthly N100 and SUM06 values were adjusted for missing data as described above for the 

16 W126 metric. Annual N100 and SUM06 values were computed as the maximum sum of their 

17 respective adjusted monthly index values occurring in three consecutive months (January –

18 March, February – April, etc.). Three-month periods spanning two years (November – January, 

19 December – February) were not considered because the seasonal nature of O3 dictates that it is 

20 very unlikely for the maximum values to occur at that time of year. 

21 The N100 and SUM06 metrics were calculated for each individual year for all 5 years 

22 (2006 to 2010) and used in the Kohut analysis, which is discussed in more detail in Chapter 5. In 

23 addition, the W126 and N100 value was calculated for 3-month and 7-month values for the 

24 Kohut analysis and analyzed for each individual year of 2006 to 2010.

25 4.3.1.2 National-scale Air Quality Inputs

26 In addition to ambient monitoring data, the welfare risk and exposure assessment also 

27 analyzed a national scale spatial surface of W126 for the three-year period of 2006-2008 and for 

28 each individual year: 2006, 2007 and 2008. This analysis employed a data fusion approach to 

29 take advantage of the accuracy of monitor observations and the comprehensive spatial 

30 information of the CMAQ modeling system to create a national-scale “fused” spatial surface of 

31 seasonal average O3. The spatial surface is created by fusing 2006-2008 measured O3

32 concentrations with the 2007 CMAQ model simulation, which was run for a 12 km gridded 

33 domain, using the EPA’s Model Attainment Test Software (MATS; Abt Associates, 2010), 
4-6

1 which employs the enhanced Voronoi Neighbor Averaging (eVNA) technique (Timin et al.,

2 2010) enhanced with information on the spatial gradient of O3 provided by CMAQ results. The 

3 2006-2008 W126 national-scale “fused” spatial surface is shown in Figure 4-3. More details on 

4 the ambient measurements and the 2007 CMAQ model simulation, as well as the spatial fusion 

5 technique, can be found in Wells et al. (2012).

6

7 4.3.2 Air Quality After Simulating “Just Meeting” Current O3 Standard

8 In addition to 2006-2008 air quality concentrations for the W126 metric, the risk and 

9 exposure assessments also consider the relative change in risk and exposure when considering 

10 the distribution of W126 after simulating “just meeting” the current O3 standard of 0.075 ppm.

11 The sections below summarize the methodology applied for this first draft REA to simulate just 

12 meeting the current NAAQS by “rolling back” the baseline distribution of recent O3

13 concentrations. More details on these inputs are provided in Wells et al. (2012).

14

15 4.3.2.1 Methods

16 The “quadratic rollback” method was used in the previous O3 NAAQS review to adjust 

17 ambient O3 concentrations to simulate minimally meeting current and alternative standards (U.S. 

18 EPA, 2007). As the name implies, quadratic rollback uses a quadratic equation to reduce high 

19 concentrations at a greater rate than low concentrations. The intent is to simulate reductions in 

20 O3 resulting from unspecified reductions in precursor emissions, without greatly affecting 

21 concentrations near ambient background levels (Duff et al., 1998).

22 Two independent analyses (Johnson, 2002; Rizzo, 2005; 2006) were conducted to 

23 compare quadratic rollback with other methods such as linear (proportional) rollback and 

24 distributional (Weibull) rollback. Both analyses used different rollback methods to reduce 

25 concentrations from a high O3 year to simulate levels achieved during a low O3 year, then 

26 compared the results to the ambient concentrations observed during the low O3 year. Both 

27 analyses concluded that the quadratic rollback method resulted in an 8-hour O3 distribution most 

28 similar to that of the ambient concentrations.

29 In this review, quadratic rollback was used to reduce O3 concentrations in all areas of the 

30 U.S. with violating monitors to just meet the current NAAQS of 0.075 ppm (75 ppb). To do this, 

31 a hierarchical method was used to group all monitors in the U.S. into hypothetical “non32 attainment” areas (Wells et al., 2012). For each of these areas, quadratic rollback was then 

33 employed to simulate just meeting the current standard. Hourly O3 concentrations were reduced 

34 so that the highest design value in each area was exactly 75 ppb, the highest value meeting the 

35 NAAQS. Finally, the 2006-2008 W126 metric was calculated from the hourly rollback 
4-7

1 concentrations. It should be noted that O3 concentrations were only adjusted relative to the other 

2 monitors included in the hypothetical “non-attainment” area. In this way, areas with all monitors

3 below 75 ppb would not have been affected by this rollback methodology and the O3

4 concentrations in those areas would not have changed. This was true even when these monitors

5 were very close to, but outside of, other hypothetical “non-attainment” areas that were adjusted 

6 to simulate just meeting the current standard.

7 To generate a national-scale spatial surface that represents 2006-2008 W126 

8 concentrations when attaining the current NAAQS, the spatial surface for 2006-2008 recent air 

9 quality was adjusted to reflect the rolled back W126 monitor concentrations. To do this, the 

10 rolled back W126 monitor values were inserted into the spatial surface at the monitor locations

11 and the W126 surface was smoothed using the Voronoi Neighbor Averaging (VNA) spatial 

12 averaging technique to minimize any sharp gradients between the national-scale spatial surface 

13 that represents 2006-2008 W126 concentrations and the rollback W126 monitor concentrations. 

14 This is described in more detail in Wells et al. (2012).

15 4.3.2.2 Results

16 Figure 4-3 shows the national-scale 2006-2008 W126 spatial “fused” surface created as 

17 described in Section 4.3.1.1, and Figure 4-4 shows the national-scale 2006-2008 W126 surface 

18 that reflects simulation of just meeting the current standard of 0.075 ppm. Figure 4-5 shows the 

19 difference between the two spatial surfaces, and shows how W126 changed when simulating just 

20 meeting the current standard. The state of California was most affected by the rollback, with 

21 average changes in W126 of around 20. Other areas with notable changes include the areas 

22 around: Atlanta, Charlotte, Denver, Phoenix, Salt Lake City and the area between Washington, 

23 D.C. and Boston (all areas that had relatively high 8-hour O3 concentrations above the current 

24 standard).

25
4-8

1

2 Figure 4- 3 “Fused” national-scale surface of W126 metric, 2006-2008
4-9

1

2 Figure 4- 4 “Fused” national-scale surface of W126 metric for 2006-2008, adjusted for 

3 simulating just meeting the current standard of 0.075 ppm.

4
4-10

1

2 Figure 4- 5 Difference between the “fused” national-scale surfaces of W126 for 2006-

3 2008 and for 2006-2008 adjusted for simulating just meeting the current 

4 standard of 0.075 ppm.

5
 5-1 

1 5 ECOLOGICAL EFFECTS 

2 5.1 INTRODUCTION 

3 This chapter presents the results of ecological risk analyses based on the causal and likely 

4 causal effects of O3 on vegetation and ecosystems described in the ISA. Recent studies reviewed 

5 in the O3 ISA (U.S. EPA, 2012a) support and strengthen the findings reported in the 2006 O3

6 AQCD (U.S. EPA, 2006). The most significant new body of evidence since the 2006 O3 AQCD 

7 comes from research on molecular mechanisms of the biochemical and physiological changes 

8 observed in many plant species in response to O3 exposure. These newer molecular studies not 

9 only provide very important information regarding the many mechanisms of plant responses to 

10 O3, they also allow for the analysis of interactions between various biochemical pathways which 

11 are induced in response to O3. However, many of these studies have been conducted in artificial 

12 conditions with model plants, which are typically exposed to very high, short doses of O3 and are 

13 not quantifiable as part of this risk assessment, which is focused on recent ambient levels of O3

14 exposure and O3 levels simulated to meet current and alternative O3 standards. 

15 The causal findings reported in the ISA based on the current science are summarized in 

16 Table 5- 1. This table includes both causal and likely causal effects. Two of the effects, 

17 alteration of below-ground biogeochemical cycles and alteration of terrestrial communities are 

18 not analyzed directly in this review. However both can be inferred as components of the i-Tree 

19 and FASOM models discussed in Chapter 6 and the scaled-biomass loss analyses presented in 

20 this chapter. 

21 Table 5- 1 Summary of O3 causal determinations for vegetation and ecosystem effects 

22 (modified from Table 9-18 in the ISA) 

Vegetation and Ecosystem Effect Conclusions from 2012 ISA 2012 REA 

Visible Foliar Injury Effects on 

Vegetation 

Causal Relationship Analyzed in this chapter at a Nationalscale and within NPS Units (Section 

5.3.2) and NPS case study areas 

(section 5.4) 

Reduced Vegetation Growth Causal Relationship Analyzed in this chapter at a Nationalscale and within NPS case study areas 

(section 5.3) 

Reduced Productivity in Terrestrial 

Ecosystems 

Causal Relationship Analyzed in Chapter 6 using pNET-CN 

(pending) 

Reduced Carbon (C) Sequestration in 

Terrestrial Ecosystems 

Likely Causal Relationship Analyzed in Chapter 6 using pNET-CN 

(pending) and i-TREE (section 6.X) 
 5-2 

Vegetation and Ecosystem Effect Conclusions from 2012 ISA 2012 REA 

Reduced Yield and Quality of 

Agricultural Crops 

Causal Relationship Yield loss data are included in the 

FASOM model (section 6.X), but 

effects on agricultural crops are not a 

focus of this review 

Alteration of Terrestrial Ecosystem 

Water Cycling 

Likely Causal Relationship Analyzed in Chapter 6 using pNET-CN 

(pending) Relationship 

Alteration of Below-ground 

Biogeochemical Cycles 

Causal Relationship Not analyzed directly in this review 

Alteration of Terrestrial Community 

Composition 

Likely Causal Relationship Not analyzed directly in this review 

1 

2 5.2 RELATIVE BIOMASS LOSS 

3 The previous O3 AQCDs (U.S. EPA, 1996, 2006) and current O3 ISA (U.S. EPA, 2012) 

4 concluded that there is strong and consistent evidence that ambient concentrations of O3 decrease 

5 photosynthesis and growth in numerous plant species across the U.S. 

6 Meta-analyses by Wittig et al. (2007, 2009) demonstrate the coherence of O3 effects on 

7 plant photosynthesis and growth across numerous studies and species using a variety of 

8 experimental techniques. Furthermore, recent meta-analyses have generally indicated that O3

9 reduces C allocation to roots (Wittig et al., 2009; Grantz et al., 2006). Since the 2006 O3 AQCD, 

10 several studies were published based on the Aspen FACE experiment using “free air,” O3 and 

11 CO2 exposures in a planted forest in Wisconsin. Overall, the studies at the Aspen FACE 

12 experimental site were consistent with many of the open-top chamber (OTC) studies that were 

13 the foundation of previous O3 NAAQS reviews. These results strengthen our understanding of O3

14 effects on forests and demonstrate the relevance of the knowledge gained from trees grown in 

15 OTC studies. 

16 The 1996 and 2006 O3 AQCDs relied extensively on results from analyses conducted on 

17 commercial crop species under the auspices of the National Crop Loss Assessment Network 

18 (NCLAN) and on analyses of tree seedling species conducted by the EPA’s National Health and 

19 Environmental Effect Laboratory, Western Ecology Division (NHEERL/WED). Results from 

20 these studies have been published in numerous publications, including Lee et al. (1994; 1989, 

21 1988b, 1987), Hogsett et al. (1997), Lee and Hogsett (1999), Heck et al. (1984), Rawlings and 

22 Cure (1985), Lesser et al. (1990), and Gumpertz and Rawlings (1992). Those analyses concluded 

23 that a three-parameter Weibull model – 
 5-3 

1 



 







 











W 126

Y e 2 

3 

4 Equation 5-1 

5 

6 is the most appropriate model for the response of absolute yield and growth to O3 exposure, 

7 because of the interpretability of its parameters, its flexibility (given the small number of 

8 parameters), and its tractability for estimation. In addition, if the intercept term, α, is removed, 

9 the model estimates relative yield or biomass without any further reparameterization. 

10 Formulating the model in terms of relative yield or biomass loss (RBL) as related to the 3-month 

11 W126 O3 index - 

12 

RBL = 1 - exp[-(W126/η)

β 13 ]

14 Equation 5-2 

15 is essential in comparing exposure-response across species, genotypes, or experiments for which 

16 absolute values of the response may vary greatly. In the 1996 and 2006 O3 AQCDs, the two17 parameter model of relative yield was used in deriving common models for multiple species, 

18 multiple genotypes within species, and multiple locations. 

19 Relative biomass loss (RBL) functions for the 11 tree species used in this assessment are 

20 presented in Table 5-2 (see the ISA (EPA 2012a) for a more extensive review of the calculation 

21 of the C-R functions). 

22 
 5-4 

1 Table 5- 2 Relative Biomass Loss Functions for Tree Species (modified from Table 9-18 

2 in the ISA) 

Species RBL Function η (ppm) β

Red Maple (Acer rubrum) 

1 – exp[-(W126/η)

β

] 

318.12 1.3756 

Sugar Maple (Acer saccharum) 36.35 5.7785 

Red Alder (Alnus rubra) 179.06 1.2377 

Tulip Poplar (Liriodendron tulipifera) 51.38 2.0889 

Ponderosa Pine (Pinus ponderosa) 159.63 1.1900 

Eastern White Pine (Pinus strobus) 63.23 1.6582 

Virginia Pine (Pinus virginiana) 1714.64 1.0000 

Eastern Cottonwood (Populus deltoides) 10.10 1.7793 

Quaking Aspen (Populus tremuloides) 109.81 1.2198 

Black Cherry (Prunus serotina) 38.92 0.9921 

Douglas Fir (Pseudotsuga menzeiesii) 106.83 5.9631 

3 

4 Figure 5- 1 shows a comparison of W126 median RBL response functions for the tree 

5 species used in this assessment. The figure illustrates how the two parameters affect the shape of 

6 the resulting curves. Differences in the shape of these curves are important for understanding 

7 differences in the analyses presented later in this chapter. The two parameters of the RBL 

8 equation (Equation 5-2) control the shape of the resulting curve. The value of η in the RBL 

9 function affects the inflection point of the curve and β affects the steepness of the curve. Species 

10 with smaller values of β (e.g. Virginia pine,) or species with η values which are above the normal 

11 range of ambient W126 measurements (e.g. ponderosa pine, red alder) have response functions 

12 with more gradual and consistent slopes. This results in more constant rate of change in RBL 

13 over a range of O3 exposure consistent with ambient exposure levels. 

14 In contrast, the species with larger β values (e.g. sugar maple, Douglas fir) have response 

15 functions that behave more like thresholds, with large changes in RBL over some ranges of O3

16 and relatively small changes at other levels. In these cases the “threshold” is determined by the η

17 parameter of the model. In the example of eastern cottonwood, β is relatively low, but because η

18 is also very low relative to the other species, so the resulting C-R curve has a very steep gradient 

19 relative to other species with similar β values. 
 5-5 

1 

2 Figure 5- 1 Relative Biomass Loss Functions for 11 Tree Species 

3 

4 5.2.1 Species Level Analyses 

5 5.2.1.1 Individual Species Analyses 

6 The C-R functions listed in Table 5-2 were used to generate RBL surfaces for the 11 trees 

species using GIS (ESRI®, ArcMAPTM 7 10). A surface was created using recent ambient O3

8 conditions and a scenario with O3 levels rolled back to simulate just meeting the current 8 hr 

9 secondary standard (see Chapter 4 for a more detailed description of the O3 surfaces). The recent 

10 ambient conditions are based on monitored data from the years 2006 to 2008 and for the 

11 remainder of this analysis we will refer to that surface as “ambient”. Two species are presented 

12 here to illustrate the results, ponderosa pine (Figure 5- 2 and Figure 5- 4) and tulip poplar (Figure 

13 5- 3 and Figure 5- 5). RBL surfaces for the remaining 8 species are presented in Appendix 5A. It 

14 is important to note that these maps represent the RBL value for one tree species within each 

0 20 40 60 80 100

0.0 0.2 0.4 0.6 0.8 1.0

O3 C-R Functions

W126

RBL

Quaking Aspen

Black Cherry

Douglas Fir

White Pine

Ponderosa Pine

Red Alder

Red Maple

Sugar Maple

Tulip Poplar

Virginia Pine

Eastern Cottonwood
 5-6 

1 CMAQ grid cell represented, so these maps should be interpreted as indicating potential risk to 

2 individual trees of that species growing in that area. 

3 Three of the tree species occur entirely in the western U.S.; ponderosa pine, Douglas fir, 

4 and red alder. Ranges for the western species were taken from the U.S. Department of 

5 Agriculture’s Atlas of United States Trees (Little, 1971) (Figure 5- 2 and Figure 5- 4). The 

6 western tree species have more fragmented habitats than the eastern species. The areas in souther 

7 California have the highest levels of O3, which can be seen as the very high areas of RBL in 

8 Figure 5-2. The area of high RBL in Figure 5-2 in Idaho is a result of high O3 levels from the 

9 2007 Idaho Forest Fires. This area is still elevated in Figure 5-4 because those areas were not 

10 near areas considered out of attainment, so were not reduced significantly in the scenario just 

11 meeting the current standard. 

12 

13 Figure 5- 2 Relative Biomass Loss of Ponderosa Pine (Pinus ponderosa) seedlings 

14 under recent ambient O3 exposure levels (2006 – 2008) 

Ponderosa Pine

RBL 

(Ambient)

0.001 - 0.018

0.019 - 0.035

0.036 - 0.054

0.055 - 0.074

0.075 - 0.102

0.103 - 0.150

0.151 - 0.210

0.211 - 0.294
 5-7 

1 Ranges for the eight eastern species were also based on the USDA Ranges (Figure 5- 3 

2 and Figure 5- 5, green outline). Additional work by the northern research station based on Forest 

3 Inventory Analysis data (FIA) was used to update the range for the 8 eastern species (U.S. Forest 

4 Service Climate Change Atlas, http://www.fs.fed.us/nrs/atlas/littlefia/index.html). These updates 

5 can be seen in Figure 5- 3 as areas outside of the green line indicating the Little’s range that are 

6 shown to have a RBL value. For this analysis, these values were only used to expand the species 

7 ranges and were not used to indicate absence inside of the Little’s range. However, this was done 

8 in the scaled analyses presented in section 5.2.2. 

9 The eastern tree species had less fragmented ranges and areas of elevated RBL that were 

10 more easily attributed to urban areas (e.g. Atlanta, GA and Charlotte, NC) or to the Tennessee 

11 Valley Authority Region. 

12 

13 Figure 5- 3 Relative Biomass Loss of tulip poplar (Liriodendron tulipifera) seedlings 

14 under recent ambient O3 exposure levels (2006 – 2008) 

15 

Potential 

Biomass Loss

(Ambient)

0.006 - 0.042

0.043 - 0.077

0.078 - 0.113

0.114 - 0.148

0.149 - 0.184

0.185 - 0.220

0.221 - 0.255

0.256 - 0.291

Tulip Poplar
 5-8 

1 

2 Figure 5- 4 Relative Biomass Loss of Ponderosa Pine with O3 exposure rolled back 

3 to meet the current (8-hr) secondary standard. 

4 

Potential 

Biomass Loss

(Current

Standard)

0.001 - 0.038

0.039 - 0.074

0.075 - 0.111

0.112 - 0.147

0.148 - 0.184

0.185 - 0.221

0.222 - 0.257

0.258 - 0.294

Ponderosa Pine
 5-9 

1 

2 Figure 5- 5 Relative Biomass Loss of Tulip Poplar with O3 exposure rolled back to meet 

3 the current (8-hr) secondary standard. 

4 

5 5.2.1.2 Combined Risk Analysis of Individual Species 

6 To assess the combined risk of the 11 tree species, the RBL values were compared 

7 between O3 exposure scenarios. The comparisons were done on using individual CMAQ 12km 

8 grid cells as individual points for comparison. A linear-fit model, the equivalent of a simple 

9 regression, was used to compare the RBL surfaces. The y-intercept forced through the origin so 

10 that the slopes of the resulting lines would be comparable. The results for ponderosa pine and 

11 tulip poplar are shown in Figure 5- 6 and the summary values for all of the species are listed in 

12 Table 5- 3. Plots for the remaining species are presented in Appendix 5A. The RBL surface for 

13 recent conditions was used as the baseline for comparison between rollback scenarios. This first 

14 draft includes only one O3 scenario, with O3 levels simulating just meeting the current standard. 

Potential 

Biomass Loss

(Current

Standard)

0.004 - 0.042

0.043 - 0.077

0.078 - 0.113

0.114 - 0.148

0.149 - 0.184

0.185 - 0.220

0.221 - 0.255

0.256 - 0.291

Tulip Poplar
 5-10 

1 The second draft will include additional scenarios with distinct secondary standards, expressed 

2 using the W126, a cumulative, seasonal index. 

3 Using this approach provides two advantages. First, it will in part correct for variability in 

4 O3 exposures in different regions. For example, one source of variability is the difference 

5 between O3 concentrations measured at the height of ambient monitors and those occurring at the 

6 height of the actual tree canopy. In the 2007 Staff Paper (U.S. EPA, 2007a) this difference was 

7 addressed by applying a 10% reduction in hourly O3 values in each grid cell. That methodology 

8 introduced uncertainty, but was a useful in comparing the effects of uncertainty in the O3

9 exposure values. 

10 The method used to generate the exposure surface in this assessment is not readily 

11 adjusted in a similar manner so the cell-by-cell comparison allows each grid cell to be compared 

12 based on the proportional change between exposure scenarios. Bias in the exposure value based 

13 on elevation should be similar between O3 exposure scenarios, so will be factored into the 

14 proportional change. The second advantage is this provides a uniform methodology to compare 

15 between endpoints. In this analysis, individual tree species are used as the endpoint of the 

16 analysis. The analysis presented in section 5.2.2 uses designated critical habitat and Class I areas 

17 as the endpoint, and the individual case study areas analyzed in section 5.3 can each be used as a 

18 distinct endpoint, but comparable analyses can be done with all 4 different endpoints. One 

19 negative of this analysis is that by forcing the model through the origin, the r-squared values are 

20 difficult to interpret. 
 5-11 

1 

2 Figure 5- 6 Linear fit model of RBL under recent ambient O3 exposure levels (2006 – 

3 2008) conditions compared to estimated values for meeting the current (8-hr) 

4 standard for ponderosa pine and tulip poplar. The dashed blue line 

5 represents the one-to-one line. The red line is the fitted line. 

6 

7 The values presented in Table 5- 3 summarize the individual species analysis. The 

8 median and maximum RBL values are listed for comparison under ambient conditions. The slope 

9 of linear fit model (Figure 5- 6, red lines, Table 5- 3), can be interpreted as the average 

10 proportion of ambient RBL that is expected under the rollback scenario. A similar value is 

11 obtained by dividing the mean RBL under the rollback scenario by the RBL value under ambient 

12 conditions. Conversely, the proportion decrease could be calculated using a paired t-test and 

13 dividing the estimated difference by the mean Ambient RBL. Because some of the RBL 

14 distributions are not normally distributed, the linear fit model was determined to be more robust. 

15 In this analysis, the ambient RBL is used as the baseline, so the proportion at ambient conditions 

16 is by definition 1, and the slope for all subsequent comparisons is always the average proportion 

of the ambient RBL. For this 1st 17 daft REA, we evaluate only the scenario for just meeting the 

18 current secondary O3 standard. Scenarios for meeting alternative O3 standards will be evaluated 

19 in the second draft REA. We have put in placeholder columns in Table 5-3 for several 

20 alternative standards to provide a sense of the structure of the comparisons. The EPA has not 

21 determined at this point the number of alternative standards that will be evaluated in the second 

22 draft REA. 

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Ponderosa Pine

PBL - Ambient Conditions

PBL - Current Standard

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Tulip Poplar

PBL - Ambient Conditions

PBL - Current Standard
 5-12 

1 Several values in Table 5- 3 are notable. Douglas fir is a relatively non-sensitive species 

2 at ambient levels of O3, however the proportional value is very low (0.357). Referring to Figure 

3 5- 1, this is because this species is only sensitive at very high O3 levels. After simulating just 

4 meeting the current secondary O3 standard, there are no areas in the country where O3 levels are 

5 high enough to cause substantial RBL for this species, so the proportional change appears very 

6 high despite a relatively low maximum RBL value when compared to other species (Table 5- 3). 

7 However, additional reductions in O3 resulting from lower levels of the standards will not result 

8 in similarly large proportional changes for this species because they will now be in a portion of 

9 the RBL function where this species shows very low levels of RBL, and therefore is not 

10 responsive to O3 changes. 

11 Sugar maple is similar, but because the maximum RBL at ambient conditions is much higher 

12 than for Douglas fir (see Figure 5- 1), reducing O3 concentrations below the “threshold”, in part 

13 controlled by the η parameter (see Table 5-2), for Sugar maple creates a much larger 

14 proportional difference. 

15 

16 Table 5- 3 Summary of Proportional Change in RBL for 11 Tree Species 

Species 

Median 

RBL 

(Ambient) 

Maximum 

RBL 

(Ambient) 

Proportion 

at Current 

Standard 

Proportion 

at Alt A 

Proportion 

at Alt B 

Red Maple (Acer rubrum) 0.009 0.039 0.707 

Sugar Maple (Acer saccharum) 0.000 0.206 0.080 

Red Alder (Alnus rubra) 0.005 0.118 0.894 

Tulip Poplar (Liriodendron tulipifera) 0.045 0.291 0.533 

Ponderosa Pine (Pinus ponderosa) 0.038 0.294 0.653 

Eastern White Pine (Pinus strobus) 0.034 0.226 0.642 

Virginia Pine (Pinus virginiana) 0.008 0.018 0.717 

Eastern Cottonwood (Populus deltoides) 0.564 0.999 0.844 

Quaking Aspen (Populus tremuloides) 0.039 0.377 0.795 

Black Cherry (Prunus serotina) 0.225 0.547 0.834 

Douglas Fir (Pseudotsuga menzeiesii) 0.000 0.001 0.357 

17 

18 The results of the individual species analyses can be combined into a single plot across 

19 O3 exposure scenarios (Figure 5- 7). In this analysis, all of the values under ambient conditions 
 5-13 

1 are, by definition, 1 as this is the baseline so the box for that category is a line. After simulating 

2 just meeting the current secondary O3 standard, the RBL is approximately 70% of the RBL under 

3 ambient conditions. Alternatively, this could be interpreted to say that RBL with O3 exposure 

4 levels simulating just meeting the current secondary O3 standard is 30% lower than under 

5 ambient conditions. We have put in placeholders in Figure 5-7 for several alternative standards 

6 to provide a sense of the structure of the comparisons. The EPA has not determined at this point 

7 the number of alternative standards that will be evaluated in the second draft REA. 

8 

9 

10 Figure 5- 7 Change in RBL across exposure scenarios for 11 tree species. Biomass 

11 loss estimates under recent ambient O3 (2006 – 2008) conditions were 

12 used as the baseline. [Alternate levels will be included in the second 

13 draft based on simulating just attaining alternative standards] 

Alt B Alt A Current Ambient

0.0 0.2 0.4 0.6 0.8 1.0

Relative change in Biomass Loss
 5-14 

1 

2 5.2.2 Relative Biomass Loss in Federally Designated Areas 

3 5.2.2.1 Importance Value Scaled Analyses 

4 In order to assess the risk to ecosystems in geographic areas from biomass loss as 

5 opposed to the potential risk to individual tree species, it is necessary to scale the RBL to reflect 

6 the abundance of each species in specific forest ecosystems. As part of the U.S. Forest Service 

7 (USFS) Climate Change Atlas (http://www.fs.fed.us/nrs/atlas/littlefia/index.html) researchers at 

8 the USFS Northeastern Research Station have calculated Importance Values for eastern Tree 

9 species (Prasad and Iverson, 2003). Prasad and Iverson’s (2003) calculation of Importance 

10 Values (IV) was based equally on relative basal area and the number of stems of each tree 

11 species within each FIA plot included in their analysis area with a range for each species ranging 

from 0 to a maximum of 100. Plot level IV’s were over a 20km2 12 scale grid for the entire study 

area. These values were merged with the CMAQ 12 km2 13 grid used for the O3 exposure and RBL 

14 surfaces, with each CMAQ grid cell assigned a weighted mean IV for each species. 

15 The resulting values were used in the preceding analysis (section 5.2.1) to update the 

16 Little’s Ranges for the eastern species. To assess biomass loss in federally designated areas, the 

17 IV’s were used to scale the RBL value for each tree species. The IV surface for tulip poplar is 

18 shown in Figure 5- 8. Similar to the preceding analysis, the Little’s Range is included for 

19 reference to illustrate where the IV indicates occurrences outside of that range; however in this 

20 analysis some areas within the species range are assigned an IV of 0 and are treated as areas of 

21 non-occurrence. Figure 5- 8 shows an expected abundance pattern for tulip poplar, with the 

22 highest abundance (as estimated by IV) near the center of its reported range, and areas near the 

23 edge of its range where the species is either very low in abundance or absent all together. 
 5-15 

1 

2 Figure 5- 8 Importance Values for Tulip Poplar. (Data from U.S. Forest Service, 

3 http://www.fs.fed.us/nrs/atlas/littlefia/index.html) 

4 

5 To scale RBL, the IV was divided by 100, giving a proportional value between 0 and 1 in 

6 each grid cell and the proportional IV was multiplied by the RBL for each tree species for each 

7 O3 exposure scenario. The resulting scaled-RBL surfaces for Tulip Poplar are shown in Figure 5- 

8 9 (Recent Conditions) and Figure 5- 10 (Current Standard). 

Importance Value

0.00 - 0.77

0.78 - 1.89

1.90 - 3.56

3.57 - 5.77

5.78 - 8.57

8.58 - 12.19

12.20 - 18.48

18.49 - 41.65

Tulip Poplar
 5-16 

1 

2 Figure 5- 9 Scaled Relative Biomass Loss for Tulip Poplar under recent ambient O3

3 exposure levels (2006 – 2008) 

4 

5 It is important to note that the scaled-RBL values highlight different areas as being the 

6 highest area relative to the un-scaled RBL. In Figure 5- 3 the areas of highest RBL for tulip 

7 poplar, with values above 0.25 are predominantly in the south. In Figure 5- 9 the southern areas 

8 are still high, but the areas around Washington D.C and Baltimore appear much higher, as does 

9 western Pennsylvania and West Virginia, relative to the un-scaled RBL values. 

IV-Scaled 

Biomass Loss

(Ambient)

0.000 - 0.001

0.002 - 0.003

0.004 - 0.005

0.006 - 0.009

0.010 - 0.015

0.016 - 0.024

0.025 - 0.043

0.044 - 0.089

Tulip Poplar
 5-17 

1 

2 Figure 5- 10 Scaled Relative Biomass Loss for Tulip Poplar after simulating just meeting 

3 the current (8-hr) secondary O3 standard. 

4 

5 To assess the overall risk to ecosystems federally designated areas, the scaled-RBL 

6 values were summed across the 8 eastern species generating a summed-RBL value, with each 

7 species weighted by its scaled-RBL. Figure 5- 11 illustrates these values across the eastern U.S. 

8 The very high values in Figure 5- 11 are directly related to the presence of Eastern Cottonwood. 

9 Cottonwood is a very sensitive species and in many areas where it occurs it is a dominant tree 

10 species. Figure 5- 12 shows the same summed value with Eastern Cottonwood removed. The 

11 highest summed-RBL value decreases from 0.854 to 0.204, demonstrating the effect of 

12 cottonwood. Figure 5- 13 and Figure 5- 14 show the summed-RBL surfaces under the current 

13 standard rollback scenario for all eastern species and excluding eastern cottonwood respectively. 

14 There are two important things to note with respect to the IV scaled analysis. First is that 

15 the IV’s do not account for total cover, only the relative cover of the tree species present. This is 

IV-Scaled 

Biomass Loss

(Current Standard)

0.000 - 0.001

0.002 - 0.003

0.004 - 0.005

0.006 - 0.009

0.010 - 0.015

0.016 - 0.024

0.025 - 0.043

0.044 - 0.089

Tulip Poplar
 5-18 

1 most noticeable with cottonwood, which has IV’s near 100 in some areas (see Appendix 5A), but 

2 particularly in the western portions of its range, the absolute cover is probably much lower than 

3 100%. Although this affects the direct interpretation of the values presented here, by focusing on 

4 the proportional changes in summed-RBL between O3 exposure scenarios, the overall effect of 

5 the variability in absolute cover values in reduced. 

6 The second important point is that this analysis only accounts for the 8 eastern species 

7 with C-R functions. Other species may also be sensitive to O3 exposure and it is possible that 

8 other species that are not sensitive may be indirectly affected through changes in community 

9 composition and competitive interactions. 

10 

11 Figure 5- 11 Summed Relative Biomass Loss (scaled) for 8 Eastern tree species recent 

12 ambient O3 exposure levels (2006 – 2008) 

IV-Scaled

Biomass Loss

(Ambient)

0.000 - 0.008

0.009 - 0.021

0.022 - 0.041

0.042 - 0.071

0.072 - 0.121

0.122 - 0.212

0.213 - 0.388

0.389 - 0.854

Eastern Tree Species (Summed)
 5-19 

1 

2 Figure 5- 12 Summed Relative Biomass Loss (scaled) for 7 species, excluding 

3 eastern cottonwood, under ambient O3 conditions 

IV-Scaled

Biomass Loss

(Ambient)

0.000 - 0.004

0.005 - 0.009

0.010 - 0.015

0.016 - 0.025

0.026 - 0.039

0.040 - 0.060

0.061 - 0.094

0.095 - 0.204

Eastern Tree Species (Summed)
 5-20 

1 

2 Figure 5- 13 Summed Relative Biomass Loss (scaled) for 8 Eastern tree species 

3 after simulating just meeting the current (8-hr) secondary O3

4 standard. 

IV-Scaled

Biomass Loss

(Current Standard)

0.000 - 0.008

0.009 - 0.021

0.022 - 0.041

0.042 - 0.071

0.072 - 0.121

0.122 - 0.212

0.213 - 0.388

0.389 - 0.854

Eastern Tree Species (Summed)
 5-21 

1 

2 Figure 5- 14 Summed Relative Biomass Loss (scaled) for 7 species, excluding eastern 

3 cottonwood, after simulating just meeting the current (8-hr) secondary O3

4 standard. 

5 

6 5.2.3 Potential Biomass Loss in Federally Designated Areas 

7 5.2.3.1 Class I Areas 

8 Federally designated Class I areas were analyzed in relation to the W126 surface and the 

9 scaled RBL surfaces. Figure 5- 15 shows the Class I areas and W126 values. Many of the Class I 

10 areas are in the western U.S., where IV’s were not available to scale the RBL values. This 

11 analysis uses only the Class I areas in the eastern U.S., many of which are small, and are difficult 

12 to see at the scale of Figure 5- 15, or even when expanded to show only the eastern U.S. Maps of 

13 each area as in Appendix 5B. 

IV-Scaled

Biomass Loss

(Current Standard)

0.000 - 0.004

0.005 - 0.009

0.010 - 0.015

0.016 - 0.025

0.026 - 0.039

0.040 - 0.060

0.061 - 0.094

0.095 - 0.204

Eastern Tree Species (Summed)
 5-22 

1 

2 Figure 5- 15 Recent O3 conditions in Class I Areas 

3 

4 The analyses of Class I areas were completed in the same manner as for individual 

5 species (see Figure 5- 6), with each designated area treated as a geographic endpoint. The areas 

6 were analyzed using the same linear model approach and the results are summarized in Table 5- 

7 4. We have put in placeholders in Figure 5-7 for several alternative standards to provide a sense 

8 of the structure of the comparisons. EPA has not determined at this point the number of 

9 alternative standards that will be evaluated in the second draft REA. 

10 Plots of the analyses are presented in Appendix 5B. Many Class I areas occur where the 

11 ambient O3 levels are very low and simulation of just attaining the current secondary O3 standard 

12 resulted in very little, or no change in O3 exposure in these areas so the cumulative analysis was 

13 done twice, first with all eastern Class I areas included (Figure 5-16A) and a second analysis 

14 excluding areas where the ambient W126 was below 10 (Figure 5-16B). 

W126

0.7 - 5.0

5.1 - 10.0

10.1 - 15.0

15.1 - 20.0

20.1 - 25.0

25.1 - 30.0

30.1 - 35.0

35.1 - 65.6

Class I Areas
 5-23 

1 Areas in Table 5- 4 with the proportion listed as NA were not included in the analysis. 

2 These areas were excluded either due to small sample size (e.g. Rainbow Lake Wilderness), or 

3 because the summed RBL values in all, or all but 1, grid cells were 0. 

4 

5 Table 5- 4 Proportion of Ambient summed-RBL in Eastern U.S. Class I areas 

6 

Class I Area 

Mean 

W126 

(PPM) 

Number of 

Grids 

Proportion 

of Current 

Standard 

Proportion 

at Alt A 

Proportion 

at Alt B 

Acadia National Park 6.74 9 0.724 

Badlands/Sage Creek Wilderness 7.53 11 NA 

Boundary Waters Canoe Area Wilderness 5.24 67 1.000 

Bradwell Bay Wilderness 6.90 4 0.990 

Breton Wilderness 16.28 4 NA 

Brigantine Wilderness 13.7 2 0.386 

Caney Creek Wilderness 9.15 2 0.995 

Cape Roman Wilderness 12.63 13 1.000 

Chassahowitzka Wilderness 11.66 5 0.803 

Cohutta Wilderness 13.12 5 0.716 

Dolly Sods Wilderness 7.8 2 0.996 

Everglades National Park 7.25 62 1.000 

Great Gulf Wilderness 7.55 2 0.892 

Great Smoky Mountains National Park 16.64 26 0.445 

Hercules-Glades Wilderness 6.00 4 0.966 

Isle Royale National Park 7.11 16 1.00 

James River Face Wilderness 9.1 2 0.992 

Joyce Kilmer-Slickrock Wilderness 14.07 3 0.496 

Linville Gorge Wilderness 10.83 3 0.910 

Lye Brook Wilderness 6.83 4 0.889 

Mammoth Cave National Park 13.53 6 0.981 

Mingo Wilderness 13.6 4 0.845 

Moosehorn Wilderness 1.93 4 1.000 

Okefenokee Wilderness 8.65 21 0.993 

Otter Creek Wilderness 7.87 3 0.946 

Presidential Range-Dry River Wilderness 7.52 5 0.914 
 5-24 

Class I Area 

Mean 

W126 

(PPM) 

Number of 

Grids 

Proportion 

of Current 

Standard 

Proportion 

at Alt A 

Proportion 

at Alt B 

Rainbow Lake Wilderness 5 1 NA 

Saint Marks Wilderness 8.93 9 0.999 

Seney Wilderness 7.18 4 0.990 

Shenandoah National Park 10.85 22 0.922 

Shining Rock Wilderness 12.65 4 0.679 

Sipsey Wilderness 14.53 4 0.765 

Swanquarter Wilderness 14.55 4 0.949 

Theodore Roosevelt National Park 6.78 9 1.000 

Upper Buffalo Wilderness 7.17 3 0.997 

Voyageurs National Park 5.08 13 1.000 

Wichita Mountains 9.87 6 NA 

Wind Cave National park 10.96 5 NA 

Wolf Island Wilderness 8.93 3 NA 

1 

2 The combined analyses indicate that simulating just meeting the current secondary O3

3 standards, the proportion of ambient summed RBL is approximately 95% relative to ambient 

4 conditions when all eastern Class I areas are included (Figure 5-16A). When only areas with 

5 ambient O3 levels above 10 ppm are included, the proportion decreases to approximately 80% 

6 (Figure 5-16B). 
 5-25 

1 

A. B. 

2 

3 Figure 5- 16 Proportion of ambient scaled biomass loss in (A) all analyzed eastern 

4 Class I Areas and (B) eastern Class I areas with average ambient O3

5 W126 metric exceeding 10 ppm 

6 5.2.3.2 Critical Habitats 

7 Federally designated critical habitat areas for endangered species were analyzed in 

8 relation to the W126 surface and the scaled RBL surfaces. Figure 5- 17 shows the critical habitat 

9 areas with W126 values. Like the Class I areas, many of these are in the western U.S. where IV’s 

10 were not available, so were not used in this analysis. Also like the Class I areas, many of the 

11 critical habitat areas are difficult to see at the scale of Figure 5- 17 and are included as smaller 

12 maps in Appendix 5C. 

13 

Alt B Alt A Current Ambient

0.0 0.2 0.4 0.6 0.8 1.0

Relative change in Biomass Loss

Alt B Alt A Current Ambient

0.0 0.2 0.4 0.6 0.8 1.0

Relative change in Biomass Loss
 5-26 

1 

2 Figure 5- 17 Recent O3 conditions in designated critical habitat areas. 

3 

4 Analyses of designated critical habitat areas were completed in the same manner as for 

5 Class I areas, with the linear model results summarized in Table 5- 5 and the complete analyses 

6 including figures presented in Appendix 5C. We have put in placeholder columns in Table 5-5 

7 for several alternative standards to provide a sense of the structure of the comparisons. EPA has 

8 not determined at this point the number of alternative standards that will be evaluated in the 

9 second draft REA. 

10 Areas in Table 5- 5 with the proportion listed as NA were not included in the analysis. 

11 These areas were excluded either due to small sample size (e.g. San Marcos gambusia), or 

12 because the summed RBL values in all, or all but 1, grid cells were 0 (e.g. Cape Sable seaside 

13 sparrow). 

W126

0.5 - 5.0

5.1 - 10.0

10.1 - 15.0

15.1 - 20.0

20.1 - 25.0

25.1 - 30.0

30.1 - 35.0

35.1 - 65.7

Designated Critical habitat
 5-27 

1 This analysis is not intended to indicate risk to the specific endangered species within the 

2 designated area; rather the intent is to use the designated critical habitat to define an endpoint for 

3 evaluating risk to locations that might be more sensitive to adverse effects from O3 exposure. For 

4 example, analysis of the critical habitat area for Gulf sturgeon is focused on the terrestrial 

5 ecosystems within the designated habitat area, not on the aquatic system, or the Gulf sturgeon. 

6 The implication in the aquatic and marine areas in particular is that effects on neighboring 

7 terrestrial ecosystems will affect the aquatic or marine system, but quantifying that linkage is not 

8 possible at this time. 

9 Table 5- 5 Proportion of ambient summed-RBL in Eastern U.S. Critical Habitat Areas 

Designated Critical Habitat Area 

Mean 

W126 

(PPM) 

Number of 

Grids 

Proportion 

at Current 

Standard 

Proportion 

at Alt A 

Proportion 

at Alt B 

Gulf sturgeon 14.69 116 0.695 

Appalachian elktoe 11.70 22 0.685 

Reticulated flatwoods salamander 9.16 35 0.983 

Frosted flatwoods salamander 9.16 35 0.983 

Cape Sable seaside sparrow 7.06 21 NA 

Braun’s rock-cress 15.77 3 NA 

Helotes mold beetle 11.63 6 NA 

Houston toad 7.89 7 NA 

Gray wolf 5.08 283 1.000 

Piping plover 8.51 472 1.000 

Salt Creek tiger beetle 2.93 4 NA 

Robber Baron Cave meshweaver 7.30 4 NA 

Madla’s Cave meshweaver 11.27 12 NA 

Braken Bat Cave meshweaver 10.40 31 NA 

Virginia big-eared bat 6.63 7 0.970 

American crocodile 6.65 53 NA 

Haha 5.47 17 NA 

Fountain darter 7.90 5 NA 

Niangua darter 7.88 17 0.910 

San Marcos salamander 7.90 4 NA 

San Marcos gambusia 7.90 1 NA 

Whooping crane 7.77 43 NA 

Mississippi sandhill crane 12.28 6 0.759 
 5-28 

Designated Critical Habitat Area 

Mean 

W126 

(PPM) 

Number of 

Grids 

Proportion 

at Current 

Standard 

Proportion 

at Alt A 

Proportion 

at Alt B 

Johnson’s seagrass 9.27 13 NA 

Comal Springs riffle beetle 7.98 5 NA 

Mountain golden heather 11.05 2 0.892 

Zapata bladderpod 4.08 4 NA 

Canada lynx 4.46 523 1.000 

Waccamaw silverside 8.30 2 0.926 

Spruce-fir moss spider 14.78 6 0.906 

Government Canyon Bat Cave spider 10.40 31 NA 

Concho water snake 5.47 17 NA 

Arkansas River shiner 12.40 78 NA 

Cape Fear shiner 14.00 7 0.667 

Topeka shiner 5.57 235 0.988 

Rice rat 5.82 6 NA 

Amber darter 18.84 7 0.708 

Conasauga logperch 19.00 4 0.686 

Leopard darter 7.04 21 0.961 

Choctawhatchee beach mouse 12.42 5 NA 

Alabama beach mouse 17.87 3 0.798 

St. Andrew beach mouse 10.70 11 0.889 

Perdido Key beach mouse 18.40 2 0.730 

Everglade snail kite 9.90 58 1.000 

Atlantic salmon 3.17 312 0.925 

Hine’s emerald dragonfly 9.50 30 0.669 

Peck’s cave amphipod 8.43 3 NA 

Comal Springs dryopid beetle 8.30 3 NA 

Cokendolpher Cave harvestman 7.30 4 NA 

West Indian manatee 9.45 211 0.991 

Louisiana black bear 9.95 90 0.771 

Texas wild-rice 7.90 6 NA 

Rhadine exilis (No common name) 11.35 22 NA 

Rhadine infernalis (No common name) 11 30 NA 

1 
 5-29 

1 The cumulative analyses indicate that across all eastern critical habitat areas, the 

2 proportion of the ambient summed-RBL was between 90% and 95% under the current standard 

3 rollback scenario (Figure 5-18A). When areas with ambient O3 levels below 10 ppm are 

4 excluded, the proportion decreases to approximately 75% (Figure 5-18B). 

5 

A. B. 

6 

7 Figure 5- 18 Proportion of ambient scaled-biomass loss in (A) all analyzed eastern 

8 critical habitat areas and (B) eastern critical habitat areas with 

9 average ambient O3 W126 metric exceeding 10 ppm 

10 

11 5.2.4 National Park Case Study Areas 

12 The National Parks provide excellent case study areas for more refined analyses of O3

13 exposure risks. The National Park Service (NPS) conducts ongoing O3 monitoring in many 

14 parks, and these monitors were used when possible in the creation of the O3 exposure surfaces 

15 for the parks. In addition, recreational use data are available for the parks for analyses of 

16 recreational value presented in Chapter 6. Three parks were chosen as case study areas: Great 

17 Smoky Mountains National Park (GSMNP), Rocky Mountain National Park (RMNP), and 

18 Sequoia/Kings Canyon National Park (SKCNP). 

19 Vegetation mapping has been completed in all three parks by the NPS in conjunction 

20 with the United States Geological Survey (USGS). These maps were used to estimate the percent 

Alt B Alt A Current Ambient

0.0 0.2 0.4 0.6 0.8 1.0

Relative change in Biomass Loss

Alt B Alt A Current Ambient

0.0 0.2 0.4 0.6 0.8 1.0

Relative change in Biomass Loss
 5-30 

1 cover of the tree species included in the risk assessment. These values were then used in a similar 

2 way to the IV’s in the preceding section, but on a much finer scale. The vegetation maps for the 

3 parks are available through the USGS Vegetation Characterization Program 

4 (http://biology.usgs.gov/npsveg/apps/). The vegetation map for GSMNP was completed in 2004 

5 (Madden et al. 2004). 

6 The National Vegetation Community codes assigned to each vegetation community were 

7 used to obtain cover estimate data through plots stored in VegBank 

8 (http://vegbank.org/vegbank/index). Whenever possible, only plots from within the park were 

9 used. In some cases, no plots were available from within the park and in those cases plots from 

10 the same vegetation community in nearby areas were used. In a few cases there were no plots 

11 available, and those communities were excluded. 

12 The W126 surface for each park was intersected with the vegetation polygons and the 

13 RBL values for the tree species present were scaled using the percent cover of each tree species 

14 the same as in the preceding section when IV was used. These values were then summed within 

15 each polygon in the GIS shapefile to create a detailed surface for each park. To assess the 

16 proportional change in scaled RBL in each park a linear model was used as in the preceding 

17 sections. In this analysis each polygon was treated as an individual point as opposed to CMAQ 

18 grid cells as in the preceding analyses. 

19 

20 [GSMNP is the only park completed at present, the linear model results will be combined into a 

21 combined analysis when more parks are included] 

22 

23 5.2.4.1 Great Smoky Mountain National Park 

24 Recent (2006 – 2008) ambient O3 levels (3-month 12-hr W126) in GSMNP range from 

25 9.3 PPM along the southeastern boundary to 23.3 PPM along the northwestern boundary (Figure 

26 5- 19). After simulating just attaining the current secondary O3 standard, (Figure 5- 20) the 

27 W126 values decrease to 7.7 PPM to 13 PPM. 

28 
 5-31 

1 

2 Figure 5- 19 Recent (2006 – 2008, 12-hr 3-month W126) O3 Exposure in GSMNP 

3 

4 

W126

9.3

9.4 - 10.0

10.1 - 15.0

15.1 - 20.0

20.1 - 25.0

25.1 - 30.0

30.1 - 35.0

35.1 - 65.0

Great Smoky Mountains National Park
 5-32 

1 

2 Figure 5- 20 O3 Exposure in GSMNP after simulating just meeting the current (8-

3 hr) secondary standard. 

4 

5 The vegetation map for GSMNP included 34 vegetation communities. Six of the eastern 

6 tree species occurred within the park. The resulting scaled RBL values for the ambient and 

7 current standard surfaces are shown in Figure 5- 21 and Figure 5- 22. The linear model results 

8 for GSMNP indicate a proportionally large decrease (slope = 0.493) in summed-RBL when 

9 comparing the current standard to ambient conditions (Figure 5- 23). 

10 

W126

(Current Standard)

7.7

7.8 - 10.0

10.1 - 15.0

15.1 - 20.0

20.1 - 25.0

25.1 - 30.0

30.1 - 35.0

35.1 - 65.0

Great Smoky Mountains National Park
 5-33 

1 

2 Figure 5- 21 Summed-RBL in GSMNP, scaled using percent cover of species, under 

3 recent O3 conditions. White areas within the park represent areas where no 

4 data were available or were developed, with minimal vegetation. 

5 

Potential Biomass Loss 

(Scaled)

0.001 - 0.005

0.006 - 0.011

0.012 - 0.018

0.019 - 0.027

0.028 - 0.043

0.044 - 0.074

0.075 - 0.114

0.115 - 0.165

Great Smoky Mountains National Park
 5-34 

1 

2 Figure 5- 22 Summed-RBL in GSMNP, scaled using percent cover of species after 

3 simulating just meeting the current secondary O3 standard. 

4 

Potential Biomass Loss 

(Scaled)

0.000 - 0.005

0.006 - 0.011

0.012 - 0.027

0.028 - 0.043

0.044 - 0.074

0.075 - 0.079

0.080 - 0.114

0.115 - 0.165

Great Smoky Mountains National Park
 5-35 

1 

2 Figure 5- 23 Linear Fit Model comparing RBL under ambient conditions and a 

3 scenario just meeting the current standard. 

4 

5 5.2.4.2 Rocky Mountain National Park 

6 [To be added in the second draft] 

7 5.2.4.3 Sequoia/Kings National Park 

8 [To be added in the second draft] 

9 5.2.4.4 National Park Case Study Area Summary 

10 

11 Table 5- 6 Proportion of summed-RBL in National Park Case Study Areas 

12 

Designated Critical Habitat Area 

Mean W126 

(PPM) 

Max W126 

(PPM) 

Proportion 

at Current 

Standard 

Proportion 

at Alt A 

Proportion 

at Alt B 

Great Smoky Mountains National Park 16.45 23.30 0.493 

Rocky Mountain National Park 

Sequoia/Kings National Park 

13 

0.00 0.05 0.10 0.15 0.20

0.00 0.05 0.10 0.15 0.20

GSMNP

RBL - Ambient Conditions

RBL - Current Standard
 5-36 

1 

2 

3 [This will include a summary of the linear model results, presented in similar to the 

4 boxplots presented in preceding sections] 

5 5.3 VISIBLE FOLIAR INJURY 

6 Visible foliar injury resulting from exposure to O3 has been well characterized and 

7 documented over several decades on many tree, shrub, herbaceous, and crop species (U.S. EPA, 

8 2012a, 2006, 1996, 1984, 1978). Visible foliar injury symptoms are considered diagnostic as 

9 they have been verified experimentally in exposure-response studies, using exposure 

10 methodologies such as CSTRs, OTCs, and free-air fumigation (see Section 9.2 of the ISA for 

11 more detail on exposure methodologies). Although the majority of O3-induced visible foliar 

12 injury occurrence has been observed on seedlings and small plants, many studies have reported 

13 visible injury of mature coniferous trees, primarily in the western U.S. (Arbaugh et al., 1998) and 

14 to mature deciduous trees in eastern North America (Schaub et al., 2005; Vollenweider et al., 

15 2003; Chappelka et al., 1999a; Chappelka et al., 1999b; Somers et al., 1998; Hildebrand et al., 

16 1996). 

17 Although visible injury is a valuable indicator of the presence of phytotoxic 

18 concentrations of O3 in ambient air, it is not always a reliable indicator of other negative effects 

19 on vegetation. The significance of O3 injury at the leaf and whole plant levels depends on how 

20 much of the total leaf area of the plant has been affected, as well as the plant’s age, size, 

21 developmental stage, and degree of functional redundancy among the existing leaf area. Previous 

22 O3 AQCDs have noted the difficulty in relating visible foliar injury symptoms to other vegetation 

23 effects such as individual plant growth, stand growth, or ecosystem characteristics (U.S. EPA, 

24 2012a, 2006, 1996). As a result, it is not presently possible to determine, with consistency across 

25 species and environments, what degree of injury at the leaf level has significance to the vigor of 

26 the whole plant. However, in some cases, visible foliar symptoms have been correlated with 

27 decreased vegetative growth (Somers et al., 1998; Karnosky et al., 1996; Peterson et al., 1987; 

28 Benoit et al., 1982) and with impaired reproductive function (Chappelka, 2002; Black et al., 

29 2000). Conversely, the lack of visible injury does not always indicate a lack of phytotoxic 

30 concentrations of O3 or a lack of non-visible O3 effects (Gregg et al., 2006). 

31 
 5-37 

1 5.3.1 National-Scale Analysis of Foliar Injury 

2 5.3.1.1 National Summed Importance Values 

3 The NPS has published a list of known and suspected O3 sensitive species (NPS, 2003), 

4 which was updated in 2006 (NPS, 2006). This list of species was used together with the IV’s 

5 from the USFS (Prasad and Iverson, 2003). A map of the eastern U.S. was generated showing the 

6 summed IV’s of species sensitive to foliar injury from O3 (Figure 5- 24). This essentially shows 

7 the abundance of trees likely to be impacted by elevated O3 levels. 

8 

9 [Analysis is not complete, waiting on data from John Coulston with the USFS to complete this 

10 analysis] 

11 

12 Figure 5- 24 Summed Importance Values for Sensitive Species in the Eastern U.S.

13 5.3.1.2 Forest Health Monitoring Network 

14 

Summed Importance Values of Sensitive Tree Species

Summed IV

0 - 20

21 - 40

41 - 60

61 - 80

81 - 100
 5-38 

1 5.3.2 Updated Assessment of Risk of Visible Foliar Injury in National Parks 

2 A study by Kohut (2007) assessed the risk of O3-induced visible foliar injury on O3

3 bioindicators (i.e., O3-sensitive vegetation (NPS, 2006)) in 244 national parks as part of the NPS’ 

4 Vital Signs program. Kohut (2007) estimated O3 exposure using hourly O3 monitoring data 

5 conducted at 35 parks from 1995 to 1999 and estimated O3 exposure at 209 additional parks 

6 using kriging, a spatial interpolation technique. Kohut (2007) qualitatively assessed risk based on 

evaluation of three criteria: the frequency of exceedance of foliar injury thresholds1 7 using several 

8 O3 exposure metrics, the extent that low soil moisture constrains O3 uptake during periods of high 

9 exposure, and the presence of O3 sensitive species within each park. Kohut (2007) concluded 

10 that the risk of visible foliar injury was high in 65 parks (27%), moderate in 46 parks (19%), and 

11 low in 131 parks (54%). We have updated this assessment using more recent O3 exposure and 

12 soil moisture data for a subset of parks with O3 monitors. 

13 5.3.2.1 Foliar Injury Risk Methods 

14 We applied the approach used in Kohut (2007) using more recent O3 monitoring and soil 

15 moisture data from 2006 to 2010. For this 1st draft REA, because we did not replicate the spatial 

16 interpolation of monitor data in Kohut (2007) due to uncertainties introduced using this 

technique, we conducted this updated risk assessment only in parks with O3 monitor data.2 17 As 

18 noted by Kohut (2007), monitoring provides the most accurate assessment of O3 exposure, but it 

19 may not reflect differences in exposure throughout the park. 

20 O3 Exposure: We used more recent monitoring data from 2006 through 2010 and the 

21 same metrics in this analysis (i.e., SUM06 (3-month), W126 (12-hr, 7-month), N100 (7-month)) 

22 as Kohut (2007). In addition, we added W126 (12-hr) and N100 metrics calculated over 3 

23 months to be consistent with other analyses in this REA and to determine how sensitive the risk 

24 ratings were to the different W126 metrics. Each of these metrics are described in more detail in 

25 Section 4.3.1. These data reflected 59 O3 monitors located within park boundaries covering 43 

 1

 Kohut (2007) uses the term “foliar injury thresholds”. It is unclear whether these are true biological thresholds 

below which no vegetation effects occur or whether these are simply concentration benchmarks. We use the term 

“thresholds” to be consistent with the terminology in Kohut (2007). 2

 For the 2nd draft REA, we anticipate expanding this updated assessment to include additional parks. One method 

would assign an ozone monitor if it fell within a certain distance of a park’s boundaries (e.g., 10km, 50,km, etc). 

A second option would use the ozone surfaces for 2006, 2007, and 2008 described in Chapter 4. While either 

method would provide ozone exposure data at parks that has additional uncertainty relative to the data at parks 

with ozone monitors within their boundaries, neither would add as much uncertainty as the kriging interpolation 

of monitor data. 
 5-39 

1 separate parks, which is more than the 35 parks with O3 monitors in Kohut (2007). If a park 

2 contained more than one O3 monitor, we used the highest monitor in the park as an indication of 

3 the potential risk. For two parks, Badlands National Park and Glacier National Park, we used 

4 data from an additional park monitor to fill in missing data years at the highest monitor. 

5 Based on the foliar injury thresholds for O3 exposure used by Kohut (2007), we assigned 

6 exposure risk ratings associated with O3 exposure alone to each park with an monitor. Consistent 

7 with Kohut (2007), O3 exposure must meet the criteria for both the W126 index as well as the 

8 N100 metric in order to receive a higher risk rating. We provide the specific criteria applied in 

9 this updated risk assessment, which are derived from Table 5-7 in Kohut (2007). Overall, 

10 considerably more parks exceed the W126 criteria alone than in conjunction with the N100 

11 criteria. Specifically, 35 of 37 parks exceed 5.9 ppm-hrs using the 7-month W126 metric for at 

least 3 years, whereas only 5 parks exceed 6 hours using the 7-month N100 metric in any year.3 12 

13 Only 3 parks exceeded 8 ppm-hrs using the SUM06 metric in any year, which corresponds to 

14 Kohut’s lowest injury threshold for natural ecosystems. 

15 

16 Table 5- 7 Risk Criteria for O3 Exposure Metrics, Sensitive Vegetation, and Soil 

17 Moisture. 

Risk Criterion and Metric Higher Risk Lower Risk 

O3 Exposure 

SUM06 Exceeds 8 ppm-hrs Less than 8 ppm-hrs 

W126/N100 

(3-month) 

Exceeds 4.1 ppm-hrs 

AND Exceeds 6 hrs over 100 ppm 

Less than 4.1 ppm-hrs AND Less 

than 6 

W126/N100 

(7-month) 

Exceeds 5.9 ppm-hrs 

AND Exceeds 6 hrs over 100 ppm 

Less than 5.9 ppm-hrs AND Less 

than 6 

Sensitive 

Vegetation Indicator species Present Not present 

Soil Moisture Palmer Z No relation Inverse 

(not used to lower risk rating) 

18 

19 The primary difference between a high risk rating and a moderate risk rating is the 

20 number of years that exceed the O3 exposure metrics. If a park exceeded the risk criteria for 1 or 

21 2 years, we assigned a risk rating of moderate. If a park exceeded the risk criteria for at least 3 

 3

 In order to assess risk using the 3-month W126 metric, we calculated an adjustment to the foliar injury threshold 

for highly sensitive species. Based on a regression analysis described in Appendix 5D, we determined that a foliar 

injury threshold of 5.9 ppm-hrs for a 7-month W126 metric is approximately equivalent to a foliar injury threshold 

at 4.1 ppm-hrs for a 3-month W126 metric. 
 5-40 

1 years, we assigned a risk rating of high. If a park did not exceed the risk criteria in any year, we 

2 assigned a risk rating of low. 

3 Soil Moisture: To evaluate soil moisture, we followed Kohut’s approach by using Palmer 

4 Z data for 2006 to 2010 (NCDC, 2012b). The Palmer Z Index represents the difference between 

5 monthly soil moisture and long-term average soil moisture (Palmer, 1965). These data typically 

6 range from -4 to +4, with positive values representing more wetness than normal and negative 

7 values representing more dryness than normal. Values between -0.9 and +0.9 could be 

8 interpreted as normal soil moisture, whereas values beyond the range from -3 to +3 could be 

9 interpreted as extremely unusually soil moisture (either extreme drought or extreme wetness). As 

10 described in the ISA (U.S. EPA, 2012a), plants generally uptake less O3 when soil moisture is 

11 reduced, thus the risk of foliar injury is generally lower during periods of drought. 

12 The soil moisture index is calculated for each of the 344 climate regions within the 

13 continental U.S. defined by the National Climatic Data Center (NCDC) (NOAA, 2012a). We 

14 assigned each monitored park to the climate region in which the park was located. For the 

15 monitored parks that were located in more than one NCDC region, we selected the region 

16 corresponding to the monitor location. We decided not to average the Palmer Z values across 

17 regions because the NCDC regions are much larger geographic areas (e.g., sometimes hundreds 

18 of miles in diameter) than the parks themselves. Because we did not have soil moisture data 

19 outside of the continental U.S., we did not evaluate parks in Alaska, Hawaii, Puerto Rico, or 

20 Guam. In addition, due to the size of these regions, soil moisture will vary within each region 

21 and potentially even within a park. For example, some species along riverbanks may still 

22 experience sufficient soil moisture during periods of drought to exhibit foliar injury. For this 

23 reason, we provide the soil moisture data and assess the relationship with O3 exposure, but we 

24 have not lowered any risk ratings in the updated assessment for insufficient soil moisture. We 

25 identify the regions in Figure 5- 25, and we provide the Palmer Z data for each park in Appendix 

26 5D. 
 5-41 

1 

2 Figure 5- 25 344 climate regions with Palmer Z soil moisture data (source: NCDC, 

3 2012a). 

4 

5 Because monthly estimates of soil moisture are highly variable over time, we focused on 

6 the monthly values from May to October for each year in order to be consistent with the potential 

7 time period of the W126 calculation. Evaluating soil moisture is more subjective than for O3 

8 exposure because Kohut (2007) did not outline specific numerical criteria for this determination. 

9 We compared the soil moisture during the years of highest O3 exposure and during the years of 

10 lowest exposure to determine whether there was a consistent trend. Based on our review of the 

11 soil moisture data in the updated assessment, several parks showed a potentially inverse 

12 relationship between high O3 exposure years and soil moisture. 

13 Sensitive Vegetation Species: Consistent with Kohut (2007), we identified the parks 

14 containing O3 sensitive vegetation species (NPS, (2003, 2006). Based on the NPS list, all of the 

15 parks in this updated assessment contain at least one sensitive species. 

GIS Analysis: Using GIS (ESRI® ArcMAPTM 16 9.3), we spatially overlaid the O3 exposure 

17 monitor data, NPS boundaries (USGS, 2003), and soil moisture Palmer Z data to link these data 

18 to each park. In total, 43 parks had O3 monitoring data, including 9 parks that contained more 
 5-42 

than one O3 monitor. We excluded 5 parks with fewer than 3 years of monitoring data4 1 and one 

2 park (i.e., Denali NP in Alaska) with an absence of soil moisture data. After these exclusions, 37 

3 parks were included in this updated risk assessment, which are identified in Figure 5- 26. All of 

4 the monitored parks excluded from this updated assessment received risk ratings of “low” in 

5 Kohut (2007), except for City of Rocks, National Reservation, which had a risk rating of 

6 “moderate”. 

7 

8 Figure 5- 26 37 National Parks with O3 monitors included in the updated risk assessment. 

9 

10 5.3.2.1 Foliar Injury Risk Results and Discussion 

11 As explained in Kohut (2007), determining the overall risk level is not quantitative, but 

12 instead depends on a subjective evaluation of how much and how often O3 exposure metrics 

13 exceeded certain criteria, the soil moisture conditions during high exposure periods, and the 

14 presence of sensitive vegetation species. Similar to Kohut’s subjective evaluation, we also 

15 categorized each park as at high, moderate, or low risk for foliar injury based on these criteria. 

 4

 These 5 excluded parks for less than 3 years of ozone monitoring data are Agate Fossil Beds National Monument, 

City of Rocks National Reservation, Olympic National Park, Padre Island National Seashore, and Scotts Bluff 

National Monument. 
 5-43 

1 For the 37 parks assessed in the updated risk assessment, we found generally similar risk 

2 levels as Kohut (2007). Based on his analysis of all 244 parks, Kohut (2007) found that the risk 

3 of foliar injury was high in 65 parks (27%), moderate in 46 parks (19%), and low in 131 parks 

4 (54%). Limiting the assessment to the same 37 parks in the updated risk assessment, Kohut 

5 found the risk of foliar injury was high in 10 parks (27%), moderate in 4 parks (11%), and low in 

6 23 parks (62%). The updated risk assessment of 37 parks found the risk of foliar injury was high 

7 in 2 parks (5%), moderate in 4 parks (11%), and low in 31 parks (84%). We provide the risk 

8 results for each park included in the assessment in Table 5-8, and we provide all of the O3 and 

9 soil moisture data in Appendix 5D. 

10 Based on our updated assessment, most parks (70%) received the same risk rating as 

11 Kohut (2007), while 30% received lower risk ratings. The decrease in risk rating corresponds to 

12 lower O3 concentrations in more recent years, particularly for the N100 metric. In general, results 

13 were insensitive to whether we used the 3-month or 7-month W126 metric. Only 1 park, Acadia 

14 National Park, would have a different risk rating if we used the 3-month W126 metric rather than 

15 the 7-month W126 metric. 

16 In the original assessment, Kohut (2007) provided an appendix explaining the risk 

17 analysis for Cape Cod National Seashore. Based on O3 exposure ranged from 17 to 25 ppm-hrs 

18 using the SUM06 metric, 33.6 to 40.4 ppm-hrs using the 7-month W126 metric, and 6 to 52 

19 using the 7-month N100 metric, Kohut concluded that the risk level is high because these 

20 exposure levels are significantly greater than the injury thresholds using all metrics. In the 

21 updated assessment, we assigned a risk level of moderate to Cape Cod National Seashore based 

22 on O3 exposure that ranged from <1 to 3 ppm-hrs using the SUM06 metric, 14.5 to 33.1 ppm-hrs 

23 using the 7-month W126 metric, and 0 to 11 using the 7-month N100 metric because exposures 

24 exceed the injury thresholds using both criteria for the W126 index (W126 and N100) in only 

25 one year. 

26 As another example, we assigned a risk level of low to the Great Smoky Mountains 

27 National Park because O3 exposure levels exceeded the W126 injury thresholds (7-month and 3-

28 month) but not the N100 thresholds. When assessing the 3 other O3 monitors in the park, only 2 

29 monitors exceeded 100 ppm using the 7-month N100 metric once apiece between 2006 and 

30 2010. This is a substantial decline from the 1995 to 1999 O3 data, which showed up to 107 hours 

31 above 100 ppm in a single year at the highest monitor (NPS, 2004). While O3 levels are still 
 5-44 

1 consistently high enough to elevate the W126 levels in the more recent monitoring data, there are 

2 many fewer hours where O3 concentrations spike above 100 ppm. In addition, there appeared to 

3 be a slight inverse relationship between O3 exposure and soil moisture in the Great Smoky 

4 Mountains National Park using more recent soil moisture data. 
 5-45 

1 Table 5- 8 Levels of Risk of Foliar Injury in 37 Parks with an O3 Monitor. 

Park Name Park Monitor 

State 

Kohut (2007) Risk 

Level 

Updated Risk 

Level Change 

Acadia National Park ME Moderate Moderate No 

change 

Badlands National Park SD Low Low No 

change 

Big Bend National Park TX Low Low No 

change 

Blue Ridge Parkway NC Low Low No 

change 

Canyonlands National Park UT Low Low No 

change 

Cape Cod National Seashore MA High Moderate Decrease 

Carlsbad Caverns National Park NM Low Low No 

change 

Colorado National Monument CO Low Low No 

change 

Congaree Swamp National 

Monument SC Low Low No change 

Cowpens National Battlefield SC High Low Decrease 

Craters of the Moon National 

Historic Park ID Low Low No change 

Cumberland Gap National Historic 

Park KY High Low Decrease 

Death Valley National Park CA Low Low No 

change 

Devils Tower National Monument WY Low Low No 

change 

Dinosaur National Monument CO Low Low No 

change 

Glacier National Park MT Low Low No 

change 

Great Basin National Park NV Low Low No 

change 

Great Smoky Mountains National 

Park NC High Low Decrease 

Grand Canyon National Park AZ Low Low No 

change 

Indiana Dunes National Landmark IN High Low Decrease 

Joshua Tree National Park CA High High No 

change 

Lassen Volcanic National Park CA Low Low No 

change 
 5-46 

Park Name Park Monitor 

State 

Kohut (2007) Risk 

Level 

Updated Risk 

Level Change 

Mesa Verde National Park CO Low Low No 

change 

Mojave National Preserve CA High Moderate Decrease 

Mount Rainier National Park WA Low Low No 

change 

Petrified Forest National Park AZ Moderate Low Decrease 

Pinnacles National Monument CA High Low Decrease 

Saguaro National Park AZ Low Low No 

change 

Saratoga National Historic Park NY Low Low No 

change 

Sequoia & Kings Canyon National 

Park CA High High No change 

Shenandoah National Park VA Moderate Low Decrease 

Theodore Roosevelt National Park ND Low Low No 

change 

Tonto National Monument AZ Moderate Low Decrease 

Voyageurs National Park MN Low Low No 

change 

Wind Cave National Park SD Low Low No 

change 

Yellowstone National Park WY Low Low No 

change 

Yosemite National Park CA High Moderate Decrease 

1 

2 5.3.3 National Park Case Study Areas 

3 For the National Park case study areas, staff used the O3 sensitive species list from the 

4 preceding section and cover data from VegBank plots (see section 5.3). The resulting maps give 

5 cover estimates for sensitive O3 sensitive species at the finer scale of the NPS vegetation map 

6 (Figure 5- 27). It is important to note that the cover estimates are separated into vegetation strata 

7 (herb, shrub, tree). In the preceding analyses we only used tree species, so the cover never 

8 exceeded 100%. For this analysis we did not distinguish between strata, so the cover metric can 

exceed 100. [This analysis will be completed in the 2nd 9 draft with the addition of the 2 additional 

10 NPS case study areas] 

11 5.3.3.1 Great Smoky Mountain National Park 

12 
 5-47 

1 

2 Figure 5- 27 Cover Index of Sensitive Species in GSMNP 

3 5.3.3.2 Rocky Mountain National Park 

4 [To be added in the second draft] 

5 5.3.3.3 Sequoia/Kings National Park 

6 [To be added in the second draft] 

7 5.4 DISCUSSION 

8 

9  For individual tree species the RBL was, on average, 30% less under the current standard 

10 scenario. In Class I areas with higher O3 exposure this reduction was approximately 20% 

11 and in Critical Habitat areas it was 30%. 

12  Individual tree species show different patterns of change with respect to changes in O3. 

13 Douglas fir has a very large proportional change when O3 is meeting the current 

14 standard, however further reductions in O3 will likely have very little effect on that 

15 species. Sugar maple also had a large proportional change when meting the current 

Sensitive Species Cover

Index

0.00 - 3.50

3.51 - 9.88

9.89 - 20.85

20.86 - 39.01

39.02 - 52.17

52.18 - 60.92

60.93 - 77.88

77.89 - 160.08

Great Smoky Mountains National Park
 5-48 

1 standard. Further reductions in O3 will have some effect to a point beyond which we 

2 expect very little change. Other species are expected to exhibit continued gradual change 

3 in RBL relative to ambient as O3 levels are reduced. 

4  Many Class I and Critical Habitat areas occur in areas of low ambient O3 and these areas 

5 generally show very little change in summed RBL relative to ambient. In areas with 

6 higher ambient O3 levels, the proportion of ambient summed RBL decreases by as much 

7 as 20%. 

8  Within the GSMNP this value was higher, around 45%, but this analysis needs to be 

9 expanded with additional parks. 

10  There are significant areas with high abundance of O3 sensitive tree species. Not all of 

11 these areas co-occur with areas of high O3. This is an analysis that is not complete. 

12  There are areas within GSMNP where the sensitive species cover is very high. The 

13 relationship of these to areas of recreational use is presented in Chapter 6. 

14  Overall, these analyses indicate that decreasing O3 from ambient conditions to a rollback 

15 scenario just meeting the Current Standard had a significant impact, but additional 

16 rollback scenarios are needed to fully interpret this observation. 
6-1

1 6 OZONE RISK TO ECOSYSTEM SERVICES 

2 6.1 INTRODUCTION 

3 EPA has begun using an ecosystem services framework to help define how the damage to 

4 ecosystems informs determinations of the adversity to public welfare associated with changes in 

5 ecosystem functions. 

6 The following sections address the risks to ecosystem services resulting from O3

7 exposure. While most of the impacts of O3 on these services cannot be specifically quantified, it 

8 is important to provide an understanding of the magnitude and significance of the services that 

9 may be negatively impacted by O3 exposures. For many services, we can estimate the current 

10 total magnitude and, for some, the current value of the services in question. The estimates of 

11 current service provision will have embedded within them the loss of services occurring due to 

12 historical and present O3 exposure, and provide context for the importance of any potential 

13 impacts of O3 on those services. In addition, in some cases we can provide information on 

14 locations where high O3 exposures occur in conjunction with significant ecosystem service 

15 impairment. 

16 6.2 NATIONAL SCALE ECOSYSTEM SERVICES ASSESSMENT 

17 The national scale assessment will address O3 impacts on ecosystem services following 

18 the framework of the Millennium Ecosystem Assessment (MEA, 2009). Following that 

19 framework the subsequent sections are divided into supporting, regulating, provisioning, and 

20 cultural services. 

21 Two major effects of O3 exposure on ecosystems considered in this assessment are biomass loss 

22 (or decrease in growth rate) and visible foliar injury. Each of these ecological effects can have 

23 negative effects on vegetation related to ecosystem services. To illustrate 
6-2

1 Table 6- 1 lists the trees identified as sensitive to O3 in studies cited in the ISA and their 

2 uses. 

3
6-3

1 Table 6- 1 O3 Sensitive Trees and Their Uses 

Tree Species O3 Effect Uses 

Black Cherry 

Prunus serotina 

Biomass loss, 

Visible foliar injury 

Cabinets, furniture, paneling, veneers, 

crafts, toys 

Cough remedy, tonic , sedative 

Flavor for rum and brandy 

Wine making and jellies 

Food for song birds, game birds, and 

mammals 

Douglas Fir 

Pseudotsuga menziesii 

Biomass loss Commercial timber 

Medicinal uses, spiritual and cultural uses 

for several Native American tribes 

Spotted owl habitat 

Food for mammals including antelope and 

mountain sheep 

Eastern Cottonwood 

Populus deltoides 

Biomass loss Containers, pulp, and plywood 

Erosion control and windbreaks 

Quick shade for recreation areas 

Beaver dams and food 

Eastern White Pine 

Pinus strobus 

Biomass loss Commercial timber, furniture, 

woodworking, and Christmas trees 

Medicinal uses as expectorant and 

antiseptic 

Food for song birds and mammals 

Used to stabilize strip mine soils 

Hemlock 

Tsuga canadensis 

Biomass loss Commercial logging for pulp 

Habitat for deer, ruffled grouse, and 

turkeys 

Important ornamental species 

Hickory Biomass loss Used in furniture and cabinets, fuelwood 

and charcoal 

Edible nuts 

Food for ducks, quail, wild turkeys and 

many mammals 

Ponderosa Pine 

Pinus ponderosa 

Biomass loss, 

Visible foliar injury 

Lumber for cabinets and construction 

Ornamental and erosion control use 

Recreation areas 

Food for many bird species including the 
6-4

Tree Species O3 Effect Uses 

red-winged blackbird, chickadee, finches, 

and nuthatches 

Quaking Aspen 

Populus tremuloides 

Biomass loss, 

Visible foliar injury 

Commercial logging for pulp, flake-board, 

pallets, boxes, and plywood 

Products including matchsticks, tongue 

depressors, and ice cream sticks 

Valued for its white bark and brilliant fall 

color 

Important as a fire break 

Habitat for variety of wildlife 

Traditional native American use as a food 

source 

Red Alder 

Alnus rubra 

Biomass loss, 

Visible foliar injury 

Commercial use in products such as 

furniture, cabinets, and millwork 

Preferred for smoked salmon 

Dyes for baskets, hides, moccasins 

Medicinal use for rheumatic pain, 

diarrhea, stomach cramps – the bark 

contains salicin, a chemical similar to 

aspirin 

Roots used for baskets 

Food for mammals and birds – dam and 

lodge construction for beavers 

Conservation and erosion control 

Red Maple 

Acer rubrum 

Biomass loss Revegetation and landscaping esp. 

riparian buffer 

Red Oak 

Quercus rubrum 

Biomass loss Important for hardwood lumber for 

furniture, flooring, cabinets 

Food, cover, and nesting sites for birds 

and mammals 

Bark used by Native Americans for 

medicine for heart problems, bronchial 

infections or as an astringent, disinfectant, 

and cleanser 

Short Leaf Pine 

Pinus echinata 

Biomass loss Second only to loblolly pine in standing 

timber volume. 

Used for lumber, plywood, pulpwood, 

boxes, crates, and ornamental vegetation 
6-5

Tree Species O3 Effect Uses 

Habitat and food for bobwhite quail, 

mourning dove, other song birds and 

mammals 

Older trees with red heart rot provide redcockaded woodpecker cavity trees 

Sugar Maple 

Acer saccharum 

Biomass loss Commercial syrup production 

Native Americans used sap as a candy, 

beverage – fresh or fermented into beer, 

soured into vinegar and used to cook meat 

Valued for its fall foliage and as an 

ornamental 

Commercial logging for furniture, 

flooring, paneling, and veneer 

Woodenware, musical instruments 

Food and habitat for many birds and 

mammals 

Virginia Pine 

Pinus virginiana 

Biomass loss, 

Visible foliar injury 

Pulpwood, strip mine spoil banks and 

severely eroded soils 

Nesting for woodpeckers, food for 

songbirds and small mammals 

Yellow (Tulip) Poplar 

Liriodendron tulipifera 

Biomass loss, 

Visible foliar injury 

Furniture stock, veneer, and pulpwood 

Street, shade, or ornamental tree – unusual 

flowers 

Food for wildlife 

Rapid growth for reforestation projects 

1 Sources: USDA , http://www.plants.usda.gov.plantguide; U.S. Forest Service Silvics of North 

2 America, http://www.na.fs.fed.us/spfo/pubs/silvics_manual; North Carolina State University, 

3 http://www.ncsu.edu/project/dendrology/ 

4

5 The National Park Service has published a list of trees and plants considered sensitive 

6 because they exhibit foliar injury at or near ambient concentrations in fumigation chambers or 

7 have been observed to exhibit symptoms in the field by more than one observer. This list 

8 includes many species not included in Table 6-1, such as various milkweed species, asters, 

9 coneflowers, huckleberry, evening primrose, Tree-of-heaven, redbud, blackberry, willow, and 

10 many others. The full list is included in Appendix X and the O3 ISA (EPA, 2012). Many of 
6-6

1 these species are important for non-timber forest products, recreation, and aesthetic value among 

2 other services.

3 6.2.1 Supporting Services 

4 Supporting services are the services necessary for all other services. For example nutrient 

5 cycling is required for any ecosystem service including provision of food and timber. While 

6 other categories of services have relatively direct or short-term impacts on people the impacts on 

7 public welfare from supporting services are generally either indirect or occur over a long time. 

8 The next sections describe potential impacts of O3 on some of these services. 

9 6.2.1.1 Net Primary Productivity 

10 The ISA determined that biomass loss due to exposure to may have adverse effects on net 

11 primary productivity (NPP). According to Pan et al. (2009) net primary productivity in U.S. 

12 Mid-Atlantic temperate forests decreased 7-8% per year from 1991-2000 due to O3 exposure 

13 when compared to preindustrial conditions in 1860 even with growth stimulation provided by 

14 elevated carbon dioxide and nitrogen deposition. In another study Felzer et al. (2004) estimated 

15 O3 impact on NPP for the conterminous U.S from 1950-1995 compared to a presumed pristine 

16 condition in 1860. They found the largest decreases in NPP occurred in the agricultural region 

17 of the Midwest during the mid-summer. This decrease was as high as 13% per year in some 

18 areas. Primary productivity underlies the provision of many subsequent services that are highly 

19 valued by the public including provision of food and timber. Due to data and methodology 

20 limitations the loss of value to the public due to the negative effects of O3 exposure on this 

21 supporting service is unquantifiable. 

22 6.2.1.2 Community Composition 

23 Community composition or structure is also affected by O3 exposure. Since species vary 

24 in their response to O3 those species that are more resistant to the negative effects of O3 are able 

25 to out-compete the more susceptible species. For example in the San Bernardino area Arbaugh 

26 et al. (2003) have shown that community composition in high O3 sites has shifted toward O3

27 tolerant species such as white fir, sugar pine, and incense cedar at the expense of ponderosa and 

28 Jeffrey pine. Changes in community composition underlie possible changes in associated 

29 services such as herbivore grazing, production of preferred species of timber, and preservation of 

30 unique or endangered communities or species among others. See Figure 5-17 for a map showing 

31 current W126 O3 levels in critical habitat areas. 
6-7

1 6.2.2 Regulating Services 

2 Regulating services as defined by the MEA (2005) are those that regulate ecosystem 

3 processes. Services such as air quality, water, climate, erosion, and pollination regulation fit 

4 within this category. The next sections describe potential impacts of O3 on some of these 

5 services. 

6 6.2.2.1 Climate Regulation 

7 Biomass loss due to O3 exposure affects climate regulation by ecosystems by affecting 

8 carbon sequestration by plants and trees. Reduction of carbon uptake by forests results in more 

9 carbon in the atmosphere and negative effects on climate. The studies cited in the ISA show a 

10 consistent pattern of decrease in carbon uptake because of O3 damage with some of the largest 

11 reductions projected over North America. In one simulation (Sitch et al., 2007) the indirect 

12 radiative forcing due to O3 effects on carbon uptake by plants could be even greater than the 

13 direct effect of O3 on climate change. 

14 The Forest and Agriculture Sectors Optimization Model – Greenhouse Gas version 

15 (FASOMGHG) can calculate the difference in carbon sequestration by forests and agriculture 

16 due to biomass loss caused by O3 exposure. Details of the model itself and the analyses done for 

17 this risk and exposure assessment are available in Appendix X. [We will be providing results in 

18 terms tons carbon sequestered in supplemental materials. We will model current ambient 

19 conditions and the results of simulations just meeting the current standard.] 

20 In addition to its direct impacts on vegetation, O3 is a well-known greenhouse gas that 

21 contributes to climate warming (U.S. EPA, 2012a). A change in the abundance of tropospheric 

22 O3 perturbs the radiative balance of the atmosphere, an effect quantified by the radiative forcing 

metric. The IPCC (2007) reported a radiative forcing of 0.35 W/m2 23 for the change in 

24 tropospheric O3 since the preindustrial era, ranking it third in importance after the greenhouse 

gases CO2 (1.66 W/m2) and CH4 (0.48 W/m2 25 ). The earth-atmosphere-ocean system responds to 

26 the radiative forcing with a climate response, typically expressed as a change in surface 

27 temperature. Finally, the climate response causes downstream climate-related ecosystem effects, 

28 such as redistribution of ecosystem characteristics due to temperature changes. While the global 

29 radiative forcing impact of O3 is generally well understood, the downstream effects of the O3-

30 induced climate response on ecosystems remain highly uncertain. 
6-8

1 Since O3 is not emitted directly but is photochemically formed in the atmosphere, it is 

2 necessary to consider the climate effects of different O3 precursor emissions. Controlling 

3 methane, CO, and non-methane VOCs may be a promising means of simultaneously mitigating 

4 climate change and reducing global O3 concentrations (West et al. 2007). Reducing these 

5 precursors reduces global concentrations of the hydroxyl radical (OH), their main sink in the 

6 atmosphere, feeding back on their lifetime and further reducing O3 production. In contrast, NOx 

7 reductions decrease OH, leading to increased methane lifetime and increased O3 production 

8 globally in the long-term. The resulting positive radiative forcing from increased methane may 

9 cancel or even slightly exceed the negative forcing from decreased O3 globally (West et al. 

10 2007). Of the O3 precursors, methane abatement reduces climate forcing most per unit emission 

11 reduction, as methane produces O3 on decadal and global scales and is itself a strong climate 

12 forcer. Since they may have different effects on concentrations of different species in the 

13 atmosphere, all O3 precursors must be considered in evaluating the net climate impact of 

14 emission sources or mitigation strategies. 

15 6.2.2.2 Hydrologic Cycle 

16 Regulation of the water cycle is yet another ecosystem service that can be adversely 

17 affected by the effects of O3 on plants. McLaughlin et al. (2007) reported that increased water 

18 use by O3 impacted forests decreased modeled late-season stream flow in watersheds in eastern 

19 Tennessee in or near the Great Smoky Mountains. Ecosystem services potentially affected by 

20 such a loss in stream flow could include habitat for species such as trout that are dependent on an 

21 optimum stream flow or temperature. Downstream effects could potentially include a reduction 

22 in the quantity and/or quality of water available for irrigation or drinking water, and recreational 

23 use. The United States Forest Service (U.S. FS) and the National Oceanographic and 

24 Atmospheric Administration (NOAA) jointly surveyed Americans age 16 and over for the report 

25 on Uses and Values of Wildlife and Wilderness in the United States as part of the National 

26 Survey on Recreation and the Environment (NSRE) (U.S.D.A., 2002). The NSRE (U.S.D.A., 

27 2002) specifically asked for respondents to rank the importance of water quality as a benefit of 

28 wilderness. 91% of respondents ranked water quality protection as either extremely or very 

29 important. Less than 1% of respondent s ranked this service as not important at all. 
6-9

1 6.2.2.3 Fire Regulation 

2 Fire regime regulation is also negatively affected by O3 exposure. Grulke et al. (2008) 

3 reported various lines of evidence indicating that O3 pollution may contribute to forest 

4 susceptibility to wildfires by increasing leaf turnover rates, and litter thereby creating increased 

5 fuel loads on the forest floor, O3 increased drought stress, and, because both foliar and root 

6 biomass are negatively affected, trees store carbohydrates in the bole over winter increasing 

7 susceptibility to bark beetle attack. Taken together these factors increase susceptibility to 

8 wildfire. In the United States in 2010 over 3 million acres burned in wildland fires and an 

9 additional 2 million acres were burned in prescribed fires according to the National Interagency 

10 Fire Center (http://www.nifc.gov/fireInfo/fireInfo_statistics.html). Over the 5-year period from 

11 2004 to 2008 Southern California alone experienced, on average, over 4,000 fires a year burning, 

12 on average, over 400,000 acres (National Association of State Foresters [NASF], 2009). 

13 The short-term benefits of reducing the O3 related fire risks include the value of avoided 

14 residential property damages, avoided damages to timber, rangeland, and wildlife resources; 

15 avoided losses from fire-related air quality impairments; avoided deaths and injury due to fire; 

16 improved outdoor recreation opportunities; and savings in costs associated with fighting the fires 

17 and protecting lives and property. For example, the California Department of Forestry and Fire 

18 Protection (CAL FIRE) estimated that average annual losses to homes due to wildfire from 1984 

19 to 1994 were $163 million per year (CAL FIRE, 1996) and were over $250 million in 2007 

20 (CAL FIRE, 2008). In fiscal year 2008, CAL FIRE’s costs for fire suppression activities were 

21 nearly $300 million (CAL FIRE, 2008). Figure 6- 1 shows current ambient O3 levels over the 

22 fire risk in California. The highest fire risk and highest O3 levels overlap with each other and 

23 significant portions of the California range of species sensitive to O3 damage specifically 

24 ponderosa pine. 
6-10

1

2

3 Figure 6- 1 Overlap of fire risk, current O3 levels and California range of 

4 ponderosa pine 

5 In the long term, decreased frequency of fires could result in an increase in property 

6 values in fire-prone areas. Mueller et al. (2007) conducted a hedonic pricing study to determine 

7 whether increasing numbers of wildfires affect house prices in southern California. They 

8 estimated that house prices would decrease 9.71% after one fire and 22.7% after a second 

9 wildfire within 1.75 miles of a house in their study area. After the second fire, the housing prices 

10 took between 5 and 7 years to recover. 

11 Additionally, long term decreases in wildfire would be expected to yield outdoor 

12 recreation benefits consistent with the discussion of scenic beauty in subsequent sections. 

13 6.2.2.4 Pollination 

14 The ISA O3(ISA) (2011 ref) identifies O3 as a possible agent affecting the travel distance 

15 and loss of specificity of volatile organic compounds emitted by plants, some of which act as 
6-11

1 scent cues for pollinators. While it isn’t possible to calculate the loss of pollination services due 

2 to this negative effect on scent the loss is embedded in the current estimated value of all 

3 pollination services, managed and wild, in North America (U.S., Canada, and Bermuda) which is 

4 $18.3 billion dollars in 2010 (Gallai et al., 2009). 

5 6.2.3 Provisioning Services 

6 Provisioning services include market goods such as forest and agricultural products. The 

7 direct impact of O3 exposure induced biomass loss can be predicted for the commercial timber 

8 and agriculture markets using the Forest and Agriculture Optimization Model (FASOM). This 

9 model provides a national scale estimate of the effects of O3 on these two market sectors 

10 including producer and consumer surplus estimates. Non-timber forest products (NTFP) such as 

11 foliage and branches used for arts and crafts or edible fruits, nuts, and berries can be affected by 

12 the impact of O3 through biomass loss and foliar injury. USDA has assessed the harvest and 

13 market value of these products in commercial markets. There is as well a significant portion of 

14 NTFP that are valuable to subsistence gatherers. Subsistence practices are much more difficult 

15 to assess as these forest users are not required to obtain a permit for use of federal public lands 

16 and are therefore more difficult to enumerate. 

17 6.2.3.1 Commercial Timber and Agriculture 

18 We used FASOMGHG (Forest and Agricultural Sector Optimization Model—Green 

19 House Gas version) to calculate the resulting market-based welfare effects of O3 exposure in the 

20 forest and agricultural sectors of the United States. Even though agricultural impacts are not a 

21 focus of this risk assessment, a proper understanding of impacts on commercial forests requires 

22 us to model the effects of O3 on agriculture because of the interactions between competing 

23 demands for land for forestry versus agricultural crops. We used data obtained from the Forest 

24 Inventory and Analysis National Program (FIA) and the O3 related biomass loss concentration25 response functions from the ISA as inputs into FASOMGHG, which enabled us to adapt the 

26 growth rates for tree and crop species in the model to account for the impact of O3 on vegetation. 

27 See Appendix X for a full discussion of the model and methodology. 

28 [We will provide results of modeling runs for current ambient conditions and meeting current 

29 standards in supplemental materials. The results will be in terms of timber and crop yield loss.] 

30 In addition to the direct effects of O3 on tree growth O3 causes increased susceptibility to 

31 infestation by some chewing insects (USEPA, 2006). Chewing insects include the southern pine 
6-12

1 beetle and western bark beetle, species that are of particular interest to commercial timber 

2 producers and consumers. These infestations can cause economically significant damage to tree 

3 stands and the associated timber production. Figure 6- 2 and Figure 6- 3 illustrate the damage 

4 caused by southern pine beetles in parts of the south. 

5

6

7 Figure 6- 2 Southern pine beetle damage. Courtesy: Ronald F. Billings, Texas 

8 Forest Service. Bugwood.org 

9 According to the USDA Forest Service Report on the Southern Pine Beetle (Coulson and 

10 Klepzig, 2011), “Economic impacts to timber producers and wood-products firms are essential to 

11 consider because the SPB causes extensive mortality in forests that have high commercial value 

12 in a region with the most active timber market in the world.” The economic impacts of beetle 

13 outbreaks are multidimensional. In the short term the surge in timber supply caused by owners 

14 harvesting damaged timber depresses prices for timber and benefits consumers. In the long term 

15 beetle outbreaks reduce the stock of timber available for harvest, raising timber prices to the 

16 benefit of producers and the detriment of consumers. However, USDA estimates that these long 

17 term impacts are much smaller than the short term impacts. 

18 The Forest Service further reports that over the 28 years covered in their analysis (1977-

19 2004) timber producers have incurred about $1.4 billion or about $49 million per year and 

20 wood-using firms have gained about $966 million or about $35 million per year due to beetle 

21 outbreaks. This results in a net $15 million per year economic impact. All dollar values are 

22 reported in constant $2010. These annual figures mask the fact that most of the economic 

23 impacts are the result of a few catastrophic outbreaks causing the impacts to pulse through the 

24 system in large chunks rather than being evenly distributed over the years. It is not possible to 
6-13

1 attribute a portion of these impacts due to the effect of O3 on trees’ susceptibility to insect attack 

2 however, such losses are already embedded within the losses quoted and any welfare gains from 

3 decreased O3 would positively impact these numbers. 

4

5

6 Figure 6- 3 Southern pine beetle damage. Courtesy: Ronald F. Billings, Texas 

7 Forest Service. Bugwood.org 

8 In the western United States O3 sensitive ponderosa and Jeffrey pines are subject to attack 

9 by bark beetles. Figure 6- 4 shows western bark beetle mortality from 2003- 2007. The map 

10 includes Douglas fir and other western species vulnerable to bark beetles as well as ponderosa 

11 and Jeffrey pine. According to the Western Forestry Leadership Coalition (2009) approximately 

12 22 million acres of forest lands are at risk for bark beetle damage. 
6-14

1

2 Figure 6- 4 Western bark beetle mortality obtained from State and Private 

3 Forestry aerial-detection surveys (2003-2007). Source: Western 

4 Forestry Leadership Coalition (2009) [This figure will be updated 

5 with O3 concentrations in supplemental materials.]

6 

7 In 2006 the California was the largest producer of ponderosa and Jeffrey pine timber 

8 from public lands. California accounted for 99 million board feet of saw logs – almost 40% of 

9 the total production (U.S. Forest Service, 2009 available at: 

10 http://srsfia2.fs.fed.us/php/tpo_2009/tpo_rpa_int2.php). California also experiences high O3

11 levels that may contribute to susceptibility to bark beetle attack. While it isn’t possible to 

12 attribute a quantified impact of O3 to economic loss due to bark beetle damage that impact is 

13 already accounted for within the loss attributed to bark beetle infestation. Reducing O3 impacts 

14 would likely reduce economic loss to California timber production.

15 The photographs and map above illustrate the impact insect outbreaks can have major 

16 effects on aesthetic values such as scenic beauty in addition to the impacts on timber production. 
6-15

1 The value of the impact of O3 and insect attack susceptibility on aesthetic values, as shown in the 

2 Nox/SOx Policy Assessment (EPA, 2011), may be even greater than the market value of the 

3 timber. We will address those impacts in Section 6.2.4. 

4 6.2.3.2 Commercial Non-Timber Forest Products 

5 In addition to timber forests provide many other products that are harvested for 

6 commercial or subsistence activities. These products include: 

7  edible fruits, nuts, berries, and sap 

8  foliage, needles, boughs, and bark 

9  transplants 

10  grass, hay, alfalfa, and forage 

11  herbs and medicinals 

12  fuelwood, posts and poles 

13  Christmas trees 

14 For the 2010 National Report on Sustainable Forests (USDA, 2011) these products were divided 

15 into several categories including nursery and landscaping uses; arts, crafts, and floral uses; 

16 regeneration and silviculture uses. Table 6- 2 details selected categories of non-timber forest 

17 products (NTFP) harvested by permit in 2007. These harvests are reported in measures relevant 

18 to the specific articles i.e., bushels of cones, tons of foliage or boughs, individual transplants. 

19

20 Table 6- 2 Quantity of non-timber forest products harvested on U.S. Forest Service and 

21 Bureau of Land Management land 

Product Category Unit Harvest All U.S.

Arts, crafts, and florals Bushels 70,222

Pounds 3,442,125

Tons 620,773

Christmas trees Each 151,274

Lineal foot 94.758

Edible Fruits, nuts, berries, 

and sap 

Bushels 250

Pounds 1,614,565
6-16

Product Category Unit Harvest All U.S.

 Syrup Taps 10,686

Fuelwood ccf 35,800

Cords 417,692

Grass, hay, and alfalfa Pounds 4,265,952

Forage Tons 480

Herbs and medicinals Pounds 101,365

Nursery and landscape Each 766,645

Pounds 25,689

Tons 316

Regeneration and 

silviculture 

Bushels 7,627

ccf 8

Each 21,265

Pounds 247,543

Tons 110,873

Posts and poles ccf 5,281

Each 1,684,618

Lineal foot 326,312

1 Note: ccf = 100 cubic feet Source: USDA 2011 

2

3 According to the ISA O3 exposure causes biomass loss in sensitive woody and 

4 herbaceous species which in turn could affect forest products used for arts, crafts, and florals. 

5 For example, Douglas fir and red alder among others are used on the Pacific Coast for arts and 

6 crafts, particularly holiday crafts and decorations. The effects of O3 on plant reproduction (see 

7 ISA Table 9-1, 2012) could affect the supply of seeds, berries, and cones. Foliar injury impacts 

8 on O3 sensitive plants would potentially affect the harvest of leaves, needles, and flowers from 

9 these plants for decorative uses. Likewise the same O3 effects would impact harvest of edible 

10 fruits, nuts, berries, and sap. Note that this category includes blueberries, pine nuts, and sap for 

11 maple syrup to name just a few. The use of native grasses as forage is a significant aspect of 
6-17

1 forest-land management in the western U.S. (Alexander et al. 2002). O3 effects on community 

2 composition particularly changes in the ratio of grasses to forbs (broad-leaved herbs other than a 

3 grass) and nutritive quality of grasses can have effects on rangeland quality for some herbivores 

4 (Krupa et al., 2004, Sanz et al., 2005), and therefore effects on grazing efficiency. The negative 

5 impacts of O3 on plants would similarly affect the harvest in the rest of the categories as well. 

6 According to the Census Bureau’s County Business Patterns data in 2006 this activity is 

7 captured in the industry code 1132, forest nurseries and gathering of forest products, and 

8 employed 2,098 people accounting for an annual payroll ($ 2006) of $71,657,000 with an 

9 average annual income of $34,155 (U.S. Census Bureau, County Business Patterns, at 

10 http://www.census.gov/econ/cbp/). 

11 The USDA estimates the proportion of the national supply of NTFP represented by U.S. 

12 FS and BLM lands is approximately 10%. Retail values for NTFPs harvested on Forest Service 

13 and Bureau of Land Management lands are approximately $1.4 billion. These are very rough 

14 estimates based only on permit or contract sales. These estimates could be low due to harvests 

15 taken without permit or contract and sold through complex commodity chains that can combine 

16 wild-harvested and agriculturally grown commodities. 

17 It is important to realize that while we cannot estimate the loss of production and 

18 therefore values for the loss of benefit to this sector that is due strictly to the effects of O3 those 

19 losses are already embedded within the harvest and values reported here. 

20 The preceding paragraphs detailed the harvest and value of permit or contract sales of 

21 NTFPs on Forest Service and BLM managed lands. Since permits or contracts are not required 

22 for gathering activities for personal use the analyses done by USDA are not able to account for 

23 the subsistence use of non-timber forest products. 

24 6.2.3.3 Informal Economy or Subsistence Use of Non-Timber Forest Products 

25 Most people gathering NTFPs are doing so for personal use (Baumflek et al., 2010 and 

26 USDA, 2011). In fact by one estimate (Baumflek et al., 2010) up to 80% of the people collecting 

27 NTFPs in Oregon and Washington are collecting for personal reasons. Such personal use may be 

28 characterized as either part of the informal economy or as subsistence activity. Participants in 

29 the informal economy may earn a wage or salary and participate in gathering NTFPs for other 

30 reasons than recreation (Brown et al., 1998). The term subsistence has usually been applied to 

31 special groups such as Native Americans or the Hmong people. The term “subsistence” has 
6-18

1 generally been understood to imply an extremity of poverty such that these activities are essential 

2 to a minimum of the necessities of life (Freeman, 1993). However, Freeman points out 

3 researchers stress that economic goals are only a part of the impetus for these activities. 

4 Brown (1998) proposed a composite definition that captures both the informal economy 

5 as practiced by those who are not necessarily a part of a special population and subsistence as 

6 generally referenced to those special populations. “Subsistence refers to activities in addition to, 

7 not in place of, wage labor engaged in on a more or less regular basis by group members known 

8 to each other in order to maintain a desired and/or normative level of social and economic 

9 existence.” This definition allows consideration of the cultural and social aspects of subsistence 

10 lifestyles. These non-economic benefits range from maintenance of social ties and relationships 

11 through shared activity to family cohesiveness to retreatism and a sense of self-reliance for the 

12 individual practitioner (Brown et al., 1998). 

13 While there is general acknowledgement of subsistence activities by Native Americans 

14 and specific treaty rights for tribes guaranteeing access to lands for hunting, fishing, and 

15 gathering there has been a lack of research focused on other populations (Emery and Pierce, 

16 2005). However there are some studies that make it clear that subsistence activities provide 

17 valued resources for a variety of people in the coterminous United States. Baumflek et al. and 

18 Alexander et al. (2010 and 2011) have documented the collection and use of culturally and 

19 economically important NTFPs in Maine and the eastern United States respectively. Brown et 

20 al. (1998) reports on subsistence activities among residents of the Mississippi Delta. Emery 

21 (2003) and Hufford (2000) examine activities in the Appalachians and Pena (1999) reports 

22 activities by Latinos in the Southwest. 

23 As with the commercial harvest of NTFPs subsistence gathering of these forest products 

24 can potentially be affected by the adverse effects of O3 on growth, reproduction, and foliar injury 

25 to the sensitive plants in use for nutrition, medicine, cultural, and decorative purposes. It is 

26 important to note that some plants may have more than one use or significance. For example, the 

27 Mi’kmaq and Maliseet Indian tribes in Maine do not differentiate between blueberries’ 

28 nutritional, medicinal, and spiritual uses. Blueberries are a food, and a medicine that is often 

29 incorporated into ceremonies (Baumflek et al., 2010). And while we cannot quantify the size of 

30 the harvest of subsistence gathered items or monetize the loss of benefit due to O3 effects a 
6-19

1 comparison to the commercial harvest may provide perspective on the significance of these 

2 activities to the people who engage in them. 

3 6.2.4 Cultural Services

4 Cultural services include recreation, habitat for endangered species, and non-use values 

5 (i.e., existence and bequest values) that can be directly or indirectly impacted by O3 exposure. 

6 The foliar injury induced by O3 exposure may have a negative impact on people’s satisfaction 

7 with outdoor activities especially those associated with natural environments. Slowed growth or 

8 changes in community composition may impact habitat for endangered species both flora and 

9 fauna. Non-use values are impacted as well. According to responses to the National Survey on 

10 Recreation and the Environment large majorities of Americans wish to preserve natural or 

11 pristine areas even if they do not intend to visit themselves. 

12 According to the National Report on Sustainable Forests (USDA, 2011) there are 

13 approximately 751 m (Figure 6- 5); one-third is federally owned. All of these lands are assumed 

14 to be protected to some degree but specific protections apply to wilderness areas which comprise 

15 about 20% of public land, 7% is protected as national parks, 13% is designated as wildlife 

16 refuges while 60% is protected managed forests including national forests, BLM lands and other 

17 state and local government lands. The protections afford preservation of cultural, social, and 

18 spiritual values. 

19

20 Figure 6- 5 Percent of forest land in the United States by ownership category, 2007 

21 (percentages sum to 100) (Almost all forest lands are open for some form of 

22 recreation, although who may have access may be restricted). Source: USDA 

23 Forest Service 

24

Corporate forest

industry, 6.8% Local, 1.5%

State, 9.2%

Federal,

33.1%

Other

noncorporate, 2.9%

Family

individual,

35.1%

Other corporate,

11.5%

Forest land ownership (percent)
6-20

1 6.2.4.1 Non­Use Services

2 The National Survey on Recreation and the Environment (NSRE) (USDA, 2002) is an 

3 ongoing survey of a random sample of adults over the age of 16 on their interactions with the 

4 environment. NSRE surveys track American’s attitudes toward various benefits derived from 

5 the environment including non-use values. When people value a resource even though they may 

6 never visit the resource or derive any tangible benefit from it they perceive an existence service. 

7 When the resource is valued as a legacy to future generations a bequest service exists. 

8 Additionally there exists an option value to knowing that you may visit a resource at some point 

9 in the future. Data provided by the NSRE indicates that Americans have very strong preferences 

10 for existence, option, and bequest services related to forests. Significantly, according to the 

11 survey, only 5% of Americans rate wood products as the most important value of public forests 

12 and wilderness areas and even for private forests only 20% of respondents rated wood products 

13 as most important. Table 6- 3 details the survey responses to these questions. 

14

15 Table 6- 3 NSRE Reponses to Non-Use Value Questions 

Service 

Extremely 

Important Very Important 

Moderately 

Important Total 

Existence 36 38 18 92 

Option 36 37 17 90 

Bequest 81 12 4 97 

16

17 Studies (Haefele et al., 1991, Holmes and Kramer, 1996) indicate that the public places a 

18 high value on protecting forests and wilderness areas from the damaging effects of air pollution. 

19 Studies conducted to assess willingness-to-pay (WTP) for forest protection for spruce-fir forests 

20 in the southeast from air pollution and insect damage (Haefele et al., 1991, Holmes and Kramer, 

21 1996) confirm that the non-use values held by the respondents to the survey were in fact greater 

22 than the use or recreation values. The survey presented respondents with a sheet of color 

23 photographs representing three stages of forest decline and explained that, without forest 

24 protection programs, high-elevation spruce forests would all decline to worst conditions. Two 

25 potential forest protection programs were proposed. The first program would protect the forests 

26 along road, and trail corridors spanning approximately 1/3 of the ecosystem at risk. This level of 
6-21

1 protection may be most appealing to recreational users. The second level of protection was for 

2 the entire ecosystem and may be most appealing to those who value the continued existence of 

3 the entire ecosystem. Median household WTP was estimated to be roughly $29 (in 2007 dollars) 

4 for the minimal program and $44 for the more extensive program. Respondents were then asked 

5 to decompose their value for the extensive program into use, bequest, and existence values. This 

6 resulted in values that represented components of 13% use value, 30% bequest, 57% existence 

7 value (Table 6- 4). 

8 While these studies are specific to damage due to excess nitrogen deposition and the 

9 wooly balsam adelgid (a pest in frasier fir) the results are relevant to O3 exposure in forests. In 

10 the southeast loblolly pine is a prevalent species and O3 foliar injury can cause visible damage. 

11 O3 exposure may result trees to be more susceptible to insect attack which in the southeast would 

12 include damage caused by the southern pine beetle. 

13

14 Table 6- 4 Value Components for WTP for Extensive Protection Program for Southern 

15 Appalachian Spruce-Fir Forests 

Type of Value Proportion of WTP Component Value in $2007 

Use 0.13 5.72 

Bequest 0.30 13.20 

Existence 0.57 25.08 

Total 1.0 44.00 

16 

17 6.2.4.2 Habitat Provision 

18 In addition to non-use values the NSRE provides data on the values survey respondents 

19 place on the provision of habitat for wild plants and animals. Table 6- 5 summarizes the 

20 responses to survey questions regarding the value of wildlife habitat and preservation of unique 

21 or endangered species. 

22
6-22

1

2 Table 6- 5 NSRE Reponses to Wildlife Value Questions 

Service 

Extremely 

Important Very Important 

Moderately 

Important Total 

Wildlife Habitat 51 36 9 96 

Preserving 

Unique Wild 

Plants and 

Animals 

44 36 13 93 

Protecting Rare 

or Endangered 

Species 

50 33 11 94 

3

4 There exist meta-analyses on the monetary values Americans place on threatened and 

5 endangered species. One such study (Richardson and Loomis, 2009) estimates the average 

6 annual willingness to pay for a number of species. The authors report a wide range of values 

7 dependent on the change in the size of the species population, type of species, and whether 

8 visitors or households are valuing the species. The average annual WTP for surveyed species 

9 ranged from $9/year for striped shiner to $261/year for Washington state anadromous fish, 

10 hatched in fresh water, spends most of its life in the sea and returns to fresh water to spawn, populations 

11 in constant 2010$. 

12 6.2.4.3 Aesthetic Value 

13 Aesthetic services not related to recreation include the view of the landscape from 

14 houses, as individuals commute, and as individuals go about their daily routine in a nearby 

15 community. Studies find that scenic landscapes are capitalized into the price of housing. Studies 

16 document the existence of housing price premia associated with proximity to forest and open 

17 space (Acharya and Bennett, 2001; Geoghegan, Wainger, and Bockstael, 1997; Irwin, 2002; 

18 Mansfield et al., 2005; Smith et al., 2002; Tyrvainen and Miettinen, 2000). In fact according to 

19 Butler (2008) approximately 65% of private forest owners rate providing scenic beauty as either 

20 a very important or important reason for their ownership of forest land. 
6-23

1 These services are at risk of impairment due to O3-induced damage: directly due to foliar 

2 injury, and indirectly due to increased susceptibility to insect attack. Data is not available to 

3 quantify these negative effects however the damage would be included in the price premia 

4 already mentioned. In other words, without such damage the associated price premia for scenic 

5 beauty incorporated into housing prices would likely be higher. 

6 6.2.4.4 Recreation 

7 With few exceptions, publicly owned forests at all levels are open for some form of 

8 recreation. Based on the analysis done for the USDA Report on Sustainable Forests referenced 

9 in Section 5.1.4 almost all of the 751 million acres of forest land are at least partially managed 

10 for recreation. Of the 751 million acres 44% are publicly owned (federal, state, or local). 

11 Americans enjoy a wide variety of outdoor pursuits many of which are subject to 

12 negative impacts due to O3 exposure especially its effect on foliage, insect susceptibility, habitat, 

13 and community composition. The effects related to scenic beauty (foliar injury and insect 

14 damage) affect not only the scenery viewing but satisfaction with other scenery dependent 

15 activities. 97% of NSRE survey respondents rated scenic beauty as an important to extremely 

16 important aspect of their wilderness experience. 

17 Scenic quality has been found to be strongly correlated to recreation potential and the 

18 likelihood of visiting recreation settings and the correlations apply to both active and passive 

19 recreational pursuits (Ribe, 1994). According to Ribe (1994), differences in scenic beauty 

20 account for 90% of the variation in participant satisfaction across all recreation types. 

21 Perceptions of scenic beauty are dependent on a number of forest attributes including the 

22 appearance of health and the effects of air pollution and insect damage, visual variety, species 

23 variety, and lush ground cover (Ribe 1989). The ISA concludes that there is a causal relationship 

24 between O3 exposure and visible foliar injury. Chapter 5 of this document also discusses the 

25 effects of O3 on foliar injury. Figure 6- 6 shows the effects of foliar injury on ponderosa pine, 

26 milkweed, and tulip poplar. The presence of downed wood, whether caused by O3 mortality, 

27 insect attack, or slash from harvest activities has a negative impact on scenic beauty assessments 

28 (Ribe, 1989; Buyhoff, et al, 1982). Species composition of forests may also influence 

29 preferences. According to Ribe (1982) these preferences may be affected by cultural, regional, 

30 or contextual expectations which would include the expectation of the presence of certain species 

31 in specific areas such as the presence of ponderosa pine in California. Additionally there is a 
6-24

1 positive effect for ground cover rather than bare or disturbed soil (Brown and Daniel, 1984, 

2 1986). Thus the damage to scenic beauty O3 inflicts on sensitive plants by way of foliar injury 

3 extends beyond large trees to the grasses, forbs, ferns, and shrubs that comprise the understory of 

4 a forest setting. 

5

6 Figure 6- 6 Examples of foliar injury due to O3 exposure. Courtesy: National 

7 Park Service 

8

9 The NSRE provides estimates of participation in many recreation activities. According 

10 to the survey some of the most popular outdoor activities are walking including day hiking and 

11 backpacking, camping, bird watching, wildlife watching, and nature viewing. Participant 

12 satisfaction with these activities is wholly or partially dependent on the quality of the natural 

13 scenery. Table 6- 6 summarizes the survey results for these and other popular activities 

14 including the percent participation and the number of participants nationally, the number of days 

15 participants engage in recreation activities annually, and their WTP for their participation. 

16

17

18
6-25

1 Table 6- 6 National Outdoor Activity Participation 

Activity 

% 

Participation

# 

Participantsa 

# 

Activity 

Daysa

Mean 

WTP/Dayb 

Mean Total 

Participation 

Valuea,b 

Day Hiking 32.4 69.1 2,508 60.63 152,060 

Backpacking 10.4 22.2 224.0 13.33 2,986 

Picnicking 54.9 116.9 935.2 20.70 19,359 

Camping (developed and 

primitive sites) 

42.3 90.1 757.5 19.98 15,135 

Visit a wilderness area 32.0 68.2 975.4 N/A N/A 

Birdwatching/Photography 31.8 67.7 5,828.1 49.74 289,773 

Wildlife 

watching/Photography 

44.2 94.2 3,616.5 48.72 176,196 

Natural vegetation 

viewing/Photography 

43.9 93.6 5,720.8 N/A N/A 

Natural scenery 

viewing/Photography 

59.6 126.9 7,119.7 N/A N/A 

Sightseeing 50.8 108.2 2,055.0 45.94 94,407 

Gathering (mushrooms, 

berries, firewood) 

28.6 60.9 852.7 N/A N/A 

2 Source: NSRE 2000-2001 and 2003 National Report on Sustainable Forest Management 2003 

3 National Report: Documentation for Indicators 35, 36, 37, 42, and 43 available at: 

4 http://warnell.forestry.uga.edu/nrrt/NSRE/MontrealIndDoc.PDF and Recreation Values 

5 Database available at: http://recvaluation.forestry.oregonstate.edu/

a

 in millions, b 6 $ 2010, N/A not available 

7

8 The relationship between scenic beauty and recreation satisfaction for camping has been 

9 quantified by Daniel, et al (1989) in a contingent valuation study. The authors surveyed campers 

10 regarding their perceptions of scenic beauty, as indicated by a photo array of scenes along a 

11 spectrum of scenic beauty, and their willingness to pay (WTP) to camp in certain areas. All else 

12 being equal scenic beauty and WTP demonstrated a nearly perfect linear relationship (correlation 
6-26

1 coefficient of 0.96). This suggests that campers would likely have a greater willingness to pay 

2 for recreation experiences in areas where scenic beauty is less damaged by O3. As mentioned 

3 previously Ribe (1994) found that scenic beauty plays a strong role in recreation satisfaction and, 

4 in fact, explains 90% of the difference in recreation satisfaction among all types of outdoor 

5 recreation there is reason to believe that this linear relationship between scenic beauty and WTP 

6 would hold across all recreation types. It would follow that decreases in O3 damage would 

7 generate benefits to all recreators. We cannot estimate the incremental impact of reducing O3

8 damage to scenic beauty and subsequent recreation demand however given the large number of 

9 outdoor recreation participants and their substantial WTP for recreation even very small 

10 increments of change in WTP or activity days will generate significant benefit to these 

11 recreators. 

12 Another resource for estimating consumer’s economic value for their recreation 

13 experiences is the data available on their actual expenditures for recreation and the total 

14 economic impact of recreation activities. Economic impacts across the national economy can be 

estimated using the IMPLAN® 15 model, a commercially available input-output model that has 

16 been used by the Department of Interior, the National Park Service, and other government 

17 agencies in their analyses of economic impacts. For this document we will refer to analyses 

18 done for the 2006 National Survey of Fishing, Hunting, and Wildlife-Associated Recreation 

19 (FHWAR) (U.S. Department of the Interior and U.S. Department of Commerce, 2006) and an 

20 analysis performed by Southwick and Associates for the Outdoor Industry Foundation , The 

21 Economic Contribution of Active Outdoor Recreation – Technical Report on Methods and 

22 Findings (OIF, 2006). See Appendix X for further detail. 

23 The FHWAR and the OIF report provide estimates of trip and equipment related annual 

24 expenditures for wildlife watching activities in the United States. The Outdoor Industry 

25 Foundation (OIF) study provides estimates of recreationist’s annual expenditures on trail-related 

26 activities, camping, bicycling, snow-related and paddle sports. For this review we include the 

27 data on trail-related activities and camping as the most relevant for analysis of O3 related 

28 damages. 

29
6-27

Table 6- 7 Expenditures for Wildlife-Watching, Trail, and Camp Related Recreationa 1

Expenditure 

Type 

WildlifeWatchingb Trailc Campc Totalc 

Trip-Related 13.9 31.8 108.6 153.3 

Equipment & 

Services

25.0 3.6 9.3 37.9 

Other 

Expenditures

10.4 10.4 

Grand Total for 

all Expenditures 

 200.1 

a

 in $ 2010 billion, b data from 2006 FHWARc 2 , data from 2006 OIF report, N/R not reported 

3

4 According to these analyses the total expenditures across wildlife watching activities, 

5 trail based activities, and camp based activities are approximately $200.1 billion dollars 

6 annually. See Table 6- 7 for details. While we cannot estimate the magnitude of the impacts of 

7 O3 damage to the scenic beauty upon which satisfaction with these activities depend the losses 

8 are embedded within the values reported. 

9 The impact of these expenditures has a multiplier effect through the economy as a whole 

which was estimated by OIF using the IMPLAN® 10 model. The model estimates the flow of goods 

11 and money through the economy at scales from local to national. According to the OIF report 

12 (2006) trail activities generated over $83.7 billion dollars in total economic activity including 

13 $33.4 billion in retail sales and $42.7 billion in salaries, wages, and business earnings. The same 

14 report estimates the total economic activity generated by camping related recreation at $273 

15 billion including $109.3 billion in retail sales and $139.2 billion in salaries, wages, and business 

16 earnings. The total economic activity estimates also include state and federal tax revenues. 

Assumptions and Caveats to the IMPLAN® 17 Results: Statistics regarding the precision of 

18 the final economic impacts were not produced by OIF due to feasibility issues, Harris Interactive 

19 survey results combine several parameters from the data, and outside data from the Census 

20 population estimates and IMPLAN multipliers were used. 
6-28

1 6.3 CASE STUDY ANALYSIS 

2 The next sections highlight four national parks and several urban areas selected as case 

3 study areas to provide a more detailed analysis of the ecosystem services at risk due to O3

4 exposure in the protected areas of our country and in the urban areas where the majority of the 

5 U.S. population lives. 

6 National Parks are especially significant to the public welfare in that the public as a 

7 whole, through their elected representatives, have designated these areas to be of special value by 

8 creating the parks. While national parks supply supporting and regulating services this analysis 

9 focuses on the cultural services these areas provide. The supporting and regulating services at 

10 risk are described in the national scale analysis. Provisioning services generally do not apply 

11 since timber harvest and agriculture are prohibited in the parks. 

12 The criteria for selection of the specific parks included here are discussed in Chapter 5. 

13 The methodology for the ecosystem services analysis for each park is consistent between the 

14 case studies. For each park the maps generated in Chapter 5 were overlayed with the locations of 

15 park amenities in order to illustrate the extent of O3 impacts on vegetation and that impact on the 

activities important to park visitors. Park use surveys1 16 and public use statistics (National Park 

17 Service Public Use Statistics Office, http://www.nature.nps.gov/stats/index.cfm) provide data on 

18 numbers of visitors who engage in activities in the parks and recreation value surveys (Kaval and 

19 Loomis, 2003) provide estimates of average willingness to pay for these activities within the 

20 park region. 

21 The National Park Service (National Park Service, 2011) has produced estimates of 

22 visitor spending for each park and the impact of visitor spending on local economies surrounding 

23 the parks. These analyses provide a total value related to the specific case study parks and do not 

24 model changes in value due to O3 impacts. However the loss to the local economies due to O3

25 damage in the parks is captured in the current values. These values would likely be higher absent 

26 O3 impacts. 

27 The urban case study analysis utilizes the iTree model developed by the Forest Service to 

28 quantify the benefits of urban forests. These urban forests are vulnerable to the adverse effects 

29 of O3. The iTree model is designed to provide estimates of the effects of forests on carbon 

                                                           

1 These studies are conducted by the Visitor Services Project at the University of Idaho.  Reports for individual

parks are available at: http://www.psu.idaho.edu/vsp.reports.htm  
6-29

1 sequestration, volatile organic chemical production, and pollution removal and can be modified 

2 to allow estimation of the biomass loss due to O3 exposure and that effect on services. 

3 6.3.1 Southeast Region – Great Smokey Mountains National Park 

4

5

6 Figure 6- 7 Mount Le Conte, Summer Great Smoky National Park. Courtesy: 

7 National Park Service 

8 Great Smokey Mountains National Park (GRSM) welcomed approximately 9.5 million 

9 visitors in 2010 (NPS Public Use Statistics Office, http://www.nature.nps.gov/stats/index.cfm) 

10 making it the most visited national park in America. Overlapping the border between North 

11 Carolina and Tennessee the park is valued for the diversity of its vegetation and wildlife, the 

12 scenic beauty of its mountains including the famous fogs that give the Smoky Mountains their 

13 name, and the preservation of the remnants of Southern Appalachian culture. It is also subject to 

14 high ambient O3 levels. 

15 As shown in Chapter 5 the extent of sensitive species coverage in GRSM is quite 

16 substantial. The “whole park” services affected by such potential O3 impacts include the 

17 existence, option, and bequest values discussed in section 6.2.4.1 and habitat provision discussed 
6-30

1 in section 6.2.4.2. Recreation value specific to the park is discussed later in this section. Focusing 

2 the analysis showing the percent cover of foliar injury sensitive species in the park in Chapter 5 

3 on the areas where recreation services are provided can give some perspective on the level of 

4 potential harm to scenic beauty and therefore recreation satisfaction within the park. 

5 The National Park Service 2002 Comprehensive Survey of the American Public Southeast 

6 Region Technical Report includes responses from recent visitors to southeast parks about the 

7 activities they pursued during their visit. By using the annual visitation rate from 2010 and the 

8 regional results from the Kaval and Loomis (2003) report on recreational use values compiled for 

9 the NPS estimates for visitors’ willingness to pay for various activities was generated and 

10 presented in Table 6-8. In addition to the activities listed in Table 6- 819% or 1.8 million park 

11 visitors availed themselves of educational services offered at the park by participating in a 

12 ranger-led nature tour suggesting that visitors wish to understand the ecosystems preserved in the 

13 park. 

14

15 Table 6- 8 Value of Most Frequent Visitor Activities at Great Smoky Mountains 

16 National Park 

Activity 

% 

Participation 

# Participants 

(thousands) 

Mean 

WTP 

(in $2010)

Total Value of 

Participation 

(millions in $2010) 

Sightseeing 82 7,790 53.34 416 

Day 

Hiking 

40 3,800 69.93 266 

Camping 19 1,805 29.87 54 

Picnicking 50 4,750 42.42 201 

Total 937 

17

18 The report Economic Benefits to Local Communities from National Park Visitation and 

19 Payroll (NPS, 2011) provides estimates of visitor spending and economic impacts for each park 

20 in the system. Visitor spending and its economic impact to the surrounding area are given in 

21 Table 6- 9 for the Great Smoky Mountain National Park. The median value of the components 

22 of that spending is presented in Table 6- 10. 
6-31

1 Table 6- 9 Visitor Spending and Local Area Economic Impact of GRSM 

Public Use Data Visitor Spending 2010a 

Impacts on Non-Local Visitor 

Spending

2010 

recreation 

Visits 

2010 

Overnight 

Stays 

All 

Visitors 

Non-Local 

Visitors 

Jobs Labor 

Incomea 

Economic 

Impacta 

9,463,538 393,812 818,195 792,547 11,367 303,510 504,948 

a 2 ($000’s) Source: Economic Benefits to Local Communities from National Park Visitation and Payroll (NPS, 

3 2011) available at: http://www.nature.nps.gov/socialscience/docs/NPSSystemEstimates2009.pdf

4

5 Table 6- 10 Median Travel Cost for GRSM Visitors 

Expense Median $ Amounts Spent (in $2010) 

Gas and Transportation 73 

Lodging 182 

Food and Drinks 73 

Clothes, gifts, and 

souvenirs 

 61 

Total per visitor party 389 

6 Source: The National Park Service 2002 Comprehensive Survey of the American Public 

7 Southeast Region Technical Report (available at: 

8 http://www.nature.nps.gov/socialscience/archive.cfm) 

9 Each of the activities discussed above are among those shown in the national scale 

10 analysis to be strongly affected by visitor perceptions of scenic beauty. As in the national 

11 analysis it is not possible to assess the extent of loss of services due to impairment of scenic 

12 beauty due to O3 damage however those losses are captured in the estimated values for spending, 

13 economic impact, and WTP for the park. 

14 On the other hand, we can quantify the extent of the hiking trails present in areas where 

15 sensitive species are at risk for foliar injury. Of the approximately 1287 kilometers of trials in 

16 GRSM, including a more than 114 km of the Appalachian Trail, over 1040 km or about 81% of 
6-32

1 trail kilometers are in areas where species sensitive to foliar injury occur. Figure 6- 8 maps the 

2 hiking trails in GRSM including the relevant portion of the Appalachian Trail overlayed with the 

3 species cover index. The accompanying pie chart, Figure 6- 9, shows the number of trail miles 

4 in each cover category. The categories with species cover index from 60-160, the middle to 

5 highest values, account for 635 km of trails or about 50% of trail kilometers. 

6

7

8 Figure 6- 8 Hiking trails within GRSM and sensitive species cover 

Sensitive Species Cover

Index

0.0 - 3.5

3.6 - 9.9

10.0 - 20.9

21.0 - 33.3

33.4 - 45.6

45.7 - 60.9

61.0 - 77.9

78.0 - 160.1

Appalachian Trail

Great Smoky Mountains National Park
6-33

1

2 Figure 6- 9 Trail kilometers by species cover category 

3

4 Although we cannot quantify the incremental loss of hiker satisfaction with their 

5 recreation experience due to the effect of O3 on scenic beauty along the trails this analysis 

6 illustrates that very substantial numbers of trail kilometers are potentially at risk. With 3.8 

7 million hikers using the trails every year willing to pay over $266 million for that activity the 

8 even a small benefit of reducing O3 damage in the park could be significant for these park 

9 visitors. 

10

[We will produce other maps of amenities (camp sites) and overlays of sensitive species for 2nd 11

12 draft.] 

13

14

15

16

17

18

19

116.4

33.0

208.1

430.7

124.6

203.9

0.0

0.0

182.7

Trail Length (KM) by Sensitive Species Cover

Index No Data

0

1 to 20

20 to 40

40 to 60

60 to 80

80 to 100

100 to 120

120 to 160
6-34

1 6.3.2 Intermountain Region – Rocky Mountain National Park 

2

3

4 Figure 6- 10 Sheep Lakes, Rocky Mountain National Park. Courtesy: National 

5 Park Service 

6

7 Rocky Mountain National Park welcomed 3.0 million visitors in 2010 (NPS Public Use 

8 Statistics Office, http://www.nature.nps.gov/stats/index.cfm) to its 415 square miles of mountain 

9 ecosystems. Rocky Mountain National Park allows visitors to enjoy vegetation and wildlife 

10 unique to these ecosystems along over 300 miles of hiking trails. 

11 [We will produce maps of amenities (hiking trails, camp sites) and overlays of sensitive species 

for 2nd 12 draft.] 

13 The National Park Service 2002 Comprehensive Survey of the American Public 

14 Intermountain Region Technical Report includes responses from recent visitors to southeast 

15 parks about the activities they pursued during their visit. By using the annual visitation rate from 

16 2010 and the regional results from the Kaval and Loomis (2003) report on recreational use 
6-35

1 values compiled for the NPS estimates for visitors’ willingness to pay for various activities was 

2 generated and presented in Table 6- 11. 

3 Table 6- 11 Value of Most Frequent Visitor Activities at Rocky Mountain National Park 

Activity 

% 

Participation 

# Participants 

(thousands) 

Mean 

WTP 

(in $2010)

Total Value of 

Participation 

(millions in $2010) 

Sightseeing 85 2,550 28.17 72 

Day 

Hiking 

51 1,520 46.03 70 

Camping 27 810 41.47 34 

Picnicking 38 1,140 33.77 38 

Total 214 

4

5 In addition to the activities listed in Table 6-11 11% or 330,000 park visitors availed themselves 

6 of educational services offered at the park by participating in a ranger-led nature tour suggesting 

7 that visitors wish to understand the ecosystems preserved in the park. 

8 Each of the activities discussed above are among those shown in the national scale 

9 analysis to be strongly affected by visitor perceptions of scenic beauty. As in the national 

10 analysis it is not possible to assess the extent of loss of services due to impairment of scenic 

11 beauty due to O3 damage; however those losses are captured in the estimated values for 

12 spending, economic impact, and WTP for the park. Were O3 impacts decreased these estimates 

13 would likely be higher. 

14 The report Economic Benefits to Local Communities from National Park Visitation and 

15 Payroll (NPS, 2011) provides estimates of visitor spending and economic impacts for each park 

16 in the system. Visitor spending and its economic impact to the surrounding area are given in 

17 Table 6- 12 for the Rocky Mountain National Park. The median value of the components of that 

18 spending is presented in Table 6- 13. 

19

20

21
6-36

1 Table 6- 12 Visitor Spending and Local Area Economic Impact of Rocky Mountain 

2 National Park 

Public Use Data Visitor Spending 2010a 

Impacts on Non-Local Visitor 

Spending

2010 

Recreation 

Visits 

2010 

Overnight 

Stays 

All 

Visitors 

Non-Local 

Visitors Jobs 

Labor 

Incomea 

Economic 

Impacta 

2,955,821 174,202 170,804 170,804 2,641 77,625 129,666 

a 3 ($000’s) Source: Economic Benefits to Local Communities from National Park Visitation and 

4 Payroll (NPS, 2011) available at: 

5 http://www.nature.nps.gov/socialscience/docs/NPSSystemEstimates2009.pdf

6

7 Table 6- 13 Median Travel Cost for Rocky Mountain National Park Visitors 

Expense Median $ Amounts Spent (in $2010) 

Gas and Transportation 63 

Lodging 100 

Food and Drinks 63 

Clothes, gifts, and 

souvenirs 

 45 

Total per visitor party 271 

8 Source: The National Park Service 2002 Comprehensive Survey of the American Public 

9 Intermountain Region Technical Report (available at: 

10 http://www.nature.nps.gov/socialscience/archive.cfm) 
6-37

1 6.3.3 Pacific West Region – Sequoia/Kings Canyon National Parks

2

3 Figure 6- 11 Kings Canyon. Courtesy: National Park Service 

4

5 Sequoia/Kings Canyon National Parks are located in the southern Sierra Nevada 

6 Mountains east of the San Joaquin Valley in California. The two parks welcomed 1.6 million 

7 visitors in 2010 (NPS Public Use Statistics Office, http://www.nature.nps.gov/stats/index.cfm) to 

8 experience the beauty and diversity of some of California’s iconic ecosystems. 

9 [We will produce maps of amenities (hiking trails, camp sites) and overlays of sensitive species 

for 2nd 10 draft.] 

11 The National Park Service 2002 Comprehensive Survey of the American Public Pacific 

12 West Region Technical Report includes responses from recent visitors to southeast parks about 

13 the activities they pursued during their visit. By using the annual visitation rate from 2010 and 

14 the regional results from the Kaval and Loomis (2003) report on recreational use values 

15 compiled for the NPS estimates for visitors’ willingness to pay for various activities was 

16 generated and presented in Table 6- 14. 

17

18
6-38

1 Table 6- 14 Value of Most Frequent Visitor Activities at Sequoia/Kings Canyon National 

2 Parks 

Activity 

% 

Participation 

# Participants 

(thousands) 

Mean 

WTP 

(in $2010)

Total Value of 

Participation 

(millions in $2010) 

Sightseeing 81 1,300 24.21 31 

Day 

Hiking 

58 928 27.77 26 

Camping 33 528 124.65 66 

Picnicking 45 720 76.72 55 

Total 178 

3

4 In addition to the activities listed in Table 6- 14 14% or 224,000 park visitors availed 

5 themselves of educational services offered at the park by participating in a ranger-led nature tour 

6 suggesting that visitors wish to understand the ecosystems preserved in the park. 

7 Each of the activities discussed above are among those shown in the national scale 

8 analysis to be strongly affected by visitor perceptions of scenic beauty. As in the national 

9 analysis it is not possible to assess the extent of loss of services due to impairment of scenic 

10 beauty due to O3 damage however those losses are captured in the estimated values for spending, 

11 economic impact, and WTP for the park. Were O3 impacts decreased these estimates would 

12 likely be higher. 

13 The report Economic Benefits to Local Communities from National Park Visitation and 

14 Payroll (NPS, 2011) provides estimates of visitor spending and economic impacts for each park 

15 in the system. Visitor spending and its economic impact to the surrounding area are given in 

16 Table 6- 15 for the Sequoia and Kings Canyon National Parks. The median value of the 

17 components of that spending is presented in Table 6- 16. 

18

19
6-39

1 Table 6- 15 Visitor Spending and Local Area Economic Impact of Rocky Mountain 

2 National Park 

Public Use Data Visitor Spending 2010a 

Impacts on Non-Local Visitor 

Spending

2010 

recreation 

Visits 

2010 

Overnight 

Stays 

All 

Visitors 

Non-Local 

Visitors 

Jobs Labor 

Incomea 

Economic 

Impacta 

1,320,156 438,677 97,012 89,408 1,283 37,299 60,504 

a 3 ($000’s) Source: Economic Benefits to Local Communities from National Park Visitation and Payroll (NPS, 

4 2011) available at: http://www.nature.nps.gov/socialscience/docs/NPSSystemEstimates2009.pdf

5 

6 Table 6- 16 Median Travel Cost for Sequoia/Kings Canyon National Parks Visitors 

Expense Median $ Amounts Spent (in $2010) 

Gas and Transportation 75 

Lodging 150 

Food and Drinks 98 

Clothes, gifts, and 

souvenirs 

 63 

Total per visitor party 386 

7

8 6.3.3 Urban Case Study 

9 Urban forests are subject to the adverse effects of O3 exposure in the same ways as 

10 forests in rural areas. These urban forests provide a range of ecosystem services such as carbon 

11 sequestration, pollution removal, building energy savings, and reduced stormwater runoff. The 

12 analyses described in this section focus on carbon sequestration and air pollution removal using 

13 the iTree model. The iTree model is a peer-reviewed suite of software tools provided by USDA 

14 Forest Service. See Appendix X for details of the model and the methodology employed for 

15 these case studies. 
6-40

1 [We will provide results in the form changes in tons of carbon sequestered and tons of 

2 pollution removed due to O3 effects on tree growth in supplemental materials.] 

3 6.4 DISCUSSION 

4 O3 damage to vegetation and ecosystems causes widespread impacts on an array of 

5 ecosystem services. Biomass loss impacts numerous services including supporting and 

6 regulating services such as net primary productivity, community composition, habitat, and 

7 climate regulation. Provisioning services are also affected by biomass loss including timber 

8 production, agriculture, and non-timber forest products. Cultural services such as non-use 

9 values, aesthetic services, and recreation are all affected by the damage to scenic beauty caused 

10 by foliar injury due to O3 exposure. It is possible for several aspects of O3 effects to interact to 

11 contribute to an impact on ecosystem services. For example biomass loss directly impacts timber 

12 provision but other contributing effects include increased susceptibility to drought and insect 

13 attack. 

14 Many of these services are very difficult to quantify and even more difficult to assign a 

15 quantified impact of O3 exposure. For instance we were not able to quantify changes to 

16 community composition due to O3 or even identify the current level of service provided. Some 

17 services, such as recreation, lend themselves to evaluation of total participation and measures of 

18 total value but assessing the impact of O3 effects on these services is not possible at this time. A 

19 very few services, such as timber provision, are amenable to quantification and monetization of 

20 the actual incremental effects of O3 exposure. 

21 For the supporting services identified as potentially affected by O3 exposure we were not 

22 able to quantify the impacts for community composition. [However, for net primary productivity 

23 we may have quantified results from PnET model runs for the second draft of this document.] 

24 The regulating services indentified as potentially affected by O3 exposure include 

25 climate, water, pollination, and fire regulation. We will have quantified impacts of O3 on carbon 

26 sequestration in the form of results of model runs from FASOMGHG, national scale, and iTree 

for the urban case studies for the 2nd draft. For the 2nd 27 draft we are considering using the PnET 

28 model to assess water cycle regulation effects. Pollination and fire effects remain unquantified 

29 however we do have measures of total values of these services. 
6-41

1 The effects of O3 on the provision of timber and agriculture will be quantified and 

monetized using the FASOMGHG model for the 2nd 2 draft with related impacts of increased 

3 susceptibility to insect attack described but not quantified. Non-timber forest products markets 

4 are described and total values are included however subsistence use can only be described. 

5 Cultural services are described in terms of total value since there are not data and 

6 methods available to quantify O3 impacts on these services. For example, outdoor recreation 

7 activity participation rates range from 10% of the population for backpacking to 60% for natural 

8 scenery viewing. The millions of participants have WTP values as high as $152 billion per year 

9 for these activities and just three of these (wildlife watching, camping, and hiking) generate over 

10 $200 billion per year in expenditures and over $385 billion in total economic activity. For the 

11 case study national parks we are able to quantify the amenities potentially affected by O3 impacts 

12 on sensitive vegetation in the parks. In Great Smoky Nation Park, for example, about 50% of the 

13 trail kilometers are in the middle and highest categories for sensitive vegetation cover. [We will 

have expanded case study analysis for the 2nd 14 draft.] 

15 The urban case studies will provide quantified and monetized iTree model results for 

16 carbon sequestration and pollution removal for urban forests in supplemental materials. 

17 Although we are unable to quantify the O3 impacts on these services we do know that 

18 these impacts exist and that the loss of service due to those impacts is captured in the current 

19 values of the services. Those values would be higher by some unknown amount were O3

20 impacts eliminated. Given the very high values for many of the services even very small 

21 incremental changes in O3 effects could potentially lead to large gains in benefits to the public 

22 and society. 

23 

24 
7-1

7 SYNTHESIS

This assessment has estimated exposures to O3 and resulting risks to ecosystems for both 

recent O3 levels and O3 levels after simulating just meeting the current secondary O3 standard of 

0.075 ppm for the 4th highest 8-hour daily maximum, averaged over 3 years, which was set to be 

identical to the current primary O3 standard. The results from these assessments will form part 

of the basis for considering the adequacy of the current secondary O3 standard in the first draft 

Policy Assessment. 

The remaining sections of this chapter provide key observations regarding the biomass 

loss risk assessment (Section 7.1), foliar injury risk assessment (Section 7.2), ecosystem services 

risk assessment (Section 7.3), and a set of integrated findings providing insights drawn from 

evaluation of the full assessment (Section 7.4). 

7.1 SUMMARY OF KEY RESULTS OF BIOMASS LOSS RISK ASSESSMENT

The first draft biomass loss risk assessment included two spatial scales of analysis 

including a national scale analysis and several case studies focused on national parks containing 

O3 sensitive vegetation. The biomass loss risk assessment focused on relative biomass loss for 

11 tree species for which concentration-response (C-R) functions are available. Relative 

biomass loss is measured as the proportion of biomass lost relative to biomass if ozone 

concentrations were zero. The assessment of individual tree species gives an estimate of the 

potential relative biomass loss, calculated across the established species ranges. A second 

analysis incorporated the abundance of those tree species in different ecosystems to assess the 

overall ecosystem level effects of the relative biomass loss. In addition, the biomass loss risk 

assessment evaluated risks occurring in several important subareas, including federally 

designated Class I areas, and federally designated critical habit areas for threatened and 

endangered species. The analysis provides estimates of the percent biomass loss associated with 

recent (2006-2008) O3 concentrations, and the proportion of the O3-related biomass loss that 

would remain after just meeting the current secondary O3 standard. 

Key results include:

• Relative biomass loss associated with recent O3 concentrations varies 

substantially between species and across the ranges for individual species, 

reflecting differences in sensitivity to O3 and differences in O3 concentrations 

across the ranges of the tree species.

• Across species, the estimated potential O3-related biomass loss associated with 

recent O3 concentrations ranged from 0.1 percent for Douglas fir to almost 100 

percent for Eastern Cottonwood. The estimated median potential O3-related
7-2

biomass loss for individual species ranged from 0 percent for Douglas fir to 56 

percent for Eastern Cottonwood.

• The C-R function for some species (e.g. sugar maple) demonstrates a very rapid 

change in biomass loss over a small range of O3 concentrations, 30 to 35 ppm for 

sugar maple, that behaves similar to a threshold. 

• After simulating just meeting the current secondary O3 standard, the estimated

potential O3-related biomass loss for individual tree species was on average 70 

percent of the estimated potential biomass loss at recent O3 levels, with a range

between 8 and 89 percent.

• In eastern U.S. federal Class I areas, simulating just meeting the current O3

standard resulted, on average, in a 5 percent reduction of the estimated potential 

O3-related abundance-weighted biomass loss relative to estimates at recent 

ambient O3 exposure levels. When areas with recent ambient O3 levels lower than 

a W126 of 10 ppm are excluded, this reduction was on average approximately 20 

percent. 

• In eastern U.S. federally designated critical habitat areas, simulating just meeting 

the current O3 standard resulted on average in approximately a 10 percent 

reduction of the estimated potential O3-related abundance-weighted biomass loss 

relative to estimates at recent ambient O3 exposure levels. When areas with recent 

ambient O3 levels lower than a W126 of 10 ppm are excluded, this reduction was 

approximately 25 percent. 

• In the Great Smoky Mountains National Park case study area, simulating just 

meeting the current O3 standard resulted in a 51 percent reduction of the estimated 

potential O3-related abundance-weighted biomass loss relative to estimates at 

recent ambient O3 exposure levels, with weighted biomass loss estimates reduced 

from as high as 16.5 percent to a maximum of 7.9 percent.

7.2 SUMMARY OF KEY RESULTS OF FOLIAR INJURY RISK ASSESSMENT

The first draft foliar injury risk assessment included two spatial scales of analysis 

including a national scale analysis and several case studies focused on national parks containing 

O3 sensitive vegetation. The foliar injury risk assessment focused on recent ambient O3

exposure. Two general assessments of foliar damage are included in this first draft: 1) maps of 

the abundance of tree species sensitive to foliar damage from O3 exposure, and 2) foliar injury 

risk index values for 37 national parks based on the frequency of exceedance of O3 exposure 

benchmarks using different O3 exposure metrics (i.e., SUM06, W126, and N100), soil moisture, 

and the existence of O3-sensitive species within each park. 
7-3

Key results include:

• In the eastern U.S., where tree cover data were available, tree species that are 

considered sensitive to O3-related visible foliar damage account for over 80% of 

the tree cover in some areas as measured by the summed importance values 

(measures of relative abundance of species).

• Of the 37 parks assessed, based on the screening level risk assessment method 

used in Kohut (2007), the estimated risk of foliar injury was high in 2 parks (5%), 

moderate in 4 parks (11%), and low in 31 parks (84%).

• In the Great Smoky Mountains National Park case study area, there are large areas 

with high cover of O3-sensitive species based on assessment using the National 

Park Service sensitive species list and vegetation mapping from the United States 

Geological Survey.

7.3 SUMMARY OF KEY RESULTS FOR ECOSYSTEM SERVICES RISK 

ASSESSMENT

There are a wide range of ecosystem services associated with the ecosystem effects 

(biomass loss and visible foliar injury) that are causally related to O3 exposure. These include 

supporting, regulating, provisioning, and cultural services. The first draft risk assessment 

includes both qualitative and quantitative assessments of ecosystem services. The majority of 

ecosystem services impacted by O3 exposures are not quantifiable using existing tools and data. 

As a result, the risk assessment focuses on providing contextual information about these services 

in terms of overall magnitude of the service relative to public use and where possible, economic 

value of the service. We emphasize that for these ecosystem services this contextual information 

does not provide estimates of the incremental ecosystem damages associated with recent O3

exposures, nor can it provide estimates of the reduction in O3-related damages that would occur 

from just meeting the current O3 standards. The magnitude of ecosystem services is provided 

solely to provide context for discussions of the adversity to public welfare posed by damages to 

these ecosystem services from ozone exposures.

For a few ecosystem services, including commercial forestry yields, carbon sequestration, 

agriculture yields, reduced productivity in terrestrial ecosystems, and alteration of terrestrial 

ecosystem water cycling, models exist that can be used to estimate risks from O3 exposure. This 

first draft REA includes estimates of risks associated with 1) exposure of commercial forests to 

O3, including estimates of changes in yields and resulting changes in welfare for producers and 

consumers of forest products and changes in carbon sequestration, using the FASOM model, 2) 

changes in carbon sequestration in urban forests and changes in urban forest pollution removal, 

using the iTree model. [The iTree and FASOM results will be provided in supplemental 
7-4

materials to be submitted for public review when the first draft Policy Assessment is released in 

August 2012]. 

Key results include:

• While the economic costs of the O3–related impacts on ecosystem services is 

largely unquantifiable, the overall economic value of the set of ecosystem services 

is estimated to be large, and therefore damages from O3 have the potential to be 

significant.

• Ozone-related impacts on ecosystem services associated with commercial timber 

production include lost economic value due to yield losses and reductions in 

carbon sequestration. The estimated value of the yield reductions associated with 

recent O3 levels for the 11 species for which we have concentration-response 

functions are $XXX. The estimated reduction in carbon sequestration is XXX 

tons of carbon per year in 2006 to 2008. [These will be provided in supplemental 

materials to be released in August 2012]

• Ozone-related impacts on ecosystem services associated with urban forests 

include reductions in carbon sequestration and reductions in removals of air 

pollution by urban trees. For the 11 species for which we were able to model O3

damages, the estimated reduction in carbon sequestration is XXX to YYY tons of 

carbon per year across the urban case study areas in 2006 to 2008. The estimated 

reductions in tons of pollutants removed is XXX to YYY tons across the urban 

case study areas in 2007. [These will be provided in supplemental materials to be 

released in August 2012]

• Simulating just meeting the current O3 standard is estimated to increase the value 

of commercial forest yields by $XXX in 2006 to 2008, and to increase carbon 

sequestered in commercial forests by XXX tons of carbon in 2006 to 2008. [These 

will be provided in supplemental materials to be released in August 2012]

• Simulating just meeting the current O3 standard is estimated to increase carbon 

sequestration by urban forests in the case study areas by XXX to YYY tons of 

carbon. Removal of air pollution is estimated to increase by XXX to YYY tons 

across the urban case study areas. [These will be provided in supplemental 

materials to be released in August 2012]
7-5

7.4 OBSERVATIONS

[These observations have been prepared based on the risk estimates available for the 

July public release of the first draft REA. We anticipate providing an updated draft of Chapter 9 

which integrates the results of the FASOM and iTREE ecosystem service risk analyses when we

provide supplemental REA materials along with the submissions of the first draft Policy 

Assessment for public review in August]

Looking across the biomass loss, foliar injury, and ecosystem service risk analyses, there 

are a number of observations that can provide insight into the nature and patterns of risk. The 

results suggest that due to the importance of O3 sensitive species of trees in Eastern forest 

ecosystems, the potential relative biomass loss associated with recent O3 concentrations is high, 

with median values for the most sensitive species, eastern cottonwood, as high as 56%. The 

damages to forest ecosystems due to reductions in biomass loss for sensitive species include 

commercial losses, but may also include losses to recreational users and to subsistence 

populations. Because many of these trees are abundant near urban areas with elevated O3 levels, 

simulating just meeting the current O3 standard results in reductions in potential biomass loss of 

30% on average. 

National parks and wilderness areas that have been designated as Federal Class I areas 

represent important geographic endpoints (e.g. Class I and critical habitat areas) where O3

damages may be important to consider. For the Great Smokey Mountain National Park case 

study area, there are areas within the park where the sensitive species cover is very high. This 

park has a large number of hiking trails with heavy public use. Of the approximately 1287 

kilometers of trials in the park, including more than 114 km of the Appalachian Trail, over 1040 

km or about 81% of trail kilometers are in areas where species sensitive to foliar injury occur. 

50 percent of the trail kilometers are in the highest class of sensitive species cover.

There are several important factors to consider when evaluating risks to ecosystems 

associated with recent exposures to O3. First, there is significant variability in the sensitivity of 

tree species to O3 exposures. Some species, such as Douglas fir, show little response at lower 

concentrations, but can have substantial response at higher O3 exposure levels (W126 > 50 to 60 

ppm for Douglas fir). Other species, such as sugar maple, show a distinct threshold at lower 

concentrations of O3, 30 to 35 ppm, but once the threshold is exceeded show rapid response over

a very narrow range of O3 concentrations. These differences in response functions have a direct 

impact on the change in biomass loss that is estimated to occur after simulating just meeting the 

current primary O3 standard. 

Second, as a result of the differences in concentration-response relationships, individual 

tree species show different patterns of change with respect to changes in O3. Douglas fir has a 

very large proportional change when O3 is meeting the current standard, however further 
7-6

reductions in O3 will likely have very little effect on that species. Sugar maple also had a large 

proportional change when meting the current standard. Further reductions in O3 will have some 

effect to a point beyond which we expect very little change. Other species are expected to exhibit 

continued gradual change in RBL relative to ambient as O3 levels are reduced.

Third, many Class I and Critical Habitat areas occur in areas where the ambient O3 is 

below the level of the current standard and these areas generally show very little change in 

summed relative biomass loss when exposure is simulated to just meeting the current standard 

compared to recent O3 levels. In areas with higher ambient O3 levels, the proportion of ambient 

summed relative biomass loss decreases by as much as 20 percent.

Fourth, the biomas loss assessments of Class I, critical habitat and national park areas are 

based on C-R functions for relatively few tree species. This makes it difficult to assess the 

absolute values of biomass loss because the response to O3 levels of the remaining species in 

those areas is not quantifiable at this time, so the absolute values would not represent the 

biomass losses for the entire community. As a resultthe assessment necessarily focuses on 

proportional changes in the summed-biomass loss estimates.

This first draft REA provides preliminary estimates of exposures and risks which provide 

information that can be used to begin discussions in the Policy Assessment regarding the 

adequacy of the current standard. The second draft REA will further refine the estimates of 

exposure and risk by incorporating additional modeling of impacts on commercial forests and 

urban forests using FASOM and iTREE. In addition, U.S. Forest Service Forest Health 

Monitoring data on visible foliar injury will be included, allowing for additional insights into the 

impacts of recent ozone levels on this potential measure of recreational ecosystem services 

(associated with enjoyment during hiking activities). We are also evaluating the pNET model for 

use in estimating risks due to changes in productivity in terrestrial ecosystems, reduced carbon 

sequestration in terrestrial ecosystems, alteration of terrestrial ecosystem water cycling. The 

second draft REA will also evaluate any alternative O3 standards identified in the first draft 

Policy Assessment following evaluation of any advice and comments on those potential 

alternative standards provided during the review by the CASAC O3 Panel. Finally, we anticipate 

that the second draft REA will incorporate an improved approach to adjusting O3 concentrations 

based on simulations of just meeting the current and alternative O3 standards.
8-1

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United States

Environmental Protection

Agency

Office of Air Quality Planning and Standards

Air Quality Strategies and Standards Division

Research Triangle Park, NC

Publication No. EPA 452/P-12-004

July 2012